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2010, 29 (1): 0-0 doi:

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DEVELOPMENT OF LARGE-SCALE GEOMECHANICAL MODEL TEST SYSTEM UNDER TRUE TRIAXIAL LOADING AND ITS APPLICATIONS

ZHU Weishen，ZHANG Qianbing，LI Yong，SUN Linfeng，ZHANG Lei，ZHENG Wenhua

2010, 29 (1): 1-7 doi:

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To study the stability analysis of underground cavern groups at great depth and under high geostress field，a large-scale geomechanical model test system under true triaxial loading is newly developed. The model test system mainly consists of a steel structural frame and a hydraulic loading control system，which adopts active loading on six surfaces of the model block with a true triaxial stress considering trapezoidal loading steps in two horizontal directions. Newly-developed combinational ball-type sliding walls are installed on each side of the major loading surfaces，which can significantly reduce friction. Based on the system，a large-scale geomechanical model test for an underground cavern group is carried out. Major innovations and improvements have been made in terms of experimental techniques and advanced measurement methods/techniques. Precast blocks of analog materials are piled up and bonded to enhance the consistent mechanical properties of the whole model system. Digital photogrammetric technique，fiber Bragg grating(FBG) technology-based displacement sensing bars，and a newly developed mini-extensometers are employed to measure the deformation of surrounding rock mass. A new unique technique of grouted anchor and prestressed cables are conducted. The development process and phenomenon of fracture patterns of rock surrounding are observed and analyzed during excavating and overloading tests. The test results are compared with those of numerical simulations. These achieved results would provide certain guiding significance for study of similar practical engineering projects.

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THREE-DIMENSIONAL VECTOR SUM METHOD EMPLOYED IN SLOPE AND DAM FOUNDATION STABILITY ANALYSES AND ITS APPLICATIONS TO PRACTICAL ENGINEERING

GUO Mingwei，GE Xiurun，LI Chunguang，WANG Shuilin，DENG Qin

2010, 29 (1): 8-20 doi:

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Based on two-dimensional vector sum method(VSM)，the determination of the whole sliding direction of slope with 3D vector sum method is put forward；and initial sliding direction can be obtained by current stress state. Then the whole sliding direction and the factor of safety with this method is solved. This method is used in several 3D examples；and the results demonstrate that the factors of safety are in good agreement with that of the limit equilibrium method，and the results are not sensitive to element sizes of the slip surfaces. Finally，this new method is applied to the foundation stability analysis of dam section No.26 in the Three Gorges Project. Four slip paths designated through detailed investigation are analyzed with the plane vector sum method and the 3D vector sum method. The calculating results with the 3D vector sum method show that the factors of safety with the 3D vector sum method are larger than that with the 2D method；and the factor of safety of the deep slip paths is larger than the shallow ones，greater than 1.0. Therefore，the dam section No.26 under the current loads in the Three Gorges Project is safe. This new method is clear in physics and mechanics，and only one time elastic calculation or elastoplastic calculation，and the 3D factor of safety of potential sliding mass can be achieved without too many artificial assumptions. The process of this new analysis method is simple and easy to use in practical engineering projects.

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EXPERIMENTAL RESEARCH ON AFFECTION LAWS OF UNLOADING RATES ON MECHANICAL PROPERTIES OF JINPING MARBLE UNDER HIGH GEOSTRESS

HUANG Runqiu1，HUANG Da1，2

2010, 29 (1): 21-33 doi:

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The mechanical properties of rocks are obviously affected by initial stress state and unloading rates that are caused by excavation. Based on triaxial unloading and scanning electron microscopy(SEM) analysis，the deformation，breakage，and strength features of marble samples of the Jinping First Hydropower Station under different unloading rates and geostress conditions are studied. With unloading rates vu and initial confining pressure increasing，the brittle rupture and tensile characteristics of rock are more obvious. There are annular tensile cracks in secondary unloading direction when the rock samples are unloaded in two directions；and the meso-shapes of the tensile fracture surface under SEM consequently are presented with branch-tension，and multilayer biscuit-lancinated and slippery plane-ejected shapes. The axial strain compression increment is gradually reduced，but the confining expansion stress is increased during the process of unloading. The influence of unloading rate vu on deformation modulus E is different at the different deformation stages during process of unloading. The deformation modulus E is gradually increased before peak strength，but it gradually increases firstly and rapidly decreases afterward with vu enhanced. The Poisson¢s ratio is gradually increased during process of unloading，and it is more distinct with vu and enhancing，especially after peak strength. Relative to data of traditional triaxial loading test，the rock cohesion c is remarkably reduced but inner friction angle is a little increased under unloading test. The faster the vu is，the more c is reduced，and the less the increases.

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BOUNDARY ELEMENT ANALYSIS OF CRACK PROPAGATION PATHS IN ANISOTROPIC ROCK

KE Chienchung1，HSU Shihmeng1，CHEN Chaoshi2，CHI Shuyeong1

2010, 29 (1): 34-42 doi:

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The development of a unified numerical framework based on the boundary element method(BEM) for modeling crack propagation behavior in anisotropic rock is presented. The BEM formulation combined with the maximum circumferential stress criterion is used to predict the crack initiation angles and to simulate the crack propagation paths. To demonstrate the proposed BEM procedure to predict crack propagation in anisotropic rock，the propagation path in cracked straight-through Brazilian disc(CSTBD) specimen is numerically predicted and compared with the actual laboratory observations. Good agreement is found between the two approaches. It is therefore concluded that the proposed BEM procedure can accurately simulate the process of crack propagation for anisotropic rock.

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TEST STUDY OF STRAIN RATE EFFECTS ON MECHANICAL PERFORMANCES OF SALT ROCK

LIANG Weiguo，XU Suguo，MO Jiang，WU Di，ZHANG Chuanda

2010, 29 (1): 43-50 doi:

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Halite and thenardite，which are the main constitutes in bedded salt rock deposits，are chosen as the experimental samples. The uniaxial compression behaviors of the samples are recorded and analyzed with loading strain rates increasing from 10－5 s－1 to 10－3 s－1. It is found that the ultimate strength and the elastic modulus of the two lithologies hardly change with loading strain rate in the test scale. The uniaxial compressive strength of thenardite is larger than that of halite when they are loaded with the same strain rate. Opposite to the trend of the elastic modulus，the Poisson¢s ratios of the two lithologies decrease with strain rate for the halite and thenardite specimens. Similarly，the strains of the test specimens at the point of peak strength decrease with loading strain rate. A logarithmic relationship between deformation modulus and loading strain rate is also established with the test results. During the experiments，it is found that all the halite specimens are broken in the type of brittle tensile fracture around the specimen column face，while single shear failure along an inclined plane in the specimens is the characteristic of thenardite breakage. The damage characteristics of the halite and thenardite hardly change with the loading strain rate. Stress ratio at the point of the onset of volumetric increase to the ultimate compressive strength of the tested specimens is also calculated and analyzed；and an average value of 87.3%–91.0% of the ratio is recorded，which is obviously larger than those of general rocks. The large ratio demonstrates that salt rocks possess large deformation capacity before volumetric increase occurs during compression. It is concluded that a salt cavern wall of strain rate between 10－5–10－3 s－1 during salt cavern storage operations can guarantee the safety and stability of the cavern，while other operational demands are satisfied.

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MODEL TEST RESEARCH ON ANTI-EXPLOSION CAPACITY OF UNDERGROUND OPENINGS WITH END WAVE-DECAY BY HOLES AND REINFORCED BY DENSE ROCK BOLTS

WANG Guangyong1，2，GU Jincai3，CHEN Anmin3，XU Jingmao3，ZHANG Xiangyang3

2010, 29 (1): 51-58 doi:

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Based on anti-explosion model test device，the anti-explosion capacity of underground openings，which are reinforced by rock bolts with end wave-decay by holes and reinforced by dense rock bolts，is studied under explosive stress waves produced by focus charging. By comparing anti-explosion capacities of three underground openings，the differences of vertical stresses，relative roof-to-floor displacements of three underground openings，surface strains of three underground openings，accelerations of roof and floor of three underground openings and damage shapes of three underground openings are analyzed. The results show that under explosive stress waves，the relative roof-to-floor displacements and maximum surface strains of underground openings are reduced without severe damage；and the acceleration of roof is also decreased to certain degree. It is also shown that the fractures of underground openings are distributed at both sides of arch foots，but the fractures on the arches of two underground openings are fewer；and their surrounding rocks are lightly damaged. These conditions indicate that the underground openings with end wave-decay by holes and reinforced by dense rock bolts can increase their anti-explosion capacities.

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MESO-DAMAGE MECHANICAL ANALYTICAL METHOD FOR JOINTED SLOPE STABILITY OF HUNAN QISHAN RENRUI TEMPLE

BI Zhongwei1，2，ZHANG Ming1，DUAN Zhongyuan2，JIN Feng1，DING Dexin2

2010, 29 (1): 59-64 doi:

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Geological investigation has been carried out for the rock slopes of Hunan Renrui temple. The slope structural planes are mainly with X joints，and one group trend is 170°–265° and the other group is 105°–125°. Both the joints are with steep dip angle，and are general in the interval of 50°–90°. Mechanical parameters of rock block and joint plane are determined by six groups of tests. According to meso-damage mechanical theory，jointed rock is anisotropic material composed of rock blocks and microcracks；and the slip crack criterion of the microcracks is established by representative volume element(RVE). Stability analysis is conducted on rock slope based on the established calculation model with a slope angle of 60° and two joint inclinations of 52.5° and 90.0° by corresponding software. The plastic penetration area of rock slope is obtained by using gradual constraint removal to conduct excavation simulation. Compared with the actual landslide，the simulation result is good，which proves that the microcrack is the primary factor to control the rock slope failure；and it is very valuable for understanding the failure mechanism of the jointed slope. Simultaneously，this method can provide references to the forecast of the shape and position of jointed slope failure plane and stability analysis of complex slopes.

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EXPERIMENTAL RESEARCH ON DYNAMIC FAILURE MECHANISM OF LARGE-SCALE TALUS SLOPE

ZHANG Yuancai，HUANG Runqiu，FU Ronghua，PEI Xiangjun

2010, 29 (1): 65-72 doi:

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A large number of experimental results indicate that the content of the fine particles has fairly influence on the shear strength of granule. With the increase of the content of fine particles，granular shear strength gradually declines. Combined with in-situ investigation of the talus slope located in Tianshan highway and indoor physical simulation experiment results，it is found that fine granular layer plays controlling role in the large-scale failure process，and a three layers granular structural mode which is composed of loose granular layer，fine granular layer and frictional layer is proposed. Moreover，a new large-scale failure model，which takes on a whole failure characteristic is constructed. The kinetic mechanism of one slump is as follows：as a result of fine particle layer material，the shear strength is relatively low，the talus slope will accumulate large-scale slump along the fine particle layer，which is similar to the instability characteristics of landslide under the strong disturbance of various dynamic loads.

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MULTI-BLOCK UPPER BOUND METHOD FOR BASAL HEAVE STABILITY ANALYSIS OF BRACED EXCAVATIONS IN CLAY

QIN Huilai1，2，3，HUANG Maosong1，2，MA Shaokun4

2010, 29 (1): 73-81 doi:

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Multi-block upper bound method is employed to analyze basal heave stability of braced excavations in undrained clay. For this purpose，the kinematically admissible multi-block failure mechanism is proposed firstly. Based on the proposed multi-block failure mechanism，the energy equation of the upper bound method is deduced again. To examine the application of the multi-block upper bound method in basal heave stability analysis，a lot of comparisons have been made with other existent solutions according to some true cases and the influential factors on the basal heave stability. These factors include the width of the foundation pit，the embedment of the hard stratum，the friction between the wall and soil，the insert depth of the wall and the strength nonhomogeneity. The existent solutions adopted include the upper bound solutions obtained by Terzaghi¢s mode and Prandtl¢s mode，and the Faheem¢s solutions obtained by the finite element method with strength reduction technique，and the Ukritchon¢s solutions obtained by the limit analysis finite element method. According to the comparisons，it can be found that the multi-block upper bound method gives the optimum solutions among the upper bound methods. It can also be found that the solutions given by the multi-block upper bound method are close to those obtained by the upper bound finite element method. It should be noted that the multi-block upper bound method is easy to program and needs less workload. Based on the calculations and comparisons，it may be found that the application of proposed multi-block upper bound method is successful.

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RESEARCH ON RELATIONSHIP BETWEEN LANDSLIDES AND PEAK GROUND ACCELERATIONS INDUCED BY WENCHUAN EARTHQUAKE

WANG Xiuying1，NIE Gaozhong2，WANG Dengwei3

2010, 29 (1): 82-89 doi:

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Based on the data of strong motion records of the corresponding peak ground acceleration(PGA) and data collected from almost 3 000 landslides induced by Wenchuan earthquake，the studies of earthquake-induced landslide and PGA are carried out and some conclusions are obtained as following：(1) There is a positive correlation between PGA and earthquake-induced landslides，and the higher the PGA is，the more serious the earthquake-induced landslides hazards are. (2) A 0.2 g PGA boundary is shown in the regional scale analysis in Longmenshan area；and earthquake-induced landslides hazards are more serious in the locations where PGAs are greater than this value. (3) The lower limit of PGA which can trigger landslides is 0.05–0.07 g，and there is rarely opportunity to induce landslides when PGA is less than this threshold. (4) Different critical accelerations are presented in different strata with the variation ranging from 0.05 g to 0.15 g；and the average PGA is about 0.1 g，which shows the slopes' proneness to earthquake excitation in the disaster areas. When PGA exceeds the critical acceleration of the local site，the probability to trigger landslide will increase. Results achieved from this study are in accord with results of other researchers，which gives a good consistency when earthquake-induced landslide is measured by ground motion parameters. The relationship between PGA and earthquake-induced landslide can be used to evaluate earthquake-induced landslides hazards quickly. Moreover，it can be applied to the work of earthquake- induced landslide forecasting or zonation，in which the achievement of PGA zonation can be adopted with the practical application.

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THEORETICAL RESEARCH ON THERMAL CRACKING FRACTALS LAWS OF OIL SHALE

KANG Zhiqin，ZHAO Yangsheng，YANG Dong

2010, 29 (1): 90-96 doi:

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The oil shale thermal cracking CT images under different temperatures are considered as the analytical objects；and the basic theories of fractals to the thermal cracking procedure of oil shale are applied for the first time. The distribution laws of the thermal fissures within the range of 200 ℃–600 ℃ of oil shale square body of 7.0 mm in length are researched；and the fractals dimensions and initial distribution values of the fissures under different temperatures are obtained. The achieved results show that the thermal fissures have strong self-similarity according with fractals laws，and the values of fractal dimensions are ranged from 1.0 to 1.5. The relationship between fractals dimensions，initial distribution values and temperatures is established. With fractals theory，the thermal cracking procedure of the oil shale，distribution state and complexity of the fissures are analyzed. The derived conclusions for analyzing the evolution of micro-seepage channels in the oil shale pyrolysis have important references；and at the same time，a new method and certain ideas for thermal cracking procedure of other rocks with fractals theory are offered.

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BACK ANALYSIS OF STRENGTH PARAMETERS FOR SURROUNDING ROCKS OF TUNNEL AND ITS VERIFICATION

CHEN Fangfang1，LI Ning2，ZHANG Zhiqiang2

2010, 29 (1): 97-103 doi:

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The uniqueness of strength parameters is discussed in detail，and three aspects of this multi-value problem are discussed as following：(1) the in-situ displacement results are simultaneously concerned with elastic and strength parameters；(2) the stress-strain relationship shows multi-value under plastic softening condition；and (3) strength parameters are mutually independent，and their different combinations can make certain element of the rock with the same plastic deformation. Aiming at these problems，the new approach is presented to solve the uniqueness of strength parameters in back-analysis by assuming that the rock is an ideal elastoplastic medium；and field measurement procedures to separate elastic and plastic displacement，and the inner action mechanism in optimization method are all considered，whereas the concept of non-conformity of plastic deformation is proposed. Moreover，the feasibility of this new method is verified. Finally，the research on reliability of strength parameters in the back-analysis is developed by numerical experiments. The results show that the accuracy and stability are all favorable，and the problem of initial value sensitivity is also solved.

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RESEARCH ON TUNNEL PHOTOGRAPHY MEASURING SYSTEM

GUO Qiang1，WANG Chuanying1，WU Lixin1，2

2010, 29 (1): 104-110 doi:

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Based on existing technology，a new survey method is proposed for the tunnel photography measuring system. To get the coordinates，the system uses cameras，coder and compass. First，the fundamental principles are introduced based on the system；and the operation process，parameter setting and structural design of this device are analyzed. Then，according to the data characters，the methods to remove the false elements and to revise the imprecise elements are given. Finally，through ray analyses，it presents the mathematical model for digital tunnel¢s creation；and the results of case study are analyzed. According to the problems of the system，it presents the target of further research and the key issues that should be solved.

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NON-CONTACT MEASUREMENT OF ROCK MASS DISCONTINUITY OCCURRENCE WITH BINOCULAR SYSTEM

ZHOU Chunlin1，ZHU Hehua1，ZHAO Wen2

2010, 29 (1): 111-117 doi:

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A modified pose acquiring method is advanced，which can realize non-contact measurement of rock mass discontinuities occurrence with following steps：(1) setting camera on the cloud platform，adjusting to let camera coordinate system and cloud platform coordinate system be coincidence and fixing them；(2) reducing the number of pose parameters with regular photographing procedure，and getting them from the occurrence of platform extended plane；and (3) translating 3D digital model of rock mass generated by binocular system from local coordinate system to world coordinate system and measuring the discontinuities occurrences. After the above-mentioned steps，propagation error caused by pose measuring error is analyzed. The suggested method is used to survey the rock mass discontinuities occurrences of slope and rock tunnel excavation face in field. Compared with traditional method，the proposed method is convenient to be used in field to achieve complete non-contact measurement with good precision，and the precision can be advanced easily. With this method，the measuring range of rock mass discontinuity occurrence is expanded，and the efficiency can be advanced；and the risk of survey crew exposing under rock mass can also be avoided.

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EXPERIMENTAL RESEARCH ON SEEPAGE LAWS OF GRANITE UNDER THERMAL CRACKING ACTION WITH 3D STRESS

ZHANG Ning1，ZHAO Yangsheng1，2，WAN Zhijun2，DONG Fuke2，FENG Zijun2

2010, 29 (1): 118-123 doi:

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By using 20 MN servo-controlled triaxial rock testing machine with high temperature and high pressure，the real-time seepage laws of 4 pieces of intact granite samples under hydrostatic pressures of 25 and 75 MPa with thermal cracking action(TCA) are researched. It is the first real-time experimental study on seepage law of granite under high temperature with three-dimensional stress. This research results are listed as follows：(1) Under three-dimensional stress，there is thermal cracking phenomenon for all granite samples. Through the seepage law of intact granite rock sample，it is found that permeability shows of exponential growth function of temperature through the process of thermal cracking. (2) The permeability of granite sample has a slow growth through initial stage of thermal cracking action，a rapid growth through late stage of TCA and up to peak value of permeability in the final with increase of temperature. (3) The permeability and its rate of granite sample have a continuous growth through whole stage of TCA with increasing temperature. (4) The ratio of peak value of permeability to its initial value is up to 93 and permeability rate is up to 3.5×10—4 mD/℃. TCA has an important role in enhancing permeability of granite. Experimental data and conclusion have an important significance for construction of exploitation of hot dry rock，secondary oil exploitation and underground coal gasification.

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EXPERIMENTAL RESEARCH ON INFLUENCES OF PHYSICAL INDICES AND MICROSTRUCTURE PARAMETERS ON STRENGTH PROPERTIES OF RED STONE FROM WESTERN HUNAN

LIN Zhihong1，XIANG Wei1，ZHANG Yunming2

2010, 29 (1): 124-133 doi:

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Some experiments are conducted including measuring basic physical indices and uniaxial compressive strength(UCS)，mineral composition，grain area ratio(GAR)，packing density(PD)，and grain contact(GC) of cretaceous red sandstone from Western Hunan by physico-mechanics tests through polarized microscope analysis，and powder X-ray diffraction analysis. The average grain diameter and cumulative relative curve of red sandstone are obtained by the grain size analysis. In order to analyze the wetting soften mechanism of sandstone，the uniaxial compressive tests of different red sandstone samples are conducted under the dry state，the nature state and the saturation state. Additionally，how the basic physical indices and microstructure parameters impact the UCS and strength reduction(SR) due to wetting is investigated. Experimental results indicate that the UCS shows a negative exponential relationship with porosity and saturated water adsorption，but a positive exponential relationship with dry density，and a positive linear relationship with GAR，PD，and GC. However，the average grain diameter has no obvious influence on the UCS of red sandstone. When the clay content is higher than 25%，the UCS and SR decrease with the increase of the clay content. Among multifactorial regression analysis，the GAR and saturated water absorption are found to be the key parameters. As a result，the regression equations of UCS and SR due to wetting，in terms of GAR and saturated water absorption，are proposed.

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IDENTIFICATION OF WATER INRUSH PROCESS OF UNKNOWN WATER BODY USING MICROSEISMIC MONITORING TECHNIQUE

LI Tie，JI Hongguang

2010, 29 (1): 134-139 doi:

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The process of underground water accumulation and inrush based on the elastic waves generated by rock fracturing is investigated. It is found that before water inrush，there are a few distinct phenomena such as irregularity of wave velocity ratio VP/VS in the low value range，irregularity of amplitude ratio VSH /VPH in the high value range，and irregularity of major frequency in the low value range，waveform change，and quietness of microseismic activities before the fracturing of the main wall which bears water. It is proposed to use surface microseismic monitoring technique to detect unknown water body and reduce water inrush risks in deep mines. This technique can monitor and analyze the information carried in the seismic waves from either rock fracturing or blasting. The remote monitoring can be realized with the proposed method for the whole mine in real time for the monitoring is far way from the source，thus the presented method is deemed as a safe monitoring technique.

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RESEARCH ON CONSTRUCTION BEHAVIORS OF SUPPORT SYSTEM IN FOUR-LANE ULTRA LARGE-SPAN TUNNEL WITH SUPER-LARGE CROSS-SECTION

ZHOU Dingheng1，CAO Liqiao2，MA Yongfeng3，FANG Shitao4，WANG Kun5

2010, 29 (1): 140-148 doi:

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Based on the largest highway tunnel with two holes and eight lanes in China，the contents，technique and method of the stress monitoring of the support system are described. The tunnel stresses during different construction procedures are monitored and analyzed. The results show that：(1) The construction of the up-stage in the right hole，the down-stage in the left hole and the up-stage of the core soil are the main points changing the stress distribution of the support system greatly. (2) The enclosure of lining and using of the cross anchor are effective methods to improve the performance of lining and restrain the deformation of the tunnel. Therefore，it is important to construct the inverted arch and enclose the lining. The results can be adopted in the design，construction and research of similar tunnels.

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DISASTER-INDUCED MECHANISM AND ITS TREATMENT IN SHALLOW-BURIED KARST TUNNEL

KANG Yong1，YANG Chunhe1，ZHANG Peng2

2010, 29 (1): 149-154 doi:

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Aiming at disasters that happen in shallow-buried Yunwushan karst tunnel，the disaster-induced mechanism is theoretically analyzed；and also the stability of surrounding rock and its support system are evaluated through numerical simulation and in-situ monitoring. It shows that，the five key disaster-induced factors in shallow-buried Yunwushan karst tunnel are shallow-buried depth，soft cover，karst development and scale，groundwater supply，and engineering factors. The inrush of surface water into the collapsing area is a dominant factor for collapse expanding. From simulating and monitoring results of stresses and displacements，the surrounding rock and support system are proven to be stable after the implement of support enhancement；and the conclusions would be helpful for the further research related to shallow-buried karst tunnels and similar engineering practices in China or other regions with karst geological problems. It would be highly essential to take quick and appropriate measurements in the excavation of karst tunnel. What is more，the measurements must be subjected to the existing geological conditions，therefore，the frequency of karst disasters can be possibly reduced to avoid the increase of engineering costs，and to accelerate construction progress.

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STRUCTURE MODEL CONSTRUCTION OF ROCK AND SOIL AGGREGATE BASED ON DIGITAL IMAGE TECHNOLOGY AND ITS NUMERICAL SIMULATION ON MECHANICAL STRUCTURE EFFECTS

LIAO Qiulin1，2，LI Xiao1，ZHU Wancheng3，LIU Jishan4

2010, 29 (1): 155-162 doi:

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Digital image which describes the material by lattice data provides a good base to build the structure model of rock and soil aggregate(RSA) accurately. Based on the analysis of the digital imaging theory，the color contrast between rock and soil in RSA is analyzed. An auto-generating method of RSA structure model is proposed based on digital image to express spatial structure of RSA directly，quickly and accurately. Firstly，the differences of colors between roils and rock blocks are transferred into digital mode，and each pixel in the image of RSA is described by a digital eigenvalue. Then，the threshold for the digital eigenvalue that can represent rock block pixel is obtained by comparing RGB values or HIS values of RSA images. So each pixel is set different material properties according to the threshold；and the numerical structure of RSA is constructed. Besides，the numerical simulation of the structure model of RSA is carried out. It is shown that the nonuniform of rock distribution of RSA will cause an obvious mechanical structure effect on RSA under uniaxial compression.

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NUMERICAL SIMULATION AND EXPERIMENTAL OBSERVATION OF ROCK CRACKS UNDER ACTION OF SPHERICAL TOOTH HOB CUTTER

TAN Qing1，ZHANG Kui1，ZHOU Zilong2，XIA Yimin3

2010, 29 (1): 163-169 doi:

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On the basis of reasonably simplifying the practical tunnelling conditions，the mechanism is mainly studied with simulation and experiment. First，in view of the effects of initial stress distribution of the cutters on crack propagation，Hertz elastic contact theory is introduced into the simulation. A model indenting into sandstone by TBM double-edged spherical tooth hob is established by using 2D discrete finite element simulation software UDEC. Based on the original linear cutting test-bed，an observational experiment is designed，in which the phenomena of rock crushing and bursting are captured by the high speed camera；and the producing process of compacting rock core is discontinuously recorded by the general digital camera skillfully. Crack production and propagation are successfully simulated. Results show that along with the increasing penetration，the compacting rock core is formed in the bottom of teeth for large compress stress. Side cracks between the teeth gradually propagate and tend to merge because of the tensile stress. The rock fragmentation is formed when the cracks are completely intersected. The phenomenon of bursting crack of small rock mass is caused by the tensile failure. The simulation results，which are suitable for studying the rock breaking mechanism of TBM in shallow-buried strata，have a good consistency with the experimental results and in-situ data.

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EXPERIMENTAL RESEARCH ON GAS FLOW PROPERTIES OF COAL
SPECIMENS IN COMPLETE STRESS-STRAIN PROCESS

YIN Guangzhi1，2，LI Guangzhi1，2，ZHAO Hongbao3，LI Xiaoshuang1，2，JING Xiaofei1，2，JIANG Changbao1，2

2010, 29 (1): 170-175 doi:

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The tests on methane flow regularities of complete stress-strain processes of coal samples are performed by AG–250kNI rock mechanics testing system combined with self-developed coal triaxial creep and gas seepage equipment. The characteristics and principles for gas seepage in complete stress-strain processes of coal samples are obtained. The results show that the strain-gas seepage velocity curves are similar to stress-strain curves of coal samples，but hysteretic nature is found in strain-gas seepage velocity curve，which shows that the character of gas seepage is determined by damage evolution of coal sample during the process of loading. The lasting durations for both the adsorption-desorption processes and seepage processes of gas are the reason of hysteretic nature in strain-gas seepage velocity curve. The confining pressure shows hindering effect on gas seepage through the changes of internal structure caused by compression effect of confining pressure. The results of two kinds of coal samples composed of different particle sizes and powders show that the difference of gas seepage characters is large，and the coal sample composed of larger particle size and powder is more easily to be influenced by external conditions.

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MODELING TEST RESEARCH ON FAILURE MECHANISM OF SHIELD TUNNEL CROSSING GROUND FISSURE WITH 60°

HU Zhiping1，PENG Jianbing2，WANG Qiyao1，ZHU Qidong1，ZHAO Zhenrong1

2010, 29 (1): 176-183 doi:

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Based on the background of Xi¢an metro shield tunnel engineering and the geological environment of Xi¢an ground fissure，the physical modeling of segment lining structure experiment of shield tunnel crossing the ground fissure with 60° is designed according to similarity theory. The strains of segment concrete of longitudinal bolt and circumferential bolt，the contact soil pressure and peripheral soil pressure，the convergence displacement of segment lining，the soil settlement on the top of model and other macrophenomena all show that the main deformation and damage of segment lining structures of shield tunnel crossing the ground fissure with 60° are of shearing with local distortion and bending. The deformation and damage range are from 0.75D(D is the external diameter of segment ring) in the hanging side to 0.50D in the lying side. The distribution of concrete crack is near the bolt hole；and the deformation of longitudinal bolt near ground fissure is of shearing first with distortion and tension. The deformation and damage of segment ring are asymmetric and partial compression；and the dislocation of circumferential seam on the crown which is up to 30 mm(0.025D) is bigger than those of soffit and arch waist. It is difficult for the segment lining to undergo the deformation 20 cm(0.166 7D) of ground fissure；and the segment lining structure of shield tunnel is unsuitable for the geological environment with violent activity of ground fissure.

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ROTATIONAL HARDENING LAW BASED ON ELASTOVISCOPLASTIC CONSTITUTIVE MODEL

DAN Hanbo1，2，WANG Lizhong1

2010, 29 (1): 184-192 doi:

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Based on the proposed anisotropic elastoviscoplastic constitutive model for K0-consolidated clays，a suitable rotational hardening law accounting for changes in anisotropy due to viscoplastic strains is adopted. The expression of the rotation parameter b is presented by analyzing the soil¢s volumetric changes during isotropic loading. Series of triaxial undrained compression and extension tests have been carried out on the natural K0-consolidated Wenzhou soft clay. Followed by comparison between the predicted results and the experimental data，the proposed model with rotational hardening law is capable of capturing key features of viscoplastic behaviors of soft soil，and the importance and applicability of rotational hardening law is indicated and verified.

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EFFECTS OF CONFINING PRESSURE ON MECHANICAL BEHAVIORS OF SANDSTONE UNDER DYNAMIC IMPACT LOADS

LU Xiaocong1，XU Jinyu1，2，GE Honghai3，ZHAO Dehui1，BAI Erlei1

2010, 29 (1): 193-201 doi:

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Experiments of dynamic behaviors are carried out for sandstone specimens by split Hopkinson pressure bar(SHPB) equipment with confining pressure device at different confining pressures and different strain rates. The effects of strain rate on uniaxial dynamic compression strength and specific energy absorbency，as well as the mechanical characteristics of sandstone at the triaxial state under the circular action of impact loads are analyzed. It is demonstrated that the rates of dynamic and static Young¢s moduli increase evidently with values of 3.21–3.81. Dynamic Young¢s modulus increases slightly with the changes of strain rates，which ranges from 50 s－1 to 100 s－1. The linear relationships of specific energy absorbency and strain rate ，dynamic strength increasing factor and strain rate at the uniaxial state are all presented. It has clear brittle-ductile transformation(BDT) property for sandstone；and the stress-strain curve is shown under the yield platform at triaxial state. Along with the increase of circular action times of impact loads，the Young¢s modulus and the yield stress of specimens decrease，and the yield strain increases. The failure configurations of sandstone change with the confining pressure from axial tensile failure to compression-shear failure；and the critical confining pressure is 10 MPa. Specific energy absorbency value against lower confining pressure level is more than the value under higher confining pressure with the same energy of incident wave. The formulas among with the specific energy absorbency，the incident energy and confining pressure are put forward.

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DYNAMIC OBSERVATION AND ANALYSIS OF MOISTURE MIGRATION FOR WIND-BLOW SAND IN OPEN SYSTEM DURING FROST

MAO Xuesong1，HOU Zhongjie1，KONG Lingkun2

2010, 29 (1): 202-208 doi:

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To discover the motive power of moisture migration of the wind-blow sand during frost，the experiments are carried out on the soil samples with moisture balance by supplying water from bottom under constant temperature. Then the temperature gradient is applied to the soil samples，and the changes of both temperature and water content of the samples are dynamically observed. The flow-in flux model is revised by the experimental results. The study shows that both the matric potential and gravity potential are main motive powers of the moisture migration of the wind-blow sand under constant temperature. The moisture migration can be completed in short time. The rate of water supplying decays quickly with time increasing. According to the frost velocity and the frost depth，the soil samples can be divided into three sections，i.e.，quick frost section，transition frost section，and stable frost section under gradient temperature. During frost，the flow-in flux of the samples increases with the decrease of the frost rate. The predicted values achieved from the revised flow-in flux model agree well with field test results. After the wind-blow sand with water supplying is frosted under constant temperature，the water supplied from the bottom of the sample all flows into the frost section. So it can be concluded that the motive power of moisture migration comes from the temperature gradient during frost.

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INFLUENCES OF PORE FLUID ON NONLINEAR MESOSCOPIC RESPONSES OF ROCKS

DU Yun1，XI Daoying1，XU Songlin2，WAN Xinlin3

2010, 29 (1): 209-216 doi:

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Quantitative studies of pore fluid influence on the mechanical properties of rocks are carried out on mesoscopic scale. The nonlinear strain is decomposed into a classical part and a nonclassical contribution which is described by nonclassical elastic units(NCU). Based on the analysis of the mechanism on mesoscopic scale，fluid influences on rock mechanical behavior and stiffness under various saturations are discussed. Introducing new forms of macroscopic solid-fluid interaction functions，Preisach-Mayergoyz(PM) space under different saturations are obtained from the inversion of experimental data；and the influences of fluid saturation on PM space density are investigated. The entire variation between Young¢s modulus and compressional wave velocity with saturation is studied. When saturation increases from 0% to 20%，the dynamic modulus decreases for classical part，and the PM space density increases for nonclassical part，respectively. Whereas saturation is between 20% and 80%，the dynamic modulus and PM space density barely changes. As saturation increases from 80% to 100%，the dynamic modulus increases and the PM space density decreases，contrary to the low saturation condition. The classical and nonclassical nonlinear strains of saturated rocks are obviously larger than those of dry rocks in accord with the PM space density distribution. These numerical results are generally consistent with the experimental results. This simulation research has potential prospects for the problems such as reservoir prediction and description，safety of constructions near slope area，nuclear storehouse properties，geophysical inversion，and data interpretations.

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2010, 29 (1): 217-218 doi:

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