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2014, 33 (sl): -0
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DYNAMIC DESIGN AND RESEARCH ON EXCAVATION AND SUPPORT DESIGN OF UPPER SURGE CHAMBER CAVERNS OF JINPING II HYDROPOWER STATION

CHEN Tao，WU Xumin，CHEN Xiaojiang

2014, 33 (sl): -2599
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The upper surge chamber project of Jinping II hydropower station has large cavern group which owns big section area and high shafts. For the sake of stability of surrounding rock during the construction period，and ensuring security of concrete lining in the operation period，based on the complex geologic condition of the site，this paper adopts a three-dimensional discrete element software 3DEC to conduct dynamic excavation and support analysis mainly for the shafts of surge chamber，and the calculation results match the actual monitoring data basically，which has played a role in guiding the project design. Furthermore，this paper focuses on a complete set of procedure and method for dynamic design，and gives some suggestions to the analysis method and parameter choice. The application effect of using 3DEC and discrete element method in the field of solving structure planes controlled project is also demonstrated，which could provide some beneficial reference to other similar projects.

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MODELING TEST ON INITIATION MECHANISM OF LANDSLIDE IN OBLIQUE INCLINED THICK-BEDDED MOUNTAIN

FENG Zhen1，YIN Yueping2，CAI Qipeng3，LI Bin1

2014, 33 (sl): -2604
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This paper tries to reveal the mechanism of the Jiweishan landslide，which is known as an apparent rockslide from oblique inclined thick-bedded mountain. In previous study，a failure pattern that slide masses in the rear are key driving blocks for slope instantaneous failure was proposed. In order to validate it，centrifugal modeling test has been carried out with an optimized model to reproduce landslide initiation process and to analyze failure characteristic. The results show that the slope model slides at 73 g，which means the modeling test is approximately in agreement with the last test whose model fails at 80 g. It also indicates that a jointed model is easier to slide. Most of inner blocks are stuck on sliding surface and lateral blocks slide in apparent dip. Under 73 g，rear blocks begin to creep simultaneously with increase of centrifugal acceleration. During this phase，the key block in the front plays a role in anti-sliding. When acceleration reaches 73 g，the key block is squeezed out abruptly and triggers sliding of blocks from behind. The initiation mechanism involves transition from progressive failure to instantaneous failure and experiences a process of creeping，tensile failure，sliding，colliding in the front，apparent sliding，bursting out，disintegrating and accumulating.

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NUMERICAL ANALYSIS OF SURFACE SETTLEMENT CONTROL CONSIDERING PIPE JACKING CONSTRUCTION PROCESS

YU Jun1，GONG Xiaonan2

2014, 33 (sl): -2610
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Pipe jacking construction causes soil disturbance and leads to surface settlement and building damage. In order to reduce soil disturbance and building damage，especially in soft soils with high water level，numerical simulation is conducted to optimize construction parameters based on surface settlement control，because settlement is comprehensive response. The parameters，such as friction，pipe jacking pressure，soil anti-force，were comprehensively analyzed to control surface settlement and protect environment and construction safety. Result shows that when above mentioned three parameters are 10 kPa，0.18 MPa，15 kPa，respectively，the surface settlement is the least. The conclusion could provide the references to similar engineering.

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ANALYSIS OF SPATIAL EFFECTS OF CONSTRUCTION BEHAVIOR ON PILOT TUNNEL EXCAVATION

ZHOU Zongqing1，LI Shucai1，LI Liping1，2，SHI Shaoshuai1，WANG Qinghan1

2014, 33 (sl): -2619
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The deformation mechanism and stability control of surrounding rock are one of the key technologies in tunnel construction. According to the spatial effects of construction behavior on pilot tunnel excavation，the deformation law of surrounding rock in tunnel construction was simulated and comparatively analyzed with full face method and bench tunnel construction method by using the finite difference software FLAC3D. Results show that the displacement rate and the displacement after excavation caused by pilot tunnel construction are smaller than the other two methods，which are beneficial to the stability of surrounding rock. With the increase of buried depth，the displacement increases linearly，whereas the horizontal convergence increases linearly and the crown settlement increases non-linearly with the increase of lateral pressure coefficient. The proportion of the displacement before excavation increases with the increase of the depth，whereas the proportion of the horizontal convergence before excavation increases and the proportion of the crown settlement before excavation decreases with the increase of the lateral pressure coefficient. Combined with the field monitoring data，the reliability of conclusions was verified. The obtained conclusions have certain reference to similar projects，important significance and engineering value.

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STUDY OF DISTRIBUTION REGULARITIES AND REGIONAL DIVISION OF IN-SITU STRESSES FOR PINGDINGSHAN MINING AREA

WANG Yingchao1，2，JING Hongwen1，2，CHEN Kunfu2，WEI Liyuan2

2014, 33 (sl): -2627
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Deep underground projects are usually connected with high in-situ stress environment. Based on the research on the evolution law of geologic construction for Pingdingshan mining area，local measurement information on in-situ stress of deep stratum were collected for the mining area，and the distribution of in-situ stress was analyzed. According to the type of in-situ stress field and the distribution characteristics for the mining area，spatial division was performed with three parts：Southwest area，I，where the self-weight stress field plays an important role in this area；Middle area，II，where the construction stress field is important，and the horizontal tectonics stress is faint；East area，III，where the construction stress field is important，and the horizontal construction stress field is important. Furthermore，the distribution characteristics and the relationships between the characteristics and geologic structures of each area were investigated. To validate the results of spatial division，hollow stress relaxation method was adopted，and in-situ stresses of nine points were tested locally at different positions and depths. It was found that the local measurement results are in good agreement with those of spatial division on in-situ stresses for the mining area. The result could provide dependable information for mine field exploration，laneway layout and support design of Pingdingshan mining area，and improve the scientific significance，rationality and reliability of engineering design.

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NUMERICAL SIMULATIONS OF WATER INTERCEPTING AND DRAINAGE ASSOCIATED WITH AIR FILLING FOR LANDSLIDE TREATMENT

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

2014, 33 (sl): -2634
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On the basis of the water drainage theory with air filling and the seepage theory in unsaturated soil，the paper presents a method for controlling landslide，i.e. forming a unsaturated curtain for cutting off water in seepage path with compressed air. The process of water drainage with compressed air belongs to a very complex air-water two-phase flow process. The paper established a mathematical model to describe the real flow process for fluid on the basis of seepage mechanics，and used finite element method to analyze the effect of water intercepting and the influencing factors by using two-phase flow model for air and water. According to numerical simulations，the conclusions are drawn as follows：the air diffuses along the direction of lower water levels and the water flow direction changes to slope surface，so the effect of intercepting water is fine；the intercepting water process exists the start-up pressure and it increases with decreasing permeability coefficient；the effect of intercepting water is better with larger air pressure；the permeability coefficient and porosity have no effect on water intercepting.

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BASIC FEATURES AND PREVENTION MEASURES OF A GIANT UNSTABLE ROCK MASS AT JIEXU HYDROPOWER STATION，YARLUNG ZANGBO RIVER

WANG Jingyong1，SHI Yuchuan2，WANG Wuzhou1，CHENG Yingjian2，LI Chao2

2014, 33 (sl): -2640
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[PDF 6932 KB] (590)

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Large dangerous rock mass located outside excavation line in hydropower project construction has a significant impact on its safety and operation. It?s difficult to reach and to reinforce them，and which put forward higher requirements to geological exploration. There are deep valley，high and steep slopes on the upstream of the Yarlu Zangbo River，and there is a large dangerous rock mass，about 37.5×104 m3，in the left dam abutment of Jiexu hydropower station. By finding out occurrence boundary of the rock mass，connected state，equivalent parameters，the qualitative and quantitative methods are used to determine the overall and local stability of dangerous rock mass，buckling mode，and the corresponding control measures are put forward. It has certain guiding significance to the giant dangerous rock evaluation idea and the prevention measures.

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OPTIMIZATION RESEARCH ON BAIHETAN ARCH DAM FOUNDATION AND PEDESTAL

PAN Yuanwei1，LIU Yaoru1，ZHANG Long1，YANG Qiang1，XU Jianrong2，HE Mingjie2，LIU Xijun2

2014, 33 (sl): -2648
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As the foundation conditions of Baihetan arch dam are complicated，large pedestal should be designed to improve the stress distribution. Current research on reinforcement evaluation of dam foundation and abutment generally relies on engineering experience，and there is no comprehensive and reliable pedestal evaluation criteria yet. A new optimization design method for dam pedestal is presented. Stability of pedestal and its affec to dam are both considered，and thus the optimal scheme is verified. This method combines various factors，such as displacement，stress，plastic zone and anti-slide safety factor. Besides，unbalanced force is used to analyze dam heel cracking，and plastic complementary energy(PCE) is applied in pedestal global stability evaluation. As measurement of structural local failure，unbalanced force is effective in predicting location and direction of crack propagation in dam heel. PCE is a scalar norm of unbalanced force，which is suitable for structure stability analysis. Four pedestal design schemes are compared in the meaning of dam displacement，dam heel cracking，pedestal stability and anti-slide safety factors. The optimal scheme regards the pedestal as a part of dam and sets joints on its upstream surfaces.

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COMPOSITE ELEMENT METHOD OF LIFT JOINT SIMULATION FOR ROLLER COMPACTED CONCRETE TEMPERATURE FIELD ANALYSIS

SU Peifang1，2，WENG Yonghong1，2，CHEN Shenghong3，LU Xingli4

2014, 33 (sl): -2654
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The lift joint segments which distribute in the roller compacted concrete(RCC) are difficult to be simulated in the temperature field analysis. Based on the principle of composite element method(CEM)，the composite element model for temperature field of RCC is built. The preprocessor is simple and convenient and the lift joint segments are contained in the composite elements，thus the mesh generation of lift joint can be considerably simplified. The quantity of mesh can be easily controlled and the shape of mesh can be improved. The composite elements may contain sub-elements of arbitrary shape whose temperature can be interpolated from their corresponding mapped nodal temperatures. The temperatures in lift joint segments are calculated from mapped nodal temperatures of their neighboring sub-elements. In composite element method，the solving procedure of the mapped nodal temperatures is similar to that in conventional finite element method，and the elements containing no lift joint are degenerated to conventional finite elements automatically. The programs for composite element algorithm can be incorporated into the conventional finite element analysis procedure with intrinsic coherence. The comparative study between the composite element method and the conventional finite element method has been illustrated to verify the composite element algorithm for temperature of RCC.

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STUDY OF KEY TECHNOLOGIES OF USING ANISOTROPIC SOFT ROCK TO BUILD HIGH CONCRETE FACE ROCKFILL DAM

ZENG Zeng1，2，SHEN Guihua2，WANG Qiujie3，ZHANG Zehui2，DANG Faning1

2014, 33 (sl): -2661
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First the concept of anisotropic soft rock in concrete face rockfill dam construction(CFRD) is put forward，and it is different from hard and soft rocks in traditional sense. By studying the anisotropy of soft rock(schist stone for example)，and its derivatives heap chlorite，the physico-mechanical properties of anisotropic soft rock were given in the paper. On the basis of partition map of hard rock，sand and gravel dam，primary partition map of anisotropic soft rock dam and associated construction measures have been proposed. Taking a hydropower station CFRD project in Xinjiang，for example，combined with the special topographic and geologic conditions，a 3D model for the standard cross-section with three kinds of partition was built. Also numerical simulation based on nonlinear finite element method(FEM) was done. The results were analyzed and compared，and the recommended solutions were given to make full use of local anisotropic soft rock.

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RESEARCH ON HIGH EARTH-ROCK COFFERDAM IMPERVIOUS WALL SECURITY BASED ON MULTIAXIAL STRENGTH OF CONCRETE

WANG Yongming，REN Jinming，CHEN Yonghong，CAI Jianguo

2014, 33 (sl): -2669
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[PDF 1200 KB] (694)

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Plastic concrete was widely used in foundation impermeability treatment，especially in impervious wall of high earth rock cofferdam. There were no special guiding regulation and standard about testing method and corresponding structure calculation security evaluation criteria for this material. The triaxial compression test of rock earth material was utilized to obtain the deformation and strength parameters of plastic concrete and stress level was used to measure the safety of concrete impervious wall. But stress level was introduced in triaxial shear state of soil. It adapts for Mohr-Coulomb friction strength theory of granular material safe state. Complex stress state of deep concrete impervious wall material safety check should be carried out through the concrete strength theory. Security criterion which contains multiaxial strength of concrete was introduced. The Baihetan high earth-rock cofferdam whose impervious wall reaches 50 m is taken as an example. Comprehensive three- dimensional finite element calculation was conducted to analyze the safety state of cofferdam. The differences of safety index based on stress level and safety criterion were found. It show that the safety criterion than the stress level can be more sensitive to reflect the impervious wall security state. Stress level could reflect the safety status of the wall when the element positioned in three-dimensional compressed state. The security criterion should be used for safety check when the tensile stress region is obvious.

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STABILITY ANALYSIS OF GRAVITY PIPELINE PROTECTION RETAINING WALL SUBJECTED TO LOADS OF FLOOD IN RIVER BEND

BI Weiwei1，LI Yunpeng1，HAN Bing2

2014, 33 (sl): -2676
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Gravity pipeline protection wall，as a main type of hydraulic protection projects，is likely to be destroyed by the rushing flood. In view of the present instability problems of gravity retaining wall subjected to loads of flood in river bend and according to the structure characteristics and the actual stress state of the pipeline protection retaining wall，the paper puts forward new formulas about safety factor of wall?s stability and the lateral scour limit depth under wall，in which the factors，such as the rush of flood，the buoyancy force，the seepage water pressure，the lateral widening depth under wall and the descent velocity of flood level，are considered. Based on the formulas，the effect of each factor on the stability of the retaining wall is analyzed. The results indicate that in the period of flood level rising，owing to the loads of flood in river bend，the wall shows a decreasing horizontal slide failure trend to the river. On the contrary，the buoyancy force，the seepage water pressure，lateral widening depth and the descent velocity of flood level make the retaining wall easy to overturn and there is a non-proportional relationship between the ability to resist overturning and the water level difference before and after the retaining wall. The formulas and analytical ideas and methods cannot only be adopted to the stability analysis of gravity retaining wall along the river，but also provide a theoretical reference for the similar engineering design and research.

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COMPARISON STUDY OF PHYSICAL PROTOTYPE MODEL TEST AND NUMERICAL SIMULATION OF GONGJIAFANG LANDSLIDE IN THREE GORGES RESERVOIR

HUANG Bolin1，2，YIN Yueping2，3，LIU Guangning1，CHEN Xiaoting 1，WANG Shichang 1

2014, 33 (sl): -2684
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Physical prototype test can be used to verify the validity and accuracy of numerical simulation result. The authors compare Gongjiafang landslide physical prototype model test with numerical simulation result，which is based on water wave dynamic theory. This research suggests that the simulation can reproduce the water wave interaction phenomena in the physical test，and the water level process lines match well. There are some errors between the values from physical test and numerical simulation，which is rooted in the tsunami source model. Numerical simualation based on water wave dynamic theory has the character of validity and accuracy. This method can offer scientific basis to assess impulse wave hazard generated by landslides in long distance and large region valley，which would be the hot issue in this field in the future. This result will benefit to popularize and apply numerical simulation method based on wave dynamics.

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RESEARCH ON CONTROL INDICES AND DEFORMATION CHARACTERISTIC OF SHALLOW TUNNEL WITH WEAK INTERLAYER

WU Xuping，YANG Xin?an，LI Yacui，ZHANG Jianbo

2014, 33 (sl): -2691
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Taking construction section with center cross diagram(CRD) method in Zhongming tunnel of Nanjing—Anqing passenger dedicated line for example，deformation of surrounding rock and control effect of shallow tunnel with weak interlayer were analyzed by comparing with site measurement in different construction conditions，and the quantitative indices of surrounding rock deformation are established. The results show that deformation of surrounding rock could been controlled effectively during excavation by CRD method，and it could been reduced by employing advanced conduit grouting in surrounding rock of vault；Surrounding rock ranges affected by excavating are 3.0-3.5 times of the tunnel diameter in longitudinal section and about 4.0 times in cross-section，showing spatial effect obviously. The laws of surrounding rock deformation remained basically the same in numerical simulation and site measurement and it was more similar to curve of Panet，and the advance core pre-convergence deformation of excavation face is about 45% of total deformation. The limit value of surface and vault subsidence are 40 and 80 mm respectively，and the limit value of rate and relative subsidence are 5 mm per day and 0.64% in vault.

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COMPENSATION METHOD APPLIED FOR CONSTRUCTION OF BASEMENT NESTED IN EXISTING BUILDING

HU Xiaojing

2014, 33 (sl): -2697
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The principle of constructing basement nested in existing building is discussed. A indoor compensation method that compensates foundation worked expectedly under the influence of live loads on floor，and the coefficient confirmed to calculate foundation soil stress by multiplying live loads on floor are presented. Based on the proposed principle，the total loads of the underground space to be built can be balanced and compensated by the summary of no less than the following parts：one is the soil weight of foundation pit；the other is a part of the pre-consolidation pressure which mainly comes from the soil stress of floor live load. A construction case is illustrated. The research results and the engineering practice both show that the indoor compensation method was suitable to applying to constructing basement nested in existing building. As the excavation depth and the increased loads was determined according to the method，the foundation soil deformation affected by the indoor excavation and construction would no longer threaten existing building?s stability and would reduce the risk of damage to the existing building.

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SEISMIC DYNAMIC RESPONSE OF SAND SLOPE INDUCED BY VARIATIONS OF GROUNDWATER LEVEL

SONG Bo1，HUANG Shuai1，CAI Degou2，3，YE Yangsheng2，3

2014, 33 (sl): -2706
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Studying the seismic dynamic responses of slope where underground water exists has an important guiding significance for the slope engineering seismic design. Based on the finite element simulation and shaking table test，the influence laws of underground water level on the seismic dynamic responses of sand slope are studied. The results show that the peak acceleration dynamic amplification and the maximum horizontal displacement along the slope height increase with the rising of ground water level，and the maximum horizontal displacement with ground water is 2.35 times of that without water to the greatest extent. The rising of groundwater level leads to the decreasing of effective stress. Compared with no water of slope，the maximum effective stress is reduced by 63% under far field earthquakes in the full water depth of slope，while the maximum effective stress is reduced by 64% under near-field earthquakes，which are unfavourable for the stabilization of slope. There is a critical level of the influence of groundwater on the shear capacity of slope toe，when the groundwater level is above the critical water level，and the influence is gradually reduced. Based on the comparison of shaking table test and the numerical simulation，the accuracy of numerical simulations of this paper is verified.

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DEFORMATION CHARACTERISTICS ANALYSIS OF DIAPHRAGM WALL FOR FOUNDATION PIT SUPPORT IN SOFT SOIL

LIU Nianwu1，2，GONG Xiaonan1，2，LOU Chunhui1，2

2014, 33 (sl): -2712
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The deformation characteristic of diaphragm wall in combination with brace differs from the flexible support structure because of its higher system stiffness. In order to investigate the deformation characteristics of the diaphragm walls，a series of field data including diaphragm wall deflections，soil settlements，axial forces of supports were obtained. Based on the field data，the following major findings were obtained. The location of the maximum lateral displacement occurs between He－3 and He+1 m，the values of dhm/He scatter but have a tendency to decrease with the increase of system stiffness. The settlement behind the diaphragm wall increases first and then decreases as the distance from the diaphragm wall increases. The settlement reaches the maximum when the value of x/He is 0.67. As the value of L/He(L is the distance of the measuring point to the excavation end along the longitudinal direction) increases，the plane strain ratio(PSR) increases first and then maintains stable. The value of PSR is 0.71 in the corner of the excavation，and reaches 1.0 as the value of PSR approaches 3.0. The axial forces of concrete support of the first and second support of rock-socketed diaphragm decrease with the installation of the third and fourth steel pipe support and increase with the dismantlement of the third and fourth steel pipe support.

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RELIABILITY ANALYSIS FOR TRANSLATIONAL FAILURE OF LANDFILLS WITH AN ENGINEERED BERM

RUAN Xiaobo1，SUN Shulin2，3，HAN Xiaofeng2，LIU Wenliang2

2014, 33 (sl): -2719
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The stability of the landfill with an engineered berm against translational failure is studied by considering the randomness of the physical and mechanical parameters of the solid waste. Under the conditions of the trapezoidal three wedge method and reliability analysis method being used to the landfill with an engineered berm，the reliability index is calculated by the first order second moment method，considering the unit weight，internal friction angle，and cohesion of solid waste as random variables subjected to independent normal distribution. The results show that the requirement of safety factor with different failure modes is not the same so as to make the reliability index get to 3.0. Also，combining the safety factor with the reliability index can better assess the slope stability of the landfill with an engineered berm.

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NUMERICAL ANALYSIS FOR EFFECT OF INCIDENT ANGLE OF SEISMIC WAVE ON SEISMIC RESPONSE OF BASIN

ZHANG Jianjing1，ZHU Chuanbin1，ZHANG Ming2，YAO Shuling2

2014, 33 (sl): -2727
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This article studies the impact of incident angle of seismic waves on the ground motion responses of basin by using two-dimensional nonlinear seismic response analysis program and Ricker wave(as incident SH wave) with different incident angles，PGAs and predominant frequencies. Research results are shown as follows：The maximum amplification ratio of the PGAs is not the one from vertically incident seismic waves，roughly between 5°～25°which suggests that the results may be conservative if only vertically incident angle of seismic waves is considered in seismic safety evaluation；meanwhile，a downward trend is observed in the peak value of response spectra with the increase of the incident angle；furthermore，the rise of predominant frequency of incident seismic waves shrinks the range of incident angle that has an effect on PGA；moreover，slope angle has an significant influence on the distribution pattern of PGA along the basin surface，with the growth of slope angle，the strongest response position shifts gradually from the edge to the center of basin.

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A STRESS INTERVAL CLASSIFICATION METHOD FOR CALCULATING ROCK ELASTIC PARAMETERS IN IN-SITU STRESS MEASUREMENT

JI Dong1，2，REN Fenhua1，2，PENG Chao1，2，YAN Zhenxiong1，2

2014, 33 (sl): -2734
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Confining pressure test for trepanning core acquired from in-situ stress measurement is an important means to obtain rock elastic parameters in in-situ stress calculation. The testing results and data processing play an important role in precision of final in-situ stress value. At present，rock elastic parameters are usually calculated on the basis of stress and strain under highest pressure in testing，which could lead to major error owing to rock nonlinear characteristics and test conditions. Confining pressure tests including multiple specimens are implemented by means of confining pressure instrument. Testing results are reasonable which are modified through analysis of testing curve law and consider multiple error factors. Based on loading unloading deformation theory of rock and rock nonlinearity，a calculation method in which elastic parameters are divided by different stress intervals is put forward. In-situ stress calculation example of No.10 mine of Pingdingshan Tian?an coal mine Co.，Ltd. is used to verify this method. The results reveal that linear correlation of calculated stress value and depth is more significant，which will provide references to improvement of in-situ stress calculation accuracy.

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STUDY OF OPTIMIZATION FOR AXIS STRIKE OF ROADWAY UNDER ENVIRONMENT OF COMPLEX FRACTURED ROCK MASS

CHEN Qingfa，ZHOU Yongliang，AN Jiali

2014, 33 (sl): -2742
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[PDF 799 KB] (665)

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Optimization selection of the axis strike of roadway under the environment of fractured rock mass is important to the safety of the excavation and the long-term use of roadway，but there are two short coming in existing studies，i.e. the representative structural plane group selection and evaluation indicators is not scientific. Taking the roadways under 4 fractured rock test areas of the ore body No.92 in Tongkeng mine as engineering background，through making full use of the respective advantages of GeneralBlock procedures developed by the general block theory and Unwedge code developed by the key block theory，the selection problem of the representative structural plane group was solved and the number of direct falling block body and the minimum safety factor in line with the actual engineering was used as the block stability evaluation indicator. Thus the study of the optimization for the axis strike of roadway under complicated fractured rock mass was carried out. The results show that the techniques developed could determine quickly the test area #1，#2，#3 and #4 optimal roadway axis strike 35°，108°，37° and 32° respectively. The study results can provide reference for the optimization of the roadway axis strike in other complex fractured rock mass.

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RESEARCH ON INFLUENCE MECHANISM OF CONFINING PRESSURE ON ROCK BREAKAGE BY TBM CUTTERS

PENG Qi1，2，3，4

2014, 33 (sl): -2749
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TBM tunnels through the high mountain will inevitably encounter high stress problem，and the research on the influence mechanism of high stress on TBM breakage is very important. The influence of confining pressure on rock fragmentation by TBM cutters is successfully studied by using mechanical analysis and numerical simulation，and it implies that the impact of confining pressure is very complicated. The depths of crushed zone and lengths of cracks parallel to normal force decrease with increasing confining pressure，but confining pressure facilitates rock fragmentation and promotes chipping process，and the side cracks will develop rapidly and smoothly. The TBM in-situ penetration experiment shows that the rock is excavated more easily by TBM with increasing confining pressure. Considering the difficulty of rock chipping by TBM cutters，the results of mechanical analysis and numerical simulation and TBM in-situ penetration experiment all prove that confining pressure is favorable to TBM cutter breakage and penetration.

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UPGRADE AND VALIDATION OF THERMO-HYDRO-MECHANICAL COUPLING ANALYSIS PLATFORM

LIU Naifei1，LI Ning1，2，HE Min1，3

2014, 33 (sl): -2757
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[PDF 649 KB] (502)

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The thermo-hydro-mechanical(THM) coupling study is one of advanced problems in geotechnical engineering field，which has a wide application in frozen earth roadbed，nuclear waste disposal，geothermal development，and so on. By in-depth analysis of 3G2001 analysis platform，the deficiency of the analysis platform is pointed out and some internal weaknesses of the computation module also are revised which include some bugs of subprogram，great gaps of the equivalent stiffness matrix?s principal component and some other internal weaknesses. Besides，coupling analysis platform has been upgraded from 3G2001 to 3G2012 whose reliability and precision has been fully verified by one-way frost heaving experiment by E. Penner and T. Ueda. It shows that the analysis results of 3G2012 agre well with experimental results and results of M. Shen and B. Ladanyi，which completely accords with frost heaving laws and project experience. Especially the frost deformations by the 3G2012 are closer to the experimental results than those of M. Shen and B. Ladanyi. The 3G2012?s accuracy could fully meet the engineering requirements and could be popularized and applied to the actual geotechnical problems.

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EFFECT OF ICE THICKNESS ON DYNAMIC RESPONSES OF PIER STRUCTURES SUBJECT TO EARTHQUAKE

SONG Bo，NIU Lichao，MA Cuijuan

2014, 33 (sl): -2764
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Based on the fluid-structure coupling of ice-water-bridge pier，the paper establishes the ice-water- bridge pier fluid-structure interaction dynamic equation of different ice thicknesses under earthquakes，and studies the effect of ice thickness on dynamic response and hydrodynamic pressure with a rectangular pier as the research object. The result shows that，under the seismic loading，the larger the ice thickness，the greater the bending moment and shear farce at the bottom，the greater the hydrodynamic pressure at the side of the pier. When the ice thickness is more than 0.5 m，ice thickness of pier has more remarkable effect on bending moment and shear farce of the bottom，and the rate of bending moment and shear fore at the bottom are 88.71% and 98.15%，respectively，but has nearly no effect on the hydrodynamic pressure in the side of the pier. At the same time，the larger the ice thickness，the greater the displacement and acceleration along the pier. Therefore，the bridge seismic design in the ice water should consider the seismic response of structure influence when the ice thickness is more than 0.5 m.

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STUDY OF COMPACTING SOIL DISPLACEMENTS AROUND JACKED SINGLE PILE BASED ON EXCESS PORE PRESSURE DISSIPATION

LUO Zhanyou1，2，XIA Jianzhong1，GONG Xiaonan2，LIU Wei1

2014, 33 (sl): -2772
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Compacting soil displacements vary with the dissipation of excess pore water pressure produced by the installed pile，and this problem is still not well resolved because of the piling process complexity. According to strain path method and source-sink method，the closed-form analytical expressions of displacement fields caused by the installation of jacked pile due to the dissipation of excess pore water pressure were obtained in small strain condition. The solution taking into consideration stress-free ground surface and dissipation of excess pore water pressure was in accordance with the practical engineering，and the solution could provide the whole-depth compacting soil displacements. Based on soil deformation characteristics near the installed pile，the integrate expressions of compacting soil displacements in large strain condition were also deduced，and the differences of compacting soil displacements in small and large strain conditions were analyzed. The influences of excess pore water pressure dissipation on compacting soil displacements were analyzed by use of the theoretical solution and the analytical results of compacting soil displacement were compared with field tests. The results show that the horizontal and vertical compaction soil displacements of the installed pile reduce with the dissipation of excess pore water pressure. Theoretical solution variation trends of compacting soil displacements based on the dissipation of excess pore water pressure were in accord with measured results，and the calculating values of soil displacements were agree well with experimental results.

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STUDY OF ACOUSTIC EMISSION AND CHARACTERISTIC STRESS IN DEEP GRANODIORITE FAILURE PROCESS

QIAO Lan，WANG Xu，LI Yuan

2014, 33 (sl): -2778
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Regarding deep granodiorite(564–576 m) as the background，failure process of deep granodiorite and its acoustic emission(AE) characteristics were researched with microcomputer servo-controlled triaxial testing machine and AE monitoring system by conducting rock compression test and acoustic emission monitoring tests. By discussing the failure mechanism of granodiorite in uniaxial and triaxial compression，the regularity of various stages of AE in the process of rock failure was obtained and the envelope of crack initiation stress，crack connection stress and peak stress were obtained. Based on the test data，the relationship between AE parameters and rock failure was obtained and the preconditions for establishing engineering rock mass strength criterion were created.

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TWO-STAGE BACK ANALYSIS OF INITIAL GEOSTRESS FIELD OF DAM AREAS UNDER COMPLEX GEOLOGICAL CONDITIONS

PEI Qitao1，LI Haibo1，LIU Yaqun1，SONG Quanjie2，LI Nana1

2014, 33 (sl): -2785
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In order to accurately obtain the distribution rule of initial geostress field in Jiata dam area in West Route of South-to-North water transfer project，a new two-stage back analysis method of initial geostress field which considers the complex geological conditions and the ground denudation process is presented. Firstly，considering mainly the influence of topography，faults，folds，and development history of river valleys，a large-scale calculation model for the dam area is established. And the genetic neural network method as well as FLAC3D is applied to the first-stage back analysis of initial geostress field. Then，considering the main geological structures in the vicinity of the dam area，a small-scale refined model is created. The preliminary non-linear boundary conditions of the refined model can be obtained by fitting the stress values which are extracted from the large-scale model of the first-stage back analysis. After that，calculation for the second-stage back analysis of geostress field is conducted by optimizing the boundary parameters based on genetic neural network method. It is shown that the difference between the calculated results and the measured data is large in the vicinity of the local geological structures during the first-stage back analysis. And the calculated results are much closer to measured data in the second-stage back analysis by considering the small geological structures as well as the results in the first-stage back analysis. Therefore，the proposed method provides great reference to similar projects.

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MESOSCOPIC SIMULATION OF RELATIONSHIP OF ACOUSTIC EMISSION AND COMPRESSIVE DEFORMATION BEHAVIOUR IN SANDSTONE UNDER CONFINING PRESSURES EFFECT

MU Kang1，LI Tianbin2，YU Jin1，2，CAI Yanyan1，2，LIU Shiyu1，TU Bingxiong1，JIANG Haochuan1

2014, 33 (sl): -2793
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The macro-mechanical parameters and acoustic emission(AE) data of sandstone under various confining pressures were obtained by triaxial compression tests and AE tests. According to laboratory testing results，the spatial and temporal distributions of AE in compression deformation of sandstone under different confining pressures were simulated from mesoscopic aspect by using the particle flow code(PFC2D). Considering different development patterns of the tension and shear cracks，the relation between AE characteristics during the compression deformation of sandstone and the brittle-ductile transition is established. The study shows that under low confining pressure，AE tests experienced the“quiet period”，“developing period”，“erupting period” and “dropping period”. The cracks were mainly constituted by tension cracks with a few shear cracks，which were concentrated in the shear zone. Under high confining pressure，no obvious drop appeared after“erupting period”of AE. Before the peak strength，the dispersed shear cracks were more than the tension cracks，but concentrated connected tensile cracks were more than the shear cracks after the peak strength. The AE mainly based on tension cracks reflects a brittle characteristic of failure. And when numbers of shear cracks are developed，it indicates that the specimen is transited from brittle to ductile one.

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TESTING STUDY OF CREEP CHARACTERISTIC AND FAILURE MODE OF SOFT ROCKS AT JINCHUAN MINE

WANG Weiwei1，WANG Wenxing2

2014, 33 (sl): -2801
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金川矿区岩石具有显著流变性，开采难度极大，故对金川III矿区软弱复杂矿岩蠕变特性进行试验研究。蠕变试验采用RYL–600微机控制岩石剪切流变仪，蠕变加载方式采用分级增量循环加卸载，对试验数据分析时考虑加载历史对岩石试件变形的影响，真实地反映出岩石试件自身的流变力学行为，选取Burgers 模型反映岩石的蠕变特性。结果表明：金川III矿区矿岩蠕变试验曲线与理论曲线基本吻合，Burgers蠕变模型能较好地描述岩石的蠕变特性。通过对金川III矿区5种岩样蠕变试验变形和破坏特征及破坏形态进行分析，表明特定条件下软弱复杂矿岩蠕变破坏形态复杂，但也有其规律性：岩样沿对角线方向一般有一个贯穿整个岩样的破坏面；同种岩样的破坏形式具有相似性。岩样破坏形式多样，同种岩样的破坏荷载差异性大。

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STUDY OF ROCK UNIAXIAL COMPRESSION DEFORMATION AND FAILURE CHARACTER BASED ON AN IMPROVED WEIBULL DISTRIBUTION MODEL

TANG Xinwei1，2，ZHOU Yuande3，4

2014, 33 (sl): -2807
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Abundant test results have shown that the deformation and failure response of rock material under uniaxial compression is strongly dependent on its internal structure，boundary conditions，specimen geometry，etc. This study presents a mesoscale numerical model for rock material based on continuum mechanics，and a nonlinear damage material model is adopted to describe the deformation and failure behaviors of each mesoscale finite element. To consider the spatial correlation character of physical and mechanical properties of realistic rock material as commonly observed，a spatial correlation length factor is introduced into the traditional Weibull random distribution model. Based on the established improved mesoscale random model，a series of numerical uniaxial compression tests are conducted to investigate the effects of end friction and specimen geometry on the progressive failure response of rock specimens. The results show that the end friction and specimen slenderness ratio can significantly affect the load-deformation curves and fracture patterns. The effect of specimen geometry plays a vital role even when the end friction is reduced to a small value. The mesoscale numerical study results indicate that experimental discrepancy may be diminished by lowering the end friction and increasing the specimen height/width ratio in the uniaxial compression test.

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STUDY OF DEFORMATION AND ENERGY PROPERTIES OF MARBLE UNLOADING FAILURE

GAO Su，ZHANG Liming，WANG Zaiquan，CONG Yu

2014, 33 (sl): -2813
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Pre-peak and post-peak strength unloading failure experiments on marble under constant axial pressure were conducted. The characteristics of deformation and energy evolution during the process of marble failure were studied. Results show that the lateral deformation decreases with the increase of unloading rate. The axial deformation is relatively small. It has no relation with unloading rates under the condition of constant axial pressure. The failure mode is typical shear failure under the pre-peak or post-peak strength unloading. Unloading after the peak strength leads to obviously conjugate shear zone. Marble unloading failure process can be divided into three stages according to energy evolution：energy accumulation stage，energy dissipation stage and energy release stage. The faster the unloading rate，the more quickly and more intensely the elastic strain energy releases. The change rate of dissipated energy goes up with the unloading rate increase. And it is ten times larger than the rate of elastic strain energy. Dissipation energy plays a dominant role in the rock's failure process. The rapid energy dissipation is the main feature of marble unloading failure.

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ANALYSIS OF DYNAMIC SPLIT TENSILE TESTS OF FLATTENED BRAZILIAN DISC OF THREE ROCKS

XU Jinyu，LIU Shi，SUN Huixiang

2014, 33 (sl): -2819
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In order to study the influence of strain rate on the dynamic split tensile properties of rock，the dynamic split tensile tests of flattened Brazilian disc specimens of amphibolite，sericite-quartz schist and sandstone，are carried out by using split Hopkinson pressure bar(SHPB) equipment with a diameter of 100 mm improved by copper waveform shaper. The changing rules of tensile sensitivity coefficient，radial strain，tensile Young?s modulus and failure modes are analyzed. Experimental results show that the tensile sensitivity coefficients of three rocks increase with the increase of strain rate，amphibolite is most sensitive to strain rate and sandstone is least sensitive to strain rate. The radial peak strain of three rocks is proportional to strain rate，and the radial ultimate strain of sandstone is the biggest. The Young?s moduli of three rocks in unloading process are greater than those in loading process. The failure modes of three rocks are closely related to impact velocity.

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DEVELOPMENT OF TRUE TRIAXIAL ROCK TEST SYSTEM OF COUPLED STRESS-SEEPAGE AND ITS APPLICATION

YIN Liming，GUO Weijia，CHEN Juntao

2014, 33 (sl): -2826
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According to complicated occurrence environment such as high in-situ stress and strong seepage pressure，a true triaxial rock test system of coupled stress-seepage is developed，and its main structure，function and usage method are introduced in detail. This system could apply different three-dimensional(3D) stress values independently by servo control and real-time track the process of fissure propagation and evolution by acoustic detection system under 3D stress and seepage pressure. The influence of 3D stress and seepage pressure on permeability characteristics is studied through true triaxial rock test system on granite joint specimens with large size under different seepage pressures，and the test results better reveal the coupled stress-seepage characteristics of deep rock. The development of rock test system of coupled stress-seepage and test results enrich the method of studying rock mechanics properties under high in-situ stress and strong seepage pressure，and provide scientific experimental basis for research of stability and seepage disaster control technology of mining surrounding rock when meeting water.

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METHOD OF RANDOM CONFIGURATION GENERATION FOR POLYBASIC MIXED MEDIUM AND ITS APPLICATION

WANG Haili1，2，SHI Chong1，2，WANG Shengnian1，2，ZHANG Yulong1，2，CHEN Kaihua1，2

2014, 33 (sl): -2834
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Soil-rock polybasic mixed medium is a kind of non-uniform and discontinuous body whose internal structure is complex. The mechanical characteristics and failure mechanism of this mixture are determined by the non-uniformity of its mesostructure to a great extent. From its mesostructural characteristics，a random configuration generation system of polybasic medium based on arbitrary concave and convex polygonal and circular rock blocks (M-MRMS2D) has been developed by using Visual C++ programming language with interdisciplinary techniques involving statistics，geometry，computer and so on. Polybasic mixed medium numerical model is generated by the M-MRMS2D on the basis of block shape，smoothness，block material，medium content，and spatial distribution. With this system，the composition of accumulation body of the landslide for Zhenggang in Gushui hydroelectric station is built，and the stress-strain curve of numerical experiments，deformation and failure characteristics and macro-mechanical characters of polybasic mixed medium are analyzed. The method is important to understand mechanical properties of soil-rock polybasic mixed medium.

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STUDY OF FUZZY EVALUATION METHOD OF DAGANGSHAN ROCK SLOPE STABILITY BASED ON CONTRIBUTION RATE OF ROCK PARAMETERS ANALYSIS

LIU Jie，LI Jianlin，WAN Liangpeng，CAI Jian，XIAO Lei

2014, 33 (sl): -2843
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Taking abutment slope of the Dagangshan as an example，the safety factor of the slope is calculated by overall and local reduction deformation modulus，cohesion and internal friction angle of different rocks，and the contribution for the specific slope stability at different parameters in different locations are obtained，which applied to evaluating system after the quantization process. The weight distribution is scientifically calibrated for parameters of the different rocks and on this basis the membership of the slope body comprehensive mechanical parameters is determined. According to the requirements of the Code，with safety factors of 1.30，1.175 and 1.05 for boundary，the grading standards of the different parameters of the specific projects are given；on that basis，the stable levels within different parameters in different rocks are determined. Combined with area ratio among the analysis area，the membership grade matrix revised by the comprehensive contribution of different rocks and the different parameters are obtained. The method precisely deals with the fuzzy parts of the comprehensive evaluation system based on the finite element method(FEM) calculation，weakens the uncertain effects caused by subjective factors in the four major evaluation segments of weight distribution，determine the membership grade，grading standards，and comprehensive mechanical parameters of slope，which is more targeted to engineering and results are more scientific and reasonable compared to experience.

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RESEARCH ON UPPER BOUND METHOD FOR STABILITY OF ROCK SLOPE BASED ON RIGID BLOCKS ASSEMBLAGES

LI Ze1，WANG Junxing2，ZHANG Xiaoyan3

2014, 33 (sl): -2852
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The block rock slope is investigated in this paper，and the rock slope is discretized into three- dimensional geometries which contain rigid blocks and interfaces. Then based on the upper bound theorem of plastic limit analysis and nonlinear mathematical programming，the three-dimensional upper bound method of rigid blocks assemblages interacting through interfaces is presented. The translation displacement rate and angular displacement rate of blocks and interfaces are taken as unknown parameters in the proposed method. Based on the deformation compatibility conditions of rigid blocks and interfaces，plastic flow conditions that take into account associated flow rules，yield conditions，equilibrium equations，boundary conditions and additional constraints conditions，the nonlinear programming models of upper bound limit analysis are established，which could solve the strength safety factors and overload safety factors of rock slopes. And then，the optimization strategy of nonlinear mathematical programming problem is provided. Finally，three cases of rock slopes are used to study stability，and the rigorous upper limit values of the safety factor of slope are obtained. The results are compared with those produced by other classical approaches，and the validity of the proposed method is indicated.

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ANALYSIS AND STUDY OF STATISTICS OF SHEAR STRENGTH PARAMETERS OF ROCKFILL DAM MATERIAL FOR PUMPED STORAGE STATION

ZHAO Xiaoju，QI Junxiu，ZHENG Hailun

2014, 33 (sl): -2860
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The shear strength parameters of rockfill material are the main factors in calculation of dam stability against sliding，thus shear tests of rockfill materials should be conducted for all the rockfill dam projects. In order to further obtain the exact parameter values，regularity and main effective factors of shear strength，according to the classification of weathering degrees of the rockfill materials and with the method of data statistical analysis，this paper provides a statistical analysis on the shear strength parameters and regularities of rocks，crushed gravel soil and sandy pebble soil taken as main rockfill，secondary rockfill，cushion，and transition materials based on the test data of 101 specimen groups from 7 projects designed by HydroChina Beijing Engineering Corporation. Further analysis is made on the effects of immersion saturation，compaction，grain gradation(＜5 mm content)，roundness，weathering degree，and lithology to the shear strength parameters of rockfill materials. The result shows that the effect of weathering degree of rockfill material on the shear strength parameters is the most obvious，other effects are in different degrees.

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APPLICATION OF FUZZY ANALYTIC NETWORK PROCESS IN RISK ANALYSIS FOR CONSTRUCTION OF HIGHWAY MOUNTAIN TUNNEL

LIU Baoguo1，SHEN Minglong1，MA Qiang2

2014, 33 (sl): -2869
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The construction of highway mountain tunnel is affected by various uncertain factors with random and fuzzy characteristic，which cannot be exactly analyzed by current risk assessment method. This paper proposes the fuzzy-analytic network process(F-ANP) which is composed by Delphi method，analytic network process and fuzzy comprehensive evaluation. Based on the analysis of the whole process in the construction of the highway mountain tunnel，a synthetic evaluation index system for the construction of highway mountain tunnel is established. A fuzzy relation matrix is established by evaluating the evaluation index with expert investigation，by using Delphi method to compare and using triangular fuzzy number to represent the judgment matrix，a fuzzy super matrix is established with the analytic network process，by evaluating its limit matrix can obtain the comprehensive weight，then obtain the level of construction risk. Finally，empirical research to Longtouling tunnel shows that the method is reasonable and practical，it can provide reference to risk analysis for future similar projects，ensure construction safety and reduce potential losses.

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INFLUENCE OF SHIELD TUNNELING WITH TUNNELS FOLLOWED BY WELL EXCAVATION ON SEGMENT OPENING

YANG Chunshan，MO Haihong，CHEN Junsheng，LI Wei

2014, 33 (sl): -2877
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In order to study the influence of shield tunneling with tunnels followed by well excavation on segment opening，under the precondition that it cannot easily be measured and tested，an elasto-plastic simulation is carried out with FEM program to analyze segment opening caused by the tunnels followed by well excavation. In combination with the typical engineering example，the influences of mechanical properties of soil，local reinforcement soil and groundwater level are discussed. The results indicate that influencing scope is mainly in five segment length near the continuous wall of work well，so analysis of seepage control during the construction should consider emphatically four joints near the work well. Segment opening is strongly impacted by the soil stiffness and it decreases with the increase of stiffness. Segment opening is not affected by soil strength index. It can use local reinforcement to effectively reduce the segment opening to prevent leakage of shield tunnel. The existence of groundwater above the segment has significant influence on segment opening，influencing scope is mainly in five segment length，but the water level has a tiny effect on segment opening. It suggests that it is necessary to perform local reinforcement in five segment length near the continuous wall of work well when adopting tunnels followed by well excavation to ensure the safety of tunnel.

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FIELD MONITORING EXPERIMENTAL STUDY OF SEA-CROSSING SHIELD TUNNEL SEGMENT IN ZHANJIANG BAY

ZHANG Junlu1，2，DUAN Fenghu1，2，LIAO Wenlai1，2，HU Hanlin1，2，CHEN Xiaowen1，2，YANG Guanghua1，2

2014, 33 (sl): -2884
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Zhanjiang bay tunnel is the deepest sea-crossing shield tunnel inland，which withstands a hydraulic pressure of 60 m during the construction and operation periods. Combined with the local conditions for tracking test，the external water pressure and earth pressure of the segment，reinforcement stress in segment and contact stress between segments were monitored successfully. The loose zone scope of the shield tunnel construction and the concrete structure stress of the segment were calculated，and they are useful to follow the structure safety status in time，and offer the measured parameters for safety construction. An osmometer installation method was proposed to monitor the shield tunnel segment external water pressure successfully，as well as innovations on the other sensor installation methods. Monitoring results show that，in the seabed soil shield tunnel project，the external structure load were mainly composed of water pressure，even in the clay layer with small permeability coefficient. The monitoring methods and results could be used for coastal shield tunnel in soft soil area with offering a valuable reference for its monitoring，design and construction in the future.

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KARST WATER INRUSH MECHANISM AND RISK MITIGATION OF TUNNEL HOSTED IN CARBONATE OF NAPPE STRUCTURE BELTS

XU Ying1，ZUO Changqun1，CHEN Zhichao1，2，FANG Xiaorui3

2014, 33 (sl): -2893
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In this paper，the similarities and differences of numbers of water inrush in Dapingshan tunnel have been comprehensively studied in combination with site-specific geological tectonic environment，rock lithology，and hydrogeological environment in Wudang nappe structure belts. The effect of nappe belts on water inrush，the controlling effect on reservoir structure，and the hydrogeological environment associated with construction condition have been considered to analyze the mechanism of karst water inrush. On basis of the conclusion，a risk assessment model has been established considering five risk-evaluation geological factors. Fuzzy optimum theory was used to screen the optimum combination of geo-environments which are most dominant factors to potentially inducing karst water inrush. In addition，the risk mitigation method in terms of the key point of geo-environmental risk assessment associated with comprehensive geophysical method was put forward，and the site-specific construction conditions on working face were used to verify its rationality. Results show that the risk prediction method proposed can play an important role in risk mitigation in karst tunnel. In addition，the conclusion mentioned above also shows that geological analysis as the core in comprehensive geophysical prospecting method is the main focus of geological forecast in terms of risk mitigation.

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DETERMINATION OF STIFFNESS PARAMETERS OF JOINTED ROCK MASSES WITH 3DEC SIMULATIONS

WANG He，GAO Yongtao，JIN Aibing，ZHANG Kai

2014, 33 (sl): -2900
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[PDF 9390 KB] (718)

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Aiming at the issue in determining the stiffness parameters of jointed rocks，numerical analysis with distinct element code (3DEC) was carried out. By means of direct shearing test of rock structure in combination with theoretical analysis，the empirical formulae representing rock stiffness parameters were obtained. Then a modified empirical formula is developed considering Bandis empirical formula with new function f(τ/τp). The results indicate that the contact parameters of normal stiffness Kn and shear stiffness Kst obtained by empirical formula through fitting could reflect the deformation behaviours of rocks before shearing failure of structural plane. Accordingly，numerical results were used to verify laboratory test results. It is thereafter believed that the shear stiffness(Kst) could be used to understand the shearing behaviours of joints before failure.

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EFFECT OF TRENCH CONSTRUCTION OF RETAINING STRUCTURE IN METRO FOUNDATION PIT ON ADJACENT BUILDING SETTLEMENT AND MONITORING DATA ANALYSIS

LIU Fengzhou1，XIE Xiongyao2

2014, 33 (sl): -2907
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The settlement control of adjacent building is a critical issue in foundation pit construction. The impacts of the construction of both three-axis high-pressure rotary jet grouting piles and diaphragm wall on a historical building in a subway station of Tianjin were analyzed based on the real time monitoring data，focusing on the effect of trench construction of diaphragm wall on the adjacent building settlement. The settlements in the retaining structure construction phase，the foundation pit excavation phase and the whole construction period were compared，to explore the impacts of three-axis high-pressure rotary jet grouting piles retaining structure and diaphragm wall on the building settlement. The reasons for building settlement caused by different retaining structure forms were emphatically analyzed and settlement control methods were proposed for building protection. The results obtained could provide reference to similar projects.

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RESEARCH ON DEFORMATION FEATURES AND INFLUENTIAL FACTORS OF WATER-SATURATED SOIL TUNNEL

QU Xing，LI Ning，CHEN Yongting

2014, 33 (sl): -2917
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Based on the monitoring data of the Xinjiang Kuyu diversion tunnel，the deformation properties and influential factors of the water-saturated soil tunnel are in-depth analyzed. According to the deformation law of soil tunnel，the process of the effect of deformation after excavation could be divided into three phases：The first phase is the response under the horizontal spatial effect，the second phase is the response under the combination of longitudinal spatial effect and the time effect，the final phase is only influenced by the time effect. The horizontal spatial effect is the main factor leading to roof collapse and landslide during excavation. To reduce the effects of it，the advanced support method or reducing the area in horizontal direction could be adopted；As the longitudinal spatial effect and the time effect dominate the deformation in second phase，a rational separation of them would provides a basis for parameter inversion. In third phase，the time effect primarily is rheological deformation，which appears much more obviously in saturated low liquid limit silt(clay). According to the analysis of the monitoring data which are measured under different classes of surrounding rocks，different buried depths and different supporting intensities，it could indicate that the integration of the silty clay is good，and its main deformation is significantly associated with the buried depth. The deeper the depth is，the more the degree of deformationis. It presents the rheological behavior in some degree simultaneously. During excavation，small-scale landslide is more likely to occur in sand-layered silt and gravel-layered fine sand due to the large water discharge. The deformation is mainly expressed as the looseness of surrounding rock mass and strongly associated with spatial positions of sand layer，while the buried depth of tunnel have no significant influence on it. By using strengthened supporting method and partial excavation method，monitored values of the deformation are mostly small，obvious difference is observed among the deformation properties of supporting structures of the vault and sidewall. The vault can reach stability quickly with little deformation. Plastic area of surrounding rock of sidewall increases as the buried depth in low liquid limit silt(clay)，the time effect of stress release is obvious，which manifests as the increasing deformation pressure and large convergence deformation. Steel arch is more significant than the steel grid to limit the deformation of surrounding rock for soil tunnel. Considering the construction cost factor，selection of supporting methods should depend upon different soil properties and different buried depths.

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MONITORING ANALYSIS AND STABILITY EVALUATION OF PILE-BOLT SUPPORT SYSTEM IN DEEP PIT

WANG Chao1，ZHU Yong2，ZHANG Qiangyong1，ZHANG Xutao1，3，WANG Youfa1

2014, 33 (sl): -2923
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The development and utilization of urban underground space have made it critically important for the stability evaluation of deep pits. In this paper，through analyzing the monitoring data from the project of Mass Media Mansion Underground Garage，the stability of pile-bolt supporting system in deep foundation pits was evaluated by adopting the linear-fitting control chart method. The results show that，(1) an abnormal horizontal displacement at the point five meters below the pile top can be observed，(2) the abnormal pit top settlement basically occurs between May and June，and (3) both the horizontal displacement of the supporting piles and the pit top settlement are within the allowable value. The monitoring data of the foundation pit were fed back to construction units in order to take effective measures for the purpose of security and stability of the foundation pit. Accordingly，this technique adopted is able to timely locate the abnormal monitoring points，which contributes to the decision-making of taking early-warning measures.

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EXPERIMENTAL STUDY FOR INFLUENCE OF CONTENT AND DISTRIBUTION OF RHEOLOGICAL MATERIAL ON SOFT SOIL CREEP PROPERTIES

YUAN Jie1，2，FANG Yingguang1，2，GU Renguo1，2，HU Guixian1，2

2014, 33 (sl): -2929
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[PDF 776 KB] (743)

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With the improved direct shear creep apparatus，seven sets of creep tests were conducted on specimens containing organic clay，quartz and feldspar with different weight percentages and different spatial distribution under the same experimental conditions. The relationships of the sample average coefficient of viscosity with rheological material content and dimension were obtained. The influence of content and distribution of rheological material on soil creep properties were discussed. Some conclusions were drawn：the average coefficient of viscosity reduces with decreasing rheological material size as well as increasing spatial distribution uniformity，and tends to be a critical value. Rheological material content has a notably significant effect on the creep characteristic. With the increase of organic matter content，average viscosity coefficient decreases linearly. When the soil rheological material size is less than the critical size，soil creep characteristics are only related to the content and properties of rheological material，but not related to its shape and distribution form.

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EXPERIMENTAL STUDY OF UNIAXIAL COMPRESSIVE STRENGTH ON GEOMEMBRANE BAG WITH SAND

CHEN Junsheng1，2，MO Haihong1，2，LIU Shuzhuo1，PENG Hongbo1

2014, 33 (sl): -2935
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[PDF 982 KB] (827)

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The uniaxial compression tests are conducted on geomembrane bag with different compactness to obtain stress-strain curves and uniaxial compressive strength，and the failure pattem under uniaxial compression is discussed. The study indicates that the uniaxial compressive strength decreases with compactness increases. The 80%–85% compactness is adequate. Uniaxial compressive strength of geomembrane bag with sand is much larger than that of sand，which is 1 MPa with nearly 100% compactness，and the corresponding with sand ultimate load height is about 50 m. With the compactness decreases，the uniaxial compressive strength of geomembrane bag increases obviously，and the stress-strain curves are different.

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A MODIFIED METHOD FOR 3D FINITE ELEMENT ANALYSIS OF SAND GROUND IMPROVED BY VACUUM PRELOADING

SHI Hongyan1，BAI Lin1，LI Wei2

2014, 33 (sl): -2941
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[PDF 653 KB] (556)

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Based on the characteristics of sand ground improved by vacuum preloading，a modified method for three-dimensional(3D) finite element(FE) analysis of the ground is presented. The method uses the superposed elements in replace of the different nodes of displacements and pore pressures associated with homogenized ground surface，and thus the element numbers of nodal displacements and pore pressures can be reduced and effectively determined. As a result，computer memory resources can be significantly saved，and ill-conditioned stiffness matrix can be properly addressed.

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STUDY OF WORKING DEPTH IN PORT GROUND UNDER HEAVY VEHICLE LOAD

ZHANG Jun1，SHEN Junmin1，GAN Tian2，YUAN Jingbo3

2014, 33 (sl): -2949
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[PDF 11414 KB] (546)

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A three-dimensional numerical simulation was conducted by FLAC3D software to simulate the field test. A model calibration was conducted to ensure that the numerical modeling was a realistic representation by the measured data. Finally，a sensitivity analysis was performed to investigate influence factors，such as the thickness of sand cushion，area of thrust surface and wheel pressure. The research results indicated that：(1) Under the vehicle load，when the ratio of additional stress to gravity stress was equal to 0.2 and 0.1，the corresponding depths were 1.63 and 2.03 m，respectively. (2) The maximum vertical strain occurred at the top of the mucky clay. (3) The lateral displacement increased first and then decreased along the depth and horizontal direction. (4) With the increase of thickness of sand cushion，the maximum vertical strain and the largest lateral displacement of the ground increased firstly and decreased lastly. (5) When the thickness of medium-coarse sand was about 1.25 m，the working depth was right at the bottom of medium-coarse sand. (6) The working depth，the maximum vertical strain and the maximum lateral displacement of ground increased with the increase of the area of thrust surface and wheel pressure.

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A UNIFIED ALGORITHM FOR WATER AND EARTH PRESSURES BASED ON PRINCIPLE OF EFFECTIVE STRESS

WU Xiaofeng，LI Guangfan，WANG Xiaoliang

2014, 33 (sl): -2956
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[PDF 2935 KB] (650)

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The idea that the water film around soil particles should be brought into bearing surface area of effective stress is presented. Based on the mechanical calculation model bringing the water film into bearing surface area，the equation of extended effective stress principle is obtained. Combined with the physical meaning of permeability coefficient and substantial experimental data，the fitting equation between new physical parameters of channel rate and the permeability coefficient is established. According to Mohr-Coulomb criterion，the soil strength index under groundwater is obtained. Based on above，we obtained a unified algorithm for water and soil pressure，which realizes the transition between separate calculation and combined calculation of water and earth pressures. The unified algorithm makes water and earth pressures calculation more closely linked with basic physical and mechanical properties of soil，which has a significant meaning on the comprehensive and systematic study with clay soil mechanics problems.

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SUBSIDENCE CONSTRUCTION TECHNOLOGY FOR ULTRA-LARGE- SCALE CAISSONS FOUNDATION IN COMPLEX GEOLOGICAL AREA

HUANG Haiou，SUN Xiaowei

2014, 33 (sl): -2963
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[PDF 1068 KB] (723)

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The Xiangjiaba open caissons group is part of the diversion works for Xiangjiaba Hydropower Station，and it is an important part of the main structure on the left bank. It consists of ten open caissons groups with size of 23 m×17 m. The maximum sinking depth is 60 m. The caissons must penetrate into strong permeable layers including sandy gravel layer，sandy layer and sandy gravel layer with collapsed stones，and embed into fine sandstone layer. The caisson construction is tremendous difficult in the world. According to special hydrogeological conditions，the rational caisson sinking sequences and caisson sinking technique are determined，and the caissons group sinking is completed successfully. A series of construction methods for caisson sinking are summarized.

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CALCULATION METHOD FOR SLOPE REINFORCED BY GRILLAGE PRE-STRESSED ANCHOR BASED ON STABILITY OF EXCAVATION PROCESS

LI Zhong1，2，CHEN Siyang1，ZHU Yanpeng1，2，GAO Jianxiang3

2014, 33 (sl): -2970
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[PDF 965 KB] (642)

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Considering the effect of the supporting structure and anchor on the slope stability in the excavation process，the stability calculation model is established for the slope reinforced by pre-stressed anchor and grillage beam，and the calculation model of the optimal solution of each anchor tension based on the stability of the whole process of excavation is presented. It realizes the real-time analysis and checking of slope stability in the process of excavation. The example calculation shows that：(1) The slope stability changes with the dynamic change of the design parameters of anchor and grillage beam. As a result，it is relatively more accurate and reasonable using dynamic search model to determine the critical slip surface of the slope reinforced by pre-stressed anchor and grillage beam. (2) By introducing the height influenced coefficient of anchor tension，the relation of each anchor layout and the slope height of different excavation stages are set up，and one group of optimal solution of anchor tension can be obtained，which can satisfy the stability requirements of the different excavation stages simultaneously. The results are consistent with the actual situation of project. It is further evidence that the method is reasonable and practical.

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ANALYSIS OF INFLUENCE OF RIVER ENVIRONMENT ON ADDITIONAL PRESSURE OF TUBE SIDEWALL DURING TUBE IMMERSING

MO Haihong1，2，LI Yadong1，2，CHEN Junsheng1，2

2014, 33 (sl): -2976
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[PDF 677 KB] (886)

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The tube section was influenced obviously by the river environment in the process of tube immersing. The additional pressure of the tube sidewall during the tube immersing can be obtained from numerical simulation on different river environments by computational fluid dynamics method. The analytical results show that when half tube is immersed in foundation trench at the particular moment，the difference of pressure around the tube surfaces changes significantly. Position of the left-right maximum differential pressure raises around the side，while the position of upper-lower maximum differential pressure reaches maximum as the tube is immersed. The river level has no effect on the additional pressure，and the location of the maximum pressure differential point scrolls horizontally. The river flow velocity has a great influence on sidewall additional pressure，and the relationship between the maximum difference in gradient and the river flow velocity near special place can been obtained. The analysis results can provide valuable reference for similar projects.

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MODEL TEST AND NUMERICAL SIMULATION OF REINFORCED SOIL FAILURE SURFACE

XIANG Yuzhou1，ZHENG Yingren1，ABI Erdi2，TANG Xiaosong1

2014, 33 (sl): -2982
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[PDF 7231 KB] (544)

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This paper demonstrates that the failure surface of reinforced soil is close to plane through comparing the reinforced soil model test with finite element limit analysis method. Angles between the failure surface and horizontal surface are basically consistent，which verifies that using finite element limit analysis method is feasible. The angle between failure surface and horizontal surface after reinforcement is 8° larger than that before reinforcement，which indicates the reinforced effect is apparent. Because the impact factors of cohesion and internal friction angle are different，so the improvements in the calculation models in the current software and the parameters selection are needed.

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DISTRIBUTED DETECTION OF DEFORMATION AND BEARING MECHANISM ON BORED PILE UNDER HORIZONTAL LOAD

YANG Jianping1，PIAO Chunde2，3，CHANG Hongfei1，LI Ting3

2014, 33 (sl): -2988
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[PDF 5016 KB] (649)

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In order to explore the mechanism of pile-soil interaction under horizontal load，this paper studies the deformation of the bored pile under horizontal load by pre-installing sensing fibers in the pile body. The formula of the pile deflection and moment is derived based on BOTDR technology，and the pile-soil interaction of the pile in Inner Mongolia in China under horizontal load is analyzed by using ANSYS software. The results show that the deformation of the bored pile under horizontal load is distributed in the range of 6 m underground. With the increase of the horizontal load，the pile body moment rises nonlinearly and the maximum point of moment transfers gradually to the deep part. As the load increases，the bending curve of pile-soil contact force shifts from the tendency of nonlinearity to the tendency of increase and then decrease，and its maximum inflection point fits well with the point of the maximum moments. Through comparing the theoretical calculation values of pile deflection with the measured values and the numerical simulations，it can be found that，due to the effect of the stiffness of pile，the deflection values of numerical simulations are relatively higher，while the theoretical calculation values are basically in accord with the measured values，which proves that the pile deformation formula based on BOTDR is practical and reliable.

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EXPERIMENTAL TEST ON CONSTITUTIVE RELATIONSHIP OF NANJING FROZEN SILTY CLAY CONSIDERING DUNCAN-CHANG MODEL

SUN Guyu，YANG Ping，LIU Guanrong

2014, 33 (sl): -2995
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[PDF 925 KB] (711)

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Through triaxial shear tests，the shear strength and deformation characteristics of frozen silty clay of Nanjing Metro were mainly focused on. Then，Duncan-Chang model for frozen silty clay was established，considering the coupling of confining pressure and temperature. The results show that the shear strength increases with decrease of temperature. Accordingly，the parameters a and b can be obtained. In addition，the ratio of breaking strength to ultimate strength is acquired with value between 0.77 and 0.91，averaging 0.86. Comparing with the ( )- curve calculated by Duncan-Chang model and that obtained by experiments，it is observed that the two match well，suggesting that the model can reflect strength and deformation characteristics of frozen silty clay under different confining pressures and temperature conditions. The results will provide reference to the artificial freezing method employed in Nanjing Metro.

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EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF LONG-TERM K0 CONSOLIDATED CLAY UNDER HIGH STRESS DURING UNLOADING

CHEN Guoqing1，2，WANG Yansen1，LENG Yangguang1，ZHANG Chunhu1

2014, 33 (sl): -3002
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[PDF 695 KB] (745)

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For special conditions of deep soils in extra-thick alluvia in shaft construction，the mechanical properties of deep clay under the condition of unloading lateral stress and constant axial stress which has experienced long-term high-stress K0 consolidation were studied. The deviatoric stress-strain curves and the triaxial compressive strength were obtained；and the influences of consolidation time and stress on the clay?s deformation and strength were analyzed. The following conclusions are drawn：for the deep remolded clay，the deviatoric stress-strain curve is similar to perfect rigid-plastic curve. The consolidation time and stress have great influence on its triaxial compressive strength. When the consolidation stress is constant，the compressive strength increases with the consolidation time in nearly logarithm relation，and the increasing rate of the compressive strength decreases gradually. When the consolidation time is constant，the compressive strength increases with the consolidation stress obviously. This study is helpful for further investigation into the in-situ mechanical properties of deep cohesive soil.

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ANISOTROPIC RESEARCH ON SHEAR STRENGTH PARAMETERS OF DISCONTINUITY BASED ON THREE-DIMENSIONAL LASER SCANNING TECHNOLOGY

YOU Zhicheng1，WANG Liangqing1，YANG Yanxia2，SHI Changbai3

2014, 33 (sl): -3008
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[PDF 927 KB] (938)

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Joint roughness coefficient(JRC) is one of the key factors affecting the discontinuity shear strength. The research on the discontinuity roughness and shear strength anisotropy is of great significance to engineering rock mass deformation and stability analysis. Currently，there are few papers reported on the discontinuity fractal dimension and its shear strength anisotropic analysis based on three-dimensional(3D) laser scanning technology. Taking a dam site in Guizhou Province for example，discontinuity surface morphology data obtained through 3D laser scanning are used to establish a digital elevation model to evaluate shear strength anisotropic of dolomite joint. On the basis of the variation function method，the anisotropy of discontinuity fractal dimension is studied and corresponding functional relationship between JRC and fractal dimension(D) is established. According to Barton standard contour curve and the actual stress state of dolomite，anisotropies of shear strength parameters based on the Barton equation are examined. The results show that cohesion and fiction angle change within the range of 0.20 to 0.75 MPa and 9.09° to 36.87°，respectively. The anisotropies of cohesion and friction angle are obvious，and the cohesion increases as the friction angle decreases in the same shear direction.

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A STRENGTH REDUCTION METHOD CONSIDERING TENSILE FAILURE

YUAN Wei，LI Xiaochun，BAI Bing，SHI Lu

2014, 33 (sl): -3014
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[PDF 1808 KB] (668)

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Strength reduction method(SRM) is widely used for calculating the safety factor of the slope. In realistic slope engineering，shear failure is not the only mode in rock masses，the tensile failure may also occur in certain areas，which means that the tensile failure should also be taken into consideration in SRM. In this paper，a strength reduction method considering tensile failure is proposed，indicating that the tensile strength，internal friction angle and cohesion should satisfy an inequality during strength reduction process. Based on this inequality，the drawback of the current SRM considering the tensile failure is pointed out. At last，the validity of the proposed method is verified through a case study.

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ANALYSIS OF DYNAMIC CHANGES OF ANISOTROPIC PERMEABILITY COEFFICIENT WITH VOLUMETRIC STRAIN IN SEEPAGE COUPLING

WANG Chunbo1，2，DING Wenqi1，2，LIU Shubin3，WANG Jun3，TANG Zhicheng4

2014, 33 (sl): -3021
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[PDF 822 KB] (754)

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Permeability coefficient is a bridge of linking stress field and seepage field. Establishing relationship between permeability coefficient and stress field or seepage field can reflect the influence of stress field on seepage field and achieve real seepage coupling analysis. Based on three-dimensional seepage coupling Boit consolidation theory，the relationship between anisotropic permeability coefficient and volumetric strain is built on the basis of Kozeny-Caman equation，and relevant program is embedded with FISH program in FLAC3D software. Then soil mass unit is assigned dynamic permeability coefficients to reflect the influence of stress field on seepage field，realizing real seepage coupling analysis of stress field and seepage field. A case study of foundation pit is presented for validation. Result shows that permeability coefficient changes with strain field or stress field. The permeability coefficient decreases with negative volumetric strain but increases with positive volumetric strain. The volumetric strain has larger influence on horizontal permeability coefficient than vertical permeability coefficient. It may provide a reference for dynamic seepage coupling analysis of geotechnical engineering.

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APPLICATION AND ANALYSIS OF HARDENING SOIL MODEL IN DEEP FOUNDATION PITS IN WUXI DISTRICT

LIU Shubin1，WANG Chunbo2，3，ZHOU Libo1，TANG Zhicheng4

2014, 33 (sl): -3028
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[PDF 6251 KB] (1048)

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The deep foundation pit is characterized by large-scale excavation，deep excavation depth and complex stress path. The choice of soil constitutive model is the key to numerical analysis of deep foundation pit. On the basis of theoretical analysis of hardening soil(HS) model and model parameters，HS model parameters of the typical soil in Wuxi district are determined through different stress paths experiments in laboratory. Numerical analyses for construction process of station foundation pit in #2 line of Wuxi metro and Henglong foundation pit are performed using three-dimensional Z_Soil software，and numerical results are in good agreement with actual monitoring data. Research shows that HS model can reflect not only the nonlinear characteristics of soil′s stress and strain，but also the complex stress path of deep foundation pit. HS model is suitable for the hard soil in Wuxi district，and the HS model parameters decided by experiment can be applied to calculation of deep foundation pit in Wuxi district，and the numerical method is reliable.

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ANALYSIS OF PNEUMATIC FRACTURING EFFECT WITH VACUUM PRESSURE

PU Juyi，HAN Wenjun，LIU Songyu，ZHANG Dingwen

2014, 33 (sl): -3035
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[PDF 855 KB] (584)

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A series of model tests are developed to investigate the effect of pneumatic fracturing with or without vacuum pressure. The model test results indicate that pneumatic fractures are concentrated on jet in horizontal direction，and the dissipation of excess pore pressure is divided into fast dissipation stage and slow dissipation stage. The results also show that the number of fractures is decreased with vacuum pressure. The maximum excess pore pressure is increased with air injection pressure，and decreased with vacuum pressure. The fast dissipation stage lasts for 20–30 minutes and dissipation pressure is about 70% of maximum excess pore pressure. The dissipation rate is increased with vacuum pressure. According to the test results，the instantaneous and low- pressure pulse is suggested in the process of vacuum preloading.

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ANALYSIS OF EQUIVALENT COEFFICIENT OF SUBGRADE REACTION CONSIDERING VARIABILITY OF LAYERED SOILS

ZHU Ling1，2，DING Wenqi1，2，WANG Rui3，LIU Hongzhou4，FANG Lei5

2014, 33 (sl): -3041
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[PDF 5195 KB] (758)

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Determination of coefficient of subgrade reaction is the key to solve the engineering problems with load-structure method. In order to study the distribution characteristics and statistical parameters of layered soils foundation with variability，a calculation method with the compression modulus of each layer soil as the input parameter was derived based on the principle of consistent final settlement，and the variability of soil was considered with the aid of Monte Carlo method. Besides，the proposed method was realized by using Matlab software. The results were applied to the Hong Kong-Zhuhai-Macao immersed tunnel，and a two-dimensional analytical model was established based on the load-structure method. The following conclusions can be drawn: (1) The equivalent coefficients of subgrade reaction of the typical section K9+843 approximately obey normal distribution. The mean value is 985 kPa/m，and the coefficient of variation is 0.265. (2) The settlements of this section approximately obey logarithmic normal distribution when taking the variability of soils into consideration， which has a significant difference. (3) The settlements of this section are close to those obtained from three-dimensional analysis model based on stratum-structure method under the same condition，which validates the rationality of the proposed method to calculate the equivalent coefficient of subgrade reaction.

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INVESTIGATION OF MECHANICAL PROPERTIES OF SOFT AND HARD INTERBEDDED COMPOSITE ROCK MASS BASED ON MESO-LEVEL HETEROGENEITY

LI Ang1，SHAO Guojian1，FAN Hualin1，DU Peirong2，ZHU Yihuan1

2014, 33 (sl): -3049
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[PDF 7859 KB] (658)

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For the soft and hard interbedded composite rock mass of Jinping I underground carves，interior heterogeneity information of meso-level is obtained by the technique of image segmentation based on region growing algorithm. Computational grid to reflect actual meso-structure is established. Then，a finite difference software package FLAC is used to study failure process under uniaxial compression test，considering effect of orientation angle by elasto-brittle-plastic model. The results show that with the change of orientation angle，stress distribution in rock mass is closely related to heterogeneity of rock materials in meso-level. All the fracture propagation process of samples initiates with tensile failure and ends in formation of main shear band. Furthermore，the appearance of failure along the long and short axial directions of soft rock is similar to experimental results in laboratory.

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STUDY OF PORE-PRESSURE MODEL OF SATURATED SANDS UNDER IRREGULAR LOAD

MENG Shangjiu1，LIU Tianhua2

2014, 33 (sl): -3055
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[PDF 509 KB] (701)

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A pore pressure model suitable for analyzing irregular loading effects is proposed，which is based on liquefaction test with constant amplitude of load，pore pressure model，accumulated principle of residual pore pressure，using differential method and superposition method. Using liquefaction test with constant load，liquefaction test with artificial modulation irregular load and dynamic triaxial liquefaction test with input earthquake wave，the proposed model is verified，and the results are drawn as follows：(1) The model can better simulate the results of liquefaction test with constant load；(2) The model can better describe the results of liquefaction test with artificial modulation irregular load；(3) The model can describe pore-pressure growth law under earthquake wave，and also can better analyze differential pore-pressure under different types of earthquake waves；(4) The model has few parameters and can analyze pore-pressure in real time and easy to use.

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ANALYSIS OF LATERAL DISPLACEMENT OF CAISSON FOUNDATION BASED ON COULOMB LAW OF FRICTION

HU Feng，SHAO Guojian

2014, 33 (sl): -3061
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[PDF 578 KB] (646)

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The friction effect between basement and soil was simplified as spring model in the traditional theoretical methods on the lateral displacement analysis of caisson foundation for simplicity of computation. This simplicity not only deletes the mutation of the basement friction but also makes the difficulty of obtaining the parameters，which leads to the lateral slide critical load cannot be computed. To address this problem，the classic Coulomb law of friction is used to replace the hypothetical spring model at the caisson basement，and the soil reaction along the well bore is computed by using Winkler model. According to the displacement coordination condition on the structure-soil interfaces，the formulas of lateral displacement，slide critical load，relation between enhancement factor of lateral bearing capacity and depth are derived. From the contrast of examples，it is clear that the friction parameter is convenient to be obtained，and the displacement shows remarkable mutant characteristics. The slide critical load can be deduced directly，and the formulas proposed can be applied to practical engineering conveniently.

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INFLUENTIAL FACTORS OF PILE-SOIL INTERFACE OF LARGE-DIAMETER ROCK-SOCKETED PILE AS ITS SIDE RESISTANCE STRENGTHENS

CAI Jiangdong1，2，XIA Hongchun3

2014, 33 (sl): -3067
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[PDF 924 KB] (834)

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It is well known there are many factors influencing the shaft resistance of rock-socketed pile. Statistics indicate that the shaft resistance of rock-socketed pile has a tendency to increase when the bearing capacity of the layer under the pile is high. This paper tries to calibrate the factors influencing the shaft resistance of the pile by direct shear test. In the test，the shear rate is controlled to simulate the settlement velocity of piles；and also soil contact relationship is considered. Main results are shown as follows：(1) Subsidence velocity of pile is manly affected by the strength of the layer under the pile. Settlement rate of the pile is greater when the layer is soft，then interaction between soil and pile will spread along interface layer. (2) The shaft resistance along the pile shows characteristics of hardening when the bearing layer is hard. The greater thickness of soil layer around the pile (which will produce greater lateral earth pressure)，the more significance of hardening will show. (3) The contact relationship of the strata around the pile will play importance role in the shaft resistance. Under larger lateral pressure around the pile，the side resistance may produce a superimposed effect，and thus is greater than that calculated by shear strength according to the theoretical formula.

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LOAD TRANSFER MECHANISM OF COMPOSITE PILE COMPOSED OF JET-MIXING CEMENT AND PHC PILE WITH CORE CONCRETE

LI Juncai1，ZHANG Yonggang1，DENG Yaguang2，HUA Xiaolong1

2014, 33 (sl): -3076
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[PDF 2651 KB] (814)

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The composite pile composed of jet-mixing cement and PHC pipe pile with core concrete(CPCP) is a new kind of composite pile used in soft ground treatment. For practical project，the static load test associated with fiber Bragg grating(FBG) stress tests and numerical simulations was conducted to understand the load transfer mechanism of the composite pile. With the pile tests，the side friction resistance and the tip resistance were measured in terms of axial stresses under different loads. Then the compatible deformation of pipe pile and cement-soil is obtained associated with their stress distribution. The change rule of compression of each segment is also achieved with the imposed top load. Finally，the differences between general pipe pile and CPCP in terms of resistance characteristics were compared. It shows that：(1) load-displacement(Q-s) curve of pile head varies gradually；(2) pipe pile rather than cement-soil bears a majority of structural load，whilst the bearing capacity characteristics of the composite pile are similar to those of the rigidity piles；(3) pile tip resistance takes a rather smaller percentage of the top load，suggesting the same performance as that of friction piles. Distribution of pipe pile and cement-soil friction resistance is similar，about the ratio of CPCP diameter to PHC diameter.

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PRELIMINARY STUDY OF CO2 GEOLOGICAL SEQUESTRATION AND ENHANCEMENT OF GEOTHERMAL EXPLOITATION INTEGRATION IN CHINA

XIE Heping1，2，XIONG Lun1，2，XIE Lingzhi1，2，HOU Zhengmeng1，2

2014, 33 (sl): -3086
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[PDF 13868 KB] (904)

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As a renewable clean energy，geothermal energy has a great potential development. Using CO2 to enhance the geothermal recovery with simultaneous sequestration of carbon is a novel approach. The integration technology of two current main types(hot dry rock and hydrothermal) of geothermal recovery technology with simultaneous sequestration of carbon is analyzed. Then as for the specific geological conditions of a saline aquifers CCS(CO2 capture and storage) site in the northwest of China，the flow efficiency/pressure change of CO2 and water between the production and injection wells under the same conditions are compared. Moreover，the heating extraction rates of water/CO2 under two different kinds of reservoir conditions are calculated，and then the corresponding amount of carbon sequestration，safety and economic feasibility are analyzed. These results show that CO2 is superior to water in its ability to heat exploitation from the hot reservoir. Therefore，using CO2 to enhance the geothermal recovery with simultaneous sequestration of carbon has a strong feasibility in China.

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RESEARCH ON ASYMPTOTIC DEFORMATION AND DESTRUCTION MECHANISM OF MUDSTONE TUNNEL SURROUNDING ROCKS

LI Ning，LIU Bo，LU Gao

2014, 33 (sl): -3092
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[PDF 1073 KB] (757)

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In order to solve the problem of sustained large deformation of mudstone tunnel surrounding rock after construction，the geological conditions revealed by tunnel excavation and measured deformation law are combined，as well as the corresponding numerical experiments. Result shows that some impermeable layers exist in the tunnel surrounding rocks and subsequent excavation led to destruction of surrounding rock impermeable layer. Then the groundwater flows to dry zone and softens the surrounding rocks of original dry zone gradually，which result in re-deformation of stabilized surrounding rock and damage of supporting structures. Through the comprehensively comparative analysis of treatment measures in numerical experiments and field tests，the measure of platoon and guide is more reasonable，economical and effective.

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THREE-DIMENSIONAL FEEDBACK ANALYSIS OF ROCK SLOPE STABILITY BASED ON MICROSEISMIC MONITORING

XU Nuwen1，2，3，LIANG Zhengzhao4，TANG Chun?an4，DAI Feng1，ZHOU Zhong5，SHA Chun5

2014, 33 (sl): -3104
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[PDF 39398 KB] (790)

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Plenty of seismic events have been recorded at the left bank slope of Jinping I hydropower station since the microseismic monitoring system was installed. On the basis of spatio-temporal analysis of microseismic activity at slope during the periods of excavation and reinforcement by grouting，rock mass damage regions were identified and delineated. However，how to utilize the abundant microseismic data effectively to quantitatively evalvate the stability of slope was the key issue of this study. First of all，research methods on rock slope stability were summarized and concluded. Then，the necessity of feedback analysis on slope stability based on microseismic monitoring was also outlined. A damage evolution model of rock mass based on microseismic data was put forward. The elements in the coverage of microseismic damage were searched automatically and their corresponding mechanical parameters were also reduced. The relation among microseismic activity induced by rock mass damage during slope instability processes，strength degradation and dynamic instability of slope was explored；and the slope stability was thus quantitatively evaluated. The results indicate：(1) The influence induced by rock mass actual damage could be taken into account based on three-dimensional feedback analysis of slope stability with microseismic monitoring. (2) The safety factor of rock slope considering microseismic damage effect decreased by 0.11，comparing to the case without regard to microseismic damage effect. This result demonstrated that microseismic activity induced by construction disturbances such as excavation and reinforcement by grouting had effect on stability of left bank slope. The feedback analysis method of 3D rock slope stability put forward in this study could be referred in stability evaluation of similar rock slopes.

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NUMERICAL ANALYSIS OF LONG-TERM STABILITY OF LEFT BANK ABUTMENT HIGH SLOPE AT JINPING I HYDROPOWER STATION

WANG Rubin1，XU Weiya1，MENG Yongdong2，CHEN Hongjie1，ZHOU Zhong3

2014, 33 (sl): -3113
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[PDF 44643 KB] (609)

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The long-term stability of left bank abutment high slope greatly affects the normal operation and safety of Jinping I hydropower station. In order to sufficiently understand the long-term stability of left bank abutment high slope，a geomechanical model containing weak structural planes of f5，f8，f2，f42–9 and lamprophyre veins X is established. The long-term creep behavior of slope rock mass is simulated under normal water level condition by using of Nishihara model and finite difference numerical calculation method. Results of numerical analysis show that the basic tendency of change for long-term creep numerical calculation results and field monitoring data of engineering are consistent. After a period of time，the specific creep deformation of slope rock mass gradually tended to be constant，and the creep rate went to a steady value. The Nishihara rheological model could reflect the rheological deformation characteristics of slope rock mass in Jinping I hydropower station. Creep deformation was obvious in many positions，such as the outcrop regions of f5，f8，f2，f42–9 and lamprophyre veins X，dangerous rock slope，cableway platform slope upper the elevation of 1 960 m，excavation slope in the elevation of 1 885～1 960 m，“bulk mass”，deep rock mass of PD44X. The creep deformation of intersection parts between excavation platform of spandrel groove and weak structural plane in 1 730 m were more apparent under the thrust at push force of arch abutment condition，which needed to pay more attention and strengthen monitoring.

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STUDY OF DEM AND FEM COMBINATION METHOD FOR STOCHASTIC STRUCTURAL PLANE IN JOINTED ROCK SLOPE

LIU Tianping，LI Shihai，LIU Xiaoyu

2014, 33 (sl): -3122
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[PDF 13154 KB] (616)

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According to the joint distributing character of jointed rock slope，a numerical method of combined distinct element method/finite element method(DEM/FEM) for stochastic structural plane is presented based on continuum-discontinuum element method(CDEM). Compared with the elastic results of FEM，the method is indicated to be credible. Assuming all the points on the potential sliding surface are in the critical failure status simultaneously，there is almost no difference between the value of safety factor calculated by the method and limit equilibrium method(LEM)，which proves stress result of the method is credible once again. And it is also concluded that LEM shows the mean stress state，while the method aims to simulate the progress failure of slope. The slope may become instable caused by progressive failure which is concluded to be stable by LEM when the method is used without hypothesis of LEM. Wulong landslide is simulated and the consistent phenomenon with the real failure progress is got. The failure progress of the Wulong landslide shows that the development of cracks inside the slope is very important to analyse the stability of slope. Tracking and analyzing the failure progress of important slopes are helpful in taking proper supporting measures in advance to avoid disasters.

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RESEARCH ON COORDINATION MECHANISM OF SLOPE ANCHORING AND REINFORCEMENT

LIN Xingchao1，2，WANG Xiaogang1，2，CHEN Wenqiang1，2，WANG Yujie1，2，JIA Zhixin1，2，

2014, 33 (sl): -3128
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[PDF 11772 KB] (600)

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The interaction between slope and its reinforcement measures makes the research about coordinated sharing mechanism of reinforcement measures very complicated，and it is difficult to determine by conventional numerical calculation. A method based on modern numerical simulation technology to solve this problem is put forward，which needs to build a slope model at unsteady state and simulate the reinforcement measures. Based on the research about coordinated sharing mechanism of prestressed anchors and shear cave working independently and cooperatively in different conditions，and the optimized combination of comprehensive reinforcement measures，this paper puts forward a comprehensive design method of slope reinforcement.

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REALIZATION OF AUTOMATED SEARCHING BY GIS FOR MOST DANGEROUS SLIP SURFACE OF RESERVOIR BANK SLOPE BASED ON SWEDISH SLICE METHOD

WANG Xiaodong1，2，3，DAI Fuchu1，HUANG Zhiquan3

2014, 33 (sl): -3134
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[PDF 711 KB] (750)

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In the stability analysis of cohesive soil slope，the procedures based on Swedish slice method are usually defected by low automation and poor visualization. Because part of reservoir bank slope is submerged in the water，failure is more likely to occur. Based on the high-resolution digital elevation model(DEM)，applied geographic information system(GIS) component development technology，the paper suggests a new method to evaluate the stability of reservoir bank slope through computing the minimum safety factor and drawing the most dangerous slip surface. It has three advantages compared to the traditional method：(1) The profile can be extracted by drawing a line section on the DEM，also the information of multi-layers can be drawn with high degree of automation；(2) Slice parameters can be set in different values，which is beneficial to compare the test result；(3) The process and result of stability analysis can be expressed visually，hence the errors can be easily found.

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DYNAMIC CACULATION METHOD OF FRAME PRESTRESSED ANCHORS FOR SLOPE STABILITY UNDER SEISMIC EFFECT

DONG Jianhua1，2，3，ZHU Yanpeng1，2，MA Wei3

2014, 33 (sl): -3143
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[PDF 731 KB] (699)

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In order to accurately carry out dynamic analysis and seismic design of the new slope anchorage structure，the study of its dynamic properties and seismic design theory is very necessary and urgent. The movement characteristics satisfy the theory of elastic foundation beam under the prestressed anchor action. A dynamic calculation model of frame with prestressed anchors for slope stability is established based on Winkle elastic beam theory. Under the horizontal earthquake excitation，the equation of vibration for slope supported by frame with prestressed anchors and slope is deduced considering the influence of beam and retaining plate，and the analytical solution is obtained. Finally，the proposed method is applied to a project case for illustrating its capability of earthquake response. In order to investigate the effectiveness and reliability of this method，it is compared with finite element method and shaking table test，the results show a good agreement. The analysis of slope with supporting and without supporting reveals that this structure can evidently decrease the earthquake response and has better seismic performance. The calculation model provides a new approach for earthquake analysis and seismic design of slope supported by frame supporting structure with prestressed anchor.

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ROCK CRACKING MECHANISM DRIVEN BY EXPLOSIVE STRESS WAVE

ZHANG Yuzhu1，2，LU Wenbo1，2，CHEN Ming1，2，YAN Peng1，2，YANG Jianhua1，2

2014, 33 (sl): -3149
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[PDF 1051 KB] (391)

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Aiming at the drilling and blasting excavation method for rock，the explosive stress wave variation with time and space as well as the influence of which on the rock cracking process are analyzed with stress intensity factor. Results show that under the action of explosive stress wave，the stress in the rock media will be in compression-shear or tensile-shear state with time order. In the field near blast hole，the rock cracking is controlled by the compression-shear stress state；while the tensile-shear stress state plays a major role in rock cracking when it is far from the blast hole；with the increasing of distance，rock cracking is mainly controlled by tensile-shear stress state，which is primarily composed of a combination of radial tensile stress and tangential tensile stress. The influence of tensile shear stress state on the cracking zone cannot be ignored especially for low-strength rock.

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KEY TECHNIGUES STUDY OF PARTICLE FLOW SIMULATION FOR THREE-DIMENSIONAL HOLLOW TORSIONAL SHEAR TEST

LI Bo，CAI Yuanqiang，GUO Lin

2014, 33 (sl): -3156
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[PDF 13518 KB] (1140)

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Hollow cylinder apparatus is a valuable tool to investigate the stress-strain relation of granular materials in complex state. Based on the three-dimensional discrete element method(3D-DEM)，the stacked rigid wall technique is introduced to simulate behavior of hollow cylinder samples in complex stress path. The mechanical response of hollow cylinder sample can be observed in the fixed principal stress rotation including micro-response. The superiority of this technique is discussed，which suggests that the boundary could capture the localization effect of soil sample. Finally，the stress-strain relationship and its micro-parameters evolution are presented in the certain shearing direction. Compared to the results of lab test，the simulation can reasonably capture the stress-strain behavior and dilatancy of the sand. Further，the micro-parameters，including evolution of the stress and strain localization，porosity and void ratio are investigated. The capability and limitation of the hollow cylinder are discussed. In conclusion，the DEM technique as an alternative tool does complement the element test and provide the possibility to investigate the macro- and micro-scopic behavior of granular materials.

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ENERGY EFFICIENCY EVALUATION MODEL IN DRILLING BASED ON FRACTAL FRAGMENTATION CHARACTERISTICS OF ROCK CUTTINGS

YAN Tie1，ZHANG Yang2，DU Shuming3

2014, 33 (sl): -3163
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[PDF 681 KB] (683)

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According to the theory of fractal rock mechanics，energy efficiency evaluation model in drilling is established by analyzing fractal fragmentation characteristics on rock cuttings and drilling behavior characteristics，which contains crushing energy consumption model and energy efficiency model. The relationship between energy consumption and energy efficiency with fractal crushing characteristics of debris is studied. Results show that fractal dimension of particle-size distribution，maximum size and rock feature constant are dominant affecting factors for crushing energy consumption. And hydraulic decontamination coefficient and fractal dimension of particle-size distributionare are main affecting factors for energy efficiency. Energy efficiency is increasing with hydraulic decontamination and fractal dimension in exponential trend. Adjacent granularity similarity ration of rock cuttings has a little effect on energy efficiency.

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EXPERIMENTAL STUDY OF TRIAXIAL COMPRESSION DEFORMATION AND STRENGTH CHARACTERISTICS OF RED SANDSTONE

SU Chengdong1，FU Yisheng2

2014, 33 (sl): -3169
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[PDF 557 KB] (917)

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Characters of failure，strength and deformation for red sandstone are analyzed with uniaxial compression，conventional triaxial compression and Brazil split tests by using RMT–150B rock mechanics test system. Five conventional triaxial strength criteria are fitted to the test data with least absolute deviation，and the predicted values of uniaxial compressive strength，tensile strength and fracture angle are compared to the test ones. Results show that the Mohr-Coulomb criterion presents large misfit which overestimates strengths at low and high confining pressures. The Hoek-Brown criterion，generalized Hoek-Brown criterion，Rocker criterion and the exponential strength criterion present uniaxial compressive strength just the same with experimental value of 68.0 MPa，but partial higher in tensile strength estimation. The value of prediction in generalized Hoek-Brown criterion is most closed to calculations of tensile strength and the fitting effect is better. Fracture angles of red sandstone are 52.5°–66.6° in test，which correlated with confining pressure negatively. Prediction of fracture angle in Mohr-Coulomb criterion is 65° which is larger than the actual one. The fracture angles predicted by other four criteria decrease with the increase of confining pressure and correspond with the test results.

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NUMERICAL EXPERIMENTS OF DYNAMIC RESPONSE CHARACTERISTICS OF ROCK DRILLING ON STRATIFIED ROOF IN COAL ROADWAY

LIU Shaowei，FENG Youliang，LIU Dongliang

2014, 33 (sl): -3176
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[PDF 9227 KB] (415)

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Horizon combination as well as physico-mechanical characteristics severely influence the stability of rock bolting roof in coal roadway，and the drilling device of anchoring holes has different responses to different types of rock，which provides information of thickness and strength on rock. In order to overcome concealment problems of roof in coal roadway，design bolting parameters reasonably and prevent roof falling，numerical experiments about drilling characteristics on roof in coal roadway were carried out. Study shows that the drilling on roof in coal roadway is discontinuous and anchoring holes are deepened step by step like jump. Under the condition of homogeneous rock，the drilling speed from high to low is sandy mudstone，siltstone，mudstone and sandstone，while the resistance of bore bit from large to small is siltstone，sandstone，mudstone and sandy mudstone. Above indices are monitored by related instruments during drilling anchoring holes，which are very significant to distinguish the type and thickness of roof rock within the scope of anchoring holes in coal roadway.

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DEVELOPMENT OF GAS-LIQUID COMPOSITE LOADER FOR ROCKBURST SIMULATION

HE Yongsheng1，DING Xingbo1，2，MING Zhiqing1，FAN Junqi1，PANG Weibin1

2014, 33 (sl): -3184
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[PDF 11297 KB] (473)

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A special gas-liquid composite fast-compensating loader for rockburst simulation is developed，and its design principles and technical characteristics are introduced. The loader which has four cavities simulates rockburst by using adiabatic expansion of compressed gas in energy storage cavity for fast-compensating pressure fall at failure of sample. Result shows that the loader has good capability in high rigidity，stable operation performance and reliable high-speed sealing. The key issues could be solved including eliminating back pressure in return cavity，preventing gas from getting into hydraulic cavity and sealing high-speed guide. It can realize rockburst modeling in different intensity degree under the condition of uniaxial loading. Moreover，some issues of loader in further study are discussed.

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EXPERIMENTAL STUDY OF STATIC AND DYNAMIC MODULI FOR ANISOTROPIC ROCK

TANG Jie

2014, 33 (sl): -3191
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[PDF 6808 KB] (1003)

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Shales are important source rocks and sealing rocks with intrinsic anisotropy. The character of stress-strain response and ultrasonic speed response for shales are obtained by experimental measurement，and the features of static and dynamic moduli on anisotropic rock are studied. The dynamic modulus of anisotropic rock is gained by measuring vertical and horizontal wave velocities of core under different directions，and the static modulus is obtained through the measurement of stress-strain characteristics in loading process. Characteristics of wave velocity and elasticity modulus of anisotropic rock under quasi-static and dynamic conditions are analyzed. Except the difference of loading frequency，the strain amplitude difference are obtained respectively under static and dynamic measurements. Study of geophysical response characteristics for anisotropic rocks is of great significance.

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STUDY OF ELASTOPLASTIC DAMAGE-HEALING MODEL FOR ARGILLITE

QU Jiawang1，2，LIU Quansheng1，2，HE Jun1，2，LIU Zhiping1，2

2014, 33 (sl): -3197
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[PDF 511 KB] (741)

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Under the action of high stress and water chemistry in underground space，cracks of the damaged argillite would healed by themselves thus their physico-mechanical performance will recover. This character of argillite greatly influences stability of surrounding rocks as well as radionuclide migration and isolation in high level radioactive waste disposal repository buried in argillite. According to generalized thermodynamic and continuum damage mechanics，based on maximum dissipation principle，an internal variable describing the healing property of argillite is introduced，and an elastoplastic damage-healing model for argillite is developed which is able to depict deformation，damage and healing evolution characters of argillite. Then the proposed model and a model formed by removing healing part are used to simulate triaxial compression experiments of argillite under different confining pressures，respectively. Simulation values of the two models are compared with experimental data. Results indicate that the developed model can reasonably and effectively describe main mechanical characters of argillite which has healing effect，and the healing part of model significantly influences performance of model.

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NUMERICAL SIMULATION OF ACOUSTIC EMISSION FOR DEFECTIVE ROCK

HAN Tongchun1，2，ZHANG Jie1，2

2014, 33 (sl): -3204
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[PDF 15253 KB] (5273)

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Rock is a heterogeneous material which consists of grains with different strengths. Studies show that different homogeneous rock materials possess different acoustic emission characteristics in uniaxial compression. Researches of these characteristics have an important role in forecasting rockburst. Fish function is drew to realize model which contains random defect units and records events of acoustic emission. Acoustic emission on homogeneous and random defective material in uniaxial compression is simulated with FLAC3D. The differences of homogeneous model and defective model are discussed，as well as the influence of number of defective units on acoustic emission. Results have an important significance for study of rock acoustic emission characteristics.

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RESEARCH ON DAMPING TESTING METHODS OF ROCK MASS BASED ON BLASTING EXCITATION

SONG Quanjie1，2，LI Haibo1，LI Junru1，HUANG Xiaocheng1，JIANG Jungang1

2014, 33 (sl): -3211
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[PDF 795 KB] (703)

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Rock mass damping ratio，as an important dynamic parameter of rock mass，is widely tested by block excitation testing method which costs much. Blasting excitation is a simpler and more efficient method than block excitation for rock mass damping ratio. It needs to consider influence of geometric damping induced by geometric diffusion of energy. Formula of calculating rock mass damping ratio in attenuation of surface wave is derived with viscoelastic model. In Haiyang Nuclear Power Plant，a test consisting single hole and porous blasting excitation was conducted and the test data were analyzed by wavelet packet. In order to verify result of blasting excitation test，block excitation method was tested under the same condition. Results show that the ratio from blasting excitation test is larger than that from block excitation test，and the ratio from blasting excitation test decreases with the increasing distance between explosion source and measuring point. Moreover，the rock mass damping ratio was affected by blasting vibration frequency. Comparison of experimental results showed that rock mass damping ratio could be obtained through blasting vibration information.

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EXPERIMENTAL STUDY OF FATIGUE DAMAGE PROPERTIES OF SANDSTONE SAMPLES UNDER CYCLIC LOADING WITH LOW FREQUENCIES

ZHANG Shishu，LIU Enlong，ZHANG Jianhai

2014, 33 (sl): -3218
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[PDF 1211 KB] (700)

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The fatigue damage properties of intact sandstone samples subjected to axially cyclic loads with different frequencies at confining stress state were investigated，and influence of frequency on dynamic mechanical features of sandstone was studied. The apparatus employed was the MTS–815 rock and concrete test system，three levels of confining pressure(2，10 and 40 MPa) and three sets of frequencies(0.1，1.0 and 3.0 Hz) were applied. The dry sandstone samples were extracted from Wenchuan with average diameter of 48.9 mm and the ratio of height to diameter of 2∶1. Results demonstrated that：(1) The frequency has a strong influence on residual deformation，fatigue stiffness and failure mode under the same confining pressure. The higher the frequency，the bigger the residual axial strain and the more number of cycles at failure，and the larger the initial stiffness. (2) The damage variable D proposed could describe the fatigue damage process of sandstone samples under dynamic cyclic loading.

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EXPERIMENTAL STUDY OF NONLINEAR MOTION LAW FOR GAS SEEPAGE IN COAL SEAMS

LI Bo1，2，WEI Jianping1，WANG Kai2，JIA Yannan1

2014, 33 (sl): -3224
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[PDF 624 KB] (729)

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Taking the raw coal samples of Zhaogu mine in Jiaozuo as a object of study，with a self-developed equipment for thermo-fluid-solid-stress coupling of coal containing methane，experimental studies of the relationship between the coal sample permeability and effective stress as well as the motion law of gas in the coal samples are conducted on the basis of considering the adsorption deformation，pore gas compression volume and temperature expansion. Relationship equation between loaded coal permeability and effective stress and motion equation which describes the nonlinear seepage law of coal seam gas have been established. Results show that：(1) Permeability represents nonlinear decreasing relationship with increasing effective stress，possessing the law of negative exponent；(2) The gas transfusion law under different pore barometric gradients in fixed confining pressure and axial compression is studied，and gas seepage velocity presents nonlinear under the action of coal transformation. Meanwhile，through fitting the experimental data with equation，it can been seen by relevance that test results are consistent with fitting results，which indicates that the established motion equation and method are reasonable.

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INFLUENCE ANALYSIS OF EXPLOIT DEPTH AND VERTICAL IMPACT LOAD ON ANOMALOUSLY LOW FRICTION ROCKBURST

LI Liping1，PAN Yishan1，WANG Xiaochun2，TANG Jupeng1

2014, 33 (sl): -3230
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[PDF 750 KB] (711)

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The frequency and intensity of rockburst are more and more serious with the increasing of exploit depth. But the mechanism of rockburst in deep mine is not clear. Based on the actual situation of deep exploit，the anomalously low friction rockburst is put forward，and the anomalously low friction effect is introduced. With the vertical impact load and crustal stress，theoretical block model of anomalously low friction rockburst is established，and the variation of normally dynamic load on interface of coal rock mass is deduced. The study indicates that the normally dynamic load on interface of deep rock mass periodically changes under the vertical impulse load，and the generating of rockburst has critical depth zone，when the depths are 400–600，800–1 000，1 200 m，the wave period of normally dynamic load on interface is smaller，the frequency of wave is much faster，which is corresponding with the result of spot observe and the existing conclusion，and verifies the rationality of model. The normally dynamic load on interface changes sharply with different exploit depths，and cubic polynomial is satisfied between the maximal variance ratio of normally dynamic load on interface and exploit depth at 800–1 200 m. With the increasing of the intensity of impulse load，the maximal change amplitude of normal load reduces firstly and increases subsequently，and reaches to constant value at last. When the intensity of impulse load is 1 MPa，the maximal change amplitude of normal load is least，the static friction on interface changes to dynamic friction，the coal mass will slide and the anomalously low friction effect will be generated，thus the rockburst would be induced easily.

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CHARACTERISTICS OF INTERACTION PROCESS BETWEEN DEEP ROCK OF LOWER COAL SEAM FLOOR AND WATER UNDER DIFFERENT TEST CONDITIONS

ZHU Shuyun1，SONG Shuguang2，SUN Qiang1，YAN Biao1，WANG Chengtian2

2014, 33 (sl): -3237
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[PDF 1413 KB] (626)

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In order to study the characteristics of interaction process between deep rock of lower coal seam floor and water in Jibei mining area，five different types of rocks are used for water stability test in laboratory by natural water and saturated salt water soaking. Through water stability test and conductivity measuring for 52 days，the results are drawn as follows. (1) The water stability of nature soaked rocks is good，and none of them have basic degradation according to phenomena and test results of 20 samples in dropping residue，superficial cranny，rock cracking，strength change，swelling and degradation. However，the samples have obvious degradation by wetting- drying cycle effect. (2) There are three phases to conductivity increasing range in natural water by normal condition and wetting-drying cycle effect，but the conductivities of same sample under different conditions show big difference in increasing over time. The conductivity in wetting-drying cycle effect is obviously larger. (3) It is positive relevance between rock conductivity and decreasing rate of mass. The study results provide references for micro-mechanism study of deterioration for rocks under water-rock interaction in the deep coal mining.

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REVIEW OF NEW PROGRESS IN TAILING DAM SAFETY IN FOREIGN RESEARCH AND CURRENT STATE WITH DEVELOPMENT TRENT IN CHINA

YU Guangming1，2，SONG Chuanwang1，2，PAN Yongzhan1，2，LI Liang1，2，LI Ran1，2，LU Shibao1，2

2014, 33 (sl): -3248
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[PDF 727 KB] (1161)

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Tailing pond is a major risk source，which the 18th in the international disaster accident rankings and poses a serious threat to the safety of downstream residents and facilities. Aiming at the tailing dam safety research and management problem，a large number of foreign research literature of tailing dam safety was collected. New progress in foreign research in tailing dam stability，safety management and environment protection was reviewed. Analysis methods and research of foreign scholars in the tailing dam failure reason，safety management and environmental pollution problems were analyzed and discussed. At the same time，the present situation in tailing dam stability，seismic performance，safety management and on-line monitoring research were described and compared with corresponding international studies. Following conclusions are drawn. (1) The study of tailings dam at home and abroad are mainly concentrated on the dam body safety，environmental protection，tailing pond management and so on，especially the tailings dam stability. Countries pay more and more attentions to tailing dam safety and environmental protection. (2) In the tailings dam safety management and environmental protection，Foreign countries are more rigorous and standardized than China. The management of tailings reservoir is strengthened in tailings dam design，construction and training. (3) Domestic research on stability of tailing dam and safety monitoring has accumulated some experience. Analysis has an important reference value to the safety management and environmental protection of tailings dam in China. Also the implementation of online monitoring with high technology for tailings dam safety is supposed to be the development trend of safety management in China. Research contents and trend are summarized according to nearly 10 tailing dam online monitoring projects.

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STUDY OF GROUTING TECHNOLOGY OF OVERBURDEN-SEPARATION TO REDUCE GROUND SUBSIDENCE IN HUAFENG COAL MINE

WANG Zhiqiang，GUO Xiaofei，GAO Yun，CHEN Chaofan，LI Pengfei，WANG Lei，ZHAO Jingli

2014, 33 (sl): -3255
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[PDF 1069 KB] (774)

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Based on the drilling holes layout of grouting into overburden-separation of #4 coal seam in Huafeng coal mine，theoretical analysis，regional dynamic planning and indoor simulation experiment are employed. By analyzing existing technical problems including the short face length，wrong judgement of coal pillar and rupture steps which can cause low efficiency of reducing subsidence，a new method is issued including arrangement of dip grouting drilling holes with technology of overburden-separation continuous integration grouting and arrangement of strike grouting drilling holes with method of regional dynamic planning. With the result of simulation experiment，it is shown that there are some improvements in aspects of inadequate overburden mining，goaf activation caused by pillar failure and difficult separation below the conglomerate and so on with using the continuous integration technology. Finally，the method of layout of continuous integration grouting drilling holes along the dip direction below greatly thick conglomerate and layout of six grouting holes along the strike direction outside the roadway 80 m of face is employed. And results show that the extent of mining is adequate beneath the separation zone，and the efficiency of reducing subsidence reaches to 44.6% with recycling more than 9.4×107 kg of coal resources，and quantity of drilling work reduces by 930 m along the dip direction.

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NUMERICAL SIMULATION AND SPECTRUM CHARACTERISTICS ANALYSIS OF VIBRATION WAVE PROPAGATION EFFECTS PRODUCED BY ROCKBURST IN SURROUNDING ROCKS OF ROADWAY

NIU Jianchun1，2，LIU Botao2

2014, 33 (sl): -3262
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[PDF 1507 KB] (693)

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In order to study the propagation attenuation law of vibration wave produced by rockburst in surrounding rocks of roadway and the surrounding rocks response characteristics，a numerical model is built by FLAC3D software based on propagation effects analytical model. The vibration source is loaded in the model，and the monitoring points of vibration wave produced by rockburst are emplaced in designated position. The model is analog calculated through dynamic analysis module，and the spectrum characteristics of vibration signals collected by monitoring points are analyzed with MATLAB software. Then vibration wave propagation effects produced by rockburst in surrounding rocks of roadway can be further studied. Results show that：(1) The power attenuation relationship between vibration wave produced by rockburst and focal distance is found along roadway. Vibration wave decays rapidly at the short distances while it decays slowly at longer distances. (2) Vibration wave energy produced by rockburst on roof is the maximum. Vibration influence on shoulders is smaller and minimum on sides and floor. These conclusions provide certain theoretical foundation on further research of vibration wave produced by rockburst propagation law and roadway destructive characters.

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ANALYSIS OF PRE-WIDENING EFFECT OF THERMAL INSULATION BERM ON HIGHWAY RECONSTRUCTION IN PERMAFROST REGIONS

YUAN Kun1，2，3，ZHANG Jinzhao1，2，ZHU Dongpeng1，2

2014, 33 (sl): -3269
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[PDF 738 KB] (677)

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In order to study the early stage effects of thermal insulation berm on embankment temperature field of widen embankment，the ground temperature near permafrost table and the change process of permafrost table are analyzed according to observation data of the insulation berm test road along the Qinghai—Tibet highway. A numerical simulation model is established for widen embankment and the early stage effects of insulation berm on permafrost，the thermal stability of permafrost under the shoulder after embankment widening are calculated. Results show that the degradation of permafrost under the berm in sunny slope is accelerated by berm itself，this influence in warm permafrost regions is greater than that in cold permafrost regions and the insulation berm in shady slope has less effect on the thermal stability of permafrost. The pre-melted effect is brought by berm in sunny slope，and the permafrost table under the shoulder does not have significant decrease after embankment widening，which shows as pre-widening effect and it is beneficial to stability of widen embankment. The berm in shady slope has less effect on widen embankment，regardless of whether the insulation berm，the permafrost table change process have less difference after embankment widening.

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BAO Shufeng1，2，3，QIU Qingchang1，2，LUO Yan1，2，WANG Pan1，2，HUANG Junwen1，2，WANG Bingwen1，2

2014, 33 (sl): -3276
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[PDF 5626 KB] (887)

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In order to guide the construction of the foundation pit composed of soil and rock effectively，the related monitoring techniques were deeply studied. The failure mode of pit composed of soil and rock was qualitatively analyzed. Based on an under-construction foundation pit composed of soil and rock in the mileage section DK799+450–DK800+750 in Pearl River Delta Area，a typical cross-section was computed with three-dimensional finite element method and monitoring. After synthesis analysis of monitoring results and calculation results，it was pointed out that，based on the existed code，it should mainly monitor deformations and internal forces of guard piles and axial forces of inner bracing for foundation pit composed of soil and rock，especially for the foundation pit whose in-situ stratified rock was a little influenced by groundwater. In addition，the surrounding environment of foundation pit should be also paid some attentions according to the engineering condition.

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STUDY OF STOPE ROOF MECHANICAL MODEL AND WALL ROCK DISTURBANCE LAW OF STEEPLY-INCLINED THIN OREBODY MINING USING MEDIUM-DEEP HOLE

FU Jianxin1，2，SONG Weidong1，2，DU Jianhua1，2，SUN Xinbo1，2

2014, 33 (sl): -3283
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[PDF 624 KB] (648)

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Taking Guoluolongwa gold mining for engineering background，based on the elastoplastic theory，the roof of steep thin ore-body stope using medium-deep hole was simplified as high statically indeterminate beam which clamped at both ends，and the mechanics analysis model was established. The roof deformation process was divided into four stages，including elastic stage，the stage plastic zone occurring in the region close to both fixed ends，the stage of both fixed ends broken and becoming simple-support and the stage entire roof becoming plastic flow. The limit span of each stage were 7.38，9.27，9.53 and 10.43 m. Based on Kachanov creep damage theories，this paper made a prediction for the roof fracture time of different stages which were 51.8，15.3 and 14.5 d，and given the function relation between fracture time and roof span which presented substantially cubic function relationships. Finally，according to the on-site stress monitoring，the surrounding rock stress variation in the mining process was analyzed. Surrounding rock stress experienced four stages of slow increase，sharp increase，sharp reduce and slow recovery.

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ANALYTICAL SOLUTION OF VERTICAL VIBRATION RESPONSE OF LARGE DIAMETER PIPE PILE IN HYSTERETIC DAMPING SOIL

ZHENG Changjie1，2，DING Xuanming1，3，HUANG Xu1，2，KONG Gangqiang1，2

2014, 33 (sl): -3290
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[PDF 863 KB] (719)

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Considering the hysteretic damping of soil and coupled vibration between pile，outer and inner soil，the frequency-domain vertical vibration response of cast-in-place concrete large diameter pipe pile in viscoelastic soil is investigated. The pile and the soil are treated as one-dimensional rod and axisymmetric viscoelastic medium，respectively. The frequency domain solutions of outer and inner soil are obtained by Laplace transformation technique and separation of variables method. The dynamic response of pile is then obtained based on the continuity assumption of displacement and stress between pile and outer soil as well as inner soil. The solution is compared with that of solid pile to verify its rationality. Moreover，by analyzing the effects of pile length，shear modulus of soil and pile radii on the complex stiffness of pile，the regularity of variations of vibration characteristic with parameters is obtained. Analysis shows that the oscillation amplitudes and resonance frequencies of complex impedance of pile decrease with the increasing pile length，but when pile length increases to a critical length，the effect tends to vanish；the oscillation amplitudes of complex impedance decrease with the increasing shear modulus of soil，and the effect of shear modulus of outer soil is larger than that of inner soil；the oscillation amplitudes of complex impedance increase with the increasing outer radius or decreasing inner radius.

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RESEARCH ON FRICTION CHARACTERISTICS AND FAILURE MECHANISM OF ANISOTROPIC SAND BASED ON MICRO-STATISTICS

CHEN Liping，ZHANG Dingli，FANG Qian，YING Guogang，WANG Jianchen

2014, 33 (sl): -3298
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[PDF 1071 KB] (625)

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With the method of microscopic statistics，the mechanism of anisotropic sand and impact of bedding angle on sand frictional properties and shear strength are analyzed. Based on the research above，two micro-factors including shear capacity coefficient and stability of particles are studied，which influence the frictional properties and peak strength of anisotropic sand. Moreover，in order to study the action mechanism of these two factors，“plastic hinge-wedge” model is established and a method to calculate the peak friction angle of sand is proposed. Finally，the modified direct shear test indicates that the theoretical results coincide with the experimental ones well. Results are hence obtained：(1) The orientation arrangement of internal particles is the main factor to cause the anisotropy，and the inherent anisotropy and induced anisotropy have the same formation microscopic mechanism；(2) The bedding angle has a great influence on the distribution of particle direction angle and affects the macroscopic mechanical properties of sand；(3) The bearing capacity of sand is mainly affected by the distribution of particle direction angle，the stability of particles and the friction properties of particle surface. These three factors lead to the ultimate strength of soil which can be calculated.

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EXPERIMENTAL STUDY OF DYNAMIC DEFORMATION AND DYNAMIC STRENGTH PROPERTIES OF SATURATED SILTY SAND

CHU Feng，SHAO Shengjun，CHEN Cunli

2014, 33 (sl): -3305
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[PDF 5280 KB] (631)

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In order to study the dynamic characteristics of silty sand，tests of dynamic deformation and strength properties in different conditions( =100，200，300，400 kPa， =1.0，1.5，2.0) by dynamic triaxial apparatus are studied. A series of changing regulations of the relation between dynamic stress and strain，damping，dynamic stress ratio are analyzed，then the preliminary exploration on the influence of mud and sand ratio on the dynamic characteristics is carried out. Tests indicate that，consolidation stress condition has great influence on the relation between dynamic stress and strain of saturated silty sand. Damping ratio increases with the increasing of dynamic shear strain. Under the condition of same consolidation confining pressure，damping ratio increases with the increasing of the consolidation ratio. Under the condition of different consolidation stresses，dynamic stress decreases with the increasing of the failure cyclic number. Under the condition of same consolidation ratio and different consolidation confining pressures，the relation between and is normalized. The mud and sand ratio has great influence on dynamic characteristics. On the condition of same dynamic strain，dynamic stress decreases with the increasing of mud content. On the condition of same consolidation confining pressure，damping ratio increases with the increasing of mud content. Dynamic strength does not increase monotonically along with the increasing of mud content. When the mud content is 20%，the dynamic strength is the lowest.

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EFFECTS OF SOLAR RADIATION AND GLOBAL WARMING ON BEARING CAPACITY OF SINGLE PILE IN PERMAFROST REGION

GUO Chunxiang，WU Yaping

2014, 33 (sl): -3311
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[PDF 5320 KB] (602)

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Based on the theory of heat transfer，the heat analysis model for single pile foundation in permafrost region is established. Considering the pile exposed to air absorbing solar radiation and transferring heat through natural air convection，phase change in frozen soil and global warming，the change processes of ground temperature and bearing capacity of a single pile in representative humid permafrost region of Qinghai—Tibet plateau in next 40 years are analyzed with finite element method. The effects of pile length exposed to air and annual average temperature on ground temperature and bearing capacity of the pile are analyzed. Results show that solar radiation and global warming would rise the temperature at pile-soil interfaces and reduce the bearing capacity of pile. The longer the pile length exposed to air，the more the absorption of solar radiation which is obvious in winter with temperature rising and bearing capacity declining，while it is not obvious in summer. The initial annual average temperature significantly influences the bearing capacity of pile foundation. When the initial annual average temperature increases by 1 ℃，the bearing capacity of pile decreases by 800–1 000 kN in winter and 400–700 kN in summer.

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A LINEAR DISTRIBUTION SOLUTION OF EARTH PRESSURE ON RETAINING WALL

KE Caitong，CHEN Yibo，ZHU Jia

2014, 33 (sl): -3317
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[PDF 559 KB] (679)

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Based on the sliding plane hypothesis of Coulomb earth pressure theory，diagonal slice method is used to deduce the formula of active and passive earth pressures，application position of resultant force and formula of earth pressure which considers the cohesion on sliding plane，the adhesive force on interface of soil and retaining wall，the uniformly distributed load，the critical rupture angle of explicit solution are also deduced. The formula effectively proves the Coulomb theory which assumes the earth pressure behind retaining wall is in linear distribution，besides the prevailing classical Rankine and Coulomb earth pressure formulas are two special examples of the formula that are simplified under the condition of relevant assumptions，which is an important supplement for the application of this method.

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EXPERIMENTAL STUDY OF EFFECT OF WATER-SATURATED STATE ON COMPACTION PROPERTY OF CRUSHED STONE FROM COAL SEAM ROOF

CHEN Xiaoxiang1，SU Chengdong1，TANG Xu2，GUO Wenbing1

2014, 33 (sl): -3326
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In order to study the effects of water-saturated state on crushed stone，the compaction tests on sandstone，mudstone and sandy mudstone from #3 coal seam roof of Yima Xin'an mine are conducted by using self-developed apparatus. The crushed stones are in two different conditions，one is natural and the other is water-saturated. The compaction stress is 27 MPa which is 1.5 times as high as the vertical geostress. Stress-strain relations of six particle sizes are obtained. Results show that the effects of water on crushed stones in different strengths are varied；the influenced degree of crushed stones is related with rock strength and the degree is decreasing along with the following order：mudstone，sandy mudstone and sandstone. The compaction property of small particle size is easier influenced by water compared with large ones. The rock strength has negative correlation with decreasing amplitude of residual bulking factor，residual void ratio and compactness respectively，and it also has good linear relation with each residual parameter. Compared with natural crushed stone，the parameters of water-saturated crushed stones all decreased such as residual bulking factor，residual void ratio and compactness；the decrease amplitudes of residual bulking factor for mudstone，sandstone and sandy mudstone are 14.21%，9.24% and 11.10%，respectively；and those of compactness are 9.47%，5.05% and 8.56%，respectively.

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STUDY OF DISTRIBUTION CHARACTERISTICS OF SUBSURFACE SETTLEMENT CAUSED BY TUNNEL CONSTRUCTION IN SANDY SOIL WITH MODEL TEST

WANG Fei，MIAO Linchang，WANG Zhengxing，WANG Ranran，ZHOU Yixin

2014, 33 (sl): -3332
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Researches of the settlement caused by tunnel construction mostly focus on the settlement at the ground surface at present. However，the increasing number of the failure cases of underground structures during tunneling reveals the importance of estimating the subsurface settlement. In order to solve this problem，sand of Yangtze River was filled in a self-developed model box with adjustable bottom on the box to simulate the tunneling effect. During the testing process，settlements were measured at different depths to investigate the subsurface movements caused by tunneling in sand. Test results show that the relationship of the maximum settlement at a given depth，the depth and the maximum bottom plate lowering distance is linear；the volume of settlement trough is not constant，it increases with the increasing depth. And it is only half of the volume of stratum loss；the settlement trough width parameter i is only related to the depth，and has no obvious relationship with the maximum settlement at the same depth.

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MATHEMATICAL MODEL OF EFFECTIVE STRESS OF COAL RESERVOIR BASED ON DAMAGE MECHANICS

NI Xiaoming1，2，ZHANG Chongchong1，WANG Yanbin3，WANG Xianghao3

2014, 33 (sl): -3339
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In order to accurately determine the stress of coal matrix in different coal reservoir properties and different surrounding rock stress conditions，the stress mathematical model of coal matrix by fully considering the coupling effects among the solid，liquid and gas in reservoir was established. Considering the compositions of internal material of the coal reservoir，the coal reservoir geometry concept model was established based on the spherical pore structure. Combined with the elastoplastic mechanics theory，the mathematical model about the effective stress coefficient was gained. Considering the damage evolution processes of coal total stress and pore stress with damage mechanics theory，the effective stress mathematical model of coal reservoir matrix was established. Taking the original reservoir parameters in Fanzhuang block for example，the effective stress changing laws were gained in different reservoir parameters：the effective stress is larger influenced by porosity and gas saturation. When other conditions are the same，with increasing of porosity or gas saturation，the stress of the coal matrix is exponentially decreasing. However，the influence of porosity is more intense than that of the gas saturation，the exponential relation curve between effective stress and gas saturation is more obvious than the porosity. The distributions of pores size and stresses are different. Under the same porosity conditions，with the increase of proportion of the biggest holes，it is logarithmic reduction. The effective stress is linearly reduced with water saturation increases.

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STUDY OF SHAKING TABLE MODEL TEST OF TUNNEL THROUGH SOIL INTERFACE

ZOU Yan，JING Liping，LI Yongqiang

2014, 33 (sl): -3348
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In order to study the seismic responses of tunnel through different soil layers in the earthquake，the shaking table model test was carried out. Shear box developed independently was used to reduce the boundary effect；lateral non-uniform site was made up by clay and sand；the axis of tunnel was vertically through the interface. After El-Centro seismic waves of different amplitudes were input from the base，acceleration and strain data were collected and analyzed. The features of seismic wave propagation in different soil layers were studied and the influences of soil interface on seismic responses of tunnel were analyzed. Results demonstrate that the deformation of tunnel is mainly controlled by relative displacement of the soil around it. Moreover，the differences between clay and sand in dynamic characteristics and restraints to tunnel will cause different responses of tunnel on both sides of the interface，and then the relative displacement will lead to spin，bend and twist-shear of tunnel.

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QUANTIFATIVE STUDY OF STRESS SENSITIVITY IN ULTRALOW PERMEABILITY FRACTURE MEDIA RESERVOIR

ZHANG Haiyong1，HE Shunli1，LUAN Guohua1，2，JIAO Chunyan1，3，MO Shaoyuan1，LIU Hao1

2014, 33 (sl): -3354
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In order to quantitatively describe the effect of microfractures on the stress sensitivity features of ultra low permeability reservoir，the stress sensitivity features of ultralow permeability fracture media from the mechanism of fracture medium deformation were analyzed by introducing a permeability stress sensitive theoretical model of single fracture. Then the experiment of stress sensitivity was conducted with microfracture cores fabricated by Brazil experiment and the features of permeability stress sensitivity were analyzed. Finally，the experimental data were contrasted with the theoretical curves. Results indicate that：(1) The theoretical curves quantitatively reveal the stress sensitivity features and the relationships with the microfracture content and roughness；the curves have the stress sensitivity features of fracture media reservoir. (2) The fabricated microfractures can proximately simulate the real situations of microfracture media reservoir and be used in the experiment. (3) The evaluation of stress-dependent permeability of cores should begin with the in-situ stress，or it would be overestimated；the permeability hysteresis loss of tensile-stress microfracture core is smaller and the permeability recovery degree is high so the permeability stress sensitivity is not strong；(4) The theoretical curve accords with the experimental data well，which indicates that the theoretical model can reveal the stress sensitivity characteristics of ultralow permeability fracture media accurately.

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CALCULATION METHOD FOR CREEP DEFORMATION OF AXISYMMETRIC ROUND WELL WITH CHANGING SUPPORT FORCE

HOU Gongyu1，LI Jingjing1，YANG Yue1，2，WANG Yaxiao1，LI Qingwei1，LIANG Yonghui1

2014, 33 (sl): -3360
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In order to find a creep solution which can reflect continuous changes of passive support force for axisymmetric round well，an iterative algorithm based on the creep solution of constant passive support force was raised by taking the continuous changes of creep deformation of surrounding rocks into account. The algorithm which shows the changing process of passive support force was already used to calculate the creep deformation of surrounding rock. Result indicates that creep deformation of surrounding rocks is sensitive to the value of initial stress. Under certain support stiffness，the increasing rate of support force is sensitive to the value of initial stress. Support force has little effects on the control of surrounding rocks creep deformation in condition of large in-situ stress.

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APPLICATION OF DEEP BOREHOLE BLASTING TO TOP-COAL PRE-WEAKENING AND GAS EXTRACTION IN FULLY MECHANIZED CAVING

LIU Jian1，2，LIU Zegong1，2，GAO Kui1，2，JIANG Erlong1

2014, 33 (sl): -3367
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In order to solve the problem that the top-coal cannot be broken fully in mines under ground pressure causing the low recovery ratio of resources and violent strata behaviors in hard，thick and high-gas coal seam by fully mechanized top coal caving mining，the deep holes blasting forced roof caving was taken to pre-weaken the top-coal and gas drainage. The pre-weakening roof and pressure relief gas extraction mechanism was expounded by numerical simulation and theoretical analysis method. After dynamite blasting in hard top-coal，the surrounding coal of blasting holes produces a large number of fissures and significant displacement by explosion stress waves，stress was redistributed and thick top-coal was caved. At the same time，gas was desorbed and flowed along the fissure，the loose blasting crushing circle was formed around the hole and the efficiency of gas extraction was improved. Finally，the application of deep-hole blasting to pre-weakening roof and pressure relief gas extraction field test was taken in the 3801 working face of Shuiliandong coal mine. It is a good reference to high gas and hard top-coal caving working face in special thick seam mining under similar conditions.

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STUDY OF CHARACTERISTICS OF b VALUE FOR MICROSEISMIC EVENTS IN HIGH ROCK SLOPE

XU Nuwen1，2，DAI Feng1，ZHOU Zhong3，SHA Chun3，TANG Chun?an4

2014, 33 (sl): -3374
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The magnitude-frequency relation(b value) of microseismic events recorded at the left bank slope of Jinping first stage hydropower station was analyzed. In order to in-depth investigate the slope stability and resolve the complex surface conditions of highly fractured rock mass，a microseismic monitoring system was implemented at the rock slope in June 2009 based on common monitoring instrument including multipoint extensometer and graphite rod convergence gauge. Seismic source parameters such as magnitude，location and time were captured during the monitoring period. The variation of b value was thus determined with time and excavation-induced microcrackings were identified and delineated after analyzing the monitoring data recorded from June 2009 and to 2011. Results show that rock mass damage is closely related with b value. The b value of microseismic events at the dam spandrel equals 0.87，showing the microseismicity plays little effect on the rock slope stability. Meanwhile，the little increase of b value(from 0.49 to 0.65) at the unknown geological structure indicated the hazard probability of rock mass failure inside the unknown geological structure of left slope decreased. Results can provide references for predicting rock mass instability and improving monitoring accuracy in similar rock slopes.

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MICROSEISMIC MONITORING SYSTEM AND ITS ENGINEERING APPLICATIONS OF DEEP-BURIED UNDERGROUND POWERHOUSE

LI Biao1，DAI Feng1，XU Nuwen1，ZHU Yongguo2，SHA Chun3，XIAO Peiwei2，HE Gang3

2014, 33 (sl): -3383
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The underground powerhouse of Houziyan hydropower station is a typical deep-buried powerhouse with the depths of 280–510 m horizontally and 400–660 m vertically. The ground stress is high and the geological conditions are very complicated. In order to monitor and analyze the surrounding rock mass stability during continuous excavation of underground powerhouse and locate the potential instability failure areas，an ESG (engineering seismology group) microseismic monitoring system manufactured in Canada was installed in April，2013. The wave velocity range of rock mass in underground powerhouse was measured by digital acoustic instrument. The overall equivalent wave velocity of P wave was 5 700 m/s in monitoring system which was determined through several blasting tests. The seismic source location error was less than 10 m. The microseismic event waveforms were manually processed to acquire high position accuracy and the interference events were filtered out. On the basis of geological conditions and field observation，micro-fracture clustering areas of surrounding rock mass and the potential instability risk areas in the underground powerhouse of Houziyan hydropower station were revealed and delineated by the tempo-spatial evolution laws of microseismicity. Results could provide some references for later excavations and supports in the underground powerhouse of Houziyan hydropower station. Furthermore，a new research idea is opened up for the stability analysis of deep-buried underground powerhouse subjected to excavation-induced unloading.

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DETECTION AND ANALYSIS OF HEIGHT OF WATER FLOWING FRACTURED ZONE IN UNDERWATER MINING

GAO Baobin1，2，3，LIU Yunpeng1，3，PAN Jiayu 1，3，YUAN Tian1，3

2014, 33 (sl): -3390
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In order to accurately detect the height of water flowing fractured zone in overlying roof strata after the mining face has been mined and ensure that mining underwater is safe and reliable，empirical formula calculation，downhole plugging drilling section water injection(put) crack measurement system and drilling television detecting system are used to detect the development of water flowing fractured zone. Results show that，using the above three methods respectively，the heights of water flowing fractured zone，which are 25.24–36.50，26.83–28.33 and 25.50–29.20 m，are obtained. The results verify that using downhole plugging drilling section water injection(put) crack measurement system to detect the height of water flowing fractured zone is reasonable and reliable，and it not only provides a theoretical support for Sitai coal mining underwater，but also provides reference for other coals to detect water flowing fractured zone.