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2013, 32 (s2): 0-0

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LOW-TEMPERATURE LPG AND LNG STORAGE CAVERNS AND RELATED RESEARCH REVIEW OF ROCK MECHANICS

XU Bin1，LI Ning2，LI Zhongkui1，YAN Na3

2013, 32 (s2): 2977-2993

(107)

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Firstly，the construction technology of the low-temperature liquefied petroleum gas(LPG) and low- temperature liquefied natural gas(LNG) underground storage caverns is introduced. The field experiments and theoretical analysis for low-temperature LPG and LNG underground storage caverns engineering are summarized. And the frozen rock mechanics problems related to these engineering are introduced，from the four following reviewed researches：(1) Rock physical properties under low temperature or freeze-thaw cycle；(2) Effect of low-temperature freezing or freeze-thaw cycle on fractures of rock；(3) Moisture migration；(4) The frozen rock mass coupled thermo-hydro-mechanical model under low-temperature freezing condition. Due to the differences of freezing in the laboratory and field conditions，the mechanism of the frozen action to intact rock and rock mass is explored. Moisture migration and temperature filed of frozen rock mass are also considered. The last，the construction technology and stability of LPG and LNG underground storage caverns are discussed.

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STUDY OF MECHANICAL CHARACTERISTICS OF LIMESTONE UNDER UNLOADING CONDITION

ZHAO Guobin1，ZHOU Jianjun2，WANG Sijing1

2013, 32 (s2): 2994-2999

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Under unloading condition，the mechanical characteristic of rock sample is notably different from that under loading condition. Because of constructing of tunnel，loading and unloading experiments are carried out to study the unloading mechanical characteristics of –3 limestone. After analyzing test data，some conclusions are drawn：(1) The lateral deformation and volume dilatancy of rock sample along unloading direction are the dominant failure characteristics. (2) Brittle characteristic of rock is more notable than that under loading condition for this rocks，especially after peak strength. So rockburst may take place when underground engineerings are constructed. (3) Under unloading condition，compressive strength is less than that under loading condition. As far as this rock is concerned，the peak strength is reduced by 25.65% and residual strength by 73.15%. (4) For shear strength，peak strength and residual strength of cohesion both decrease and those of inner friction angle increase. (5) Under two kinds of testing conditions，deformation modulus E50 and Poisson?s ratio are related with confining pressure. The different is that deformation modulus decreases firstly and when confining pressure reaches to some value，deformation modulus begins to increase. Then for poisson?s ratio，the trend of changing is opposite to deformation modulus.

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GENERALIZED DAMAGE MODEL FOR ASPERITY AND SHEAR STRENGTH CALCULATION OF JOINTS UNDER CYCLIC SHEAR LOADING

LIU Bo，LI Haibo，LIU Yaqun，XIA Xiang

2013, 32 (s2): 3000-3008

(101)

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Degradation mechanism of the shear strength of rock joints under cyclic shear loading and corresponding analysis model are bases for accurate assessment of rock engineering safety under seismic load. Joint specimens with three kinds of joint wall strengths and five kinds of asperity angles were prepared，then a series of cyclic shear tests were performed under four normal stress levels. Test curves，destruction process of tooth-asperity and the residual form of tooth-asperity were discussed according to test results. And further，a generalized damage model for residual form of tooth-asperity is proposed. Using the proposed model，the mathematical relationships between snipped rate of tooth-asperity，dilation rate，angle of base friction and average dilation angle were established separately. In addition，an empirical formula of the average dilation angle was given according to the cyclic shear experimental results. Thus，the cyclic shear strength calculation formula was established based on the average dilation angle formula and Ladanyi-Archambault shear strength formula. Finally，calculation results of cyclic shear strength were compared with test results. It is indicated that，the calculation results have good agreement with the test results，but there exists certain deviation for the high angle joints specimens.

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COMPUTATIONAL MODEL OF PROGRESSIVE FAILURE PLANE IN GEOLOGICAL BODY AND FAILURE CRITERION OF SHEAR PLANE

LI Shihai，ZHOU Dong

2013, 32 (s2): 3009-3015

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Multiscale computational framework is proposed to describe progressive failure of geological body. Calculation condition and determination method of physical parameters in multiscale are established. Engineering geological model is divided into three computational scales，which include size of actual model from hundreds to thousands meters，size of mathematical mesh with meter scale and characteristic size of fracture corresponding to experimental sample scale. Strength parameters from lab can be used to describe failure in this multiscale computational framework. A new strength criterion based on distribution of shear strain strength on shear plane is introduced，in which strain is used as the strength index and shear strain strength complies with a certain distribution law. Area where shear strain is below the shear strain strength keeps linear elastic，while the rest turns into Coulomb?s friction. Nonlinear behavior of material such as yielding and strain softening can be described. Elasto-brittle model，strain softening model and ideal elasto-plastic model can be naturally obtained through the variation of the interval of upper limit and lower limit of strain strength. Numerical result of discrete element method shows that it is reasonable to describe the internal microscopic damage with elastic microplane and fracture microplane which are expressed with linear elastic and Coulomb?s friction parameters，respectively.

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MECHANISM STUDY OF ACID ON MECHANICAL PROPERTIES OF LIMESTONE

HE Chunming，GUO Jianchun

2013, 32 (s2): 3016-3021

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Through systematic experiments test includes static rock dissolution experiments，dynamic rock flow experiments，triaxial mechanical tests and microstructure analysis of rocks，the mechanical strength reduction of limestone reacting with different acids were studied from the macroscopic and microcosmic perspective. Static and dynamic dissolution experiments showed that gelled acid could create many small solution caves on the rock face，while viscosity acid was mainly of surface dissolution. triaxial mechanical test indicated that the compression strength of rock was reduced by 18%，and Young?s modulus by 26% after reaction with gelled acid，which was much larger than the mechanic strength reduction that dissolved by viscosity acid. Stress-strain curve showed that the compaction densification process after reaction continued for a long time，and showing more plastic behavior. Scanning electron microscope observation indicated that there were many small dissolution holes in the rock after reacting with gelled acid，while the viscosity acid was mainly of uniform dissolution，which has little damage to the internal structure of rock. The difference of dissolution structure for different acids maybe the fundamental reason for the difference of mechanical strength. For high closure stress reservoirs，it should be care more about the mechanical strength reduction that caused by acid-rock reaction，which means to choose leak off-control acids.

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2013, 32 (s2): 3022-3027

(114)

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HIGH PRESSURE PERMEABILITY PROPERTIES OF FRACTURED ROCK MASSES

NI Shaohu1，2，HE Shihai1，WANG Xiaogang2，LU Kang1，BIAN Kang3

2013, 32 (s2): 3028-3035

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With rapid construction of hydropower stations and deep underground projects under high water pressure，there are more and more seepage failure risks in these projects. As a result，the in-situ high pressure permeability must be tested and the high pressure permeability properties and seepage stability of rock masses must be systematically and thoroughly studied. In this work，according to the revealed phenomenon in field and the water-rock interactions，the seepage failure mechanisms and failure modes of fractured rock masses under high water pressure are discussed. In addition，based on high pressure packer tests or high pressure permeability tests of several hydropower sataions under high water head，the permeability properties such as hydraulic fracturing，seepage deformation，erosion resistance and long-term seepage stability are studied. The results indicate that：(1) The permeability properties of fractured rock masses can be remarkably changed by high water pressure. (2) The changes of permeability properties are quite correlative with water pressure，supporting environment of stress and fracture fillings.

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STUDY OF MODEL OF SLUG TESTS PERFORMED IN WELLS WHEN WELLS SCREENED ACROSS WATER TABLE

GAO Bin1，2，CHEN Jiansheng1，3，CHEN Liang1，JI Chunbo1

2013, 32 (s2): 3036-3041

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For the slug tests performed in wells screened across the water table in phreatic aquifer，the water injects into the wells through the upper and lower parts of the water table. By calculating the amount of the water flowed away from the lower part of the water table using the technique of tracer test with the concentration of solute，a new model of slug test in phreatic aquifer is built up；and the analytical solution of the new model is given. It?s different from the traditional ways to solve this problem，which usually do it by changing some coefficients to correct the radius of the wells. To demonstrate the correctness of this theory，a series of slug tests are conducfed in a fully penetrating well in the Jiangxiong Reservoir in Tibet. And then the hydraulic conductivity of the formation is calculated using the method. By comparing the result of this value to the calculating results of Bouwer-Rice slug，the results show that the proposed model can truly reflect the permeability characteristics of the formation. By analyzing the standard recovery curve of the slug test，it shows that curve can truly reflect the permeability characteristics of the aquifer when the curve decreases in a slower rate.

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TEST STUDY OF SANDSTONE CRACKING AND PROPAGATION PROCESS UNDER COMPRESSIVE-SHEAR STRESS

XU Jiang1，2，LIU Jing1，2，WU Hui1，2，CHENG Lichao1，2，LU Lifeng1，2

2013, 32 (s2): 3042-3048

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Using self-developed meso-shear test equipment for coal and rock containing gas and PCI–2 acoustic emission testing and analytical system，the compressive-shear tests of sandstone at normal stresses with 0.0，1.5，3.0，4.5，6.0 MPa under the shear load condition were carried out. The deformation and AE characteristics were studied，and the mesoscopic feature of the cracks? evolution was analyzed. The data shows that as normal stress increases，the shear strength increases，and the peak shear force and corresponding peak displacement increase linearly. Under the condition of different normal stresses，the rock has some distinctions on shapes or appearances. However，they basically extend along the expected shearing surface. As normal stress increases，the crack initiation and propagation will get later，the instability and failure of the rock become more difficult. By the impacts of normal stresses，the AE event rate doesn?t reach the maximum value along with the shearing stress increases to the peak value. The fact is that the AE event rate increases rapidly after the shear stress reaches the peak value，also with the tiny cracks spread suddenly. With these two conditions，the AE event rate finally reaches the maximum value，then the rock unstable failure had been destroyed after those cracks went through it. As normal stress increases，the friction of particles between two sides of shear surface also increases. Meanwhile，the major crack is wider and the shapes of cracks become more complicated due to effects of the unbalanced stress distributions and also the internal structures heterogeneity of materials.

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DAMAGE EVOLUTION MODEL OF SATURATED SANDSTONE UNDER FREEZE-THAW CYCLES

JIA Hailiang1，LIU Qingbing2，XIANG Wei1，2，ZHANG Weili1，LANG Linzhi1

2013, 32 (s2): 3049-3055

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Freeze-thaw cycles applying to saturated sandstone are considered as a kind of low frequency fatigue load after the analysis of its features. And the stress condition of sandstone under freeze-thaw cycles can be simplified to cycles of uniaxial tension. According to the above analysis，damage evolution equation is established based on the fatigue damage theory. Then，the open porosity of sandstone which has been tested during the freeze-thaw experiment is selected as the damage variable. After that，the new damage evolution model is tested and verified by the comparison between experiment data and theoretical value，and how to get the values of parameters in the equation is also discussed. The new model is proved to be able to describe the basic damage evolution law of sandstone，this could be the reference for similar researches.

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TEST FOR INFLUENCE LAW OF EXPANDED POLYSTYRENE(EPS) PARTICLE SIZE ON STRENGTH CHARACTERISTICS OF MIXED LIGHT-WEIGHT SAND

XIE Shumeng1，2，XU Guangli2，YE Sanxia3，HU Huanzhong2

2013, 32 (s2): 3056-3063

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A series of triaxial tests were carried out to investigate the influence law of expanded polystyrene size(EPS) on strength characteristics of light-weight sand(4 kinds of EPS sizes in range of 2–6 mm)，cement mass ratio is 13% and 20%，EPS volume ratio is 1.8). Results show that the light-weight sand is a kind of structural soil，nonlinearity，multi-stage，strain hardening and strain softening are the properties of its stress-strain relation curves. Broken line and straight line are the two different types of Mohr failure envelope，which depends on the structural strength and consolidation pressure. Deformation modulus and compressive strength are adjustable，both growing with the increase of cement mixed ratio. For a certain mixed ratio，with the increase of EPS size，deformation modulus decreases linearly and compressive strength decreases exponentially. Cohesive strength and internal frictional angle decrease with the increase of EPS size，but the reduction of internal frictional angle is smaller. The cement mixed ratio has a big influence on the cohesive strength and little influence on the internal frictional angle. The reduction rate of unit price is far more greater than that of strength，with the increase of EPS size from 2 to 5 mm，but the advantage is not obvious when the EPS size continues to grow. The difficulty of sample preparation is highly increased when the EPS particle sizes are 5–6 mm. Take all factors into consideration，4–5 mm particle sizes of EPS are recommended in practical engineering.

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(1. 西安理工大学土木建筑工程学院，陕西西安 710048；2. 西安理工大学岩土工程研究所，陕西西安 710048)

2013, 32 (s2): 3064-3072

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NEW ALGORITHM TO DETERMINE ROCK MASS DISCONTINUITY TRACE LENGTH PROBABILISTIC DISTRIBUTION AND MEAN TRACE LENGTH BASED ON SEMI-TRACE SCANLINE SURVEYS

CHENG Hao，TANG Huiming，SUN Miaojun，LEI Guoping，WU Qiong，WANG Liangqing，HUANG Lei

2013, 32 (s2): 3073-3082

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Semi-trace scanline survey is one of the most widely used method to measure discontinuity geometrical parameters in field，while it is hardly to find some correlative researches on discontinuity based on semi-trace scanline method in literature. Technique of determining probabilistic distribution of discontinuity trace length and estimating of mean trace length based on semi-trace scanline surveys was improved. By considering the influence of the discontinuity orientation，three new types of traces and scanline?s intersection probability models and one type of semi-trace length cumulative probability model were built. Hence the probability density functions of trace length and the value of mean trace length with the influence of joints? orientation were obtained. With different types of probability density functions of semi-trace length，the probability density function of trace length expressed with explicit formula by semi-trace length probability density function was determined. Then the geometrical parameters of Laohuzui rock slope discontinuities in Wenchuan area were used to prove the new method. Results of network were compared with the real measured semi-trace length sample. It showed that the average simulative semi-trace lengths from improved model were much closer to the field semi-trace length data than the results obtained by previous method，which indicated the superiority of the proposed method. Finally several suggestions about discontinuities sampling by using scanline surveys were given according to the analysis result of the relationship between the mean trace length and discontinuity orientation.

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DISCRETE ELEMENT ANALYSIS OF CRACK PROPAGATION IN ROCKS UNDER BIAXIAL COMPRESSION

ZHANG Sherong1，SUN Bo1，WANG Chao1，YAN Lei2，3

2013, 32 (s2): 3083-3091

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Based on the theory of particle discrete element，the crack propagation and failure mode of Hwangdeung granite with two pre-existing flaws are researched under biaxial compression. The results show that confining pressure has a significant effect on crack propagation and failure mode. The effect of the horizontal flaw shielding the inclined flaw from a vertical load enhances with the increase of confining pressure. And the larger flaw inclination angle is，the more obvious the protective effect is. When flaw inclination angle ，the number of microcracks increases with the increase of confining pressure at the end of tests. When ，the number of microcracks firstly increases and subsequently decreases with the increase of confining pressure. Crack initiation stress of rock specimen increases with the increase of confining pressure except . Peak strength of rock specimen also increases with the increase of confining pressure. Confining pressure has different effects on crack initiation stress and peak strength of rock specimen with different flaw inclination angles. The size relation of crack initiation stress and peak strength of rock specimen with different flaw inclination angles exhibits no clear increasing or decreasing trend under the same confining pressure，for they are related to failure modes of rock specimen. On the whole，confining pressure has the largest impact on the mechanical properties of rock specimen with flaw inclination angle of 60°.

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EXPERIMENTAL STUDY OF EFFECT OF STRESS PATHS ON MECHANICAL CHARACTERISTICS OF CRACKED SAMPLES

HAN Tielin，CHEN Yunsheng，SHI Junping，LI Weihong

2013, 32 (s2): 3092-3099

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Triaxial compression tests for cracked samples under axial loading and constant confining pressure，axial loading and radial unloading，constant axial pressure and radial unloading—three stress paths were carried out by using WDT–1500 multi-function material testing machine. The deformation property，strength property and failure mechanism of cracked samples were researched. It shows that there is significant change in mechanical parameters under this three stress paths. The strength of cracked samples of axial loading and radial unloading，constant axial pressure and radial unloading were lower than that of axial loading and constant confining pressure. Under different stress paths，the strength of crack samples decreases first and then increases with the crack angle increases，and reaches minimum at crack angle of 30°or 45°. The mechanical characteristics of cracked samples are mainly related to the crack angle，the loading paths and the initial confining pressures，and the greatest influence factor is the crack angle，the intermediate is the unloading velocity of confining pressure，and the least is the initial confining pressure. The failure characteristics of samples present shear failure under axial loading and constant confining pressure，but it often presents mixed Tensile-shear failure under axial loading and radial unloading，constant axial pressure and radial unloading. Tensile-crack is less under axial loading and radial unloading，but it develops significantly under constant axial pressure and radial unloading.

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FUZZY-SYNTHETICAL EVALUATION METHOD ON THE SYSTEM OF GEOLOGICAL STRENGTH INDEX

CAO Ruilang，HE Shaohui，GUO Yanwei，WANG Fang

2013, 32 (s2): 3100-3108

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When evaluating geological strength index(GSI)，there are great randomness and fuzziness to confirm the value of its basic elements. As a consequence，it is difficult to accurately measure the impact of each influential factor. The fuzziness of the parameter of rock mass characteristics reflects its inherent uncertainty. The fuzzy mathematics theory provides strong measures to depict these characteristics. This article introduces the number of joint sets(Jn)，joint spacing(l) and the integrity coefficient of rock mass(Kv) to describe the structure features of rock mass and introduces large-scale waviness(Jw)，small-scale smoothness(Js) and joint altered coefficient(Ja) to describe the conditions of structural planes. Then multifactor fuzzy-synthetical evaluation is applied to the system of GSI. Meanwhile，analytic hierarchy process is adopted in determining the weight of each factor. As a result，the model of fuzzy-synthetical evaluation of GSI is established. Project applications prove that this evaluation method has strong pertinence and high accuracy and it can organically combine geological surveys，experiment data，statistics and expert opinions，so this evaluation method can decrease the subjectivity of researchers? decisions. The method of fuzzy-synthetical evaluation of GSI does provide a new approach to quantizing GSI system.

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ANALYSIS OF ENERGY DISSIPATION RULE DURING DEFORMATION AND FRACTURE PROCESS OF ROCK UNDER HIGH TEMPERATURES IN SHPB TEST

XU Jinyu1，2，LIU Shi1

2013, 32 (s2): 3109-3115

(105)

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Experimental studies of marble under different high temperatures and impact load are carried out by using the high temperature split Hopkinson pressure bar(SHPB) apparatus of 100 mm in diameter. The characteristics of energy dissipation and the influence of impact velocity and incident energy on the energy dissipation of marble during the impact process are analyzed. The relationships between the fractal dimension，average fragment-size and energy dissipation of marble are also investigated. The test results show that the specific energy absorption increases linearly as the impact velocity and incident energy increase at the same high temperature. Meanwhile，the fractal dimension increases linearly and the average fragment-size decreases exponentially with the specific energy absorption increasing. Under the same high temperature，the greater the specific energy absorption is，the smaller the average fragment-size is，the greater the fractal dimension is，the more severe fragmentation is. Consequently，the deformation and fracture process of marble can be reasonably reflected from the viewpoint of energy dissipation.

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QUANTITATIVE EVALUATION OF MICRO-PORE THROAT CHARACTERISTICS IN EXTRA-LOW PERMEABILITY SANDSTONE OF YANCHANG GROUP，ORDOS BASIN

GAO Hui1，REN Guofu2，3，MU Qianyi2，3

2013, 32 (s2): 3116-3122

(116)

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The samples of Yanchang group in Ordos basin are tested with constant rate mercury penetration technique，pore throat characteristics parameters are characterized quantitatively in order to recognize the micro-pore throat characteristics and to make definite the key factors controlling reservoir quality and development effect. The results show that difference of pore is little，pore radius distributes in 70–225 μm，peak value is about 110 μm. When the permeability is low，the throat distributes assembly，the content of small throat is high，the contribution of throat to permeability also distributes intensively and contribution of peak value is big. Distribution range of throat radius will become wide，large pore content will increase and its contribution will broaden with the increasing permeability. Average pore radius and permeability present good correlation. Fluctuation amplitude of average pore radius is great when the permeability is less than 1.0×10－3 μm2. Sensibility of extra-low permeability sandstone roots in particular throat characteristics. The poor physical properties(especially permeability) lie in the high content of small throat. The well the physical property is，the more the effective pore and throat develop. Difference of micro-pore throat mainly is presented in the pore size and its distribution. The pore controls the reservoir quality and affects development effect.

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FIELD ROLLER COMPACTION TEST AND DISCRETE ELEMENT ANALYSIS OF ROCKFILL DAM

LI Xiaozhu1，2，LIU Yang1，2，WU Shunchuan1，2

2013, 32 (s2): 3123-3133

(102)

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According to the field roller rolling compaction(RC) test of Nuozhadu coarse rockfill zone of upstream and downstream I district rockfill engineering，a numerical procedure based on discrete element method(DEM) is proposed to study the RC test process. The particle movement，the variation mechanism of density and the compaction characteristics of the rockfill during the RC process are analyzed in detail，and the effects of different particle size distributions on the quality of dam filling are also discussed. The predicted results from the numerical simulation have a good agreement with the test data，which indicates that the proposed numerical procedure is feasible to the investigation of rockfill RC characteristics，and gives a novel explanation of the variation of macro-parameters such as dry density in the RC process from the microscopic point of views. The proposed numerical procedure also gives an effective method to select the scientific and reasonable RC construction parameters，for example，the Nuozhadu I distric RC engineering，and provides a new way for the research of rockfill characteristics.

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STRUCTURE EFFECT STUDY OF DEFORMATION AND FAILURE OF ROCK AND SOIL AGGREGATE WITH CT TECHNIQUE

YUAN Weina1，2，LI Xiao1，HE Jianming1，LI Shouding1，CHENG Guowen3，LI Tengfei1，2

2013, 32 (s2): 3134-3140

(113)

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In order to study the structure effects，interior structural deformation of rock and soil aggregate(RSA) under uniaxial compression is studied through the X-ray computed tomography(CT) real-time scanning tests. Based on the scan orientation principle of CT，movement of rock fragments in RSA is analyzed. Moreover，the relationship between interior structural deformation and macroscopic deformation of RSA is studied. The results show that macroscopic deformation and failure of RSA are mainly caused by the position adjustment of interior rock fragments. It is also shown that the integral deformation of rock fragments in RSA can be represented by equivalent structure deformation. By using the method of image threshold segmentation，profiles of the sample are obtained and analyzed. The profiles indicate that interior damage and cracks of sample initiate from the contact zone between rock fragments and soil，and then extend around rock fragments，until they form fracture planes. The results can provide theoretical basis for the monitoring and warning of RSA slope.

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TESTING STUDY OF CHANGING LAW OF ANCHORING FORCE UNDER DIFFERENT LATERAL PRESSURE COEFFICIENTS

ZHA Wenhua1，2，WANG Xiaopo1，2，SHI Chong3，LIU Chunsheng4

2013, 32 (s2): 3141-3145

(138)

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In order to research the invalidation mode of anchor bolt and the changing rule of anchoring force under different lateral pressure coefficients，pull-out tests were performed. The results show that：it was dominated by losing binding between anchor bolt with anchor layer interface accompanying that breaking of anchor layer and also losing binding between anchor layer with drilling hole wall，and the largest load force enlarged with the lateral pressure coefficients increase，when the coefficient reach 1.3，the largest load force of anchor blot was received，after that it was decreased by lateral pressure coefficients increased. The elastic deformation zone，plastic slip deformation zone and the losing binding deformation zone were emerged one after another on binding interface with anchor damaged. The friction force was enhanced by radial load on slip deformation zone between anchor bolt and anchor layer interface and then the largest pull-out load was increased.

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A MESOSCOPIC NUMERICAL MODEL FOR SIMULATION OF ROCK FRACTURING

YAO Chi1，JIANG Qinghui1，2，SHAO Jianfu3，ZHOU Chuangbing1，2

2013, 32 (s2): 3146-3153

(117)

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A numerical procedure is developed to generate randomly and uniformly distributed Voronoi diagram，which is used as the basic mesh for rigid body spring method(RBSM). The midpoint contact model of original RBSM is modified into distributed interface contact model. A fracture criterion is proposed through combining Mohr-Coulomb law and tension strength，which can account for mode I and mode II fracturing at the same time. It is found from a series of numerical tests that mesh size and mesh arrangement have little effects on the relationship between macro and meso elastic parameters. A fitting relation is given to overcome the problem of mesh dependency of particle discrete element method and to simplify the complex calibration procedure of which for macro-meso parameters identification. Comparison with Vienne rock experiments shows that both strength and deformation analyzed by the proposed model are in good agreement with the experiment data. Thus，the validity of the proposed model is verified.

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RESEARCH ON EFFECT OF UNLOADING RATE OF CONFINING PRESSURE ON CAPACITY EXPANSION DAMAGE OF SALT ROCK

JIANG Deyi1，FAN Jinyang1，CHEN Jie1，REN Song1，NI Junjie2

2013, 32 (s2): 3154-3159

(94)

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For researching the influence of build-cavity-period on the damage of gas storage library?s surrounding rock，combining with the engineering practice，the triaxial unloading confining pressure experiments under different unloading rates are carried out；and the dilatation-damage model and corrects the formula with correction factor of rate are built. The results show that：(1) Under given conditions，salt rock can intuitively response the damage situation at that time. (2) In the experiments，if salt rock specimens experience the same stress path，increasing unloading rate can make the rock of the dilatation amplitude decrease，speed-up-dilatation point lag，the salt rock damage become lesser. So，the damage control more easily. (3) In the same stress condition，we find that different unloading rates will impact the damage of salt rock. The negative logarithm of rate and damage are linearly correlated.

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STATISTICAL DAMAGE SOFTENING MODEL OF FRACTURED ROCK BASED ON SMP FAILURE CRITERION AND ITS APPLICATION

ZHU Jianming1，CHENG Haifeng1，YAO Yangping2

2013, 32 (s2): 3160-3168

(99)

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The rock material is a kind of non-homogeneous material and there are a large number of defects such as fissures，voids，interfaces in the broken rock. Its micro units damage more randomness under the loads. Starting from micro units strength are random distribution on the basis of damage theory，a method for measuring microcosmic element strength of rock is presented with consideration of damage threshold. Assuming the micro units strength of broken rock obey Weibull distribution，combined with the SMP criterion，which considers the intermediate principal stress，the statistical damage softening constitutive model is built. And the model parameters m and F0 are computed using some methods. Through the calculation results of two kinds of broken rock in Xiaoguanzhuang indicate that：the predicted stress-strain curves under different confining pressures agree well with the test data，and it can reflect not only the influence of damage threshold but also more desirable in the lower confining pressures. At the same time，this model can reflect the characteristic that the peak strength increases and ductility increases with the confining pressure increase，which further shows that the applicability of the model and a strong application value.

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HYDRAULIC FRACTURING INITIATION AND PROPAGATION

FENG Yanjun1，2，3，KANG Hongpu1，2

2013, 32 (s2): 3169-3179

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The initiation pressure and propagation pressure are essential to hydraulic fracturing operation. The initiation and propagation of an arbitrarily inclined borehole is considered more complicated compared with a horizontal or vertical borehole. By means of maximum tensile stress criterion，initiation pressure and orientation are analyzed and dimensionless initiation pressure(pb/?v) varying with borehole azimuth and inclination is obtained. With regard to hydraulic fracturing treatment carried out in the roof of Wangtaipu coal mine，initiation pressure and corresponding location are calculated. Finite element method is employed to explain the excessive propagation pressure during the fracturing process. The results are that：(1) When ?h = ?H，initiation pressure keeps ever-reduced as borehole rotates gradually from vertical direction to horizontal direction and maintains constant as borehole rotates from ?h direction to ?H direction. (2) Change rule of initiation pressure is closely related to in-situ stress regime with increase of ?H/?h or ?H/?v. (3) During the process of borehole rotating from vertical to horizon，initiation pressure performs uniquely subjected to normal faulting stress regime，striking slip faulting regime and reversing faulting stress regime，respectively. (4) The horizontal borehole direction requiring minimum initiation pressure exists for corresponding in-situ stress regime as it rotates from ?h direction to ?H direction. (5) Initiation pressure increases dramatically with the growth of rock tensile strength as it is close to the magnitude of in-situ stress. (6) The fracture turning during propagation would generate high pressure. (7) The magnitude，direction and type of in-situ stress are the groundwork for borehole design of hydraulic fracturing operation.

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STUDY OF PLS-LCF MODEL FOR ROCK BURST PREDICTION BASED ON PARTICLE SWARM OPTIMIZATION

YAN Zhixin1，2，HE Xiang2，GONG Bin2

2013, 32 (s2): 3180-3186

(96)

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The prediction of rock burst is a complex systemic problem. It is necessary to consider the various factors affecting the rock burst comprehensively. But when variables to be considered are very large，the multicollinearity among variables will affect the objectivity of the analysis. In order to eliminate the adverse effect and effectively predict rock burst，the affecting factors for rock burst are analyzed by means of partial least-squares regression(PLSR). A new synthesis variable with better interpretation to the dependent variable is extracted and it can preferably overcome the multicollinearity among variables. The nonlinear relationship between composition values and rock burst grades is established according to the logistic curve function(LCF). The particle swarm optimization(PSO) with the global optimization is used to optimize the parameters of LCF. So far，a PLS-LCF prediction model of rock burst based on PSO is built. The test results of the model show a very good precision. The evaluation results obtained by applying the developed model to practical engineering are well consistent with the practical situation，which indicates that the model is feasible and effective for rock burst prediction.

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NONLINEAR SEEPAGE REGULARITY OF TIGHT SANDSTONE RESERVOIRS WITH CONSIDERATION OF MEDIUM DEFORMATION

DONG Pingchuan1，LEI Gang1，JI Bingyu2，TIAN Shubao1

2013, 32 (s2): 3187-3196

(98)

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The process of water flooding met the law of non-Darcy flow and existed threshold pressure gradient in tight sandstone reservoirs. Porous medium would get deformed，and the permeability would decrease. The nanometer pore characteristics of tight sandstone through scanning electron microscope(SEM) experiment were researched. Based on the distribution of rock particles，a theory model which characterized stress sensitivity caused by medium deformation was established and medium deformation coefficient was derived. The comparison analysis of results between the theory model and experiment is performed. Moreover，a seepage mathematical model was established which took the deformation of tight sandstone into consideration. The coupling influences of the threshold pressure gradient and medium deformation on the oil-water two-phase nonlinear percolation feature are studied. The result shows that the flow resistance and formation pressure drawdown loss increase under the coupling effects of threshold pressure gradient and medium deformation. Moreover，with the increase of production duration，amplitude of pressure drawdown loss would increase.

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FULL COUPLED ANALYSIS OF SEEPAGE-STRESS FIELDS FOR HIGH ARCH DAM BASED ON COMSOL MULTIPHYSICS

WANG Rui，SHEN Zhenzhong，CHEN Xiaobing

2013, 32 (s2): 3197-3204

(99)

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Based on M language offered by COMSOL Multiphysics，a full coupled analysis model was developed，and the corresponding calculating program was complied. And then，a three-dimensional finite element model of an arch dam located on Yellow River was established. The coupled seepage-stress field was compared with uncoupled condition under a selected reservoir operation case. The seepage field，stress field and displacement field were analyzed for deep understanding of the significance of coupling analysis in the high arch dam. The results showed the same distribution of seepage，stress and displacement fields in those two cases. However，compared with the uncoupled case，the equipotential lines of seepage field were close to downstream. Every displacement component increased at different rates，the tensile stress of the upstream rock increased and the compressive stress of the downstream rock also increased in the coupled case. The uplift pressure increased in the foundation and it was not beneficial to the stability of the dam. So，it is necessary to consider the coupled seepage-stress effect for high arch dam.

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APPLICATION COMPARISON OF ENGINEERING GEOLOGICAL ROCK GROUP AND ROCK MASS CLASSIFICATION IN ROCK ENGINEERING

SHANG Yanjun1，CHEN Mingxing2，WANG Kaiyang1，SUN Yuanchun2，YANG Shujun2，LI Kun1

2013, 32 (s2): 3205-3214

(112)

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Due to existence of various unfavorable geological bodies，assessment results of rock mass quality are often varied at different stages of construction，and induce some arguments. In order to assist in rock engineering aims，the engineering geological rock grouping is necessary to carry out on analyses of lithology and physi- mechanical features，for differentiation of main components of engineering geological zonation and evaluation. The widely applied rock mass quality classification is useful in rock engineering design and construction for surrounding rock stability purpose. The former comes from the viewpoint of rock mass structural control and takes account of rock mass types from a large range，while the latter adopting single or multiple parameters for assessment rock mass quality，including rock mass itself and surrounding environment. At different stages and layers，the two methods play distinctive roles，as for large scale geological forecast and engineering design，respectively，but with somewhat joints and overlays. The obvious differences of rock mass quality indices obtained at various stages of construction，can be clarified and interpreted from views of engineering geological rock group，with respect to unfavorable geological bodies. Taking the Yanmenguan Tunnel as one case example，their roles and application process are presented and discussed. The different advantages of the two systems and obtained results could be used in other rock engineering projects.

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ACOUSTIC EMISSION CHARACTERISTICS OF GRANITE UNDER TENSILE LOADING

LI Tianyi1，2，LIU Jianfeng1，2，CHEN Liang3，XU Jin1，2，WANG Lu1，2

2013, 32 (s2): 3215-3221

(120)

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The granite samples from Beishan of Gansu Province were tested on MTS815 Flex Test GT rock mechanics test system，including direct tensile test and indirect tensile test. The mechanical behaviors of granite were studied，and the acoustic emission(AE) was monitored by PCI–2 system. The test results showed that：the average value，the maximum and minimum values of tensile strength in direct tensile tests were greater than indirect tensile tests；the tensile strain of direct tensile tests was 6.03% of that of indirect tensile tests at the peak stress. Few AE signals were monitored for direct tensile tests before the loading stress was below 40% of the peak stress. When the loading stress was larger than 40% of the peak stress，AE counts and AE energy all increased. Especially，when it was close to the peak stress，AE events were the largest. For indirect tensile tests，the AE count rate during the full process was almost similar，and the energy release ratio at initial loading stage，e.g. less than 40% of the peak stress，was larger than the latter loading stage. Due to the effect of loading mode，the energy release ratio for indirect tensile tests was larger than that for direct tensile during the full failure process.

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ANISOTROPY OF ROCKMASS STRENGTH AND ITS TRANSFORMATION CRITICAL CONFINING STRESS

GUO Songfeng，QI Shengwen，HUANG Xiaolin

2013, 32 (s2): 3222-3227

(138)

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As the confining stress is higher，rock mass strength is less anisotropic. On the basis of the friction criterion of rigid discontinuities in the rock mass and the Hoek-Brown strength criterion of rock mass，the critical confining pressure is deduced. When the confining pressure is larger than the critical value，the strength of the rock mass with rigid discontinuities would change from anisotropy to isotropy. The derivation results show that the critical confining pressure is mainly related to parameter m in Hoek-Brown strength criterion and the uniaxial compressive strength. Based on the existing tests，rock mass with continuities are modeled with FLAC3D. Then，the Hoek-Brown criterion and the critical confining pressure mentioned above are verified. The results show that the strength of rock mass with one group or two groups of rigid discontinuities is anisotropic when the confining stress is lower than the critical confining stress，but isotropic when the confining stress is higher than the critical confining stress. For the rock mass with three group of cracks，the real critical confining stress is smaller than expected due to the locking effect.

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EXPERIMENTAL STUDY OF MECHANICAL BEHAVIOUR OF DEEP GNEISS IN HONGTOUSHAN COPPER MINE

ZHANG Xiwei1，YANG Chengxiang1，ZHANG Jian2，REN Jinlai1

2013, 32 (s2): 3228-3237

(94)

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To investigate mechanical properties of the gneiss in deep stope at Hongtoushan copper mine，Fushun，and further study the mechanism concerning slight rock burst and time-efficient deformation failure，the standard triaxial specimens are made from the core to carry out the complete failure processing triaxial test，unloading confining pressure under constant deviator stress test and creep test by Rockman 207 triaxial apparatus. The test results show that：(1) The relevancy of wave velocity-density-strength is not strong and the scatter is significant in uniaxial and triaxial results. (2) The brittle failure behaviour on hard rock is observed when the confining pressure is lower than 40 MPa，which would lead to a potential rockburst. (3) The strength in the unloading confining pressure under constant deviator stress tests is lower than that in the conventional triaxial. The plastic deformation is apparent during the loading，which indicates that the unloading path affects the rockburst. (4) Creep deformation is not measured under low stress level and the step deformation can be seen prior to the typical accelerated creep under high stress level. The failure mode of the gneiss sample in the creep test is with high similarity in comparison with the practical rib spalling in situ.

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STUDY OF EFFECTS OF GYPSUM CONTENT ON SALT-GYPSUM STRATUM CREEP RATE

MA Yue1，CHEN Mian1，YANG Chunhe2，YANG Pei1，LU Yunhu1，JIA Sibo3，JIN Yan1

2013, 32 (s2): 3238-3244

(105)

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Because of the coring difficulty in deep-layer salt formation，artificial cores were made according to its field mineral composition. Creep tests were conducted which shows that the natural core and the artificial core with the same mineral composition had the same creep law. In light of this finding，further creep tests of the artificial core were carried under different confining pressures and same temperature，and the effects of contents of different mineral compositions on the creep were obtained. The test results showed that under the same stress and temperature condition，the steady-state creep rate of high-salt salt-gypsum formation was higher，while the high-gypsum salt-gypsum formation was lower. At the same time，the physico-chemical property analysis were conducted for natural core in Caspian Basin，which also verified the above conclusion. The test result was tested in two ultra-deep wells in Keshen block in Tarim oil field and was applied to determination of drill fluid density.

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SUPPORTING ANALYSIS OF JOINTED ROCK BASED ON DISCRETE ELEMENT METHOD

YU Chong1，LI Guowen2，XIA Xiang1，ZHOU Qingchun1

2013, 32 (s2): 3245-3257

(111)

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In order to study the effects of rock excavation unloading and adjacent blasting on jointed rock and support structure，based on discrete element method，static and dynamic supporting analyses are carried out for Dalian underground oil storage cavern local jointed rock masses. Firstly，according to alternative support schemes， static supporting analysis of rock excavation is carried out，and the surrounding rock stress field and displacement field are obtained. Simultaneity，feasibility and improvements of alternative support schemes are studied. Then，considering adjacent region blast vibration，the equivalent blasting load derived from field test results is applied. The dynamic supporting effect of adjacent blasting vibration is analyzed. The time curve of monitoring points and the variations of velocity，stress and displacement are got. The numerical calculation method has certain reference value for static，dynamic analysis and determining safety blasting vibration standards.

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EFFECT OF EXTERNAL EXCITATION ON DAMPING RATIO OF ROCK-LIKE MATERIAL

SONG Quanjie1，2，LI Haibo1，LI Junru1，WANG Miao1，LIU Tingting1，LU Shizhan1，SONG Liang1

2013, 32 (s2): 3258-3265

(93)

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Rock damping ratio，as an important parameter that reflects capacity of dissipating energy of vibrating rock，is influenced by multiple factors and very sensitive. To study the rock damping ratio?s change law in different excitation modes and vibrating ways，gypsum specimen?s damping ratio is obtained in experiments in the states of forced non-resonance，forced resonance and free vibration of different wave forms. The influences of strain amplitude，vibration frequency and wave forms(P wave and S wave) on the gypsum specimen?s damping ratio are considered. Test results show that adjustment stage，smooth stage，steady growth stage of damping ratio will follow in proper sequence as the specimen?s strain increasing. In the smooth stage，there is a damping ratio peak under a certain frequency. When more than this frequency，gypsum specimen?s damping ratio increases with frequency?s increasing. And when less than this frequency，gypsum specimen?s damping ratio decreases with frequency?s increasing. What?s more，the damping ratio of gypsum specimen inspired by P-wave is larger than that by S-wave.

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STUDY OF RELEVANCY BETWEEN STRESS WAVE TIME DELAYS AND STIFFNESS OF STRUCTURAL SURFACE

ZHOU Jian1，2，ZHANG Luqing1

2013, 32 (s2): 3266-3274

(103)

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First of all，the transmission coefficient and the reflection coefficient of P wave crossing a elastic joint are deduced based on the theories both of elastic waves and displacement discontinuity. According to the stress wave time delay theory，the analytical solution of phase delay and group delay are given when the joint obeys the elastic Hooke?s theory. A universal distinct element code(UDEC) is used to simulate stress waves propagation in rocks with a single joint and five parallel joints，respectively. And the incidence stress wave is cosine Gauss pulse. All of the main research results can be summarized as follows. (1) When P wave transmitting the rock model with only a single joint，the phase delay is consistent with the analytical solution calculating from the unfiltered waves，while the group delay deviates from the analytical solution. After the 97–103 Hz band-pass filtered，the phase delay and group delay are both consistent with the analytical solution. (2) For the rock models with multiparallel joints，when the distance of these joints is larger than one half of the wave length of the cosine Gauss pulse，the group delay from filtered wave is more or less in line with the analytical solution. However，if the distance of these joints is smaller than one half of the wave length，the phase delay and group delay both deviate from the analytical solution. (3) As we all know，the wave-front is never disturbed by the multiple reflection. The wave-front delays of three multiparallel joints models are in line with each other under different joint stiffnesses，and the difference between these delays and the analytical results is limited. Under the assumption that the joint is a liner elastic model，the results of this research can be used to predict the joint stiffness or number of joints in rock masses.

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QUANTITATIVE ASSESSMENT OF INTERFERENCE INDUCED BY ROOF BOLT DURING ADVANCED DETECTION WITH TRANSIENT ELECTROMAGNETIC METHOD IN MINE

HU Xiongwu1，ZHANG Pingsong1，CHENG Hua2，WU Rongxin1，GUO Liquan1

2013, 32 (s2): 3275-3282

(89)

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During the process of roadway construction in mine，the effect of advanced water exploration using transient electromagnetic method is often poor because of the interferences of electromagnetic field，in which the metal interfering the most. So，the study for the interference characteristic of metal has an important significance to improve the technology of advanced water exploration. For advanced detection，the roof bolt can be suggested as the main interference source，and the experiment of entity model is designed as its practical situation in working face. The test data analysis shows that the interference degree and stamp of roof bolt are decided by its own spatiality，including the plane coordinates(x，y) and the exposed length(L). The maximum jamming range of roof bolt d is confirmed as 3 m primarily. Among this range，the areas interfering strongly range from 0m to 1.5m and the weak range from 1.5 m to 3.0 m. And the sensitive variation range of interference by the roof bolt?s exposed length distribution is delimitated from 0 m to 0.5 m，but the range from 0.5–1.7 m remains basically stable. In addition，through the contrast between the superposed and measured values，the values of combination interference signal induced by two roof bolts are approximately equal to the vertical stacking of the amplitude of transient electromagnetic field induced by any one of roof bolts respectively. The achievements can provide a rule for the research on the technology of interference correction of metal. Last，the paper point that the validity of test data influenced by roof bolts need an intensive study.

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A NUMERICAL METHOD TO DETERMINE REAL STRAIN-RATE EFFECT FOR ROCK-LIKE MATERIALS

YU Shuisheng，LU Yubin，CAI Yong

2013, 32 (s2): 3283-3290

(105)

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It has been found recently that the dynamic compressive strength of rock-like materials testing on split Hopkinson pressure bar(SHPB) is increased with the increase of testing strain-rate. The dynamic compressive strength increasing is attributed to the combined action of material strain-rate effect，lateral inertial effect and end friction effect，and in actual SHPB tests they are coupled together and could not be separated from each other. To determine the material strain-rate effect of the rock-like materials in SHPB tests，it needed to remove the dynamic compressive strength increment caused respectively by lateral inertial effect and end friction effect. In this study，the numerical simulation method is employed to simulate the SHPB tests for rock-like materials. The effect of material strain-rate，lateral inertia and end friction is assumed to be uncoupled. In numerical SHPB tests，when the effect of material strain-rate and lateral inertia is not considered，the predicted dynamic compressive strength increment of rock-like materials induced only by the lateral inertia effect is obtained. Similarly，when the effect of material strain-rate and end friction is not considered，the dynamic compressive strength increment of rock-like materials obtained from numerical SHPB tests caused only by the end friction effect is determined. Then removing the dynamic compressive strength increment caused respectively by the lateral inertial effect and end friction effect from the dynamic compressive strength data obtained from actual SHPB tests，the material strain-rate effect of the rock-like materials in SHPB tests is determined. Finally，the assumption proposed in this study is verified by comparing the results with other research.

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EXPERIMENTAL STUDY FOR COAL BRIQUETTE ADSORPTION OF CH4/CO2 MIXTURE UNDER DIFFERENT TEMPERATURES

WU Di，SUN Keming

2013, 32 (s2): 3291-3296

(105)

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To study the adsorption law of CH4/CO2 mixture on briquette specimen under different temperatures，conduct the non-isothermal adsorption experiments for different concentrations of CH4/CO2 mixture of briquette specimen(? 50 mm × 100 mm) by using self-developed gas mixture adsorption test device controlling temperature are conducted. The results reveal that：at the same temperature，the more CO2 concentration in the mixture，the stronger gas adsorption capacity；the adsorption capacity of CO2 is greater than that of CH4；the adsorption curve of mixture gas is between that of pure CH4 and CO2，the mixture gas adsorption quantity of block coal briquette is less than that of coal powder sample obviously. Under conditions of different temperatures and same pressure，the adsorption quantity increases firstly and decreases subsequently，the maximum value occurred when the temperature reached to 40 ℃. When the adsorption reached the balance，the relative concentration of CO2 in free phase decreases generally，and the decrease amplitude is the maximum at 40 ℃. So，injecting CO2 could replace CH4 in coal seams effectively，and at 40 ℃，the more relative concentration of CO2，the more obvious the displacement effect will be.

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STUDY OF REPRESENTATIVE ELEMENTARY VOLUME FOR FRACTURED ROCK MASS BASED ON THREE-DIMENSIONAL FRACTURE CONNECTIVITY

WANG Xiaoming，XIA Lu，ZHENG Yinhe，YU Qingchun

2013, 32 (s2): 3297-3302

(111)

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Three-dimensional(3D) fracture connectivity，which can comprehensively reflect the fracture features，is a key parameter for evaluating the stability of engineering rock masses. For the purpose of determining a representative 3D connectivity value，the scale effect of 3D connectivity is investigated based on projection method and the representative elementary volume(REV) of the study rock mass is further estimated. First，fracture data collected from an exploration tunnel are statistically analyzed and used to generate a large discrete fracture network of 100 m×100 m×140 m by an inverse method. Inside the fracture network，reference planes with different sizes ranging from 5 m×5 m to 100 m×100 m are sampled 10 times on different elevations. A projection method is adopted to calculate horizontal 3D fracture connectivity of each reference plane and the relationship between the 3D fracture connectivity value and the study domain size is analyzed. The REV of the rock mass is estimated based on a series of T-tests and F-tests. The T-tests and F-tests are performed to determine whether the mean value and variance of fracture connectivity for different sizes are statistically equal to the largest size，respectively. The results show that a size of 65 m×65 m could be viewed as the REV，beyond which the mean value and variance of the connectivity converge to a stable state.

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FRACTAL DIMENSION IMPROVED ALGORITHM OF ORIENTATION POLE DISTRIBUTION FOR JOINTS

SONG Lijuan1，XU Mo1，LU Shuqiang2，ZHANG Xiaochao1，YU Chengyun1，HUANG Hui1

2013, 32 (s2): 3303-3308

(88)

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Quantitative description of the structural plane spatial distribution has been the study focus and difficulty，which could help to determine the form of the combination of unstable blocks accurately，and provides accurate and valid information for analysis of rock mass stability. Following the principle of meshing Schmidt pole diagram by equal area，an improved algorithm is suggested based on Chen Jianping?s method for calculating the fractal dimension of joint orientation pole distribution. It can mesh directly the Schmidt orientation polar plot generated by Dips software，take the ring number n for self-defined input variable and greatly simplify the programming. Based on the survey grid data of the spandrel groove internal slop of right dam foundation in Dagangshan Hydropower Station，fractal dimension D of orientation pole distribution for rock mass joints is obtained. The conclusions summarized are almost the same as concluded in the paper of Chen Jianping，which verifies the correctness and feasibility of the improved algorithm and promotes the universal application of the method of Chen Jianping?s.

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CORRECTION OF RMR SYSTEM AND ITS ENGINEERING APPLICATION

WANG Lehua，LI Jianrong，LI Jianlin，WANG Kongwei，XU Xiaoliang，WAN Liangpeng

2013, 32 (s2): 3309-

(123)

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The three indices of uniaxial compressive strength，RQD value and structural face interval in the existing RMR method evaluation system aim at the grading value of a interval，and are all applied to engineering with the conservative values. By selecting a large number of rock quality evaluation data related to the present engineering projects，the grading standard of the three indices is studied and their grading intervals are corrected. The characteristic of nonlinear step changes of the grading values is corrected，which makes the grading values become linear and continuous. The linear relationship expression between the indices value and grading value is built. The corrected results are applied to the actual projects and get good effect，which can provide a certain reference for the rock mass quality evaluation and the engineers.

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NUMERICAL SIMULATION FOR LOW-PERMEABILITY AND EXTRA-LOW PERMEABILITY RESERVOIRS WITH CONSIDERING STARTING PRESSURE AND STRESS SENSITIVITY EFFECTS

WANG Jing1，LIU Huiqing1，LIU Renjing2，XU Jie3

2013, 32 (s2): 3317-3327

(108)

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In order to reflect the influences of starting pressure and stress sensitivity on the development law of low-permeability reservoirs，the following researches are conducted. Firstly，the dynamics models of threshold pressure gradient and dynamic permeability are established based on the experimental results of threshold pressure gradient and stress sensitivity effects. Based on this，the mathematical model of water-flooding in low-permeability reservoir with considering the starting pressure and stress sensitivity is established according to the law of conservation of mass and permeation fluid mechanics theories. Also，the corresponding numerical simulation software is developed. Then，the software is used to study the influences of different features on the seepage field and development law，and the effects of starting pressure and stress sensitivity on development effect. At last，the influences of advanced water flooding，increasing injection-production ratio and increasing injection-production rate on recovery are investigated by numerical simulation method. Simultaneously，the best injection parameter is optimized. The results show that：(1) Threshold pressure gradient directly results in the lower recovery of low-permeability reservoirs. Stress sensitivity indirectly affects the recovery by increasing the threshold pressure gradient. (2) All the measures of advanced water flooding，increasing injection-production ratio and increasing injection-production rate can enhance oil recovery of low-permeability reservoirs. And the order of the enhancing extent is：advanced water flooding＞increasing injection-production ratio＞increasing injection-production rate. (3) The optimal time of advanced water flooding is 100 d，the optimal value of injection-production ratio is 1.1∶1，and the optimal value of injection-production rate is 0.000 15～0.000 25 PV/d.

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SCALE MODEL TESTS AND NUMERICAL ANALYSIS OF ARTIFICIAL FREEZING AT DIFFERENT TEMPERATURES IN COMPLICATED STRATA

LIU Bo1，CHEN Yuchao1，2，LI Dongyang1，SONG Changjun1，3

2013, 32 (s2): 3328-3336

(120)

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There is a great difference of thermal conductivity between strata in some shaft construction projects by artificial freezing method. An optimization freezing suggestion of flowing two types of negative temperature solutions in a freezing pipe is proposed to accelerate the freezing rate of local strata and to optimize cold energy adjustment. And a single freezing pipe of dual circulation system is developed for this purpose. To verify the effect of intensified freezing and the adjustment ability of the freezing pipe，a single freezing pipe test for sand and silty clay is conducted in a model test box using two sets of circulatory systems to provide calcium chloride solution of different negative temperatures for two sections of a single freezing pipe. Temperature field distribution characteristics of frozen wall in different levels of freezing pipe are analyzed. Meanwhile，the numerical simulation is adopted to calculate temperature field of the case using FLAC3D software. The results show that the difference of temperature can reach 9.1℃ between adjacent outer walls of the two different temperature sections，and the thickness and average temperature of freezing wall can be adjusted effectively. The silty clay has been intensified frozen more than sand certainly.

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STABILITY CALCULATION FOR DISCRETE FRACTURE NETWORK OF ROCK MASSES BASED ON JOINT FINITE ELEMENT METHOD

WANG Yu1，2，LI Xiao1，LIU Shuai3，HE Jianming1，LI Shouding1，LI Tengfei1，2

2013, 32 (s2): 3337-3345

(109)

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Through stability of many fractured rock masses slopes on Guangle highway，conclusion obtained that objective geological model，appropriate constitutive relation，accurate parameters and effective calculation method are the key problems for stability evaluation. The joint finite element method(JFEM) is proposed. In the method，the fractured rock massed are composed of rock block and fracture network，the properties of rock block and joint are considered simultaneously，reflecting the nonlinear relation of contaction fully. Firstly，based on the single structure surface theory proposed by Jaeger，the compression strength of fractured rock massed is calculated by JFEM，which verifies the reliability of the JFEM. Secondly，introducing discrete fracture network model，the stability of fractured rock masses is discussed based on Voronoi model，Baecher model and Veneziano model. The generalized Hoek-Brown criterion and Barton-Bandis criterion are applied to rock block and joint，respectively. Using the strength reduction method to calculate stability factor，the influences of key parameters in DFN on the slope stability are discussed. The research provides a new idea for the stability evaluation of fractured rock masses and theoretical basis to engineering decision.

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NUMERICAL SIMULATION AND ENGINEERING APPLICATION OF SOLID-FLUID COUPLED MODEL FOR SATURATED POROUS MEDIA

CHEN Wu1，PEI Wansheng1，LI Shuangyang1，ZHANG Mingyi1，JIN Xia2

2013, 32 (s2): 3346-3354

(88)

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Based on the theory of computational fluid mechanics and geotechnical mechanics，equilibrium equation of media and continuity equation of interstitial fluid are derived with the consideration of interaction of seepage and stress field. Numerical methods of solving the proposed equations as well as boundary conditions are put forward. Combined with Galerkin way，finite element method is employed to disperse equilibrium equation，while finite method is applied to the discretization of continuity equation. That is the backward differentiation formula and two order accuracy warming-beam formula. Then，a water-rich bi-directional tunnel is taken as an example，distribution of pore pressure，displacement，stress and mechanical behavior of anchorage in different construction stages are analyzed. Finally，numerical results are compared with the conclusion of related field monitoring. The study results could provide guidance for the design and construction of similar tunnel projects.

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COMPARATIVE EXPERIMENT OF ELECTROOSMOSIS OF FERRUM，GRAPHITE，COPPER AND ALUMINUM ELECTRODE

TAO Yanli1，2，ZHOU Jian1，GONG Xiaonan1

2013, 32 (s2): 3355-3362

(72)

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Laboratory tests of typical Hangzhou soft soil were conducted to investigate the electroosmosis effects of ferrum，graphite，copper and aluminum electrode under the voltage gradient of 1.58，0.79 and 0.53 V/cm respectively. By monitoring and analyzing drainage，effective voltage，water content reduction and energy consumed of each test，the following conclusions were drawn. Differences of the electroosmosis effects of ferrum，graphite，copper and aluminum electrode decrease with the drop of voltage gradient. Under higher voltage gradient，ferrum and graphite electrode performs quite accordance and their electroosmosis effects are much better than copper electrode. While with a relative lower voltage gradient，copper electrode displays slightly better than ferrum electrode，which again has a better performance over graphite electrode. Aluminum electrode represents the worst performance under all circumstances investigated. The conclusions can be reached by comparing the above results with former results that graphite electrode occupies a better performance over ferrum and copper electrode under higher voltage gradient，while performs worse than the other two electrodes under lower voltage gradient. In the real practice，the mineral constituent or ionic composition of the soil should be analyzed to select the optimum electrode material. Moreover，ferrum electrode is recommended as a preferential alternative in the electroosmosis strengthening of the soft soil in the coastal area of Zhejiang Province，while aluminum electrode is not suggested.

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EXPERIMENTAL STUDY OF PARTICLES CLOGGING IN SAND LAYER OF GROUND-SOURCE HEAT PUMP (II)

ZHAO Jun1，2，ZHANG Chengyuan3，LIU Quansheng3

2013, 32 (s2): 3363-3369

(60)

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A new experimentation equipment，which can provide directly observation on mechanisms of physical and biological clogging of ground-source heat pump(GSHP) in porous media，is developed. The system can observe real-timely and directly space change of obstruction with the tem observation. Two-way flow drive is adopted to simulate the recharge of underground water source heat pump system and back to the young's seepage conditions. The glass beads and gravel particles are used as porous mediums，and alkaline alumina particles are used as the suspended particles. The velocity of the fluid inside the pore is different caused by different pores through numerical simulation. From the simulation we find that in the least pore the fluid velocity is often the biggest，and in the smallest pore can clog particles most easily. The results can provide test base for solving environmental safety evaluation.

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MEASUREMENT AND ASSESSMENT OF PHYSICAL STATE OF COMPACTED ROCK-FILL

YAO Shigui1，SHI Minglei2，YUAN Long2，ZENG Zhijun1

2013, 32 (s2): 3370-3377

(111)

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The compaction quality of rock-fill structure was difficult to detect and evaluate. Based on the statistical analysis principles，the rock-fill particles water retention characteristics，relative density representative value and the maximum dry density were detected，and the detection method was formed to detect the physical state of compacted rock-fill road engineering. Both the float-down method and the representative specific gravity method were utilized to evaluate the granular volume rate. Supplemented detecting the outliers compaction，the effectiveness of the compaction quality evaluated by the granular volume rate was improved. At the same time，the misjudgment caused by the rock-fill particles adverse individual was avoided. The engineering example shows that the evaluation rationality and the operation of the rock-fill physical state by the proposed method are improved. The results may provide references for similar engineering projects.

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EXPERIMENTAL RESEARCH ON SHEAR CREEP AND ITS LONG-TERM STRENGTH OF WEAK INTERCALATION IN DAM FOUNDATION

WANG Yu1，LI Jianlin1，LIU Feng2

2013, 32 (s2): 3378-3384

(92)

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In order to understand exactly the creep property of weak intercalation in dam foundation rock，the shear creep test is carried out under different normal stresses by using step loading shear stress. The shear creep deformation law，failure mechanism and long-term shear strength of weak intercalation are concerned in this study. The results indicate that the empirical formulation can reflect the shear creep deformation law of weak intercalation properly，the average and steady-state shear creep rates increase at a exponential function with the shear stress increasing，and the shear creep failure of weak intercalation shows typical ductility failure characteristics. Based on a new method，called inflection-point method，the long-term shear strength of weak intercalation under different normal stresses is determined. The calculation results of inflection-point method are compared with that of steady-state rate method，and the rationality and validity of inflection-point method are test. The research results show that this method greatly improves the accuracy of determining the rock mass long-term shear strength and brings important reference for engineering practice.

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BIAXIAL COMPRESSION CREEP TEST FOR GREENSCHIST CONSIDERING INFLUENCE OF SPECIMEN WIDTH

XIONG Liangxiao1，2，3，LI Tianbin2，YANG Linde3

2013, 32 (s2): 3385-3390

(99)

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The biaxial compression creep tests for greenschist were carried out. The creep test curves were fitted by six-component viscoelastic rheological model，and the influence of specimen width on creep deformation rule was studied. The results show that the axial and lateral strain will not always increase or decrease with increasing specimen width under the same stress level，but the axial creep strain rate of second creep stage will reduce all the time. The six-component viscoelastic rheological model curve and experimental curve approximately coincide with each other，which indicates that the rheological model is appropriate for determining the viscoelastic rheological parameters of greenschist.

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POST-PEAK DEFORMATION AND FAILURE EXPERIMENTAL STUDY OF ROCK-LIKE SPECIMENS WITH DIFFERENT INCLINATION ANGLES PERSISTENT JOINTS

LI Shuchen1，WANG Lei1，2，LI Shucai1，HAN Jianxin1，3

2013, 32 (s2): 3391-3395

(98)

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The uniaxial compression test of pre-existing persistent jointed rock-like specimens is carried out by high stiffness servo control testing machine. Systematic researches on the relationship of post-peak stress-strain curve，failure form，strength after peak，the Poisson?s ratio after peak of rock masses with dip angles of persistent joints are performed. The results indicate that：(1) The post-peak stress-strain curves of specimens with joint inclination angle of 15°and complete specimens are basically the same，but the post-peak stress-strain curves of specimens with the joint inclination angle of 30°，40°，50° to 60° and complete specimens vary greatly. (2) Peak strength decreases with the increase of joint inclination angle，residual post-peak strength also generally increases as the joint angle increases. (3) Poisson?s ratio of jointed specimen increases with joint inclination angle increases，but the post-peak visual Poisson?s ratio becomes smaller in the phase of destruction with joint inclination angle increases. (4) The post-peak failure modes of specimen change with joint inclination angle. Specimens damage is splitting failure at the joint inclination angle of 15°，shear failure at the joint inclination angle of 50° and 60°， splitting and shear mixing model at the joint inclination angle of 30° and 40°. The research result can reflect mechanics，deformation and damage characteristics under uniaxial compressive loading in the phase of post-peak of rock masses with different dip angles pre-existing persistent joints.

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DISCUSSION ON DESIGN AND CONSTRUCTION MEASURES FOR A ROCK TUNNEL IN HIGH-TEMPERATURE CONDITIONS

HOU Daiping1，LIU Naifei2，YU Chunhai3，LI Ning2

2013, 32 (s2): 3396-3403

(116)

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Due to the high geothermal problems in the rock tunnel of Bulunkou—Gongur hydropower station in Xinjiang，investigations about thermal-stress induced by high temperature is performed firstly；and the reasons of the high temperature in the rock mass around this project are also discussed. It?s found that the heterogeneity of geological formations causes heat flux density to concentrate in the low thermal resistance part，i.e. graphite interlayer，which induceds the high temperature around the tunnel in the rock mass of graphite interlayer. Secondly，construction measures in high temperature are studied，and the ventilation method is reconnended，which is assisted by the spray technology using low temperature water. The support scheme is also suggested for the similar tunnel in the high temperature variation，i.e. using fire and heat-resistant concrete spray or fiber reinforced concrete spray to replace the ordinary concrete lining.

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CENTRIFUGE MODEL TESTS OF SEISMIC RESPONSE OF RECTANGULAR TUNNELS AT DIFFERENT BURIED DEPTHS

LIU Hongzhe1，2，HUANG Maosong1，2

2013, 32 (s2): 3404-3412

(108)

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Dynamic centrifuge tests of seismic response of rectangular tunnels in sandy silt are performed. Three experiments are conducted，including free-field test，shallow tunnel test and deep tunnel test. Dynamic behaviour of the soil and tunnel is presented，including soil acceleration at different depths，soil displacement in the horizontal direction，settlement of the ground surface and dynamic strain of tunnels in the transverse direction. Effect of the presence of tunnel on site earthquake response as well as the difference of seismic response of tunnels at different buried depths are analyzed through contrasting the three sets of experimental data. It is concluded that the maximal seismic deformation occurs at four corners of the tunnel，presence of the tunnel changes the dynamic property of site，and seismic response of the deep tunnel is larger than that of the shallow one.

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ANALYSIS OF CONSTRUCTION AND POST-CONSTRUCTION SETTLEMENT DATA CAUSED BY IMMERSED TUNNEL

WEI Gang1，QIU Huijie2，WEI Xinjiang1

2013, 32 (s2): 3413-3420

(97)

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The measured data of settlement from 19 immersed tunnels were collected at home and abroad. The changing regularity of construction settlement，post-construction settlement，total settlement and the differential settlement between both ends of tube and its joints were analyzed. The statistical results show that：(1) the average value of construction settlement is 53 mm，which is no more than 100 mm in general；(2) the average value of total settlement is 108 mm，which is no more than 200 mm in general；(3) the construction settlement takes an average percentage of 56% in the total settlement，indicating construction settlement is the main reason for the total settlement. The settlement grows up after the construction but the post-construction settlement is small in general；and the average differential settlement between both ends of tube caused by construction and total settlement are 21 and 40 mm，respectively. The differential settlement at the tube joints caused by construction and total settlement are 18 and 12 mm，respectively. The differential settlement between both ends of tube is larger than that in joints，which can easily lead to cracking of immersed tunnel.

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RESEARCH ON ROCKFALL IMPACT PREVENTION OF CHEDIGUAN BRIDGE PIER，DUWHEN ROAD

HE Siming1，2，ZHUANG Weilin3，ZHANG Xiong4，JI Suiwang3，CHENG Qiang3

2013, 32 (s2): 3421-3427

(110)

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Dujiangyan—Whenchuan road is the life line engineering of disaster areas hit by the 5•12 Whenchuan earthquake. Chediguan bridge on the road which stretches across the both sides of Mingjiang River collapsed due to rockfalls during the earthquake. After reconstruction，the new Chediguan bridge was open to traffic on May 12，2009. July 25，2009，at 4：40 or so，a large area collapse on the Mingjiang River bank high unstable rock occurred，rockfalls smashed the Chediguan bridge again. After investigation， there are many rocks existing in the mountains of both sides of Minjiang River，which will likely trigger the catastrophic events of rockfalls smashed the bridge. On this basis，the development of a new cushion structure of rockfalls impact piers is executed，using nonlinear finite elemnet method，considering the effects of nonlinear material properties，nonlinear geometry，nonlinear contacts and rebars during the processes. The results show that，the cushion structures could effectively buffer the impact of the rockfalls，the ability of rockfalls impact piers could be improved，and up to now，the consequences are very well.

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DEFORMATION PREDICTION OF SUBWAY TUNNEL INDUCED BY EPB SHIELD IN SOFT CLAY DURING ABOVE AND DOWN OVERLAPPED TRAVERSING PROCESS AND ITS CONSTRUCTION CONTROL

ZHANG Zhiguo1，2，3，ZHANG Mengxi2

2013, 32 (s2): 3428-3439

(109)

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Building piles，municipal pipelines，existing tunnels and other underground structures have hindered the construction space for the new tunnels because of dense city buildings and developed networks of existing subway tunnels. Then the new tunnels often inevitably overlapped cross and bypass cross the existing structures. Significant construction risks will be encountered during the complex above and down overlapped construction，and potential safety hazard will also be existed in service for the existing tunnels. Based on the tunneling case for Shanghai railway transportation line，the deformation prediction of subway tunnel in service induced by EPB shield in soft clay during above and down overlapped traversing process and its construction control are presented by using simplified theoretical method，3D finite element(FE) numerical simulation method，and in-situ monitoring method. The simplified theoretical method is originated from the Winkler foundation. The longitudinal settlement equation for existing tunnels due to above and down overlapped construction is obtained. The 3D numerical simulation method can optimize the construction scheme and shield excavation parameter. The practice case for above and down overlapped crossing with large oblique angle are analyzed. The in-situ monitoring method can obtain the measured data for subway tunnel in service induced by EPB shield and the setting rules of shield tunneling parameters，including earth pressure for cutting open，synchronized grouting，propulsion speed，segment assembling elevation，and cutter head torque. The proposed method may provide a theoretical basis for proposing correctly protective measurements of subway tunnels in service due to tunneling excavation during overlap traversing process. Furthermore，the research results can provide references to the future construction of other similar projects such as subway tunnels multi-line passing through existing structures.

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STABILITY ANALYSIS OF TUNNEL WORKING FACE IN COMPOSITED SANDY SOIL

LIU Wei1，2，TANG Xiaowu1，GAN Penglu1，SAVIDIS S2

2013, 32 (s2): 3440-3447

(89)

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The tunnel working face easily collapses when tunneling is conducted in the composited sandy soil, thus it is important to maintain the proper support pressure for the working face stability. According to the frictional characteristics of sandy soil，the upper bound analysis is applied to analyze the working face stability by using the improved 3D kenimatically admissible mechanisms, and the formula of the minimum support pressure for the working face stability is obtained. As the crossed soil is defined，the influence of the tunnel diameter，the depth ratio，the ground surface surcharge，the cohesion and the friction angle of the cover layers and the relative thickness ratio of cover layers on the support pressure is studied. This study presents an accurate estimation of support pressure for the tunnel working face stability in the composited sandy soils as well as an important theoretical reference to the similar practice projects.

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RESEARCH ON DEEP SALT ROCK UNDERGROUND GAS STORAGE SLABBING RISK BASED ON MOFM FAILURE PROBABILITY CALCULATION METHOD AND ITS APPLICATION

ZHANG Ning1，WANG Mingyang1，XIAO Junhua2，FAN Pengxian1，LI Jie1，LI Shucai3，ZHANG Qiangyong3

2013, 32 (s2): 3448-3454

(122)

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Slabbing failure is a major failure mode in deep salt rock underground gas storages. In order to research the risk level of the salt rock gas storage，a failure risk probability calculation method of the deep salt rock underground gas storage side falling was established based on the modified first-order second-moment method，according to the existing failure theory. Secondary development of the method was operated using ABAQUS platform in the part of UVARM，and the slabbing failure probability of the Jintan salt rock underground gas storage was calculated with this method. The failure probability under the low pressure operating conditions of a single storage was calculated，and multi-storage cavity failure probability caused by pressure loss of single cavern was also calculated. The results illustrate that，if the pressure of storage is higher than 6 MPa，failure probability would be less than the gas storage safety requirements. If the space of pillar is appropriate，individual cavern cavity loss pressure would cause little effect on the other cavern. The results are well in accordance with the practice of Jintan gas storage. It´s shown that this method has practical value in engineering application.

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VISCOELASTIC SOLUTION OF CIRCULAR TUNNEL UNDER ASYMMETRIC HYDROSTATIC PRESSURE CONSIDERING STRESS RELEASE

BIAN Yuewei1，2，XIA Caichu1，2，XIAO Weimin1，2，ZHU Hehue1，2

2013, 32 (s2): 3455-3465

(75)

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Firstly，taking use of the correspondence principle，the viscoelastic solution for the circular tunnel with constant ratio of stress release is obtained，based on the elastic solution of the circular tunnel under non-hydrostatic pressure. Then，the stress is released step by step during construction，and the boundary condition at the intrados will change along with the distance x between excavating face and the studred section. The distance x could be expressed as a function of excavation speed v and time t. so the boundary condition could be expressed as a function of time t and speed v. According to the Stieltjes integrals, the items of ?Fi(t)(i = 1–11) in the solution for constant ratio of stress release are replaced with the integrals of Fi(t) with respect to d?(t). The solution for the circular tunnel under non-hydrostatic pressure considering the ratio of stress release could be obtained. When the ratio of horizontal pressure coefficients k0 = 1，the solution could be transformed into the viscoelastic solution for the circular tunnel under hydrostatic pressure considering the ratio of stress release. When the ratio of stress release ? = 1，the solution will be transformed into the viscoelastic solution for the circular tunnel under non-hydrostatic pressure without considering the ratio of stress release. So the latter two solutions are special cases of the solution in the paper. The non-hydrostatic pressure assumption accords with the engineering practice，and the ratio of stress release indicates the effects of construction procedure on the stress and deformation of rock. The results could be a reference for the design and construction of tunnels.

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STATIC ELASTOPLASTIC ANALYTICAL METHOD OF CIRCULAR TUNNEL UNDER UNIFORM GEOSTRESS FIELD

XIAO Jianqing1，2，FENG Xiating2，ZHANG Lachun3，QIU Shili2

2013, 32 (s2): 3466-3477

(99)

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A lot of constitutive models，representing the properties of rock well，have not been utilized widely because of the difficulty in elastoplastic solution. So，based on the single curve and constant volume hypothesis，an analytical method that can be used more conveniently was summed up and modified firstly. Using this method，the stress of elastic and plastic zones，radius of plastic zone，equilibrium equation and superior and inferior limits of self-support geostress of surrounding rock after excavation were calculated accurately or approximately. In view of linear softening constitutive model，Lambert function was introduced to calculate the radius of plastic zone and its range in equilibrium curve of surrounding rock proved. For the Nelder nonlinear softening model，an exponential function was used to describe approximately the abscissa of inflection point and softening modulus. When the Weibull model was taken to represent the post-peak mechanical behaviour，since it is difficult to get the inverse function and limit of Whittaker function，a new idea，fitting the whole equilibrium curve with Gauss function and computing the radius of plastic zone by solving the inverse function of Gauss，was proposed. Then，comparison was taken between these results derived from six constitutive models and it is found that the superior limit of self-support geostress of surrounding rock was higher，the stress concentration factor was lower，the position that stress concentrates was in elastic zone，deviating from the interface between elastic and plastic zones，and the wedge angle in the tangential stress redistribution curve disappeared under nonlinear elastic condition，which is consistent with the practice. Therefore，for either soft or hard rock，a more perfect result from elastoplastic solution can be obtained by taking a smooth and continuous constitutive model.

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BASIC THEORY OF SEISMIC DEFORMATION METHOD IN CROSS SECTION OF TUNNEL AND ITS APPLICATION

GENG Ping，ZHANG Jing，HE Chuan，YAN Qixiang

2013, 32 (s2): 3478-3485

(110)

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In China，great quantities of tunnels are located in high seismic intensity area. As one of the main structure of the national lifeline，tunnel seismic calculation method must be paid high attention to. Based on seismic response characteristics of the tunnel as well as differential kinematics equations of underground structures and surrounding rocks，the basic theory of seismic deformation method in cross section of tunnel is summarized. The solving methods of stratum displacements in homogeneous semi-infinite formation and bedded formation under seismic load are put forward. The adaptabilities of the seismic deformation method are studied by comparative analysis in both methods of seismic deformation method and time-history analysis method. The results prove that the seismic deformation method with clear theory can reflect the vibration characteristics of soil or weak rock tunnel whose seismic response is mainly influenced by ground relative displacement，and the computational process is convenient and efficient. It is a good method for this type of tunnel seismic calculation method if having the displacement or velocity response spectrum of project site.

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DIAGNOSING AND LOCATING OF DEEP OVERBURDEN STRUCTURAL PLANE AND WEAK INTERCALATED LAYERS TAKING WUDONGDE HYDROPOWER STATION DAM SITE AT DOWNSTREAM OF JINSHA RIVER FOR EXAMPLE

LI Huaqing1，GAN Fuping1，CHEN Yuling1，CHENG Zhanlin2，RAO Xibao2，XIAO Guoqiang2

2013, 32 (s2): 3486-3492

(136)

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Deep overburden layer is a special engineering foundation. It is distributed non-uniformly in loose structure，lithologic discontinuity，genetic type and rock-soil structure，physico-mechanical properties. The structure plane in deep overburden and weak intercalated layers distribute discontinuously，which make it difficult to identify those layers. It is currently an unsolved hotspot problem of engineering geology. Field experiments to identify the deep overburden layers were implemented at Wudongde hydropower station. The geological evidence is revealed that the intact weak intercalated layers are preserved in the deep overburden layer based on cross-well electromagnetic wave Color-CT imaging findings. Through the study of cross-well Color-CT images，the threshold values are selected for separating the structure planes of rock and soil mass and the regions of different structure planes are calibrated，using the nonlinear calculation of the absorption coefficients of rock and soil mass. Finally，the weak intercalated layer regions are located based on the feature parameters of area，location and shape. The quantity and spatial distribution of the weak intercalated layers in the cross-section between holes are defined.

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ASEISMIC ANALYSIS OF LARGE STEEL VESSEL BURIED IN THE DEEP UNDERGROUND ENGINEERING

WANG Xinzheng1，ZOU Guangping2，CHEN Jianjie1，WANG Chunming1，LI Ping3

2013, 32 (s2): 3493-3500

(125)

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For the large steel vessel storing high-level radioactive waste buried in the deep underground engineering，the aseismic analysis of shielding structure from radioactivity is necessary in the long service time. On the base of analyzing the status aseismic for underground engineering，the method of combining the experiments and numerical simulation was put forward to aseismic analysis of the deep buried large scale vessel steel. After studying the observed seismic data in the basement rock，the rules of ground motion varying with depth were summarized，and the fitting curves between the amplitude ratio(acceleration，velocity and displacement) and depth were obtained. Based on above rules and curves，the investigation of active fault and the thought of the most unfavorable design ground motions，the design seismic ground motion at 300 deep m in the design site was received. It is modified from the records on the basement rock by the Loma Prieta earthquake taking place on October 18，1989. The elastoplastic Mohr-Coulomb(M-C) constitutive equation was selected to describe the bentonite and concrete，and the parameters of M-C were experimented on the Wille soil triaxial and rock triaxial apparatus respectively. At last，the seismic response of the shielding structure was analyzed with the finite element software ABAQUS. The results show that there are cracks between bentonite and steel vessel；plastic strain occurs in local region of bentonite layer； and the plastic strain of concrete layer is very small，which lies in the safety limit. The method in the paper is helpful for seismic design of underground engineering.

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RESEARCH ON MECHANISM OF LARGE DEFORMATION AND COUNTERMEASURES OF SURROUNDING ROCKS OF TUNNEL THROUGH COAL STRATA

LI Shengjie1，2，XIE Yongli1，WU Danze3，ZHU Xiaoming4

2013, 32 (s2): 3501-3508

(99)

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Surrounding rock of Anyuan highway tunnel through coal strata is made of carbonaceous shale，coal line and mudstone weak interlayer. The uniaxial compressive strength of the carbonaceous shale specimens are 3.9–4.8 MPa. The geostress measurement is carried out，and the results show that the maximum horizontal principal stress is 8–10 MPa，and the horizontal principal stress is dominant in the area of tunnel. Based on the on-site monitoring and numerical simulation，the characteristics of surrounding rock deformation are analyzed. The reasons for large deformation are summarized as follows：(1) The strength of surrounding rock is low and the rock swells easily；(2) The level of geostress is high as to the low strength of rockmass；(3) Water effect；(4) Improper construction. The mechanism of large deformation is discussed also. The countermeasures are proposed as follows：the tunnel face should be closed quickly after excavation，then the temporary support is set up，long bolts and grouting pipe are used to control the deformation，the arch is replaced after deformation become stable，the spacing of steel arch is reduced，and finally，invert and inner lining are applied timely. According to the measurement results，it is shown that the treatment measures are effective.

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IN-SITU MONITORING STUDY OF MECHANICAL CHARACTERISTICS OF PRIMARY LINING IN WEAK ROCK TUNNEL WITH HIGH GROSTRESS

LI Pengfei1，2，3，TIAN Siming2，ZHAO Yong2，ZHU Yongquan4，WANG Shudong4

2013, 32 (s2): 3509-3519

(99)

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Peripheral rock large deformation，shotcrete crack，steel frame distortion and other phenomenon of destruction often appear in the tunnels with soft rock and high geostress due to the high pressure on the primary lining. The safety of tunnel during construction and long-term operation will be affected. Taking Baozheng tunnel along Yiwan Railway as engineering background，based on statistical analysis of in-situ monitoring data，mechanical characteristics of surrounding rock pressure，stress of shotcrete and steel arch，axial force of bolts and deformation distribution of deep seated rock have been analyzed. Development law over time and spatial distribution along the tunnel ring of the above test items are discussed. During the excavation in the tunnel，rock pressure，steel arch stress and shotcrete stress change rapidly，and sensitivity decreases in turn with the character “upper larger，lower smaller” along the tunnel cross section. The analytical method and results can provide references to accurately understand the support-surrounding rock interaction and their mechanical characters.

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DEFORMATION MECHANISM ANALYSIS OF SURROUNDING ROCK AT ARCH CROWN IN UNDERGROUND POWERHOUSE

HUANG Qiuxiang1，WANG Jialin1，DENG Jianhui2

2013, 32 (s2): 3520-3526

(88)

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Aiming at the phenomenon of partial cracking and deformation of surrounding rock mass developing continuously at arch crown in the underground powerhouse，based on geology，monitoring data and construction process，qualitative analysis and quantitative analysis are made respectively combining with information of macroscopic deformation character and results of safety monitoring. The phenomena of collapse and crack occurred during the excavation of underground caverns is mainly formed by small unstable blocks because of stress distribution and blasting effect. Among the causes of its formation，the structure surface of fault and rock cracks is the main geological factor，and supporting lag is the main factor of construction. So considering the discontinuous characteristics of rock masses，it is important to take timely and effective support measures to ensure that surrounding rock mass of arch crown is in situation of stability. Parallel construction can speed up the construction progress in a certain extent，but it could have an effect on the displacement of surrounding rock. In the situation of parallel construction，although construction work has been far from arch crown，due to high construction intensity and frequent blasting，the displacement development of surrounding rock mass is still controlled obviously by construction schedule. So under the condition of complex geology，it is very necessary to avoid the parallel construction during construction process.

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STUDY AND FIELD MEASUREMENT OF ENVIRONMENTAL VIBRATION INDUCED BY UNDERGROUND HIGH-SPEED RAILWAY IN SHIZIYANG TUNNEL

XIAO Mingqing1，2，YAO Jie2，3，HUANG Dun2，YANG Guanghua3，4

2013, 32 (s2): 3527-3534

(84)

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Ground vibration induced by high-speed train in Shiziyang tunnel which lies in fine sand layer stratum is measured. At the speed of 310 km/h，the maximum acceleration on top of the tunnel is 10.78 cm/s2，while the maximum velocity is 0.034 cm/s；vibration energy is mainly concentrated within 60 Hz，main frequencies are in 30–40 Hz，and the predominant frequency decreases with distance. There is obvious amplification for acceleration in the range of 30–40 m. Analogy analysis shows that by using damping cushion in the track system the environmental vibration is small，and is in the same order of magnitude as low speed subway，lower than that of subway without dumping measures，while slightly higher than that of subway with steel spring floating slab track. In some points，the circumferential and radial vibrations are larger than the vertical vibration，so it is suggested that attention should also be paid to the influence of horizontal ground vibration on buildings beside that induced by vertical vibration. A data center of environmental response induced by underground highs-peed trains is formed，based on it prediction for ground vibration by multi-dimensional interpolation can be executed. A empirical formula of extreme value type is also put forward to describe the ground vibration distribution，by which more vibration evaluation can be accomplished conveniently.

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STUDY OF BUILDING/STRUCTURE SETTLEMENT PREDICTION METHOD SURROUNDING URBAN RAIL TRANSIT TUNNEL ENGINEERING

WU Fengbo1，2，3，JIN Huai1，SHANG Yanjun4，LIU Yongqin1

2013, 32 (s2): 3535-3544

(100)

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The building/structure settlement curve fits to the normal distribution. The Peck formula in tunnel engineering ground surface settlement prediction is derived，and its parameter meaning is changed to establish the building/structure settlement prediction formula. The single and two layer buildings load effect on the deformation are studied by the engineering cases summary and theoretical analysis. The building/structure settlements in different locations of tunnel engineering are studied by numerical simulation. With the existing parameter value of volume loss(Vl) and building/structure settlement prediction formula，the reference value of building/structure settlement trough width parameter(Ks) in different countries are calculated. The engineering practices show that the building/structure settlement prediction formula calculation result，numerical simulation result and monitoring result are in good agreement. The formula has very good practicality，and it could be applied to similar building/structure foundation settlement prediction.

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DEFORMATION CHARACTERISTICS OF TUNNEL WITH FLEXIBLE JOINTS AFFECTED BY NORMAL FAULT STICK-SLIP DISLOCATION

LIU Xuezeng1，LIN Lianglun2，WANG Xulin3，LI Xin2

2013, 32 (s2): 3545-3551

(87)

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：Based on the project of the tunnel crossing the normal active fault whose dip angle is 60°，the length of segment is 0.5D(D is the diameter of tunnel) and flexible connection between two segments design is adopted in articulated tunnel. Through a model experiment，the deformation characteristics of tunnel with flexible joints are discussed. The experiment results show that the longitudinal strain and transverse strain of articulated tunnel change greatly in the range of 1D near the fracture plane. The tunnel failure mode is the combined rotation and slab staggering，the rotation angle is 33°and 28°，and the deformation range is 2.5D. Compared the tunnel where the anti-breaking measures are taken with the flexible tunnel，under the same experiment condition，the result indicats that the longitudinal strain of tunnel with flexible joints is smaller than the complete tunnel?s，and the deformation range of the flexible tunnel is smaller than that of the complete tunnel.

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TEST STUDY OF DEFORMATION LAW OF ENTRANCE SECTION FOR LOESS HIGHWAY TUNNEL

QIAO Xiong1，2，CHEN Jianxun1，WANG Mengshu3

2013, 32 (s2): 3552-3556

(123)

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In order to study the deformation law of entrance section for loess highway tunnel，based on the right line of Liujiaping No.2 tunnel of highway from Wubu to Zizhou in Shaanxi Province，in-situ tests were conducted. The tunnel construction deformation was measured，and the regression analysis was made in data processing of in-situ test. The results show that：(1) From the arch subsidence and clearance convergence data of the same time in two sections，it is found that the arch subsidence is greater than clearance convergence，so the arch subsidence should be mainly controlled during the construction：(2) The deformation data reflect the bias voltage of the portal section. (3) Tense curve of the arch subsidence is basically stable，the main indicator is the tense curve of subsidence gently rising，but the deformation rate decreases gradually which shows that the loess strata become stable；(4) The tense curves of 6 arch subsidence in two section are basically the same，it shows that although the sidewalls and inverted arch experience a tremendous spatial variation during the construction，there is no obvious mutation in the tense curve of the subsidence. The displacement law of the Malan new set loess stratigraphy was shown，and the time effect was more significant than spatial effect. The study results can provide a theoretical basis for the design and construction of the portal section，and a reference for similar tunnel project portal section construction.

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EFFECT OF SUBWAY TUNNEL EXCAVATION WITH DIFFERENT COVERING THICKNESSES ON PIPELINE SECURITY UNDER TRAFFIC LOAD

GAO Yongtao，YU Yongyan，WU Shunchuan

2013, 32 (s2): 3557-3564

(108)

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The subway excavation has great influence on underground pipeline. The pipeline would be influenced by both excavating subway-tunnel and operating subway when they are near the pipeline. Three-dimensional finite element analysis models are established to calculate the surface settlement and settlement tough. The models are established with different covering thicknesses and with the influence of an operating subway. Parameters for ensuring security of underground pipeline are obtained by surface settlement and settlement tough，and relationships between covering thickness and the parameters are discussed. Then calculation values of surface settlement，settlement trough and parameters are compared with test values. It shows that：(1) The influence of operating subway and covering thickness can not be neglected. (2) Maximum surface slope and Smax/i grow，when soil the covering thickness increases. The trend of growth becomes slow，with the increase of coveing thickness. (3) Both the maximum settlement and surface loss coefficient express a linear growth when the covering thickness rises. (4) However，the curvature of settlement trough decreases with the enhancement of covering thickness. (5) The values from calculation are similar with that from test，and the parameters from calculation are similar with that from test too.

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TIME-DEPENDENT DEFORMATION ANALYSIS OF SURROUNDING ROCK OF LARGE-SCALE CAVERNS SUBJECT TO COMPLEX GEOSTRESS CONDITION AND ITS MECHANICAL SIMULATION

LIU Huibo1，2，XIAO Ming1，2，ZHAO Chen1，2，CHEN Juntao1，2

2013, 32 (s2): 3565-3574

(103)

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The time-dependent deformation mechanism of surrounding rock of large-scale underground caverns subjected to blast excavation and complex geostress condition is analyzed and a mechanical simulation method is proposed. Based on the analysis of monitored displacements and rockmass mechanics theory，it is identified that the high geostress mechanism and spatial effect of excavation damaged zone are two main affecting factors for the time-dependent behavior of surrounding rock of underground cavern in complex high geostress environment. With excavation process simulated by the stress release finite element method，time-dependent identification functions of excavation release loads and excavation damaged zones are established. Thus，a partition method for sequential excavation loads release based on the monitored curve of displacement vs. time and a deterioration model for deformation modulus on the basis of partial concept of excavation damaged zones are presented. Illustrated with engineering application to deformation analysis of large-scale underground powerhouse of Xiluodu hydropower plant，it is shown that，by coupling calculation of the excavation release load and spatial damaged zone，the simulation method is rational and effective for time-dependent behavior analysis of surrounding rock of large- scale caverns on the whole excavation process，which is of applicability and practical reference for the interpretation and control of deformation and damage effect of surrounding rock under complex geostress condition subjected to blast excavation，for optimizing the construction and supporting，and effective monitoring feedback analysis.

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EXPERIMENTAL STUDY OF GROUTING PLANS OF SHALLOW TUNNELING METHOD TO IMPROVE INTENSITY IN MUD GROUND

WU Yanping1，2，WANG Jun1，LIU Jianmin3，CHEN Guangzai1，CHEN Chunlei2

2013, 32 (s2): 3575-3583

(116)

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In allusion to the Wenzhou typical soft soil properties，combined with pedestrian subway channel engineering in Wenzhou No.2 subsidiary hospital，taking advantage of ordinary cement-sodium silicate double liquid，superfine cement-sodium silicate double liquid and specially made sulphoaluminate cement paste three kinds of soil improvement grouting materials，i. e. a series of indoor laboratory tests and field injectivity tests are carried out. The results show that compasion of superfine cement with the same quantity of the general cement，they have the same intensity，the superfine cement gelation time is long and it is vulnerable to be diluted by the ground water. Compared with the general cement，the superfine cement cost is about 3 times higher，so it is suggested that general cement instead of the superfine cement grouting materials to reinforce silty horizon. The in-situ experiment shows that the grout diffusion radius and compressive strength increases with the increase of grouting pressure under the same grouting time；grout diffusion radius increases with the increase of grouting speed under the same grouting pressure，but the growth trend slows down with the increase of injection rate，. Moreover，the key parameters of grouting have been ascertained and confirmed in practice，the grout diffusion radius is 1.0–3.0 m，the terminate pressure in grouting is 1.0–1.5 MPa，the reinforced depth of grouting is 4–5 m. After grouting，analysis method and sampling method after excavation are inducted to inspect the grouting effect，the results indicate that the grouting effect is in accord with the design construction requirements. The successful application of the grouting project has very good reference and broad application prospect for underground reinforcement engineering in Wenzhou region and Yangtze river delta with rich deep weak silty soil.

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EFFECT OF STEEL CASING CONSTRUCTION ON METRO TUNNEL AND DEFORMATION CONTROL

ZHANG Chao，YANG Longcai，HUANG Dawei，SONG Fugui

2013, 32 (s2): 3584-3591

(99)

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In order to reduce the effect of steel casing construction on deformation and displacement of metro tunnel，the procession of steel casing is need to be analyzed before construction. The depth of precession which affects tunnels seriously and the maximum mechanical pressure in different precession depths are obtained by numerical simulation. With the help of maximum mechanical pressure and oil pressure gauge，the precession of steel casing is strictly controlled. The field test data shows that when steel casing is under the horizontal axis of the tunnel，the height of soil column reaches the critical height and the plugging has happened. Then，the soil column begins to squeeze the lower soil and lead to the tunnel uplift，offset and produce elliptical deformation. In order to strictly control the deformation and displacement of the tunnel during the steel casing construction，the method of setting up holes beside the tunnels to relax the squeezing stress during the precession，or choosing a reasonable construction sequence to reduce the effects of excess pore water pressure on the tunnel is proposed.

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UNDERGROUND PIPELINE DEFORMATION PREDICTION AROUND URBAN RAIL TRANSIT TUNNEL ENGINEERING

WU Fengbo1，2，3，JIN Huai1，SHANG Yanjun4

2013, 32 (s2): 3592-3601

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Through summarizing the monitoring results，it is pointed that when the pipeline rigidity is large，and the settlement between pipeline and formation is large. The general deformation law of underground pipeline is basically the same to the move of stratum. When the pipeline is vertical above the tunnel，the settlement curve fits to the normal distribution. The Peck formula for ground surface settlement prediction in tunnel engineering is corrected，and the pipeline settlement prediction formula is established. Combining the former research results of stratum loss rate ，the reference value of pipeline settlement trough width parameter is calculated. The result of numerical simulation shows that the deformation of pipeline parallel above the tunnel is more than vertical above the tunnel，and the pipeline settlement prediction formula may preliminarily evaluate the deformation of pipeline parallel above the tunnel. The rigid pipeline longitudinal strain calculation formula may also be modified to get the pipeline deformation. The engineering application proves that the pipeline settlement prediction formula，numerical simulation and monitoring results are in good agreement，and the pipeline settlement prediction formula is good in application.

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RESEARCH ON COUNTERMEASURE OF WATER GUSHING WITH COLLAPSE IN PROCESS OF WUSHAOLING HIGHWAY TUNNEL CROSSING F4 FAULT FRACTURE ZONE

LI Shengjie1，2，XIE Yongli1，ZHU Xiaoming3

2013, 32 (s2): 3602-3609

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The water gushing with collapse in process of Wushaoling highway tunnel crossing F4 fault fracture zone is introduced. Combining with geological conditions of F4 fault fracture zone and features of water gushing with collapse，according to the methods of geological survey，field measurement and theoretical analysis，the mechanism of water gushing with collapse and the reasons of initial support failure caused by water gushing and collapse are investigated，and the inner links of which with the surrounding rocks，underground water and geologic structure are analyzed. The water crushing collapse is a kind of the gravel inrush hazard caused by the crushed belts of fault. The support design and construction organization scheme for segments with water gushing and tunnel face are researched，and treatment measures are proposed. According to the measurement results，it is shown that the treatment measures can achieve satisfying results and can ensure the safety of tunnel construction under complicated geological conditions. This research could play an important guiding role and provides a significant reference value for tunnel construction under similar conditions.

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MODEL TEST AND ANALYSIS OF LOOSE ZONE IN SOFT AND CRACKED SURROUNDING ROCK OF MULTI-ARCH TUNNEL

BAI Langfeng1，2，XU Qianwei3，TIAN Longgang1，2，DUAN Qunmiao4

2013, 32 (s2): 3610-3618

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In the field of multi-arch tunnel，determining loose zone of surrounding rock has important theoretical value and practical significance for taking appropriate method for support in actual projects. By taking highway multi-arch tunnel with overburden depths of 100 m for example，a model test based on similar principle is implemented to study loose zone of the soft and fractured surrounding rock，and the characteristics of stress field in loose zone are analyzed through measuring pressure of different locations by pressure cells. FLAC software is applied to simulate model test. The range of loose zone is identified by stress analysis method and ultimate tensile strain method. Comparing with results of model test shows that tangential stress is greater than radius stress in loose zone，surrounding rock is more likely to form pressure arch under deep overburden condition. The range of loose zone decided by stress analysis method is closer to the results of model test，identifying loose zone is feasible for deep overburden tunnel by stress analysis method.

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FIELD TEST RESEARCH ON INFLUENCE FACTOR OF UPWARD MOVING OF SHIELD TUNNEL SEGMENTS DURING CONSTRUCTION

JI Chang，ZHOU Shunhua，XU Kai，LI Xiaolong

2013, 32 (s2): 3619-3626

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Aiming at the problem of partially or integrally upward moving of tunnel segments during shield tunnel construction，based on the two metro shield tunnel project cases in which the great upward moving occurs in Ningbo，the field test of shield construction parameters，such as tunneling speed，vertical component force of reaction force of total thrust，synchronized grouting pressure and grout proportion，is conducted in the section that the external conditions(formation characteristic and burial depth) are similar. And combined with the monitoring data in the test section，the influence law of aforementioned single factor on segments upward moving during construction is analyzed. The results show that the amount of segment upward moving increases，when the grouting pressure of the lower segment is higher than that of the upper part. When the pressure difference is up to 0.3 MPa，the amount of upward moving increases about 20 mm. On the basis of little change of reaction force of the total thrust，when its vertical component force increases，the amount of upward moving raises correspondingly. When the component force increases by 260 kN，the amount of segment upward moving grows greater to about 15 mm. Keeping the same amount of cementitious material and mixing in equivalent non-cementitious material during synchronized grouting，the compression strength and cohesion of grout improve，the initial setting time shortens and the segment moves less higher with the reduction of ash cement ratio and water cement ratio. When the relative addition of cement in every 3 m3 of grout increases by 100 kg，the amount of segment upward moving decreases by 19.8 mm. the tunnelling speed，alone，has no distinct impact on upward moving of segments during construction.

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EXPERIMENTAL STUDY OF SEISMIC FAILURE MECHANISM OF UNDERGROUND STRUCTURE

SUN Haifeng1，2，JING Liping1，WANG Shuwei1，3，MENG Xianchun1

2013, 32 (s2): 3627-3635

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By use of self-designed laminar shear container，a shaking table test on underground structure which lays in clay is conducted. The results of comparing the acceleration time-history and Fourier spectrum of station model and soil，and the analyzing regulations of the underground structure dynamic strain and the underground structure failure macro phenomena show that the failure mechanism of underground structure under underground seismic response is mainly controlled by the surrounding soil. The softer soil is，the easier underground structure be damaged；the shallower the depth is，the more serious underground structures be damaged. Underground structure seismic damage mode is the relative displacement between adjacent layers caused by shear displacement of surrounding soil. When the displacement is too large，the floor and side-wall would appear tensile failure. Meanwhile，shear or bending moment acting on columns will cause shear damage，bending damage or combination of shear damage and bending damage.

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STABILITY CONTROL OF ULTRA SHALLOW-BURIED METRO TUNNEL WITH SUPER LARGE-SPAN IN PROCESS OF CROSSING BRIDGE

LI Dong1，2，3，HE Xingling1， QIN Le1，KANG Yong2，4，ZHOU Dongping1，3，GUO Chenye1，3

2013, 32 (s2): 3636-3642

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By analyzing the key effect factors of the stability and using numerical simulation for the complex excavation condition of Huahuiyuan metro tunnel，the corresponding control methods were proposed. And the stability of ultra shallow-buried tunnel with super large-span in the process of crossing bridge was investigated based on the monitoring results from excavation site. The results show that：(1) Its difficult to form an arch after the ultra shallow-buried tunnel with super large-span excavation and the obvious ground deformation caused by the excavation shows skewed which lead to the subsidence of No.2 pile exceeds the warning value. So，some strengthening measures must be taken. (2) The phenomenon of equivalent stress concentration in different parts of the tunnel structure has different sensitivities to the change of flat rate：the most sensitive part is skewback while the equivalent stress concentration in the vault does not change along with the flat rate. (3) The deformations of ultra shallow-buried tunnel with super large-span are mainly influenced by the excavation of each part，in which the dominant deformation is caused by core soil excavation and then by upper hole excavation. As a result，both of them are the key control parts. (4) Both sides heading method assisted by advanced small pipe grouting，backfilling grouting，short-hole micro seismic blasting and so on can control the ultra shallow-buried tunnel with super large-span stability in the process of crossing bridge effectively.

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THEORY AND EXPERIMENT RESEARCH ON REPAIR STRENGTH OF DAMAGED SHIELD TUNNEL SEGMENT

ZHOU Junhong，ZHOU Shunhua，WU Di，ZHU Huanle

2013, 32 (s2): 3643-3649

[PDF] 828 KB (4)

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Due to the complexity of shield tunnel construction，some segments will be damaged during construction and need to be repaired，and the repair quality will directly influence the safety and durability of shield tunnel. The damage characteristics of a shield tunnel were summarized after investigating the segment damage，the mechanical characteristics of repair part while occurring longitudinal deformation was analyzed，and the longitudinal equivalent stiffness model was adopted to analyze the relationship between the stress on the repair part and longitudinal deformation，so that the controlled repair strength was obtained. Furthermore，according to mechanical characteristics of repair part and damage features，laboratory test model was designed to get the reasonable repair material. The research provides guidance for repair of damaged shield tunnel segment.

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RESEARCH on stability of cave roof under pile loading in bridge construction engineering

WANG Huabin1，2，LIU Zhifeng3，ZHAO Wenfeng1，2，ZHOU Bo1，2，LI Jiwei1，2

2013, 32 (s2): 3650-3657

[PDF] 779 KB (3)

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The present research is focused on the cave roof safety thickness and stability under pile loading in karst areas. Through the analysis of the interaction between the cave roof and pile foundation，four models were introduced to be as simply-supported，clamped circular plates and rectangular plates. Firstly，the force characteristics of cave roof under pile load in karst areas were analyzed. Based on the method of elasticity mechanics and introduction of Hoek-Brown criterion，a variety of simplified models were selected under consideration of the interaction between pile and cave roof. The maximum stress of the roof was then induced for different models following the theory of elastic mechanism. After the induction of the maximum stress，the theoretical formula of safety thickness was obtained，including the cases of four simplified models and anti-punching，shearing. Within the analysis of the stability for the cave roof，an equivalent conversion method for parameters was employed from the Hoek-Brown criterion to the Mohr-Coulomb criterion. In addition，compressive，tensile strength and other calculation parameters of the pile were determined，based on Hoek-Brown criterion，according to the detailed geological data of the West River Bridge. The cave roof thickness of different simplified models under different load conditions were then calculated by the theoretical formula. Using the finite element method，the theoretical results were identified to be the same as data from the numerical simulation. The results show that，it was feasible and effective to use the Hoek-Brown criterion to determine the stability of cave roof. Meanwhile，the results can be included in the national guideline for the design of piles in the bridge engineering in Karst areas.

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EFFECTS OF EXCAVATION SUBSEQUENCE OF BUSBARS TUNNEL ON DISPLACEMENT OF SURROUNDING ROCK MASS

HUANG Qiuxiang1，DENG Jianhui2，3，SU Pengyun4

2013, 32 (s2): 3658-3665

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Generally，there are two different schemes about the excavation subsequence of main powerhouse and tunnels that intersect with it at intersecting section. One is that the part of main powerhouse is excavated first，and then the part of tunnel is excavated from side wall of main powerhouse，which is called first side wall then tunnel. While the other is on the contrary，that means the tunnel is excavated first then the part of main powerhouse is excavated from the tunnel，which is called first tunnel then side wall. With Pubugou hydropower station underground powerhouse and the Xiluodu hydropower station underground powerhouse as background，taking main powerhouse as object of study，the effect of the bus tunnel construction sequence use the scheme of first tunnel then side wall or first side wall then tunnel on surrounding rock displacement is analyzed based on monitoring data and by means of numerical simulation. Firstly，with the help of monitoring results，the displacement of surrounding rock mass of top arch，rock anchor beam，upstream side wall，as well as downstream side wall were compared part by part；then by using numerical calculation，in which main factors considered were ground stress and rock types，rock type of II or III，ground stress in high，medium，as well as low level，busbars tunnel was excavated by using the scheme of first tunnel then side wall or first side wall then tunnel，that means 12 different conditions were simulated. The research results from comprehensive analysis of monitoring results and numerical simulation results show that，the effect of bus tunnel construction sequence on surrounding rock displacement is mainly concentrated in the place of anchor beam layer and above parts，especially at layer of rock anchor beam in the downstream. From point of control surrounding rock displacement，in condition of low stress，the influence of excavation subsequence is not obvious，while in the condition of medium and high stress the opinion that tunnels are excavated first is preference. As cavern that intersect with main powerhouse and main transformer house，its excavation subsequence is rational or not has dual significance on schedule control and surrounding rock stability. Therefore，effects of excavation subsequence of busbars tunnel under different geological conditions is a subject being worthy of further investigation.

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PREDICTION FOR SURFACE COLLAPSE DEFORMATION OF SHIELD CONSTRUCTION BASED ON LSSVM

BAI Yongxue1，QI Taiyue1，LI Youdao2，WU Zhanrui1

2013, 32 (s2): 3666-3674

[PDF] 689 KB (4)

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When shield crossed the sandy cobble stratum in Chengdu metro No.1 and No.2 lines，the induced surface subsidence reached as high as dozens of times. Surface collapse deformation curve is influenced by many factors，and the influences of the factors on surface collapse deformation curve show the nonlinear characteristics. So the surface collapse deformation curve is difficult to solve with mathematical formulas. Least squares support vector is a machine learning method based on the statistical learning theory. It can avoid shortcomings of traditional neural network and analyze influencing rule on the result with complicated factors. Thereby least squares support vector machine method was introduced to establish prediction model for surface collapse deformation. Prediction model took physico-mechanical parameters of stratum，buried depth of shield and ground loss value as input parameters. Though testing sample data，the prediction mode has strong generalization ability，and its prediction result has high accuracy and reliability.

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APPLICATION EXPERIMENT OF WEAK ENERGY BLASTING TECHNOLOGY AT UNDERGROUND TUNNEL ROCK BURST GOVERNANCE

LIU Meishan，WU Xinxia，DING Xiuli，ZHAO Gen，CHEN Linyun

2013, 32 (s2): 3675-3680

[PDF] 937 KB (4)

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The paper introduced the principle of management of weak energy blasting for rock burst treatment， taken the Jinping hydropower station diversion tunnel as background engineering，the distribution of high stress was simulated by FLAC3D dydropower，the stress release sites were confirmed adopting Russenses rock burst discriminating method，four kinds of stress release blasting scheme were drafted，conducted three groups of blasting test for each scheme，the test results are analyzed. Experiments show that the weak energy blasting can release high ground stress and achieve the goal of controlling rock burst through careful control of the explosion energy. But the method is only to process the stress to the deep rock，do not eliminate stress，so timely supporting measures should be indispensable.

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ANALYSES OF DEFORMATION AND STRESS CAUSED BY GEOSTRESS ON ROCK-ANCHORED BEAM OF UNDERGROUND POWER HOUSE

YIN Ronggang1，ZHANG Jianhai1，DENG Jianhui1，GAO Chunyu1，LIAO Chenggang2，

2013, 32 (s2): 3681-3687

[PDF] 2408 KB (4)

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The rigid body limit equilibrium method is often used to design rock-anchored beam，but the follow-up excavation and rock deformation are not taken into account in this method. Underground power house of Jinping I hydropower station is located in the region with high underground stress(maximum value reaches 35.7 MPa). The stage excavation of the underground plant certainly has significant effect on the deformation and stress of rock-anchored beam. Compared with field monitoring deformation，3D nonlinear finite element method is used to study deformation and stress of rock-anchored beam of underground power house. The deformation and stress of rock-anchored beam are analyzed under each excavation stage. The results show that during excavation，a large scope of unstable failure and a pull rod yielding phenomenon will happen. The influencing mechanism of successive excavation to pull rod stress，and the stress variation behavior of pull rod are discussed. It is found that delaying of the fixing time of rock rod can effectively reduce the pull rod stress caused by following excavation.

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APPLICATION AND ANALYSIS OF GROUND SURFACE PRE-GROUTING STRENGTHENING DEEP FAULT FRACTURE ZONE

LIU Quansheng1，2，LU Chaobo1，LU Haifeng2，LIU Xuewei1

2013, 32 (s2): 3688-3695

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In order to improve the fault fracture zone strength，keep the roadway stability and create good condition for later anchorage supporting，ground surface pre-grouting reinforcement technology is applied to reinforce deep local rock mass of F104 fault fracture zone where roadways across in Gubei coal mine. Pre-stage grouting showed pressure relief characteristics，injection pressure can not rise quickly. The multistage-discontinuous- repeated grouting strategy allowed the cement slurry pre-injected into the fractures curing and larger channels blocking，it would prevent the slurry diffusion too large to escape and create conditions for grout injecting fracture with smaller opening. The grout distribution is look like wire winding shape and thick veins of grout distributed occasionally in central section of the fault fracture zone after grouting. In both sides of the fault fracture zone，the grout distribution is look like veins. Ground surface pre-grouting increasing the integrity of rock，strengthening the broken rock inter-lock ability and improving the tunnel face stability. Grouting filled and cemented the fractures would reduce the fractures free space and contain mudstone asymptotic mudding effectively which improve the strength of surrounding rock indirectly；the extremely broken surrounding rock with solidified grout is similar to concrete. Pre-grouting guarantee effectively stability and improve significantly self-bearing capacity and resistance to deformation ability of the surrounding rock mass which cause the surface convergence displacement and its’ rate decreased markedly.

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Experimental research on bursting liability index of coal samples of Chengjiao coal mine

SU Chengdong，YUAN Ruifu，ZHAI Xinxian

2013, 32 (s2): 3696-3704

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Experiments on bursting liability of coal sample of Chengjiao coal mine were carried out by the RMT–150B servo-control testing machine. The test results indicate that the deformation characteristics after post-peak stage is related to the way of load control. The stress control method should be employed when testing dynamic time of failure and the strain control method should be used when testing burst energy index. The compression strength has well positive correlation with elasticity module，burst energy index，elasticity energy index and residual energy index but has negative correlation with dynamic time to failure，which indicates that the higher the compression strength of coal sample，the more dangerous the rock burst. The burst energy index of coal samples has well positive correlation with elasticity energy index，so does the relation between elasticity energy index and residual energy index. The dynamic time to failure has well negative correlation with burst energy index. And whether the residual energy index and elasticity module can be the criterion of coal seam classification of bursting liability needs further study. Finally，based on experimental data that the dynamic time to failure，elasticity energy index，burst energy index and uniaxial compression strength of the coal samples is 306 ms，5.91，2.48 and 8.86 MPa respectively，it can be concluded by the fuzzy comprehensive method that the Two2 coal seam of Chengjiao mine belongs to the type of weak bursting liability.

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RS-TOPSIS MODEL OF ROCKBURST PREDICTION IN DEEP METAL MINES AND ITS APPLICATION

ZHOU Keping1，2，LEI Tao1，2，HU Jianhua1，2

2013, 32 (s2): 3705-3711

[PDF] 388 KB (3)

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Based on the method of technique for order preference by similarity to ideal solution(TOPSIS)，5 indices including uniaxial compressive strength，the ratio of rocks compressive tensile strength，the stress coefficient of rock，the elastic energy index of rock and integrality coefficientwere chosen as the predictor variables of rockburst. 20 rockburst cases were taken as the training and testing samples，according to the classification standard of rockburst，the supports and weighs of predictor variables were calculated by rough set theory，the RS-TOPSIS model of rockburst prediction was established. And the model was applied to practical engineering. The result shows that the method of fixing classification by calculating the relative closeness is easy；the RS-TOPSIS model of rockburst prediction has very high accuracy，the correct rate is 90%；the prediction results of Xintong mine agree well with the engineering practice. So，the RS-TOPSIS method is of practical value，can be used to predict the rockburst in deep metal mines.

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FEATURES OF COAL BUMPS INFLUENCED BY NORMAL FAULTS IN COAL MINING WITH HARD ROOF AND HARD COAL

JIANG Yaodong1，2，WANG Tao1，3，CHEN Tao4，BAI Xingping4，XIE Shuaitao2

2013, 32 (s2): 3712-3718

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The fault is an important geological structure that can induce coal bumps. A field investigation was taken in the 8935 working face in Xinzhouyao coal mine for the mechanism of coal bumps induced by fault activation. There was a series of serious coal bumps in the past 4 months. The features of coal bumps influenced by normal fault were studied through the analysis of these cases obtaining characteristics of electromagnetic radiation and microseismic before and after the coal bump. The fault has obvious influence on frequency and intensity of coal bump，which is reflected in two aspects：it has changed the physico-mechanical properties of coal and rock，and made the tectonic stress field become complicated. Seismic often occurred in the range of 230–360 m in front of the fault and the impact location is 0–60 m ahead of mining face. The impact danger is approaching when the curve of electromagnetic radiation energy and the number of pulses present the saddle form，and then the probability of coal bump is very high. Microseismic monitoring shows that the occurred energy of coal bump is between 105–106 J magnitude. There are impact dangers when microseismic with more than 105 J of the energy continues to occur and its energy has great fluctuation.

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EXPERIMENTAL RESEARCH ON ACOUSTIC EMISSION CHARACTERISTICS OF COAL AND ROCK UNDER DIFFERENT GAS PRESSURES

QIN Hu 1，2，3，HUANG Gun1，2，3，JIANG Changbao1，2，3，LI Wenpu1，2，3

2013, 32 (s2): 3719-3725

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Using self-developed triaxial servo-controlled seepage equipment for thermo-fluid-solid coupling of coal containing methane with acoustic emission(AE) monitoring system，this paper carried out experiment on AE characteristics of coal and rock under different gas pressures by conventional triaxial compression. Result of the test shows that，gas pressure plays a role in softening to coal and rock，with the increase of gas pressure，the brittleness of coal and rock weakened in the process of loading but the ductility enhanced，both compressive strength and elastic modulus show a decreasing trend. According to the experimental conclusions that both the relations of AE characteristics of coal and rock and stress-strain，and AE accumulative counts and strain，carried out that during the failure process of conventional triaxial compression，the rupture type of coal and rock without gas is sudden rupture，the rupture type of gaseous coal and rock is stable rupture. On the basis of taking into account the stress and gas pressure caused the damage of coal and rock，established the relation of the damage of coal and rock represented by AE accumulative counts under different gas pressures，and verified by experiments，verification results show that，based on the AE of the relation of the damage of coal and rock，to some extent，truly reflects the failure process and the strength characteristics of gaseous coal and rock.

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RESEARCH ON HORIZONTAL VIBRATION PROPERTIES OF UNDERWATER VENTILATION SHAFT OF TUNNEL CONSIDERING EFFECT OF SELF-WEIGHT OF STRUCTURE

CHEN Xianghong1，ZHANG Hongru1，CHEN Xi2

2013, 32 (s2): 3726-3731

[PDF] 442 KB (5)

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The seismic response of structure is a complex multi-field coupling issue considering the dynamic interaction effect of soil-water-tunnel shaft simultaneously. Based on the principle of Winkler foundation beam，and the hydrodynamic pressure is considered as the added pseudo mass，the deformation governing differential equation of the Euler beam is established according to the model in which the interface soil is simplified as spring modeling the soil-structure interaction，and the deformation and stress of structure are solved under the seismic loading using the transfer matrix method. Furthermore，a comparative analysis is employed by the usual software ANSYS，it is found that，the introduced foundation beam model and calculation method can reflect the actual vibration characteristics of tunnel shaft in soft soil effectively. Finally，the distribution of internal force along the shaft influenced by the connection joint and self-weight of structure is analyzed，through the discussion of parameters，it is concluded that，the internal force of structure can be decreased by reducing the connecting stiffness between tunnel and shaft，and the degree of structural security is increased；meanwhile，the factor of self-weight of structure is extremely important for the vibration properties of partially embedded tunnel shaft with large cross section，which can not be ignored by designers.

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RESEARCH ON CREEP PROPERTY AND CONSTITUTIVE MODEL OF ROCK IN COAL BED GAS RESERVOIR

FAN Xiangyu1，2，ZHANG Qiangui2，AI Wei3，XIA Hongquan2，HE Chuanliang4，LI Zhilin5

2013, 32 (s2): 3732-3739

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Compared with normal coal，fracture development is the main physical characteristics of coal in coal bed gas reservoir，its structure is very complicated，and its easy to be damaged under geostress，always leads to the failure and instability of drilling during the exploitation process of coal bed gas. In order to explore the law of creep instability of borehole wall in coal bed gas reservoir，the writer adopted the American RTR–1000 triaxial rock mechanical test system to test the uniaxial creep law of coal in coal bed gas reservoir. Combined the Poyting-Thomson model with Bingham model，a creep model of coal is builted in coal bed gas reservoir and each parameter of creep equation through fitting is achieved. The creep model has been verified according to the uniaxial creep test results of coal in coal bed gas reservoir under different load conditions. The results show that the creep model of coal in coal bed gas reservoir can describe the deformation properties of each creep stage well，especially the decline stage and steady creep stage，and it can reflect the long-term strength of creep well. At the same time，combining the coal creep characteristics with the selection of drilling modes，an optimal selection idea of drilling liquid for coal bed gas reservoir has been put forward，which is significant and realistic meaning to maintain the stability of coal drilling，protect reservoir effectively and build drilling with high efficiency and safety.

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Experimental study oF Horizontal Ultimate loading Capacity of new type Monolayer Freezing Shaft Lining

CHEN Xiaoxiang1，YANG Weihao2

2013, 32 (s2): 3740-3748

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Aiming at the situation that the effective excavated section utilization reduced sharply in composite shaft lining，a new type monolayer shaft lining structure was put forward. To obtain horizontal bearing capacity of this kind of shaft lining，similar simulation tests were used to study horizontal ultimate bearing capacity and deformable character on three shafts. The results indicate that：vertical strain and circumferential strain as well as vertical displacement of shaft lining better consistent with vertical stress，no mechanical hysteresis appeared；vertical pressure loading on shaft wall can be considered as uniform；the concrete strength is independent of poisson ratio，but relate to the elasticity coefficient；vertical maximum positive displacement and maximum vertical load before confining pressure being loaded related positively；vertical maximum positive displacement is almost proportional to the ratio of horizontal displacement and most horizontal load positively；Ignoring vertical pressure，radial displacement is proportional to the level stress positively；the inside compression strain is much larger than the sidewall lateral when shaft lining is crushed，the total inside compression strain is between －2 000 and －2 500 ，sometimes reaches －3 000 ，even exceeding；ultimate bearing capacity of new monolayer freezing shaft lining is higher than common concrete. Researching results have great significance in perfecting design theories of the new type of monolayer shaft lining and guiding it constructing fast and scientifically.

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EXPERIMENTAL STUDY OF FAILURE CHARACTERISTICS AND MECHANISM OF COAL UNDER COUPLED STATIC AND DYNAMIC LOADS

LIU Shaohong1，2，LI Fengming3，LAN Hang1，2，PAN Junfeng1，2，DU Taotao1，2

2013, 32 (s2): 3749-3759

[PDF] 561 KB (3)

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Failure characteristics and mechanism of coal are the foundation of studying mechanism of rockburst under impact disturbance，which is investigated by the improved split Hopkinson pressure bar(SHPB) in the laboratory. First，based on the regression analysis of experimental data，there are the unique failure characteristics of coal，as fracture half-hard brittle rock，under coupled static and dynamic loads. Then，though the discussion of experimental result，the failure mechanism is analyzed. It is found that the main reason of the unique failure characteristics is the existence of much crack. Main failure mode is brittle expansion of fracture；the dynamic loading leads to crack propagation until to destruction，meanwhile，the static loading mainly changes the number of existing fractures and the size of the elastic energy in the fissures tip. At last，based on the result of the experiment，the rockburst hazad of coal under coupled static and dynamic loads is discussed. We know that there are the critical static loading and the optimal dynamic loading under coupled static and dynamic loads. The strength under the static and dynamic loads of the coal，as a dynamic load resistance index，can reflect the capacity of the resistance to dynamic loads. Fractal dimension，as a dynamic loading energy index，can be used to measure the intensity of dynamic loads damage.

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COUPLING EXPERIMENTAL STUDY OF COAL PERMEABILITY WITH PORE PRESSURE-EFFECTIVE VOLUME STRESS-TEMPERATURE UNDER SUPERCRITICAL CARBON DIOXIDE ACTION

SUN Keming，WU Di，SU Aiguo，CHEN Zhiyu，REN Shuo，YUE Lixin，TAN Jian

2013, 32 (s2): 3760-3767

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According to the difficult problems of the generally low permeability in Chinas high gas seam and low gas extraction efficiency，using the characteristic of supercritical CO2 which could improve the permeability of porous media，research the flow rule of supercritical CO2 after injected into the low permeability coal seam sample by designing the conditions orthogonally with different temperature，pore pressure，axial compression and confining pressure. The results show that：the permeability and the permeability coefficient of the coal sample trend to be a negative exponential declining rule with the effective volume stress after the action of supercritical CO2；the permeability coefficient and pore pressure trend to be a positive exponential increasing rule；the permeability and the permeability coefficient both trend to be a negative exponential declining rule with the temperatures increasing；under the action of effective volume stress，temperature and pore pressure，the permeability coefficient satisfies the relation：，the supercritical CO2 pore pressure plays a leading rule in improving the coal samples permeability when the effective volume stress is a unchanged；the density and dynamic viscosity of supercritical CO2 present a negative exponential decreasing trend with temperatures increasing，and present a linear increasing change rule with pore pressure，and is sensitive to temperature and pressure around the critical point；after the action of supercritical carbon dioxide，intensive honeycomb like pore and fracture appears，the permeability of coal improved significantly，supercritical CO2 has a better influence on improving the permeability of the coal seam.

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THEORY AND APPLICATION OF PREVENTION OF ROCK BURST BY ADVANCED DEEP HOLE ROOF BLASTING

ZHAO Shankun1，2，OUYANG Zhenhua1，2，LIU Jun3，ZHANG Guohua3，

2013, 32 (s2): 3768-3775

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According to the analyzation of the process and influence factors of advanced deep hole blasting，its prevention and control mechanism for rock burst was demonstrated. The prevention effect was studied by changing the angle of blasting hole and the length of charge weight with ADINA numerical simulation software and its field practice effect was approved by different detecting methods from stress field and energy field. When the depth of the blast hole certain，the peak stress of high stress areas before workface reduce or transfer to deep coal at the three blasting hole arrangement in sector，which make the whole structure of coal-rock in a relatively stable low state. Furthermore，the angle of blasting hole larger and the length of charge longer，the shear stress decreasing zone bigger and the effect of rock burst control more obvious.

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RESEARCH ON SOIL PRESSURE THEORY OF DEEP SUBWAY SHAFT

ZHU Zhengguo，AN Chenliang，ZHU Yongquan，LIU Zhuo

2013, 32 (s2): 3776-3783

[PDF] 569 KB (3)

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Based on the load structure mode of Rankine soil pressure theory and continuum mode，the safety of subway deep shaft retaining structure was analyzed to investigate the applicability of Rankine soil pressure theory used for design calculations of the deep shaft retaining structure which commonly used in metro design. On this basis，considering the different stratum conditions，type of support，excavation sizes and other factors，this paper simulated the various conditions of deep shafts in three-dimension numerical simulation by means of FLAC3D finite difference calculation software to understand the soil pressure of deep shaft and deformation law. In addition，the coefficient of soil pressure and functional relationship among soil pressure，deformation of support structure and depth were proposed. Furthermore，in-site monitoring soil pressure of concrete subway shaft was carried out to confirm the applicability and reasonableness of the mentioned soil pressure for calculation. The research results can provide a reference for the design of subway deep shaft.

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DEFORMATION AND INSTABILITY-EVOLUTION ANALYSIS OF HIGH EMBANKMENT CAUSED BY WASTE AREA ACTIVATION IN FAULTAGE GEOLOGICAL STRUCTURE CONDITION

WANG Yubiao

2013, 32 (s2): 3784-3789

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Faultage geological structure will influence stability of road bed seriously which passes through waste area，thesis study that faultage geological structure“activate”influenced by coal mining to effect stability of road bed in waste area，which uses nonlinear plasticity finite element technology，to study faultage“activate”，distortion of road bed and instability of road bed，seeking a method to prevent and cure discontinuous deformation and sink of road bed surface，to offer technological basis for rational design.

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MECHANISMS AND EXPERIMENTAL STUDY OF THERMAL-SHOCK EFFECT ON COAL-ROCK USING LIQUID NITROGEN

REN Shaoran1，FAN Zhikun1，ZHANG Liang1，YANG Yong2，LUO Jiong2，CHE Hang2

2013, 32 (s2): 3790-3794

[PDF] 569 KB (5)

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Liquid nitrogen can be used for the fracturing treatment of coal-bed-methane(CBM) wells. In this study，the effects of liquid nitrogen on coal-rock samples are studied via thermal shock experiments and ultrasonic testing. A stress-strain analysis model is established to analyze the thermal effect in terms of the shrinkage of coal matrix and the expansion of freezing water in the pores of coal rocks. Experimental results show that micro-fractures can be induced inside the coal-rock matrix，which might be due to the thermal stresses exceeded the tensile strength of the coal-rock. Water in the pores of the coal-rock can freeze instantly when it contacts with liquid nitrogen，in which additional stress can be produced and it may generate micro-fractures in the coal-rock. After the liquid nitrogen treatment，the micro-fractures generated are found to be orthogonal to the plane of the natural fractures，and the results of ultrasonic testing show that both the sound velocity and amplitude reduced dramatically，indicating that the liquid nitrogen treatment can have a significant effect on the internal structure of the coal-rock samples，which is beneficial for generating a fracture network or new fractures during the fracturing treatment of CBM wells.

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RESEARCH ON MINING TECHNOLOGY OF NETHER PROTECTIVE SEAM IN INCLINED CONTIGUOUS SEAMS WITH CONTINUOUS PRESSURE-RELIEF ON OUTBURST COAL SEAM

WANG Zhiqiang，FENG Ruimin，GAO Yuan，LI Pengfei，GUO Xiaofei，CHEN Chaofan，

2013, 32 (s2): 3795-3803

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The research was basis of reasonable mining on the nether protective seam in inclined contiguous seams with continuous pressure-relief on outburst coal seam. In order to confirm the feasibility of mining protected seam and its pressure-relief effect，the similar simulation experiments initially were carried out and a division approach of“three zones”(caving zone，fractured zone and sagging zone) in stope was proposed based on the theory of key strata. Then，combined with field data，the position of protected seam in“three zones”and its pressure-relief effect can be determined；the effect of key strata between contiguous seams and the range of mining protective seam were eventually analyzed. Engineering practice，which coal seam #2 was mined as protective seam of coal seam #1，was taken as an example. Key strata between contiguous seams would affect pressure-relief effect in inclined direction in the case of original designed length of mining face；mining faces without overlap joint were assigned in coal seam #2，which made fractured zone increased，and also the level of coal seam #1 decreased in the fractured zone relatively，made pressure-relief effect more sufficient，and fulfilled pressure-relief in the direction of dip continuously and repeatedly. Finally，recovery ratio and engineering work of tunneling were considered，and compared with the original scheme of mining coal seam #2，he scheme with no pillars increases profit 0.284 billion RMB；and compared with gob-side entry driving with 5m small coal pillars，the scheme with no pillars decreases the cost of rock roadway 6 million RMB，and increases profit 0.14 billion RMB. Therefore，the research conclusions have certain technical and economic significance.

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FEASIBILITY ANALYSIS OF STEAM FLOODING WITH HORIZONTAL WELLS FOR EXTRA HEAVY OIL RESERVOIR

JI Youjun1，2，LIU Jianjun1，3，CHENG Linsong2

2013, 32 (s2): 3804-3811

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On the basis of literature investigation about steamflooding，the numerical simulation method is used to optimize the injection-production parameters of steamflooding with vertical injector and horizontal producer，subsequently，the development performance of steamflooding with horizontal wells of the entire block is forecasted. The results indicate，the best production conditions are：the horizontal producer should be located closely to the bottom of the reservoir，the vertical injector should be perforated with a distance of 20%–25% thickness to the bottom，each horizontal producer should allocated with 4 injectors，the length of the horizontal well should be 300 m，the distance between horizontal wells should be 140 m. The recovery factor will be enhanced by above 12% by using steam driving with horizontal wells. The results can be employed to guide the spot execution of steamflooding with horizontal wells.

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ENGINEERING CASES OF SWELLING ROCK AND SOIL LANDSLIDE TREATMENT IN GUANGXI

FAN Qiuyan1，XU Binglian2，ZHU Zhen2

2013, 32 (s2): 3812-3820

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As the large-scale development of engineering construction and extreme weather in Chian，numbers of swelling rock and soil landslide problem happened，but the related codes can't satisfy the requirement of swelling rock and soil landslide treatment. 44 engineering cases of swelling rock and soil landslide treatment are collected，firstly analyzing the success or failure reason to the three typical landslide treatment engineerings，pointing out that the reasonable determination of the sliding surface and shear strength are crucial to the swelling rock and soil landslide treatment；secondly statistical analyzing the shear strength index for swelling rock and soil of Guangxi，the foundation horizontal resistance coefficient and bonding strength within mudstone and mortar；finally putting forward the special rules of the conventional method used in swelling rock and soil landslide treatment：must setting up drainage system and should meet the codes for expansive soil；cutting and shedding load used in the permanent treatment should be careful；the designing of retaining wall should meet the codes for expansive soil，and should not be more than 3 meters height；the anchorage segment of anti-slide pile should be more than the influence depth of atmosphere，reducing softening by water to the rock and soil around pile when boring；the use of anchor supporting should be careful，and the anchorage segment should be more than the influence depth of atmosphere，hole should be dry-bored.

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DEFORMATION MECHANISM AND STABILITY EVALUATION OF LEFT ABUTMENT DEBRIS IN XILUODU HYDROPOWER STATION

CUI Yulong1，WEI Jinbing1，DENG Jianhui 1，ZHENG Hongchun1，WANG Dikai2，YAO Li3

2013, 32 (s2): 3821-3828

[PDF] 2204 KB (6)

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Through analyzing the deformation characteristics of ground surface and slip zone，variation of the pore water pressure，combined with geolocial structure of the debris and the verification of limit equilibrium calculation，the creep deformation mechanisms of the debris has been studied and the stability has been evaluated. These provide a reliable basis for development and implementation of engineering measures. It is found that the disturbance caused by excavation leads to a shear deformation dislocation along the old slip zone，and then formed bottom-up microcracks inside the debris. It was filled with water inside the microcracks near the slip within a certern elevation range. Groundwater within the microcracks would generate hydrostatic pressure on the sliding body and increase hydrostatic pressure in the slip zone. These changes will reduce stability facter and exacerbate the deformation of the debris. The deformation slows down because of the dissipation of the hydrostatic pressure and healing of the microcracks caused by finishing of the cutting and construction of drainage holes. The research results provide reference value for future similar comprehensive analysis of the slope monitoring data，deformation mechanisms analysis and engineering treatment.

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HAZARD RATING ASSESSMENT SYSTEM AND ITS APPLICATION FOR SURROUNDING SLOPE IN HYDROPOWER ENGINEERING

DONG Jiaxing1，2，XU Guangli1，2，SHEN Yanjun3，ZHANG Shishu4

2013, 32 (s2): 3829-3835

[PDF] 1787 KB (5)

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On the basis of combining with the relevant industry standards and considering the factors of engineering importance and hazards stability，hazard rating assessment system(HRAS) of surrounding slope，which has enough easily valued indicators，is established according to 3 first level indices (the hazard source，path and inducing factors)；9 secondary indices(stability，potential energy，hazard sources shape，paths geometric features，vegetation growth，earthquake and rainfall) and 35 basic indices. According to the level of values ，hazards rating is divided into 3 levels—high，medium，low level. Taking the surrounding slope of ground powerhouse as an example，there are 12 hazard sources of 3 high hazard rating and 9 medium. The result is largely correspondence to reality. and the system can correctly evaluate the risk degree and make guidance for dangerous source prevention and controlling.

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STUDY OF GEOTECHNICAL MECHANICAL CHARACTERISTICS OF A LARGE SOIL-ROCK MIXTURE IN A HYDROPOWER PROJECT

WANG Zigao1，2，HU Ruilin3，ZHANG Rui2，XU Wenjie4

2013, 32 (s2): 3836-3844

[PDF] 1289 KB (5)

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Soil-rock mixture(S-RM) is a kind of inhomogeneous geometrical，compared with rock mass or soil，it has variability of material composition，and more complicated space structure，up to now the experimental study of its mechanical parameters are lack of mature theory and technology. Taking a large soil-rock mixture in Liyuan hydropower project area as an example and on the basis of a large in-situ experiments，its characteristics of strength and mechanics are discussed，physico-mechanical parameters are determined by engineering geological are analyzed as well. Researched results show that it has complete shear stress to shear displacement curve and high shear strength in the natural state，it is not only to lay a foundation for stability analysis of soil-rock mixture，but also to provide relevant experience for similar project construction.

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LANDSLIDE IMPULSIVE WAVE HAZARD STUDY SUPPORTED BY GIS TECHNOLOGY

HUANG Bolin1，2，YIN Yueping2，3，WANG Shichang1，LIU Guangning1，CHEN Xiaoting1

2013, 32 (s2): 3844-3851

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Impulsive wave generated by landslide is a complex and dynamic process，wave propagation overly extended the dangerous range of landslide. Landslide impulsive wave simulation adopted wave dynamic model is hot in relative field in foreign，which can efficiently simulate long wave propagation problems. In this paper，the authors introduce wave dynamic model and form fast assessing system for tsunamis generated by geo-hazard(FAST) supported by GIS technology. FAST is made up of pre-processing module，simulation module，and post processing module，which can calculate impulsive wave according to the type of landslide failure，and can intuitively display water elevation change condition of point，line，surface and volume. It has characteristics of manageability，high efficiency and visibility. The paper takes Maocaopo landslide in Wu Gorge of Three Gorges Reservoir for example，and forecast impulsive wave generated by this landslide，verifying the feasibility and utility of FAST. The simulation result shows that the maximum wave amplitude is 25 m，the maximum run-up height is 12.5 m，and after landslide failure 444.5 s，a 2.5 m run-up wave will arrive in Wushan County. This soft offer a new analysis method and visualization platform for early warning and risk assessment work on geo-hazard impulsive wave in reservoir.

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GRAVEL-SOIL SLOPE WITH LIME IMPROVED AND NUMERICAL ANALYSIS ON STABILITY OF GRAVEL-SOIL SLOPE WITH PILE-ANCHORS

WANG Xingang1，HU Bin1，LIAN Baoqin2，JIANG Haifei1，YU Hongming1

2013, 32 (s2): 3852-3861

[PDF] 2579 KB (6)

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By compounding raw lime powder with gravel-soil taken from mining area in Bangpu of Tibet，the largedirect shear test for improved gravel-soils with lime-soil ratios of 3%，5%，7% and 9% was conducted to investigate the shear strength of gravel-soils with lime improved and the improvement effect. The tests show that：as the moisture content of the soil sample reduces，the bite friction and cohesive strength of samples increases，the shear strength of gravel-soil increase with lime addition；and the improvement effect with lime-soil ration of 9% is best. Finally，based on the indoor test results and theoretical formula，the gravel-soil slope protection with lime improves，anchor slope protection，anti-slide pile slope protection and with the above method combined slope protection in North-east Bangpu of Tibet are analyzed with FLAC3D numerical model. It shows that the maximum horizontal displacement of slope decrease significantly，and with no breakthrough of plastic zone，and the glide force reduce effectively after using the gravel-soil slope joint protection with lime addition，anchor reinforcement and anti-slide pile. The joint slope protection method can be more effective than above three separate method.

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LARGE-SCALE SHAKING TABLE TEST RESEARCH ON ACCELERATION RESPONSE RULES OF BEDDING LAYERED ROCK SLOPE AND ITS BLOCKING MECHANISM OF RIVER

DONG Jinyu1，2，YANG Jihong1，WU Faquan2，YANG Guoxiang2， HUANG Zhiquan1

2013, 32 (s2): 3861-3867

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According to dynamic model test similarity relation this paper constructed a bedding layered slope model with the physical dimension of 3.0 m(L)×0.8 m(W)×1.6 m(H) is carried out a large-scale shaking table test. And the testing results show that at the slope surface amplification effect is nonlinear and sectional，while below the 1/3 and over the 2/3 of slope height the amplifications are obvious. At the vertical direction in the slope，acceleration amplified with the slope height nonlinearly，and acceleration amplification coefficient reached to peak value at slope shoulder. At the horizontal direction，acceleration amplification coefficient at slope surface is larger than that in the slope，and it shows tend-surface effect. The mechanism of blocking the river is that arthquake inducing→tensile crack and loosen appeared of rear top→shear extrusion damage of foot of slope→high speed sliding→blocking of the opposite bank-accumulation at base of slope→formation of barrier dam.

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RESEARCH ON HYDROLOGY-MECHANICS COUPLING MODEL OF LANDSLIDE HAZARDS PREDICTION BASE ON GIS BY USING QUASI-DYNAMIC WETNESS INDEX

WANG Jiajia，YIN Kunlong，DU Juan，WANG Yili

2013, 32 (s2): 3868-3877

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Rainfall plays a key role in the regional shallow landslide hazards prediction. Considering quasi-dynamic wetness index，a hydrology-mechanical coupling model in landslide hazards prediction is proposed. It has combined the physical processes of the infinite slope model and simplified kinematic wave model based on digital elevation model(DEM)，and considered the comprehensive effect of topography and surface water infiltration and groundwater run out converted from rainfall to landslide stability. Based on geographic information system(GIS)，vector-raster coupled data is used in the slope unit hazard prediction(taking slope unit as basic study object，and using raster data to analyze the slope units stability). Firstly，it deduces and modifies the infinite slope model by limit equilibrium theory. Then，considering the rainfall intensity and duration，it calculates quasi-dynamic wetness index during rainfall infiltration and groundwater run out by simplified kinematic wave model，and the time and spatial distribution of landslide saturation factor are obtained. The hydrology model and infinite slope model is coupled on this basis. Finally，it approves the high accuracy of this model in regional shallow landslide hazard prediction by the example study in new Badong County.

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3D GEOLOGICAL MODEL AND STABILITY ANALYSIS OF SPILLWAY EXCAVATING SLOPE AND ITS APPLICATION

LIN Da，LI Mingchao，TONG Dawei，ZHONG Denghua

2013, 32 (s2): 3878-3887

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The spillway excavating slope is belonging to artificial excavating slope，which is different from general natural slope and has the characteristics of the high mountain and steep slope within the construction area. The spillway excavating slope stability is usually analyzed with limit equilibrium theory. However，as the established 3D geological model is not precise enough，the auto subdivision process visualization is not existing，and the computing interface of the stability analysis is not friendly enough，it is difficult to unify the vivacity and the clarity. In this paper，a 3D geological model of the studied region was built up，and the NURBS technology was used. The second development of the 3D geological software VisualGeo was carried out. It realized the auto subdivision of the 3D slope and the data extraction. While the improved 3D visual simulation and analysis system VisualSlope was used to calculate the stability，to analyze the sensitivity of the parameters and to research the support measures. This method realized the visual analysis and the directly demonstration of the slope stability，developing a new way for the slope stability based on 3D geological model and research of visualization analysis.

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RESPONSE RATE OF SEISMIC SLOPE MASS MOVEMENTS RELATED TO 2008 WENCHUAN EARTHQUAKE AND ITS SPATIAL DISTRIBUTION ANALYSIS

XU Chong，XU Xiwei

2013, 32 (s2): 3888-3908

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As the main phenomenon of slope mass movement response on earthquake，research of earthquake triggered landslides has important practical applications and theoretical scientific significances，especially related to the 2008 Ms 8.0 Wenchuan Earthquake. Landslides caused by the earthquake are widespread concerned due to they caused strong landscape changed，enormous loss of life and property damages. In present research，the concept of response rate of seismic slope mass movement(RRSSMM) was proposed. In the first stage，a landslide inventory map was prepared using the landslides triggered by the Wenchuan Earthquake，and was delineated from interpretation of aerial photographs，and field surveys. In the second stage，distribution raster and isoline map of RRSSMM are constructed based on“area-volume”correlation of landslides per 1 km2 grid cells. Next，Area distribution map of RRSSMM was constructed，and it showed that relationship of frequency-RRSSMM or area-RRSSMM in coincidence with power law in range of RRSSMM less than or equal to 10 m. It is showed that the maximum RRSSMM value appears at the position of Daguangbao landslide (the largest landslide triggered by the Wenchuan Earthquake)，up to 47.923 5 m. Areas of RRSSMM value exceeding 1 m almost appear in the northwest facing areas，on the hanging wall，of a section of Yingxiu-Beichuan fault (from Yingxiu Town to Beichuan County). Those areas of high RRSSMM values correspond to hanging wall of thrust fault. It is indicated that strong controlling of earthquake on landslide occurrences on hanging wall of thrust fault. Spatial distribution analysis of RRSSMM controlled by different landslide conditioning factors were carried out base on GIS technology and statistical theory. These landslide conditioning factors include topographic factors，geologic factors and seismic factors，such as，elevation，slope angle，slope aspect，slope curvature，slope position，distance from drainages，lithology，distance from the epicenter，distance from the Yingxiu-Beichuan fault，distance along the Yingxiu-Beichuan fault，peak ground acceleration(PGA)，and seismic intensity. The statistical results show that RRSSMM has positive correlation with slope angle，PGA，and seismic intensity，and negative correlation with distance from drainages，distance from the epicenter，and distance from the Yingxiu-Beichuan surface fault-rupture. It also represents the maximum value of RRSSMM appears between 1 600–1 800 m ranges in elevation. The highest RRSSMM value has preferred orientation，dominated by the eastern facing. There were small RRSSMM close to zero for plan curvature. For slope position，middle slope，lower slope and valley occupy the highest RRSSMM values. The two lithology groups of sandstone，siltstone (Z) and sandstone，siltstone，chert，slate (∈) had the highest RRSSMM values. The statistical results of RRSSMM along the Yingxiu-Beichuan fault show that the RRSSMM strongly affected by fault in thrusting movement feature. The final RRSSMM distribution data is of great significance on rivers and geomorphic evolution，and debris flow researches，and it can be timely shared to researchers in related fields，such as，tectonic geomorphology，engineering geology，environmental geology，and geological hazards etc. Research methods in this research can be applied to other regional seismic landslide events.

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RISK ANALYSIS METHOD OF ACCUMULATED LANDSLIDE BASED ON FRACTURE DEGREE

LI Shihai，ZHOU Dong，LIU Tianping

2013, 32 (s2): 3909-3917

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Basic characteristics for development of surface cracks and state of slip surface during landslide disaster is studied，and relationship between surface cracks and internal fracture state is established. Continuum-based discrete element method(CDEM) is briefly introduced. Through simulation of specific and typical landslides with CDEM，relativity of strength and surface cracks is discussed and maximum number of surface cracks is found. Maximum number of slip surface cracks is defined as the number of cracks on slip surface which is already running through. The concept of fracture degree of surface and fracture degree of slip surface are proposed，which are defined as the ratio of current number of cracks to maximum number of cracks on surface and slip surface respectively. Numerical experiments show that there is a specific corresponding relationship between fracture degree of surface and state of slip surface，which could directly describe the risk of a geological body. Result shows that fracture degree does not rely on mesh division when calculation accuracy is guaranteed，which indicates that it is feasible to use this new method based on fracture degree and CDEM to evaluate the risk of a landslide.

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CONSTRUCTION PROCESS SIMULATION AND ULTIMATE BEARING CAPACITY ANALYSIS OF XIAOWAN ARCH DAM BY 3D FINITE DIFFERENCE METHOD

GAN Haikuo1，2，LAI Guowei1，LI Yesheng3

2013, 32 (s2): 3918-3927

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To study the final failure mechanism of high arch dam and its safety factor，it's necessary to deeply analyze the ultimate bearing capacity of Xiaowan arch dam which is a typical project. Based on the three dimensional explicit three dimensional finite difference method of FLAC3D，this article accurately simulates the process of the dam construction and water storage.On that base，by using the strength accumulation coefficient method and over loading coefficient method，the ultimate bearing capacity results of Drucker-Prager criterion and Mohr-Coulomb criterion which are all with a tension cutoff are analyzed and compared with each other. Combined with the specific failure deformation，by methods of observing the connected plastic zone in the evolutionary process and recording the sudden change of the dam displacement，the gradual failure mode and the final safety factor of Xiaowan arch dam are found. The reason why the safety factors are significantly different under the two criterions is analyzed，it’s also proposed that the Mohr-Coulomb criterion is better than the Drucker-Prager criterion in the evaluation of the ultimate bearing capacity of arch dam. Finally，a sensitivity analysis on the dilatancy angle and tensile strength is made，and some useful conclusions are found.

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SAFETY ZONATION OF LARGE-SCALE SLOPES BASED ON LOCAL STRENGTH REDUCTION METHOD

XIAO Ruihua1，2，WANG Sijing1，HE Xiaohei1，ZHANG Xiaoping1，3，RAO Xiaoyu4，LUO Bin4

2013, 32 (s2): 3928-3937

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According to the characteristics of large-scale slope which may have multiple slip directions and multi-level slip surfaces，the method of safety zonation is proposed. Based on the theory of strength reduction， firstly，the typical geological section of the slope is selected to build a two-dimensional(2D) numerical model. Failure modes can be detected by applying local strength reduction to the model to search the potential failure surfaces at different depths. By using limit equilibrium method for each potential failure surface，the slope stability coefficients at varied depths and levels are obtained. Secondly，three-dimensional(3D) numerical model is established to analyze the influence area of different failure modes based on the local strength reduction. Thirdly，the safety of the slope can be zoned through aforementioned comprehensive analysis of slope stability coefficients and influence areas. Finally，the method is applied to the slope of Longjiang super large bridge；and the analysis results show that this method is effective for comprehensively demonstrating the stable state of large-scale slopes. The method can also provide guideline for the monitoring design，reinforcement design and construction design of slope.

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TIME HISTORY RESPONSE ANALYSIS OF JOINTED ROCK SLOPE UNDER SEISMIC LOADS

JIANG Tong1，LIU Yuanzheng1，MA Jin2

2013, 32 (s2): 3938-3944

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Study of the influence of seismic wave form and frequency on the time history analysis of jointed rock slope is conducted. Six different types of seismic waves are used. According to the displacement time history curves of the special monitoring points，the deformation process of jointed rock slope can be divided into three phases and two critical points. The three phases are as follows：deformation set-out phase，deformation accumulate phase and stable(unstable) phase；and the two critical points are set-out violent-slide point and deformation critical point. At the same time，edge enlarge effects of displacement are proved by the laws of dynamic response of slope. Calculation results show that the seismic wave form and frequency play important roles in the calculation. Based on this study，the limited displacement can vary about one time among four extreme cases where four different seismic acceleration sine curves are used. Sine wave of which amplitude becomes larger gradually is more reasonable to replace the actual seismic wave for the calculation. The frequency of seismic also has great effect on the deformation of slope. In fact，high frequency seismic wave controls the deformation accumulation of slope，while low frequency seismic wave controls the set-out of the slope deformation.

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FAILURE MECHANISM OF TOPPING ROCK SLOPE USING JOINTED FINITE ELEMENT SIMULATION METHOD

WANG Yu1，2，LI Xiao1，WANG Mengyao3，LI Ming3，TIAN Hao3

2013, 32 (s2): 3945-3953

[PDF] 1950 KB (6)

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The topping failure of rock slope in geological environment is a widespread phenomenon，which is particularly important to predict the response by means of simulation method scientifically. Based on the shear strength reduction of jointed finite element method(JFEM-SSR)，the deformation and damage mechanisms of the topping rock slope are researched. The rock block and joints attributes can be considered at the same time by JFEM-SSR method；and nonlinear contact relation of rock layer or rock block can also be reflected fully. In the process of obtaining the stress，displacement and plastic zone of slope，the stability factor can be got. Firstly，a toppling failure examples provided by R. E. Goodman and J. W. Bray is calculated，proving the reliability of the method. Then，based on JFEM，discrete fracture network(DFN) is used to establish geological model of a cutting slope on Guangle highway，applying JFEM to analyze the deformation and failure mechanisms，influencing factors for stability. Influences of groundwater seepage，earthquake action，dip angle of rock stratum and the rock face thickness on the deformation and failure of slope are mainly discussed，so as to provide a basis for engineering design.

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METHOD OF INTERCEPTING WATER BY FILLING SOIL WITH AIR IN EMERGENCY TREATMENT ENGINEERING OF LANDSLIDE

DU Lili1，SUN Hongyue2，SHANG Yuequan1，LIU Changdian2，KANG Jianwei2

2013, 32 (s2): 3954-3960

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Most of landslide′s catchment area is on the trailing edge of slope，and the key factor leading to rise of groundwater level is infiltration of underground water on the trailing edge. The theory of displacing water with air is analyzed. And the hydraulic conductivity will decrease with the decrease in degree of soil saturation. Therefore，the concept is put forward that water stoppage curtain of unsaturated soil area with compressed air is formed on seepage path. The test results prove the validity of intercepting water by using numerical simulation and physical model test.

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ANTISEISMIC STABILITY ANALYSIS AND REINFORCING DESIGN OF NUCLEAR POWER PLANT HIGH SLOPES

ZHENG Wentang

2013, 32 (s2): 3961-3971

[PDF] 1596 KB (8)

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The suitability of current nuclear safety guides to high slope antiseismic stability assessment of nuclear power plant is studied；and the analysis method and domestic research status of high slope stability are reviewed. Taking the typical high slope at a certain nuclear power station for example，qualitative analysis methods are combined with quantitative methods to comprehensively analyze the stability and failure mode of nuclear power plant high slopes. Firstly，red flat projection method and Chinese slope mass rating(CSMR) are applied to half quantitatively forecaste the landslide and define the design ratio of slope. Then，on the basis of typical two-dimensional calculation profile，rigid limit equilibrium method，strength reduction method and limit equilibrium finite element method based on stress field are used to calculate the slope antiseismic stability. Finally，three-dimensional(3D) fracture network model is established. 3D discrete element method is used to simulate the highly nonlinear and large deformation of jointed rock masses and qualitatively analyze failure mode and failure zone of slope. The collapse material migration process is reproduced；and its maximal migration distance is calculated under the action of earthquake. In addition，slope treatment ideas and common reinforcement method are summarized. The present research enriches the theory of high slope stability with nuclear safety grade and can provide technical support for stability analysis，assessment and engineering design of nuclear power plant slopes.

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LIDAR-BASED FINITE ELEMENT SIMULATION FOR JOINTED ROCK SLOPE

SONG Jie，HU Hui，RAFIG Azzam

2013, 32 (s2): 3972-3978

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Rock slope stability is subject to the dominant joint group. The joint system of outcrop rock-mass is automatically recognized and categorized based on point cloud data captured by terrestrial laser scanner(TLS) and fuzzy clustering method(FCM). Geometric spatial information and spatial position of several major joint groups can then be acquired. In order to determine the dominant joint group which controls rock slope stability，stereo graphic projection is applied to disclose the spatial position relationship between each major joint group and slope surface. The potential slip surface and corresponding factor of safety can be calculated by using strength reduction finite element method. The analysis results demonstrate that the slip surface mainly goes along the direction of dominant joint and extends from bottom to top. Shear failure commonly takes place along the joint fissure at the lower part of rock slope，while tensile fracture often occurs at the top part of rock slope.

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ELASTO-PLASTIC CONSTITUTIVE MODEL OF INTERFACE INCORPORATING STRAIN SOFTENING AND DILATANCY

PENG Kai1，2，3，ZHU Jungao2，FENG Shurong1，CAI Changguang1，ZHU Sheng3

2013, 32 (s2): 3979-3986

[PDF] 624 KB (8)

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The mechanical behaviors of the interface between coarse-grained soil and concrete are investigated by large-scale simple shear tests under conditions of mixed soil slurry(bentonite mixed with cement grout). The results indicate that phenomena of dilatancy and stress-strain softening are significant with presence of mixed soil slurry. The peak strength and the position where the dilatancy occurs are related to normal stress. The shear strain corresponding to the shear dilatation appears to be ahead of that corresponding to the peak value of shear stress under the same normal stress. In order to describe the interface deformation behavior，a elasto-plastic constitutive model of soil-structure interface in considering of dilatancy and strain softening is formulated in the framework of generalized potential theory；and plastic state equations are used to replace the traditional yield surface. The relation curves of shear stress and shear strain are fitted by a piecewise function composed by hyperbolic functions and resembling normal functions，as well as the relation curves of normal strain and shear strain. The entire model parameters can be identified by experimental tests. Combined with measured values，the maximum error between the results of shear stress and normal strain calculated by the model and the test values is within 10.5% and 12.7% respectively. So the validity of the model is verified.

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EXPERIMENTAL STUDY OF GENERALIZED SOIL-WATER CHARACTERISTIC CURVE OF BACKFILL SOIL FROM CANAL SLOPE AT ANYANG DISTRICT OF MIDDLE ROUTE OF SOUTH-TO-NORTH WATER DIVERSION PROJECT

ZHANG Junhao1，2，CHEN Zhenghan1，2

2013, 32 (s2): 3987-3994

[PDF] 544 KB (8)

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In order to analyze the influence of stress state and stress path on the generalized soil-water characteristic curve，namely generalized SWCC，using the triaxial apparatus for testing unsaturated soils，a series of triaxial shrinking tests with deviator stress and net mean stress being constant values，triaxial isotropic compression tests with deviator stress and matric suction being constant values and triaxial p-fixed consolidated drained shear tests with net mean stress and matric suction being constant values are carried out against the backfill soil of the canal slope at Aayang district of South-to-North water diversion project. The test results show that matric suction，net mean stress and deviatoric stress have significant effect on the discharge of water. The expression of improved generalized SWCC is proposed，which can take the effect of stress state and stress path on the discharge of water comprehensively into account，and the computed results using this expression are in good agreement with the test data.

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ESTABLISHEMENT AND ANALYSIS OF ELASTO-PLASTIC LOESS MICROSTRUCTURE AND DYNAMIC DEFORMATION MODEL

DENG Jin1，2，3，WANG Lanmin2，WU Zhijian1，2，3

2013, 32 (s2): 3995-4001

[PDF] 560 KB (7)

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Analysis of dynamic properties of loess from microstructure perspective is one of the most important direction to explore loess constitutive model. According to the micromechanism that overhead pore is the dynamic factors causing the residual deformation of elasto-plastic loess，combined with air-solid surface theory and hyperbolic formula，the pore-overhead seismic subsidence models is established by using data such as dynamic triaxial test parameters，overhead pore area and confining pressure. Computational formula for residual deformation coefficient of loess under dynamic loading is acquired in the model. By test contrast of the main loess deposition samples，the residual deformation coefficient calculated by the computational formula is very closed to the experimental value. The comprehensive analysis results show that the one-dimensional micro-pore dynamic residual model can well reflect the residual deformation actual situation induced by loess microstructure difference under different confining pressures，water contents and dry densities. The model can generally reflect the characteristics of elasto-plastic deformation of loess.

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MODEL EXPERIMENTAL STUDY OF LOESS WIDENED EMBANKMENT COORDINATION MECHANISM UNDER CONDITIONS OF DIFFERENTIAL SETTLEMENT

WENG Xiaolin，MA Haohao，LIANG Dongping

2013, 32 (s2): 4002-4009

[PDF] 1073 KB (7)

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Aiming to study the loess area highway widening project，based on the large-scale foundation settlement simulation test platform，a scale test with the geometry similarity ratio of 1∶1 is carried out；and the roadbed internal soil and the reinforcing material deformation monitoring systems is also established to analyze the response mechanism of internal soil and reinforcement of the roadbed constructed under the conditions of old and new foundation differential settlements. The results show that：under the widened embankment load，the roadbed internal soil experiences a constant process of deformation and coordination with the increasing foundation differential settlement. When the differential settlement S reaches to 9 cm，subgrade and pavement layer appear a slight void. Laying the geotextile material on old and new roadbed splicing segment can lead loose soil to form the compaction complex，which can enhance the overall stability and mechanical properties of roadbed soil and easily form the arch effect. Besides，the geogrid can digest the settlement between new and old roadbed in a certain degree，but the effect is limited. The geogrid inside the soil plays a coordination role in the subgrade soil deformation. The reinforcement force is not uniform and the corresponding alternating of tension and compression strain appears. With the increasing foundation differential settlement，strain show a increasing trend as a whole. When the differential settlement S between old and new foundation reaches to 16 cm，tension and compression strain of geogrid tend to be stable. The ultimate amount of geogrid tensile or compression changes only 2 mm，far less than the destruction limit of geogrid.

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DEEP SOAKING TEST STUDY OF COLLAPSIBLE LOESS FOUNDATION CONTROLLING REMNANT COLLAPSE

YAO Zhihua1，2，HUANG Xuefeng1，3，CHEN Zhenghan1，3，FANG Xiangwei1，MIAO Qiangqiang1

2013, 32 (s2): 4010-4018

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A site of self-weight collapse loess with heavy section is treated by four treating depths of lime soil(pure soil) compaction pile；and beneath the compaction reign，deep soaking test on the untreated loess is carried out in order to research the law of collapse deformation，treating depth and reasonable limit of remnant collapse of the self- weight collapse loess with heavy section in this soaking condition. The results show that，when the foundation of self-weight collapse loess with heavy section is treated with lime soil and pure soil，the compaction effects of lime soil and pure soil have little difference. In case of deep soaking，the deformation in treated region with 6–15 m depths cannot meet loess codes demands about upper load and presents a triple-section law：stable in the first test stage，slowly decreasing in middle stage，and suddenly dropping in later stage. According to the correlated researches of field soaking tests and neutral point of pile foundation，the concept of critical collapsibility depth of self-weight collapse loess with heavy section has been proposed firstly；and the critical depth is set as 20–25 m temporarily. In this way，the remnant collapse of deep loess layer can be decreased to certain degree；and the aim to limit treating depth of loess foundation is achieved. It is suggested that 15–20 and 10–15 m can be set respectively as the maximum treating depth of class B and C building in self-weight collapse loess area with heavy section.

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DEVELOPMENT OF MODEL TEST SIMILAR MATERIAL OF COLLAPSIBLE LOESS

ZHANG Yanjie1，2，WANG Xu1，LIANG Qingguo1，JIANG Daijun1，MA Xuening 1

2013, 32 (s2): 4019-4024

[PDF] 656 KB (6)

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The model test material of collapsible loess is the bottleneck of similar materials model research in geomechanics，which has limited the application of model tests in loess area. A model test material for collapsible loess is successfully developed after a lot of compounding tests by airfall method. This similar material is firstly mixed with barite powder and sand as non-cohesive material，and industrial salt，gypsum and bentonite as cohesive material. Then the material is mixed with water evenly. After wetted for 24 hours，the samples are produced by airfall method. At last，the samples are maintained at constant temperature of 50 ℃，which simulates the deposition mode and formation conditions of eolian loess，to obtain the targeted model test material. Odometer collapse test results show that this artificial material have similar collapsibility with natural loess；and also produce significant collapse when wetted. Shear test results indicate that shear strength parameters of the similar material are much close to natural loess. Since the density of the similar material can be adjusted widely，the model test material developed by the above method would be an ideal model test material for collapsible loess.

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ANALYSIS OF HEAT TRANSFER CHARACTERISTICS OF FROZEN SOIL FOUNDATION IN QINGHAI—TIBET DC TRANSMISSION LINE PROJECT

YU Qihao1，YOU Yanhui1，DING Yansheng2，WANG Guoshang3，QIAN Jin1，HU Jun1，GUO Lei1

2013, 32 (s2): 4025-4031

[PDF] 1301 KB (8)

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Based on field measurement data，the analysis，which is related to the heat transfer process of the permafrost engineering and the temperature change results，is vital to understand the stability trend of frozen soil foundation. Combined with the latest monitoring data of the frozen soil foundation long-term monitoring system in the Qinghai—Tibet direct current(DC) transmission line project，the heat transfer process of the tower foundation is analyzed preliminarily. It is found that the soil around the tower foundation is frozen overall after experiencing the first freezing period at the monitoring sites. Influenced by construction，permafrost conditions and other factors，the ground temperature around tower foundation differs from the natural filed below the permafrost table. Then，having experienced the melt period，the bottom soil of the tower foundation is frozen at the monitoring fields. During the heating process in the warm season，increasing rate of ground temperature and the thaw depth are mainly influenced by the form of tower foundations and permafrost condition. As a result，the temperature increasing at different monitoring sites varies from each other. The permafrost thermal regime near the pile foundation is better than that near the large excavation foundation such as column foundation and fabricated foundation. The heat pipes is used to protect the permafrost significantly at some sites. However，the heat pipes cooling effect is limited by permafrost temperature and heat transfer process at several sites when the foundation pits are excavated. Moreover，the temperature field around the foundation pit was still in dynamic changing process.

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EXPERIMENTAL STUDY OF ROADBED STABILITY IN CUTTING SECTION ALONG A HIGH-SPEED RAILWAY IN SEASONAL FROZEN REGIONS

NIU Fujun1，2，LIU Hua1，3，NIU Yonghong1，LIN Zhanju1，LU Jiahao1，3，LUO Jing1，3

2013, 32 (s2): 4032-4040

[PDF] 4224 KB (8)

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Harbin—Dalian passenger dedicated line crosses piedmont plain in the Northeast China，where is seasonal frozen ground region. As a 10 km cutting section of the line located in shallow groundwater area，frost heave is a serious problem in the roadbed construction. Based on monitoring results of hydrothermal conditions of the testing section near the Changchun west railway station，the hydrothermal processes in the roadbeds and their influences on the frost heave are analyzed；and the roadbed deformation before the operation of the railway is evaluated. The results indicated that，under the conditions of current design and construction，the subgrade is thermally stable，and the total deformation of the roadbed is less than 7 mm，while which of the upper layer occupied more than 60%. The frost heave value is negatively correlated with the ground temperature and reduces gradually with the frozen depth. The geomembrane barrier laid in the subgrade prevents the external moisture migrating into the roadbed，resulting in the relatively stable water content of the roadbed soils，thereby reducing the formation of segregation ice. The time-space distribution feature of the ground temperature is related to roadbed position and the surface structure. The ground temperature contour shows a slight elevation trend under the track panels and reinforced concrete base，as they increases the thermal resistance of the roadbed. The ground temperature slightly decreases under the traditional ballast layers of the contact lines along the two sides of the main line，caused by the cooling mechanism of the ballast layer. The frozen depth under the middle gutter is higher than that under the gutters at the two sides，due to the different engineering components used in construction of the gutters. The summarized results show that the testing roadbed has good performance of thermo-dynamic stability during monitoring period.

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DEFORMATION NUMERICAL ANALYSIS OF DEEP EXCAVATION IN SOFT SOIL BASED ON MODIFIED HARDENING MODEL

CUI Wei，WANG Ning，SONG Huifang

2013, 32 (s2): 4041-4047

[PDF] 1950 KB (5)

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Ideal elastoplastic model used in deformation analysis induced by underground engineering excavation leads to inaccurate prediction. Based on modified hardening soil model，considering the effect of small strain condition on soil behavior，a case study of deep excavation on the deformation of diaphragm wall and settlement of ground surface is numerical analyzed. The results show：according to the movement of diaphragm wall，the prediction result by using ideal elastoplastic mode—Mohr-Coulomb(MC) model is larger than observed deformation，and especially the part below the base of excavation. The result obtained from hardening soil model is consistent with but a little larger than the observed deformation. For the prediction of surface settlement，the trough obtained from MC model is deeper and wider than that obtained from modified hardening soil model，and the settlement from hardening soil model is larger. In general，because modified hardening model can be used to simulate the variation of soil behavior such as modulus and small strain during different loading and unloading states，modified hardening model is superior to MC model and hardening soil model whether in value and regular of deformation prediction.

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EFFECT OF FABRIC ANISOTROPY ON DYNAMIC SHEAR MODULUS IN K0 CONDITION

LI Bo1，2， YU Chuang1，ZENG Xiangwu3

2013, 32 (s2): 4048-4055

[PDF] 2038 KB (5)

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Dynamic shear modulus is a critical factor for sand in engineering practice. In order to evaluate the effects of fabric anisotropy on dynamic shear modulus，the measurement of wave velocity by bender element technique is conducted. The special container is manufactured to prepare the model with deposition angles of 0°，±45°and 90°. The Toyoura sand specimens with specified deposition angles are tested in loading and unloading conditions. The results show that the sand sample prepare in the deposition angle of 90° has the largest shear modulus in horizontal and vertical directions. It is found that in unloading condition，specimens with different deposition angles show different responses for stress history，and response of sand sample with deposition angle of 90° is most obvious，which verify that influence of deposition angle on small strain shear stiffness of sand is very significant. Based on the results，a micromechanical stress-strain model is validated，which could show the influences of fabric anisotropy，stress condition and particle contact characteristics on dynamic shear modulus reasonably.

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EXPERIMENTAL STUDIES OF STATIC EARTH PRESSURE COEFFICIENT OF UNDISTURBED SATURATED CLAY

HUANG Bo1，2，HU Junqing1，2，LIAO Xianbin3，HUANG Xiong3

2013, 32 (s2): 4056-4064

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A number of K0-consolidation tests are carried out on the undisturbed mud/silt clay and silty clay samples of Hong Kong—Zhuhai—Macao bridge by using advanced triaxial apparatus. The changes of static soil pressure coefficient K0 under different loading and unloading paths are studied；and the applicability of using common formula and recommended value of specifications to estimate the K0 are analyzed，as well as the prediction equation based on test results is given. The results show that：K0 of mud/silt clay at the bottom of the Hong Kong—Zhuhai—Macao bridge immersed tunnel is a basically constant value(0.47). K0 of silty clay is proportional to the preconsolidation pressure and K0 is between 0.30 and 0.45；both of the bounds are lower than the recommended values of specifications and manuals for similar soil. In addition to soil properties，the cementation of the undisturbed samples also could make the K0 reduce. K0 of the strong structural undisturbed soil would decrease to below the values of normally consolidated clay and then rebound and gradually stabilize during loading stages. We can use the empirical formula given by the predecessors to estimate the K0 of normally consolidated and over-consolidated undisturbed clays；and the internal friction angle should be the effective peak internal friction angle of normally consolidated soil.

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RESEARCH ON FAILURE CHARACTERISTICS AND DETERMINATION METHOD FOR SHEAR STRENGTH OF EARTH-ROCK AGGREGATE IN DIRECT SHEAR TESTS

DENG Huafeng1，2，YUAN Xianfan1，2，LI Jianlin1，2，LUO Qian1，2，ZHU Min1，2

2013, 32 (s2): 4065-4072

[PDF] 947 KB (7)

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In direct shear tests of earth-rock aggregate，empirical method is always adopted to determine shear strengths，while less considering the variation characteristics of shear stress-shear displacement relationship curves and failure characteristics of shear plane. Based on this，big earth-rock aggregate samples with different moisture contents are collected from typical earth-rock aggregate bank slope in Three Gorges Reservoir area to carry out the indoor direct shear test. The test emphatically analyzes the variation characteristics of shear stress-shear displacement relationship curve，failure characteristics of shear plane，and shear leap phenomenon. Meanwhile，an analytical method，using critical plastic shear strength and ultimate shear strength to determine the earth-rock aggregate shear strength，is put forward. With physical significance，the method can reflect structural characteristics of earth-rock aggregate better than conventional method，and can provide reference for engineering design.

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FINITE ELEMENT ANALYSIS OF COMPARATIVE PERFORMANCE OF LATERALLY LOADED PILE WITH OR WITHOUT PARTNER

XUE Jiangwei1，2，GE Xinsheng1，YANG Yong1，CAI Jingluo1，3

2013, 32 (s2): 4073-4081

[PDF] 994 KB (11)

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Reference on lateral load test and numerical simulation of large diameter pipe pile by using cast-in-place concrete(PCC)，finite element model of a single pile with or without pile partner under lateral load is established. Comparison calculations show that pile partner can ensure lateral loads delivering from pile cap to foundation soil，and double reduce stress and displacement of pile. Pile partner can also make some improvement on lateral bearing characters for the pile foundation with low cap even though the modulus of foundation soil is small. When pile partner is equipped，and the connection mode between pile cap and pile changing from rigid connection to hinge joint，pile body internal force can also be drastically reduced；and pile and pile caps by distance can only be considered to meet the requirement of vertical bearing capacity or optimization design of pile foundation stiffness to reduce differential settlement. Pillow is not necessary and can be cancelled in composite foundation when pile partner is applied. The height of pile partner has little influence on internal force and displacement of pile. Under rare earthquake action，pile partner may sacrifice firstly to keep pile perform well.

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AN ALGORITHM FOR QUANTITATIVELY ACHIEVING MAXIMUM DYNAMIC SHEAR MODULUS(GMAX) OF SOIL BASED ON EQUIVALENT VISCO-ELASTIC MODEL

XIANG Wei1，JIANG Jiwei2，JOACHIM Rohn3

2013, 32 (s2): 4082-4091

[PDF] 1111 KB (11)

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The maximum dynamic shear modulus(Gmax) is a very important parameter in describing the dynamic constitutive equation of soil. Gmax reflects the dynamic response of soil modulus and damping ratio directly，which changes with dynamic strain. Generally，Gmax is got by semi-quantitative formula in existed methods，and a lot of engineering experiences are needed. But in fact，Gmax is unique and constant. From this aspect，based on equivalent viscous elastic theory，the modified Davidenkov model is taken into account；and it is widely applicability for describing the dynamic behavior of soil. Based on dynamic triaxial test for three types of soil samples and according to the three parameters contain in modified Davidenkov model，the anti-analysis algorithm based on multiple regressions and self-adapting approximation is proposed to achieve Gmax and the factors required in Davidenkov model. The result shows that：with this algorithm，the dual constraints conditions above is carried out to fit test data. Under the premise of minimizing the residuals of Gmax，the fitting curve can describe the dynamic response behavior of soil very well within small strain condition. This algorithm is good at circumventing the difficulty of getting Gmax directly，and finally，the dynamic constitutive equation for three types of soil samples is achieved.

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ANALYSIS OF GROUND SETTLEMENT CAUSED BY PIPE-ROOF GROUTING FOR TUNNEL CONSTRUCTION IN SHALLOW SOFT STRATUM

ZHANG Xiangdong，LI Qingwen，LI Guixiu，GU Xuebing

2013, 32 (s2): 4091-4097

[PDF] 1421 KB (10)

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The two-dimensional computation models have been built by using the ADINA finite element program. Examples of seepage tunnels of shallow and surrounding soft rock of portal section of three-holes frame constructions are presented；and numerical analyses of the ground deformation response caused by tunnel excavation have been conducted under the condition of no support，grouting，pipe roof and grouting with pipe-roof，respectively. The minimum ground settlement is caused by grouting with pipe-roof，followed by pipe roof support and grouting support. The deformations of pipe roof and ground settlements caused by tunnel excavation are monitored in field and have been effectively controlled. The research results reveal that support effect of grouting with pipe-roof is very good in shallow soft stratum. Based on the theory of numerical calculation，the application of grouting with pipe-roof to shallow soft stratum is feasible. The validity and reliability of pipe-roof grouting are verified.

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CALCULATION OF ADDITIONAL STRESS CAUSED BY STRIP PARABOLIC LOAD IN GEOSYNTHETIC REINFORCED PILE SUPPORTED EMBANKMENT

JIA Yu，YANG Longcai，WANG Binglong

2013, 32 (s2): 4098-4104

[PDF] 6503 KB (11)

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The strict control standards for post-construction settlement of high-speed railway require high accuracy of settlement calculation，and the improvement of settlement calculation precision directly results from the high computational accuracy of additional stress，which makes the issue of calculating additional stress of significant importance. Differing from the assumption that the load acting on soil between piles in geosynthetic reinforced pile supported embankment presents uniform or symmetrical triangular distribution in the present study，the parabolic distribution form is proposed. Starting with the distribution function of strip parabolic load acting on soil between piles，the computational formula of additional stress caused by strip parabolic load in elastic foundation is put forward. The theoretical derivation is proved to be correct and reliable by numerical simulation；and the rationality and superiority of the computing method of additional stress are guaranteed by case study. The research achievements can provide reference for improving computational accuracy of additional stress along with settlement in geosynthetic reinforced pile supported embankment.

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EVALUATION OF RESONANCE METHOD FOR IMPROVING LIQUEFIABLE FOUNDATION BASED ON CPTU SOIL BEHAVIOR TYPE INDEX

ZOU Haifeng，CAI Guojun，LIU Songyu，DU Guangyin

2013, 32 (s2): 4105-4114

[PDF] 1840 KB (9)

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Combined with resonance theory，improvement of liquefiable foundation with cross-shaped vibration wing is conducted. Piezocone penetration tests are performed on the foundation before and after resonance improvement. It is shown that standards to assess the applicability of traditional vibro-compaction methods are not suitable to resonance method，since silts with fine content larger than 10% can be improved by resonance method. Nevertheless，the change of soil behaviour type index Ic，represents the variation of soil properties after improvement. Therefore，a criterion based on Ic is proposed to evaluate the applicability of resonance method. With results from standard penetration test performed on samples，relationship between Ic and clay content is promoted to determine the maximum clay content in soils to ensure the applicability of resonance method. Finally，variations of improvement to reduce liquefaction potential under different resonance schemes are studied. The reliability of criterion based on Ic is further confirmed. It is concluded that cohesionless soils with Ic＜2.40 or clay content less than 15% are suitable to be improved by resonance method. However，the effects of improvement are different depending on resonance schemes. Results show that the center of three resonance columns can be improved best，nest for the center of two resonance columns and routine points respectively. It is shown that resonance method expands the limitation of traditional vibro-compaction method，and can be spreaded in liquefiable foundation improvement.

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INFLUENCE OF OCCURRENCE MODE OF HYDRATE ON MECHANICAL BEHAVIOUR OF HYDRATE-BEARING SOILS

YAN Rongtao1，2，WEI Changfu2，FU Xinhui1，ZHONG Xiaobin3，XIAO Guiyuan1

2013, 32 (s2): 4115-4122

[PDF] 865 KB (10)

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Based on the two synthesis methods of hydrate in soils，the unsaturation sampling(US method) and gas diffusion sampling method for saturation soil(SD method)，triaxial shear tests are performed to study the effects of occurrence mode of hydrate on the mechanical properties of hydrate-bearing soils containing CO2. The experimental results confirm that the occurrence mode and saturation of hydrate have significant impact on the mechanical behaviour of soil with hydrate. In view of the microscopic mechanism，some analysis indicate that samples formed by US method，which are called as cementation mode，exhibit some structure characteristics of cementing soil. the samples formed by SD method，which are called as pore filling mode，loading mode and lenticle mode，show the properties of the friction material significantly，and exhibit strain softening due to the crushing damage of hydrate during the shearing period. Besides，by introducing a new parameter—the effective saturation of hydrate，a formula considering the influence of hydrate synthesis methods，which can predict the shearing strength of hydate-bearing soil，is proposed.

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GROUND VIBRATION INDUCED BY HIGH-SPEED RAILWAY OPERATION WITH GEOMETRIC IRREGULARITIES

CHEN Gongqi1，2，GAO Guangyun1，2，ZHAO Hong1，2

2013, 32 (s2): 4123-4130

[PDF] 627 KB (10)

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In order to precisely study the environmental vibration generated by high-speed train，based on the equilibrium equation of the trains，combined with the track bending equation，a simplified analytical expression for train dynamic load is derived considering geometric irregularities. Then，the deduced train dynamic load is input to analyze the influences of wavelength and amplitude on ground vibration by 2.5D finite element method(FEM). The results show that：the wheel-rail force and ground vibration acceleration enlarge with the increasing track irregularity amplitude considering the irregularity wavelength and train speed as constant values. The wheel-rail force and ground vibration acceleration decrease with the increasing track irregularity wavelength considering the irregularity amplitude and train speed as constant values.

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DISCUSSION ON FAILURE MODE AND ENGINEERING DESIGN OF ROCK-SOCKETED PILE IN KARST AREA

ZHANG Zhihao1，2，ZHANG Huile1，2，MA Lin1，2，SUN Yingxia1，2

2013, 32 (s2): 4130-4138

[PDF] 1869 KB (10)

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Based on indoor model tests，the failure mode of rock-socketed pile in karst area under different influencing factors is researched. The test indicate that there are four failure modes，which are punching failure mode，collapsed zone failure mode，sector plastic zone failure mode and tearing failure mode. Failure mode is mainly related with roof thickness，equatorial radius of karst cave，the ratio of polar radius to equatorial radius of karst cave. Compared with different specifications about the design of rock-socketed pile，investigate on cave safe roof thickness is extended；and a serious of credible computational formula are brought out，which are proved by engineering examples.

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EXCAVATION-INDUCED BEHAVIOR OF A RETAINING STRUCTURE USING DOUBLE-ROWED MICROPILES IN SOFT CLAY

YU Feng1，LIU Nianwu2，FANG Kai2

2013, 32 (s2): 4139-4148

[PDF] 633 KB (8)

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Double-rowed micropiles，usually served as excavation-supporting structures，have advantages such as convenient construction and satisfying lateral stiffness. In order to provide better understanding of their field performance，we investigate a full-scale retaining structure with 88 micropiles arrayed in two rows. The structure is instrumented to measure the lateral displacement，earth pressure and pile stress during excavation. The field-test results and associated numerical analyses show that the displacement of pile shaft increases with the increasing excavation depth and the maximum displacement is captured near the excavation surface. A non-zero bending moment is recorded at the pile head and the excavation depth decides the magnitude and distribution of the bending moment. The earth pressure imposed on the back-row piles can be transferred to the front ones through the upper connecting beam and the soil between the two pile rows. As the excavation proceeds，the earth pressure between the two pile rows decreases gradually above the excavation surface but increases below the surface. The measured pressures lie between the results calculated by the volume-scaling factor method and the elastic foundation beam method. Furthermore，both the active earth pressure acted on the back-row piles and the passive pressure at the bottom of pit are related to the displacement of pile shafts. The measured passive earth pressure is in good agreement with the predicted value of the elastic foundation beam method.

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RESEARCH ON ASEISMIC DESIGN OF PRESTRESSED ANCHOR SHEET PILE WALL

QU Honglue1，ZHANG Jianjing2，ZHU Dapeng1

2013, 32 (s2): 4149-4156

[PDF] 660 KB (10)

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Due to the complex stress system of prestressed anchor sheet pile wall，a series of fundamental theoretical issues are not solved completely；and its theoretical understanding lags behind its application greatly，especially in the area of aseismic design theory. To make up this gap，a new simplified method，therefore，is proposed based on previous researches. In the method，the influence of earth pressure from cable on cantilever section of pile is considered；and the influence of seismic comprehensive coefficient Cz on stress status of pile shaft is discussed. In addition，large-scale shaking table test is performed to verify the method；and correction suggestion of Cz is proposed. Through comparison of seismic earth pressures and axial forces between calculation and test under different working conditions，it is proven that the new method is feasible. In addition，the method is easy for engineers in seismic design application，as equations involved are easy to solve.

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PILE-SOIL-PILE INTERACTION BETWEEN TWO PILES MOVING ALONG DIFFERENT DIRECTIONS

KONG Linggang1，2，FAN Jiying1，2，CHEN Renpeng1，2，CHEN Yunmin1，2

2013, 32 (s2): 4157-4164

[PDF] 1081 KB (8)

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Both centrifuge modeling and numerical simulation are employed to investigate pile-soil-pile interaction between two adjacent piles with pile spacing of 3 times pile diameter moving in different directions. The influence of pile spacing，internal friction angle of sand，and different displacements of the leading and trailing piles on reduction factor are also analyzed based on numerical results. It is found that pile-soil-pile interaction is significant in two adjacent piles undergoing different movement directions. The reduction factor of the trail pile is not larger than that of the leading one in the investigated two cases. It is also found that reduction factors for the leading and trail piles almost linearly increase as pile spacing varies from 3 times pile diameter to 5 times and almost keep constant with internal friction angle. In addition，loading mode has certain effect on reduction factors of the two piles.

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SHAKING TABLE TEST FOR ANTISEISMIC BEHAVOIR OF EMBEDDED ANTI-SLIDE PILE AND NUMERICAL SIMULATION

LAI Jie1，ZHENG Yingren1，2，LIU Yun3，FANG Yushu1，WANG Yongfu2

2013, 32 (s2): 4165-4173

[PDF] 1428 KB (12)

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Finite element strength reduction method is widely used in the support of slope under static state，which has been with good economic benefit. But under the earthquake，how to calculate needs research. As to find a reasonable method of calculation，shaking table test and numerical analysis are adopted. Bidirectional Wenchuan Wolong(NE) earthquake wave is input in the test. Through increasing the input amplitude of seismic waves，soil stress，slope displacement and acceleration response of key point before and after pile shaft are monitored；and the dynamic characteristics and failure mechanism of slope under earthquake are studied. At last，numerical simulation is conducted by complete dynamic finite element method. It is demonstrated that numerical simulation results are in accordance with experimental results. The slope failure is induced by composite effect of tension-shear under earthquake. The bearing capacity with piles for seismic resistance is boosted and this research lays a good basis for the seismic design of embedded anti-slide pile.

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INFLUENCE OF ECCENTRICITY ON TWO-PILE FOUNDATION SUBJECTED TO LATERAL LOADING

KONG Linggang1，2，GU Ming1，2，CHEN Renpeng1，2，CHEN Yunmin1，2

2013, 32 (s2): 4174-4182

[PDF] 958 KB (12)

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A large scale model test of two-pile foundation in saturated silt is carried out to investigate the response under eccentric lateral loading. An ABAQUS numerical model is built and validated by the model test result. The effect of eccentricity of applied lateral loading on the behavior of the foundation is further studied using the validated model. It is found that the applied load-horizontal displacement curves of the pile cap of the two-pile foundation are close to a laterally loaded single pile curve in shape. The lateral stiffness decreases with the increasing eccentricity of the applied load. Eccentricity can induce significant difference in pile-head shearing between the two piles. The pile next to the load point undertakes more shear force and the pile-head shear resistance of another pile can be opposite to its displacement in direction under a certain eccentricity. The torsional rigidity of the individual piles is far greater than that of a corresponding single pile subjected to torsion because of the deflection-torque coupling effect in the piles，but the influence of the coupling effect decreases with the increasing eccentricity. Both torsional and lateral resistances of the individual piles contribute to resist the applied torque；and the contribution of torsional resistances of the individual piles to the applied torque significantly decreases with the increasing applied load.

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STUDY OF INACCURACY OF P-WAVE VELOCITY IN PILES BY LOW STRAIN INTEGRITY TESTING

HU Xinfa，LIU Jianxin

2013, 32 (s2): 4183-4189

[PDF] 747 KB (12)

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Field testing of piles using low strain method is carried out to study the effects of sensor position and excitation point on the first amplitudes，first-break times，reflection amplitudes and times of the end of the piles and testing wave velocities. The test results show that for the same length of piles，the larger the pile diameter is，the more occurrences of testing wave velocity is on the high side，while for the same diameter of piles，the shorter the pile length is，the more occurrences of testing wave velocity is on the high side. In order to improve the testing accuracy of wave velocity，using theoretical analysis，formulae considering the time lag are established for computing P-wave velocity in an integrate pile and the position of shaft defects of cast-in-place piles and prestressed pipe piles. For the first time formula is established to calculate the average velocity of the lower part of defect segment of the cast-in-place pile. Practice prove that the proposed formulae can correctly reflect the actual P-wave velocity of pile and actual position of defects in a pile，hence the formulae have obvious superiority over the existing ones.

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ANALYSIS OF BEARING PROPERTIES OF LARGE-DIAMETER AND SUPER-LONG BORED PILE IN COHESIVE SOIL AND SINGLE PILE SETTLEMENT

ZHANG Ruikun，SHI Minglei，NI Fujian，WANG Jin

2013, 32 (s2): 4190-4198

[PDF] 986 KB (12)

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Based on the measuring data of static load test and pile stress measurement of 4 test piles in the rail transit engineering in Taihu lacustrine-swamp sedimentary soils area，the characteristics of skin friction and tip resistance of large-diameter and super-long bored piles in cohesive soil are analyzed. The hybrid method of finite element analysis of rod structure coupling with the shear displacement method for single pile is utilized to simulate and predict the single pile settlement. The test results show that，when the load on single pile is vertical，the skin friction and tip resistance of large-diameter and super-long bored pile in soil layer are gradually exerted from top to bottom；and the two above resistances do not play simultaneously but have mutual influence on each other. The pile-soil displacement is 4–7 mm when skin friction reaches to ultimate value. It is verified that the settlement calculation hybrid method in which the anisotropy of rock and soil around pile and nonlinearity of shear sliding on boundary are considered can predict the settlement of single pile successfully.

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APPLICATION OF PIPE-ROOF METHOD TO STABILITY ANALYSIS OF SOFT GROUND

SUN Yuyong1，ZHOU Shunhua2，XIAO Hongju1，WANG Mingfang1

2013, 32 (s2): 4199-4206

[PDF] 812 KB (9)

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The stability of soft soil between pipe-roofs and tunnel face is the decisive factor which affects the display of pipe-roof and grating system. Firstly，the influencing factors of the formation of arch are studied. According to the Mohr-Coulomb shear strength theory，the determination method for the stability of soil between pipe-roof is derived，that is when the vault and skewback are both in steady state. Secondly，the tunnel face stability is assumed to be the three-dimensional slope stability problem under cover loads；and the determination method for the stability of tunnel face is derived and applied to an underpass in Hangzhou City to calculate the soil stability between pipe-roofs and tunnel face. The reasonable proposals are then put forward to ensure the tunnel safety.

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EXPERIMENTAL STUDY OF WEAKENING EFFECT OF HIGH WATER HEAD ON WEAK ROCK MASSES FROM JINPING I HYDROPOWER STATION

XU Huining1，ZHOU Zhong2，XU Jin1，REN Haonan2，NIE Ming1，WANG Lu1，ZHENG Hanhuai2，

2013, 32 (s2): 4207-4214

[PDF] 712 KB (11)

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The weakening effect of high water head on dam foundation weak rock masses after impoundment for Jinping I hydropower station is a highly concerned subject for its engineering construction. A series of testing methods are suggested to reveal the weakening effect. Based on a geological process-mechanical mechanism simulation-mechanical parameter control theory，rock mass replica specimens can be prepared with complete process of triaxial compression test and used for hydro-mechanical coupling test. A series of triaxial compression tests with the confining pressures of 5，10，15，20，25，30 MPa are performed on the replica specimens under current natural state and hydrostatic pressures of 1–4 MPa. The result has shown that，the weakening effect is quite significant in the shallow low stress rock mass，the weakening rate of strength parameter f is within 13%，while the weakening effect of c increases dramatically up to 100% with the increasing hydrostatic pressure. The weakening rates of deformation modules increase with the increasing hydrostatic pressure when confining pressure is below 20 MPa，and decrease when confining pressure increases. However，when confining pressure exceeds to 20 MPa，the weakening effect is negligible. A prediction model of rock mass mechanical parameters is established according to the results. These achievements have already been applied to the engineering construction of Jinping I hydropower station，and the research techniques have opened up a new laboratorial way for research on rock mass mechanical properties.

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RESEARCH OF DYNAMIC PROPERTIES CHANGES AND MICROSCOPIC MECHANISM OF AGEING SAND

CHEN Guangzai1，CAI Yuanqiang1，2，WANG Jun2，DONG Quanyang1

2013, 32 (s2): 4215-4223

[PDF] 1123 KB (11)

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Eleven tests of Fujian standard sand under different conditions using British GDS resonant column (RCA) system was conducted with the aim of researching the aging effects on small-strain shear modulus and damping ratio of sands and give explanations for the test results based on grain slip and contact force homogenization theory of granular materials. The experimental results show that，within a certain confining pressure，small-strain shear modulus gradually increases with time，and the damping ratio decrease gradually with time. At the same time，the research founds that the relative density，stress history and fines contents significantly effect the aging of sand. Under the confining pressure of 35 kPa，time effects of loose sand is greater than dense sand，however，when the confining pressure increase to 150 kPa，time effects of loose sand is less than dense sand. Stress history is one of the important factors affecting time effects of sand：unloading-reloading cycles and overconsolidation both can reduce the growth rate of small-strain dynamic shear modulus of sand. Aging rate of sand will be increased if dry kaoline powder was added to samples.