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2013, 32 (s2): 0-0

(31)

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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

(102)

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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

(121)

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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

(93)

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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

(90)

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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

(124)

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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

(109)

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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

(121)

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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

(76)

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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

(87)

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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

(119)

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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

(97)

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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

(114)

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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

(127)

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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

(72)

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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

(92)

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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

(60)

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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

(98)

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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

(106)

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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

(97)

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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

(109)

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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

(133)

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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

(114)

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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

(91)

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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

(93)

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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

(101)

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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

(90)

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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

(93)

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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

(95)

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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

(104)

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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

(111)

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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

(133)

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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

(89)

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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

(101)

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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

(105)

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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

(90)

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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

(96)

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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

(84)

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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

(99)

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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

(102)

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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

(103)

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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

(84)

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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-

(118)

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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

(102)

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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

(110)

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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

(105)

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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

(83)

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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

(67)

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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

(55)

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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

(105)

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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

(84)

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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

(95)

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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

(93)

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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

(108)

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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

(101)

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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

(94)

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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

(106)

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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

(102)

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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

(84)

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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

(118)

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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

(70)

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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

(97)

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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

(108)

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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

(129)

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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

(117)

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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

(93)

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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

(95)

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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

(81)

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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

(79)

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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

(95)

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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

(81)

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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

(118)

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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

(102)

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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

(98)

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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

(109)

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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

(92)

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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

(79)

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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

(65)

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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

(82)

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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.