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2010, 29 (06): -0 doi:
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STUDY OF TUNNEL STABILITY ANALYSIS WITH SEISMIC LOAD

ZHENG Yingren1，2，XIAO Qiang1，2，YE Hailin1，2，XU Jiangbo2，3

2010, 29 (06): -1088 doi:
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[PDF 366 KB] (1509)

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In order to obtain the regularity of mechanics for an unlined tunnel during earthquake，strength reduction finite element method and a large finite-difference program FLAC with tensile and shear failure analyses are combined and introduced into the tunnel stability analysis. Based on static analysis of loess unlined tunnels，a seismic dynamic finite element static analysis and a complete dynamic stability analysis methods are proposed. The analysis takes into account the tunnel tensile and shear failure to get the failure mechanism of loess tunnel with outside drive. Partial tensile failure is taken place at the top and then the general demolition is took place at the broadside of the tunnel. And it is found that the strength reduction finite element method can be used not only to tunnel static analysis but also to tunnel dynamic stability analysis. This analysis can provide a theoretical basis for seismic design of unlined cavern loess habitat，and it can be used as a foundation for seismic response analysis of loess tunnel with lining.

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EXPERIMENTAL STUDY OF SLABBING FAILURE FOR DEEP- BURIED MARBLE AT JINPING II HYDROPOWER STATION AND ITS INFLUENCES ON TBM EXCAVATION

WU Shiyong1，GONG Qiuming2，WANG Ge1，HOU Zhesheng3，SHE Qirui2

2010, 29 (06): -1095 doi:
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During the tunnel boring machine(TBM) excavation，two types of slabbing failures in these deep-buried marble tunnels are discussed. One is violent slabbing rock burst and the other is non-voilent slabbing and spalling. In order to study the slabbing failure，true triaxial experiments for modeling the rock burst at different in-situ stresses are carried out. Results show that all of the specimens appeared slabbing. The phenomena observed in the experiments are very similar to that at the tunnel site in Jinping II hydropower station. The experiment explains basically the tunnel face and tunnel side rock failure phenomena at present，and also displays the main failure types during the TBM excavation in the future. The influence of the slabbing failure at tunnel face and tunnel side on TBM excavation is analyzed and discussed.

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STUDY OF STRENGTH AND FAILURE OF HOLLOW CYLINDERS AND RINGS OF SANDSTONE UNDER COMPRESSION-TENSION STRESSES

YOU Mingqing，SU Chengdong

2010, 29 (06): -1105 doi:
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To study the strength and failure of rock under compression-tension stresses，hollow cylinders with 50 mm in outer diameter and 6–25 mm in inner diameters were cracked by inner hydraulic pressure under different axial loads；and ring specimens with 4.6–20.0 mm in inner diameters were tested with Brazilian split. The experimental results show that the cracking pressure for hollow cylinder is not influenced by the axial load when it is lower than 80% of the uniaxial compression strength. The cracked pressure decreases with the increase of the inner diameter；and the tangential stress at the hole wall also decreases slightly，but the average of tangential stress increases. The hollow cylinders can hold tensile stress much higher than that of the Brazilian disc. The cracking pressure for hollow cylinder with inner diameter of 25 mm is about 10 MPa；and the tangential stress is about 17 MPa on the inner surface and 7 MPa on the out surface. However，the maximum strength in 6 pieces of Brazilian disc is only 6.17 MPa. Hollow cylinders with inner diameters less than 20 mm failed for the deformation on the inner surface increasing to the limitation and cracked into two parts. Hollow cylinders with inner diameters of 25 mm failed for the tangential stress on the out surface increasing to the tensile strength，and single crack was produced. Two indices of deformation and stress are related to the failure of rock specimen suffered from nonuniform stresses.

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TESTING ON FORMATION AND EVOLUTION OF TBM EXCAVATION DAMAGED ZONE IN DEEP-BURIED TUNNEL BASED ON DIGITAL PANORAMIC BOREHOLE CAMERA TECHNIQUE

LI Shaojun1，FENG Xiating1，ZHANG Chunsheng2，LI Zhanhai3，ZHOU Hui1，
HOU Jing2，CHU Weijiang2

2010, 29 (06): -1112 doi:
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It presents the in-situ test on excavation damaged zone(EDZ) evolution of TBM tunnel No.3 in Jinping II hydropower station using digital panoramic borehole camera. Firstly，through the pre-excavated diversion tunnel No.2–1，several boreholes vertical to sidewall of TBM tunnel No.3 are drilled for digital camera，and a series of digital images of borehole wall are obtained during the whole TBM driven time. Afterwards，the images will be digitally processed；geological structural surface and fractures of surrounding rock mass are also analyzed，which makes it possible for the whole procedure of cracks formation，development and close to be obtained. Finally，the depth of damage zone is recognized；the relationship between fractures evolution and TBM construction progress is given；and the mechanism of EDZ evolution is discussed as well. It will not only provide the direct data for geological exploration but also contribute greatly to support design and analysis of deformation behaviors of deep-buried tunnels.

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MODEL TEST AND NUMERICAL SIMULATION FOR PROGRESSIVE FAILURE OF WEAK AND FRACTURED TUNNEL SURROUNDING ROCK UNDER DIFFERENT OVERBURDEN DEPTHS

ZHU Hehua1，2，HUANG Feng1，2，XU Qianwei1，3

2010, 29 (06): -1122 doi:
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By taking the weak and fractured surrounding rock(defined as class IV by the road tunnel code of China) for the three-lane highway tunnel with overburden depths of 25–60 m，similar materials and model test equipments are developed to reproduce the whole process of progressive failure of surrounding rock after excavation；and the characteristics of stress field in rock mass under different overburden depths are studied. Meanwhile，an elastoplastic damage constitutive model is introduced to simulate some cases of model test by FEM；and the related parameters of rock mass are determined by laboratory tests. The numerical simulation results show a good agreement with those of model test. By analyzing the results of model test and numerical simulation，the conclusions can be drawn as follows：(1) The failure zone of surrounding rock is the source of tunnel collapse load，and it is distributed mainly above the vault as well as partially at the bottom of both side walls and arch bottom. (2) The overburden depth has great influence on the dimensions of progressive failure zone around tunnel profile. As the overburden depth increases，the corresponding failure zone shows a gradual expansion trend. (3) The circumferential stress within the surrounding rock rises firstly and then decreases gradually after tunnel excavation. The location of the maximum stress corresponds to the position of earth pressure arch. With the expansion of failure zone，it continues to develop towards the inner side of rock mass and form a dynamic pressure arch. (4) The location of earth pressure arch can be determined by measuring the maximum circumferential stress within rock mass，and thus to determine the tunnel collapse load，which is theoretically feasible.

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LOADING RATE DEPENDENCY OF STRESS-STRAIN CURVE IN POST-FAILURE REGION OF ROCKS

LEI Ming，HASHIBA K，FUKUI K，OKUBO S

2010, 29 (06): -1131 doi:
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The loading rate dependency of stress-strain curve at very low stress level in the post-failure region is investigated with three testing methods. A testing method，in which a single rock sample is loaded at alternating loading rate with a predetermined strain interval ，is applied to Sanjome andesite，Inada granite and Tage tuff. With this method，two stress-strain curves corresponding to the two loading rates can be obtained. Experimental results indicated that loading rate dependency of stress-strain curve was clearly observed up to the very low stress level in the post-failure region，where failure progressed considerably. Next，unloading-reloading cycles are repeated in constant loading rate test with Sanjome andesite and Inada granite；and unloading curves at many points along stress-strain curve are obtained. Stress-strain curve at slow loading-rate obtained in alternating loading rate test is shifted along the unloading curves，and then it overlapped on stress-strain curve at a fast loading rate. A new testing method，in which alternating two loading-rates and unloading-reloading cycles are repeated with a single rock sample，is proposed and applied to Sanjome andesite，Inada granite and Tage tuff. It is found that the new testing method is easy to conduct and suitable for investigating loading rate dependency of peak strength and that of post-failure region of rocks. The percentage of change of stress in post-failure region is almost equal to that of the peak strength.

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RESEARCH ON INFLUENCES OF CRACKING OF XIAOWAN ARCH DAM ON ITS STRESS AND STABILITY

LIU Yaoru，WANG Jun，YANG Qiang，YANG Ruoqiong，ZHOU Weiyuan

2010, 29 (06): -1139 doi:
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[PDF 597 KB] (1254)

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With the three-dimensional nonlinear finite element analysis and geomechanical model of rupture test，focusing on analysis of the results of no crack working condition and crack after treatment working condition，the influences on Xiaowan arch dam stress distribution and global stability are studied as well as the possibility of crack propagation. The result indicates that the dam stress distributions of two working conditions are almost the same and the influences of crack are negligible. Under the normal water load，nearly all cracks are in the pressure- shear condition；and the tensile stress is small or does not exist，so the crack will not expand. After the dam overload test，the nonlinear load between 3.2P0 and 3.3P0(P0 is normal water load) after the crack is dealt with，which is quite close to 3.5P0 in the no crack working condition；limited parts of the dam cracks become large-crack area after overloading 3.0P0，but the influences of crack will not reach the crack area until overloading 5.0P0. The dam cracking limit state is similar to that of no crack working condition，but large difference of global stability between the two working conditions is found.

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MONITORING ANALYSIS OF ROCK STABILITY OF UNDERGROUND MAIN POWERHOUSE IN XIANGJIABA HYDROPOWER STATION

YUAN Peijin，SUN Jianhui，LIU Zhizhen，ZHU Zhaohui

2010, 29 (06): -1148 doi:
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It describes the anchoring effect and surrounding rock deformation monitoring during the excavation process of the underground powerhouse on the right bank of Xiangjiaba hydropower station. The monitoring results show that：due to better control of the excavation and support，the overall deformation of surrounding rock is little，and through analyzing the deformation monitoring data in entire process of excavation，the sphere of influence of excavation on surrounding rock and the estimation about deformation monitoring of pre-loss are obtained. This example is available for reference to similar projects.

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STUDY OF SHEAR CREEP CHARACTERISTICS OF GREENSCHIST DISCONTINUITIES

SHEN Mingrong1，2，ZHANG Qingzhao2

2010, 29 (06): -1155 doi:
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Based on the characteristics of high depth and high stress in diversion tunnel of Jinping II hydropower station，the gray marble containing greenschist discontinuities from the slope and underground rock cavern is selected as research object；and the shear creep test is carried out for the samples with greenschist discontinuities. The test results are analyzed and the rheological behaviors of greenschist discontinuities are discussed. The creep characteristics and mechanical laws of rock mass discontinuity under different normal stresses are studied；and the creep rate characteristics of discontinuities are investigated. Results show that the creep curves have obvious three stages. On this basis，the improved Burger model is selected for the analysis of creep test results；and a discussion on modified Burger model for describing the shear creep characteristics of discontinuities is presented.

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EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF GYPSUM SATURATED IN BRINE

LIANG Weiguo，ZHANG Chuanda，GAO Hongbo，XU Suguo，YANG Xiaoqin

2010, 29 (06): -1163 doi:
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[PDF 329 KB] (1382)

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In the laboratory，uniaxial compression experiments are carried out under monotone and cyclic loading states with gypsum specimens in dry，saturated and half-saturated states. The test results demonstrate that the peak strength of dry gypsum by cyclic loading is 12.3 MPa，strength decreasing of 15.8% at 14.6 MPa under monotone uniaxial compression. The strain of the specimens at peak strength also decreases from 0.39% under cyclic loading to 0.19% of monotone uniaxial compression. Both the peak strength and the corresponding strain of gypsum decrease when loaded in cyclic state. However，the elastic modulus keeps unchanged. Compared with that of dry specimens，the peak strength of the wet gypsum specimens，either saturated or half-saturated in brine，does not decrease. It demonstrates that brine corrosion effect on gypsum strength is minor. However，the elastic modulus decreases from 6.6 GPa of dry state to 4.5 and 2.8 GPa of saturated and half-saturated states，respectively. It means that the deformation ability of gypsum is enhanced greatly after saturated in brine. Due to tightness in structure and low porosity of gypsum，chemical solution can not easily immerge into it. In addition，the brine solution is acidic in chemical component in the test and no chemical reactions can happen with gypsum even less brine moving inside. Consequently，the strength of gypsum can keep undamaged when saturated in brine. However，the deformation ability will be enhanced and a softening trend will emerge because of long-term soakage in brine. It is suggested that this mechanical property should be taken into account in construction and operation of oil and gas storage in bedded salt deposit containing thick gypsum interlayers.

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OVERTURNING STABILITY ANALYSIS OF ROCK SLOPE UNDER EXTREME SNOW DISASTERS CONDITIONS

ZHANG Yongxing1，2，SONG Xicheng1，WANG Guilin1，2

2010, 29 (06): -1171 doi:
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Firstly，the calculation formula for coefficient of overturning stability under the condition of extreme snow disaster is derived. Secondly，the regularity for coefficient of overturning stability with the changes of frost depth is revealed，which considers different slope angles，slope heights，dip angles of the slide plane，and depths of tension fractures for saturated rock slope. Diagrams which express the relationship between the coefficients of overturning stability and geometric factors are drawn when the rock slope is saturated. Then the variation of the coefficient of overturning stability for unsaturated rock slope is revealed，which also considers different geometric factors such as frost depth，slope angle，slope height，dip angle of the slide plane，and the water-emerging depth of tension fractures and so on. The conclusions can be drawn that the coefficient of overturn stability of rock slope changes significantly when considering the impact of extreme snow disaster. The bigger the frost depth，dip angle of the slide plane，the depth of tension fractures and slope height are，the smaller the coefficient of overturning stability is. The smaller the slope angle is，the smaller the coefficient of overturning stability is. The frost depth is one of the main factors which impact the overturning stability of rock slopes.

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EXPERIMENTAL TEST AND FRACTURE DAMAGE MECHANICAL CHARACTERISTICS OF BRITTLE ROCK UNDER UNIAXIAL CYCLIC LOADING AND UNLOADING CONDITIONS

ZHOU Jiawen，YANG Xingguo，FU Wenxi，XU Jin，LI Hongtao，ZHOU Hongwei，LIU Jianfeng

2010, 29 (06): -1183 doi:
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[PDF 319 KB] (1971)

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Based on the uniaxial cyclic loading and unloading test results of the Xiangjiaba sandstone，combined with the mesomechanical analysis of the internal microcracks in rock，the characteristics of stress-strain curves，peak strength，fracture damage mechanical characteristics of brittle rock unloading condition are researched. A computational method for rock damage variable is presented based on the stress-strain curve；the acoustic emission test result shows that this method is reasonable. The experimental test results show that，the peak-strength of sandstone under cyclic loading and unloading conditions is less than that of the uniaxial compressive strength，which is influenced by lots of factors. Elastic constants of computation results show that，the Poisson's ratio is gradually increasing during the cyclic loading and unloading process，while the elastic modulus is increased evidently in the first cyclic loading and unloading process，and then decreases slowly. In the process of cyclic loading and unloading for brittle rock，rock damage will increase gradually，and rock damage will rapidly increase when the microcracks propagation runs into the unstable phase；the rock macromechanical characteristics depend on the mesomechanics response of microcracks.

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NONLINEAR CREEP DAMAGE MODEL OF ENGINEERED ROCK
AND ITS APPLICATION

WU Guojun，CHEN Weizhong，CAO Junjie，TAN Xianjun

2010, 29 (06): -1191 doi:
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[PDF 1243 KB] (1580)

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Aiming at the shortcomings of component creep models，such as linear constitutive relationships，converging easily and entering accelerative stage too quickly，a new empirical nonlinear damage viscoelasto- plastic model which can reflect rock creep damage effect is put forward based on creep experiments. The model is verified to be correct by means of simulating a uniaxial compression numerical test which makes use of user¢s subroutines of ABAQUS. Finally，the model is applied to simulating the whole construction process of Dagangshan underground powerhouse under two working conditions，with and without considering damage factor，respectively. By comparing the results two working conditions，it is demonstrated that the results of considering damage factor working condition can bring forward more reasonable reference than that of without considering damage factor，especially in plastic zone，damage degree and deformation of rock mass.

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RESEARCH ON COAL PERMEABILITY EVOLUTION LAWS AND MULTI-SCALE EFFECT

LI Hongyan1，2，QI Qingxin1，LIANG Bing3，PENG Yongwei1，2，DENG Zhigang1，2，LI Chunrui1，2

2010, 29 (06): -1197 doi:
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The combination method of the laboratory experiment and field experiment is used. Coal permeability stress sensitivity experiment，complete stress-strain permeability measurement experiment，and the permeability measurement field experiment of mining coal are carried out to study the coal permeability evolution laws. The results of all the experiments are compared to find the difference and the relation among the three experiments. The stress intensity and loading-unloading history are the main influencing factors for the permeability evolution of coal. The permeability value is magnitudes 2–4 lower for the laboratory scale against the engineering scale. The scope of application of the three experimental methods is summarized so as to provide reliable support for the correct choice of coal permeability.

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CHARACTERIZATION OF DEFORMATION AND FRACTURE FOR ROCK MASS IN UNDERGROUND POWERHOUSE OF JINPING I HYDROPOWER STATION

WEI Jinbing1，DENG Jianhui1，WANG Dikai2，CAI Dewen2，HU Jianzhong2

2010, 29 (06): -1205 doi:
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[PDF 448 KB] (1152)

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The deformation and fracture characteristics of the surrounding rock mass are analyzed according to the geological conditions，monitoring and geophysical prospecting data，and construction process. The analytical results indicate that under the condition of high in-situ stresses and low strength-to-stress ratio，the deformation of surrounding rock mass is no longer controlled by the opening displacement of major faults，but by the unloading relaxation of the surrounding rock. The deformation amount and relaxation depth are relatively larger. The main relaxation depth of side wall is between 12 and 15 m，some are even greater than 15 m. The deformation amount increases with the extending of relaxation depth，while the relaxation depth extends with the excavation construction and the passage of time. Therefore the time effect of rock mass deformation should be considered as the gradual expansion of rock failure，which is different from normal rheological concept. The cracks at the downstream hance of main powerhouse and main transformer house are caused by the unloading splitting and buckling failure of layered rock mass under high stress；and this rock mass failure leads to the increasing of deformation at the downstream hance. While the crack type at the upstream side wall of transformer house is of tensile failure of shotcrete layer，its causes are the compression fracture of rock mass because of stress focus during the excavation of busbars tunnels. Under the condition of high in-situ stresses，whether the scheme as first total excavation of main powerhouse and main transformer house，then busbars tunnels excavation that can be accepted in the construction of underground cavern group is a significant issue.

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ANALYSIS OF LANDSLIDE INFLUENTIAL FACTORS AND COUPLING INTENSITY BASED ON THIRD THEORY OF QUANTIFICATION

LI Junxia1，WANG Changming1，WANG Gangcheng1，LIU Wei2

2010, 29 (06): -1213 doi:
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[PDF 315 KB] (1221)

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Geographic information system(GIS) and the third theory of quantification are used to analyze the influential factors of landslide development and the coupling intensity of the factors，and to discuss the geological environment factors of landslide development in the study area of Langxian in Tibet. The results show that rainfall，lithology，average slope and the distance from the slope forward to the river are the leading factors of landslide development. The height of slope，outside force，human engineering activities and seismic intensity play important roles in landslide. The land use affects the landslide slightly. Average annual rainfall，the landslide lithology with residual slope wash and sericite phyllite，the distance within 200 m from the slope forward to the river，the average slope of 35°–45°，seismic intensity and the height of slope higher than 200 m can be taken as the controlling factors which can provide reference for the assessment of landslide. The coupling intensity of influential factors of 29 landslides in the study area can be divided into 3 levels as strong，medium and weak which are bounded by ±0.01. The higher the coupling intensity is，the higher the risk of landslide and the degree of landslide development are. The above-mentioned conclusions are important to the disaster prevention and mitigation. The analytical results have been verified by site investigation which certifies the feasibility and the adaptation of third theory of quantification and they can provide new idea for analyzing the factors of landslides.

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STUDY OF ACTIVITY INTENSITY OF DEBRIS FLOW BASED ON THREE-DIMENSIONAL DRAINAGE SYSTEM MODEL AND FRACTAL THEORY

ZHANG Chen1，CHEN Jianping1，WANG Qing1，ZHANG Wen1，QUE Jinsheng2

2010, 29 (06): -1221 doi:
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[PDF 417 KB] (1165)

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The developmental state and activity level of debris flow can be reflected by its drainage system pattern. A quantitative description of drainage system is very important to the study of debris flow activity intensity. The three-dimensional data of debris flow are extracted by a computer program based on Matlab software which is written according to fractal theory to calculate the fractal dimensions of three-dimensional drainage system along Jinsha River. The quantitative indicators of drainage system were determined to analyze the debris flow in the study area，considering the amount of loose material and length ratio of sediment supply segment. The law between the factors and the activity intensity is summarized. With the activity intensity of debris flow increasing，the index values of factors also increase. What is more，when the activity intensities are 15 and 21，respectively，the curves of the relationships between factors and activity intensities all bend sharply which prove that there is an internal link in the amount of loose material，length ratio of sediment supply segment and fractal dimensions. New judgments to define the activity intensity of debris flow are proposed to supply new method and evidence for debris flow hazard assessment. The typical debris flows along Jinsha River are studied by above-mentioned method. From the results，it can be seen that the activity intensity of Aiba groove is the largest which proves that the activity intensities of debris flows determined by new judgments are consistent with the reality. The new judgments are scientific and rational.

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EXPERIMENTAL STUDY OF SEEPAGE CHARACTERISTICS OF TINY-PARTICLE CLAY

LIANG Jianwei1，2，FANG Yingguang1，2

2010, 29 (06): -1230 doi:
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[PDF 404 KB] (1287)

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For further study of the seepage characteristics of tiny-particle clay，variable height and constant-head seepage apparatus are adopted to conduct experiments on tiny-particle artificial soil and natural soft soil from Nansha of Guangzhou with pore water of different ion concentrations and distilled water. The test results show two important characteristics of soil seepage. First，the permeability coefficient increases with the increase of ion concentration of pore water. Second，the permeability coefficients of the samples with pore water of different ion concentrations show abnormal increase or decrease trends with the reduction of hydraulic gradient. The analyses of results and mechanism suggest that the micro-electric field effect caused by surface charge on clay particles and microscale effect of seepage pore are the main reasons that influence the seepage characteristics of tiny-particle clay；and the particle specific surface area，surface potential，ion concentration of pore water and pore scale are important influence parameters that lead to the change of seepage characteristics. Micro-electric field effect and microscale effect are adopted to explain the two seepage characteristics mentioned above. However，more experiments and research are needed to study the real causes of the abnormal soil seepage phenomenon.

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EXPERIMENTAL RESEARCH ON INFLUENCE OF PARTICLE DIAMETER ON COAL AND GAS OUTBURST

XU Jiang，LIU Dong，PENG Shoujian，WU Xin，LU Qi

2010, 29 (06): -1237 doi:
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[PDF 448 KB] (1145)

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The coal and gas outburst，which threatens coal mine safety production，is an extremely complex geological phenomenon that occurs in the coal mine production. Briquette body of different particle size serves as the object of study，a series of experiments are designed by using the polarization analysis software and strain control triaxial compression apparatus；and the purpose of the study is to get physico-mechanical properties of briquette body with different particle sizes. Further more，coal and gas outburst simulation experiment device is utilized to simulate coal and gas outburst process under the same above-mentioned conditions for the sake of the influence law of different particle diameters on coal and gas outburst. The results of experiment demonstrate that coal particle size has an obvious effect on physico-mechanical properties of briquette body as well as characteristics of coal and gas outburst. Some concrete manifestations are the smaller the particle size of the briquette body is，the bigger the fractal dimension of pore structure of coal sample is and the better its adsorption property on methane gas is. Meanwhile，the smaller particle size will make the higher strength of resistance to destruction of briquette body. The results also show that the briquette body with smaller particle size offers higher intensity of coal and gas outburst and exhibits more quantity of methane adsorption of coal before outburst；whereas，its crushing effect is proved to be less obvious than that of the briquette body with larger particles.

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FRACTURING BEHAVIOR STUDY OF BIAXIAL COMPRESSION OF ROCK SUBJECTED TO DYNAMIC DISTURBANCE LOAD

MA Chunde，LI Xibing，CHEN Feng，XU Jicheng

2010, 29 (06): -1244 doi:
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[PDF 437 KB] (1052)

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The influence of stress amplitudes of cyclic dynamic disturbance on the fracturing behavior and other dynamic response of rock is investigated. Red sandstone specimens used in the testing are subjected to a preloaded biaxial compression load which reaches rock yield strength and then coupled with a cyclic fatigue loading. Sine wave cyclic loads with of frequency 2 Hz and five different stress amplitudes of 6，10，14，18 and 22 MPa are adopted as dynamic disturbance. The obtained results show that fatigue life of specimen is usually no more than several decadal cycles under present loading conditions；the fatigue life of rock，when the preloaded biaxial compression load is beyond its yield strength，is much shorter than that when the preloaded biaxial compression load is within the elastic limit. Large disperse of fatigue life can be found in the tests，even for the cyclic loads with the same stress amplitudes. However，the total axial deformation at failure point for the fatigue loads with the same stress amplitude is almost the same. It is worthy noting that the axial deformation will decrease with the increasing of stress amplitude. For the specimen with a relatively longer fatigue life，their characteristic curves of axial deformation versus fatigue cyclic times can be divided into three stages and they are quite similar to that of rock creep curves. The accumulative deformation of three stages will lead to the final failure of the rock specimen，and the proportion of each stage in total deformation，failure mode and size distribution of rock fragments are all greatly affected by the stress amplitudes.

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EXPERIMENTAL STUDY OF THERMOPHYSICO-MECHANICAL PROPERTY OF DRILLING SURROUNDING ROCK IN GRANITE UNDER HIGH TEMPERATURE AND HIGH PRESSURE

XI Baoping1，2，ZHAO Yangsheng1，2，3

2010, 29 (06): -1253 doi:
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[PDF 347 KB] (1195)

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Utilizing the 20 MN servo-controlled triaxial rock testing machine under high temperature and high pressure developed by the authors，the intensive experimental study of the thermo-elastic deformation of large size granite sample of f200 mm×400 mm with f40 mm borehole under triaxial hydrostatic pressure in depth of 6 000 m and temperatures within 600 ℃ is carried out. Based on the results of thermo-elastic deformation experiments under high temperature and pressure inversion to calculate the thermophysical and mechanical parameters，a careful analysis of the thermophysical and mechanical parameters of drilling surrounding rock in granite is carrial. The results show that：(1) The thermal deformation of the drilling surrounding rock in granite under high temperature and high pressure at different depths can be divided into three stages：low-temperature thermal deformation of a weak phase，the rapid growth stage heat distortion temperature and high-temperature thermal deformation of a smooth phase；and the depth (pressure) is significant impact on the thermal deformation of drilling surrounding rock in granite. (2) The failure mode of drilling surrounding rock in granite under high temperature and high pressure is of cutting damage，granite body in the experience of 500 ℃–600 ℃ high temperature continued to show a brittle emerged in characteristics. And rock mass destruction conditions are triaxial hydrostatic pressure in depth of about 6 000 m and temperature of 600 ℃. (3) The elastic modulus of drilling surrounding rock in granite under high temperature with a negative temperature decreases exponentially. (4) The Poisson's ratio of drilling surrounding rock in granite under high temperature with increasing temperature increases with the overall trend of its variation. (5) The thermal coefficients of expansion about surrounding rock of drilling at different hydrostatic pressures in depth and high temperature are different；the depth has a significant impact on the thermal coefficient of expansion. This experimental study can provide a theoretical basis and technical reserves for hot dry rock of deep drilling and maintenance of stability of drilling surrounding rock.

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STUDY OF METHOD OF EARTHQUKAE INPUT IN ASEISMIC ANALYSIS FOR UNDERGROUND ENGINEERING

HUANG Sheng1，CHEN Weizhong1，WU Guojun1，GUO Xiaohong2，QIAO Chunjiang2

2010, 29 (06): -1262 doi:
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[PDF 536 KB] (1661)

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A new earthquake input method based on infinite element dynamic artificial boundary is proposed. In this new method，radiation damping of the strata and reflection，scattering of the seismic wave in the strata are both considered；and equivalent earthquake load formulae in different boundary surfaces for seismic waves vertically incident from the bottom of computational domain are deduced by using the wave field separation method. Meanwhile，a numerical example is given to verify the validity and accuracy of the method. The results show that the distortional disturbance appears in the result adopting fixed boundary，whereas the results using the method proposed tally with the results using analytical method well so as to prove the effectiveness of the presented method. At last，the new earthquake input method is applied to the three-dimensional aseismic analysis of Galongla tunnel，and some meaningful conclusions are drawn.

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GEOTECHNICAL ENGINEERING RELIABILITY ANALYSIS METHOD
BASED ON RESPONSE SURFACE APPROACH AND IMPORTANCE SAMPLING

CHENG Ye1，2，ZHOU Cuiying1，2，WEN Jianhua1，2，HUANG Linchong1，2

2010, 29 (06): -1269 doi:
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[PDF 287 KB] (1560)

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The geotechnical engineering reliability is often analyzed by the response surface approach as its performance function of strong nonlinearity and it is difficult to explicitly express. But the result obtained by this approach is geometric reliability value. The substance and difference between geometric reliability value and ecumenical reliability value are clarified. It is pointed out that there is exiting error to substitute geometric reliability value for ecumenical reliability value to the strong nonlinear performance function problems in geotechnical engineering and it needs to be improved. Based on the checking points and its region response surface which worked out by response surface approach and importance sampling in V-space，the geotechnical engineering reliability value is worked out by counterchanging the original random variable space to independent random variable in V-space using Rosenblatt transformation and linear orthogonal transformation. The comparative analysis of several numerical examples and practical engineering shows that the approach proposed is feasible，effective with high precision and suitable for complex geotechnical engineering reliability analysis of strong nonlinear performance function.

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IN-SITU MONITORING ANALYSIS OF RETAINING STRUCTURES OF SMW PILES PLUS STEEL SUPPORT IN DEEP FOUNDATION PIT OF A RIVER-CROSSING TUNNEL

ZHANG Zhongmiao1，2，ZHAO Yubo1，2，WU Shiming3，WANG Bo3

2010, 29 (06): -1278 doi:
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The pit at the north side of the Hangzhou Qingchun Road river-crossing tunnel，which is the first one that crossed beneath the famous Qiantang River，is typical silt-based pit，with the maximum excavation depth of 16 m. In this project，retaining structures of steel supports with SMW(soil mixing wall) method are mainly applied，of which the longest piles are up to 27 m. According to the analysis of on-site monitoring data，it could be obtained that：(1) the maximum horizontal displacement of piles is closely related to the excavation depth and time，and the set up of piles and the internal structures played a good role in restraining the piles' displacement；and (2) changes of external conditions such as temperature，rainfall，etc. also have considerable influence on axial force. In addition，the removal of steel support of adjacent pit would also impact axial force significantly. The measured values of steel support axial force are much smaller than the design values，so it is necessary to optimize the preliminary design. The changes in effective stresses resulted from dewatering and seepage are the main factors inducing settlement of ground surface，and at the same time，the construction of adjacent pit has a certain impact on surface subsidence. The variation of groundwater levels could reflect the watertight effect of the retaining structures，which could be used as an important indicator to find out whether there is water leakage. For silt-based pit within excavation depth，it is significant to maintain the pit safety by effectively controlling the changes of water around the pit.

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SIMPLIFIED CALCULATION AND ANALYSIS OF LOAD TRANSFER BEHAVIOR FOR SINGLE JPP

REN Lianwei，LIU Xiliang，WANG Guangyong

2010, 29 (06): -1287 doi:
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Jet grouting(JG) soil-cement-pile strengthened pile(JPP) is a new kind of composite pile composed of high pressure jet grouting pile and prestressed core pile. JPP has different combination forms depending on soil conditions as well as the bearing capacity requirements. Considering combination features of JPP，a perfect elasticplastic model is used to simulate nonlinear of soil around pile，and an elastic model is used to simulate load transfer behavior of interface between soil-cement and core pile，and a double broken line function is used to simulate hardening characteristics of soil under pile tip. Based on the load transfer method，taking into account interface friction betweent soil-cement and core pile，and interface friction between soil-cement or core pile and soil around pile，a simplified calculation method is presented to analyze load transfer of different combinations of JPPs. The feasibility and reliability of the method are verified by the model test results. Load transfer mechanism of JPP is analyzed by the proposed simplified calculation method；and the main factors of JPP load transfer，different combinations，different soil-cement thicknesses，different elastic moduli of soil-cement，and different stiffness coefficient ratios，are analyzed comparatively. The calculation results show that，in view of the bearing capacity，settlement control and costs，the sub-combination JPP has better bearing capacity；increaseing soil-cement thickness can effectively improve the bearing capacity of JPP；the deformation of JPP is controlled by high-strength core pile；elastic moduli of soil-cement are less affected on JPP deformation.

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CT-TRIAXIAL TEST FOR COLLAPSABILITY OF UNDISTURBED
Q3 LOESS

LI Jiagui，CHEN Zhenghan，HUANG Xuefeng

2010, 29 (06): -1296 doi:
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The collapsability test for undisturbed Q3 loess under suction control is studied with stress controlled triaxial apparatus. 15 CT-triaxial tests are performed，including double-triaxial unloading confining pressure tests and isotropic compression tests. During the tests，computerized tomography(CT) is employed. Using the CT data，the effect of the Q3 loess¢s structure is analyzed. The results show that，for the double triaxial collapsible tests，collapsible deformation increases with net confining pressure increasing，including the volumetric strain，axial strain and deviator strain. For the isotropic compression collapse tests，the relationship between water content and the CT data is linear before the specimen is saturated. The CT data increasing velocity will slow down with high enough saturation. For the isotropic compression collapse tests，if the specimen has the same suction，the high net confining pressure versus big volumetric strain，and the value of the structural evolution have the same rule，too.

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2010, 29 (06): -1299 doi:
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