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2012, 31 (s2): -0
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STUDY EFFECT OF BLOCK-ROCK SCALE ON PENDULUM-TYPE WAVE PROPAGATION

PAN Yishan，WANG Kaixing

2012, 31 (s2): -3465
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Based on the grade blocks tectonic theory for discontinuous and self-stress rock mass in depth，the effect of block-rock hierarchy scale on pendulum-type wave propagation is studied. Acceleration response of every block-rock is solved in the block-rock dynamical model on shock loading. Acceleration and frequency characteristics including center frequency and center frequency bandwidth of the block-rock mass are calculated，under the same shock loading energy and different block-rocks scales. The comparison results show that，the higher grade of block-rock structures，the more fast attenuation of block-rock mass acceleration on shock loading，and the main attenuation area is focus on the initial area of the block-rock structures. Pendulum-type wave is a low velocity wave while propagation in the block-rock mass compared with P wave and S wave. The higher grade of block-rock structures，the more lower velocity of pendulum-type wave. Block-rock with a larger frequency band center and wider bandwidth concentrate in the initial area when the higher grade of block-rock structures. The block-rock frequency band center moving to low frequency and the bandwidth becomes smaller on pendulum-type wave propagation，which performance the characteristics of low frequency，however，the changing trend more significantly when the higher grade of block-rock structures. Degree of fragmentation and joint development in rock mass can be inversion by the time-domain and frequency-domain results and testing techniques.

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SIMULATION OF MARBLE FAILURE IN COMPRESSION WITH DIGITAL IMAGE INTERFACE STRESS ELEMENT METHOD

SHAO Guojian1，DU Peirong1，2，LI Ang1，ZHU Yihuan1

2012, 31 (s2): -3470
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Based on the inside meso-constitution of rock and guided by the structure control theory，failure mechanism of rock in compression is studied. Photographs of marble from Jinping hydropower is processed with the digital image processing techniques. Images of marble can be transformed into grayscale images and the gray value of pixel matrix can describe the mesoscale constitution and inhomogeneity of marble. Using geometry algorithms and mesh generation techniques，elements of pixels can be transformed into meshes for numerical simulation. Failure phenomenon of uniaxial compression and required material parameter are got from indoor test. With gray value distribution mesostructure is evaluated parameters. Numerical simulation of mesostructure of marble is carried out with interface stress element method for discontinuity medium. Local stress and deformation can be got as a result of inhomogeneity. The result can interpret the macro phenomena of test because of inhomogeneity.

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INFLUENCE RESEARCH OF SLOPE BLASTING EXCAVATION ON ADJACENT EXISTED TUNNEL

LI Ning1，2，ZHANG Chengke1，ZHOU Zhong3

2012, 31 (s2): -3477
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The effect of slope blasting vibration on an adjacent existed tunnel and its control are key problems of tunnel project. Since the new slope is close to existing tunnel，the seismic wave induced by blasting endangers the safety and stability of the surrounding rock and the lining of existing tunnel. For a different distance between slope and tunnel，a different rock mass damping ratio，how much safety explosive quantity for single blasting in project is in urgent need of solution. On the basis of the simulation with the dynamic finite element method(FEM)，the effects of slope blasting vibration on the surrounding rock and lining structure of adjacent existed tunnel in different distances between slope and tunnel，damping ratio，safety explosive quantity for single blasting are studied，combining with influence of slope blasting on tunnel analysis issue on Jinping I hydropower station left bank project construction. According to the tunnel wall permitted vibration velocity and lining dynamic tensile stress caused by slope blasting vibration wave，obtain maximum explosive quantity of slope blasting constructions considering different damping ratios under different distances between slope and tunnel and different rock types：grade III rock mass，when distance between tunnel and slope equal to 20 and 50 m，the explosive quantity should be controlled in 100 and 300 kg respectively；grade IV rock mass，when distance between tunnel and slope equal to 20 and 50 m，the explosive quantity should be controlled in 150 and 450 kg respectively，and the research results provide the reference and basis to construction and design of the actual project.

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DYNAMIC RESPONSE OF UNDERGROUND ARCH STRUCTURE UNDER SIDE BLAST LOAD

CHEN Hailong1，2，JIN Fengnian1，XIA Zhicheng1，ZHANG Yu2，3，FAN Hualin2，4，ZHOU Jiannan1

2012, 31 (s2): -3481
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[PDF 191 KB] (772)

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When the centre of explosion is at one side of structure，only part of the structure will subject to explosion load. In this condition，the inner stress and the types of failure of the structure will change greatly. Load distribution is discussed for side blast. The calculation of load is given out. A damping action is used to replace the interaction between structure and the surrounding soil. So the soil-structure interaction is inserted into the controlling equation. And then the exact solution can be obtained by solving the equation. Method is obtained to calculate reaction of the structure when the centre of explosion is in arbitrary position far enough from the structure. And the distribution of displacement and maximum moment are got for side blast.

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A METHOD FOR THREE-DIMENSIONAL NEPHOGRAM REAL-TIME DYNAMIC VISUALIZATION OF SAFETY MONITORING DATA FIELD IN SLOPE ENGINEERING

MENG Yongdong1，CAI Zhenglong1，XU Weiya2，TIAN Bin1，ZHOU Jianjun1

2012, 31 (s2): -3490
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Achieving three-dimensional(3D) real-time dynamic visualization of spatial monitoring data field is the key of safety monitoring online visualization analysis in the slope engineering. 3D nephogram is the most direct expression of the spatial monitoring data visualization. The drawing methods of 3D nephogram include surface rendering and volume rendering，and volume rendering is the preferred method to realize the drawing of 3D real-time dynamic nephogram of the spatial data field. According to the flexible scene interaction and rich nodes for modeling，through generating the tetrahedral network(TEN) geometric model for showing the 3D nephogram of monitoring data field，on the basis of the extracting coordinates of monitoring points and forming the monitoring data field，applying the algorithm of spatial interpolation to achieve the value of monitoring physical quantity in the TEN nodes，and mapping the specific color in specific color domain value to grid nodes，finally，the method of X3D-based 3D nephogram of spatial monitoring data visualization with volume rendering is proposed. Taking the slope of a hydropower station and some accumulation body for example，the 3D nephogram of spatial monitoring data real-time dynamic visualization in the slope engineering is realized，and the deformation trend and potential deformation failure mode of monitoring object is revealed. These may provide reference for the application of this method to the slope and underground safety monitoring fields in hydroelectric engineering and geotechnical engineering.

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STUDY OF LABORATORY SCALE EFFECT OF LIMESTONE UNDER UNIAXIAL COMPRESSION

ZHANG Houquan1，2，XU Jianfeng1，2，HE Yongnian1，2，HAN Lijun1，2，JIANG Binsong1，2，SHAO Peng1，2

2012, 31 (s2): -3496
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Scale effect is widely shown in defective materials while scale effect is mainly originated from material heterogeneity. However，most of the scale effect study followed the research results of negative power law of concrete strength. Through microstructure analysis，much difference exists between rock and concrete materials. Limestone was selected for experimental materials. The experiment data about uniaxial compressive strength and stress-strain curves，etc.，were obtained through uniaxial compressive tests. Based on these data，the scale effect and its influential factors for rock materials are analyzed and studied，which are different from the scaling laws of concrete materials. The research results show that the defect levels in limestone materials influence rock strength，its deformation and failure characteristics heavily. An evident representative scale exists in every heterogeneous rock materials and it is closely related with the defect structural level(defect scale itself and the ratio of defect scale to rock samples scale). Scale effect of rock materials is originated from its heterogeneity，not from the friction effect between the ends of rock sample and loading plate.

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DYNAMIC RESPONSE OF CASING AND CONCRETE RING CAUSED BY PLANE SH WAVES

XU Ping1，2，LI Xiaochun1，FANG Zhiming1，WANG Xiaoming3

2012, 31 (s2): -3502
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The length of casing well completion structures that composed of casing，concrete ring and surrounding rocks are much larger than their outer diameters，so the problem of dynamic response of casing well completion structures caused by incident plane SH wave can be simplified as 2D plane problems. The casing，concrete ring and surrounding rocks are all considered as homogeneous isotropic elastic bodies. The wave function expansion method and conformal mapping method of complex function are adopted. The theoretical solutions about the complex coefficients of the scattering and refracting SH waves are obtained based on the boundary conditions that the inner side of the casing is free and the casing，concrete ring and surrounding rocks are tied completely. The casing well structures of 102 well in a gas field is taken as an example. The dynamic stresses of the casing caused by earthquake SH waves are calculated. The maximum stress is larger than the yield stress. Therefore the earthquake is the direct reason that causes the casing deformation in this gas field. In the end，the dynamic stress concentration factor is introduced，and the influences of surrounding rocks and concrete ring on the dynamic stress concentration factor are analyzed. Some important conclusions are obtained，which include：(1) reduction the strength of the concrete ring would reduce its dynamic stress concentration factor；(2) the stiffer the surrounding rocks are，the lower the dynamic stress concentration factor in concrete ring would be；(3) dynamic stress concentration factor of surrounding rocks is less influenced by the thickness of surrounding rocks and modulus of concrete ring.

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DYNAMIC RESPONSE ANALYSIS OF UNDERGROUND MULTI- LAYER CYLINDRICAL STRUCTURES IN ROCKS

LI Huanqiu，ZHANG Shi，OUYANG Kefeng

2012, 31 (s2): -3507
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Cylindrical structure is commonly used in the field of the city subway tunnel structure and other underground engineering. Based on the characteristics of the underground cylindrical structures and surrounding rock，the dynamic generalized function of cylindrical structure system in rocks subjected to plane shock wave is established，the linear and nonlinear dynamic differential equations of the system are derived by using variation principle. Applying the method to cylindrical structures with soft backfill layer in rocks，the elasticplastic dynamic responses of the structure are calculated. The effect of underground cylindrical structure dynamic characteristics and dynamic response of backfill layer thickness on the structure system are also researched. Meanwhile，the clipping vibration optimum thickness of soft backfilled layer and the best acoustic impedance ratio of the rock to backfill materials are worked out. The results are applicable to antiknock structure selection and structure dynamics analysis in the underground engineering under plane stress wave or earthquake loadings.

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MECHANISM DISCUSSION ON ROCK BURSTING CAUSED BY COAL PILLAR OF S-SHAPED OVERLYING MULTI-STRATA SPATIAL STRUCTURE

SHI Hong1，WANG Cunwen2，KONG Linghai2，CHENG Yunhai3

2012, 31 (s2): -3513
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With the deepening of mining，dynamic disasters，the range of disaster-related rock formation motion is beyond the traditional plane model. The movement of overlying strata spacial structure affects the distribution of mining stress field；and the stress distribution and stress concentration of the coal pillar caused by mining are the stress condition and primary cause for rockburst. Therefore，an analysis of the movement rules and mining stress field distribution of overlying strata and a study of the pressure source which acts on the coal pillar by the movement of the S-shaped overlying multi-strata spatial structure are the theoretical basis on the study of mechanical mechanism of rockburst caused by the coal pillar. The residual coal pillar of the 6th layer in Huafeng Coal Mine is taken as research object. The movement rules of overlying strata of the 6th layer and the S-shaped overlying multi-strata spatial structure of four the 4th layer are studied，and the pressure source during the movement of S-shaped overlying multi-strata spatial structure of coal pillar is analyzed. The stress field of coal pillar is also analyzed and the mechanical mechanism and stress condition of rockburst are studied through the stress computing and the microseismic monitoring. The study results indicate that the high stress caused by the coal mining of the 6th layer and the 4th layer is the key stress condition for the rock burst of coal pillars， and the fundamental inducing factor of the rock burst of the coal pillar is the difference of high stress which exist around the coal pillar. Based on the stress computing，pressure relief methods of coal pillar are discussed.

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SURFACE DISCONTINUOUS MOVEMENT AND DEFORMATION CHARACTERISTICS OF STRONG ROCKBURST MINE

GUO Weijia，SUN Wenbin

2012, 31 (s2): -3519
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With the mining of working face，soft rock strata above working face appear obvious separation characteristics，and the rigid thick overlying strata gradually settle. When the working face advances to a certain distance，the huge bed separation provides a certain motion space for the rigid-thick strata，causing the thick overlying strata to be broken. The instantaneous energy release causes a strong impact on surrounding rock，and leading to discontinuous deformation characteristics of the surface，cracks，for instance. The larger surface cracks are located at the position of ground level with larger deformation. As the size of exploitation increases along strike，the width and depth of surface cracks are gradually enlarged，the maximum width is up to 1.5–3.0 m，and the maximum depth is up to 50–70 m. Meanwhile，the overlying strata movement can also lead to surface concentration and stagnant. when the abscission range is larger than the drawing pace of conglomerate body broken，the surface deformation increases，which causes the surface crack. What?s more，the synchronic research of the significant correlation between the surface deformation and the rock burst can provide some auxiliary references for rock burst prediction.

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INFLUENCE STUDY OF DEEP ROCK FOUNDATION PIT EXCAVATION ON ADJACENT TUNNELS

JIANG Zhaohua1，2，ZHANG Yongxing1，2，CAI Yu1，2

2012, 31 (s2): -3526
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The excavation of foundation pit has influence on the adjacent tunnel. This study is mainly concerned with the soft soil layer，but less research has been done on the soil rock layer. According to the rock deep excavation at the depth of 30 m adjacent to the tunnel in Linjiangmen，Chongqing，the main monitored results combined with numerical simulation are analyzed. The results show that the deformation of deep excavation is small. The retaining pile and reserve rock wall is an effective support system. The main deformation of supporting structures concentrates in soil strata in rocky area. When the foundation pit is adjacent to a tunnel，the bending moment of retaining pile corresponding to the arch ring is larger than that when there is no tunnel，but it corresponding to the wall section is smaller than that when there is no tunnel. Due to the influence of the continuous media and tunnel geometric shape，the tunnel will change the direction of the displacement field. The vertical displacement is larger than the horizontal displacement，the lateral deformation will appear. The bending moment of tunnel vault，left arch springing and left wall has a bigger increase. The tunnel has obvious bias effect.

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CORRELATION STUDY OF ROCK BURST TENDENCY AND ULTRASONIC VELOCITY

ZHANG Zhizhen1，2，GAO Feng1，2，LIN Bin2，TIAN Zhili2

2012, 31 (s2): -3532
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A quantificational formula between ultrasonic velocity through rock specimens and rock burst tendency with increasing strain is deduced，and it is proved reliable based on the test results of three different kinds of rock specimens under uniaxial compression. The results show that：(1) When rock burst tendency is strong，the ultrasonic velocity almost keeps constant as the strain increases in forepart of loading，and declines suddenly at the point of 90% peak strength；when rock burst tendency is weak，ultrasonic velocity declines gradually during the whole deformation process. (2) A new conception called attenuation factor of ultrasonic velocity is put forward to represent the rock burst tendency，and the classification criterion is suggested. (3) The wave velocity test is conducted in three different kinds of rocks on burst tendency under uniaxial compression，and the test data fit the quantificational formula well.

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ANALYSIS OF SLOPE DEFORMATION CHARACTERISTICS AND MECHANISM IN LEFT BANK OF BAIHETAN HYDROPOWER STATION JINSHA RIVER

SONG Xiaobing1，2，SHI Anchi1，ZHENG Weifeng3，JIN Renxiang1

2012, 31 (s2): -3538
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This study focuses on the slope deformation characteristics and mechanism in the left bank of Baihetan hydropower station on the Jinsha River. As the unloading deformation develops with the erosion of the river in geological history，the rock mass on the slope at different elevations and localities has various deformation features. It is very important to study these features. Based on the investigation data，the deformation controlled by the slightly-inclined angle dislocation interfaces as well as the NW fault zone mainly was simulated by the distinct element numerical analysis code UDEC and 3DEC after the development mode of unloading deformation was summarized，The controlling effect of key structureal plane was illustrated during the erosion of the river，proving the geological analyses further. The slope deformation mechanism was analyzed in combination with the geological investigation and numerical calculation results。

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EXPERIMENTAL ANALYSIS OF MECHANICAL BEHAVIOR OF SANDSTONE CONTAINING HOLE AND FISSURE UNDER UNIAXIAL COMPRESSION

YANG Shengqi，LIU Xiangru，LI Yushou

2012, 31 (s2): -3546
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[PDF 546 KB] (909)

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By using rock mechanics testing system and acoustic emission(AE) equipment，the mechanical behavior of sandstone(the size is 60 mm×120 mm×30 mm) containing a single hole and fissure are tested by uniaxial compression test. Based on the experimental results，the strength and deformation behavior of fractured sandstone are first analyzed. The results show that the mechanical parameters of fractured sandstone are significantly lower than that of intact sample，and the reducing extent depends on hole diameter and symmetrical distribution of flaws. With the increase of hole diameter，the peak strength and peak strain of sandstone containing a single hole decreases gradually. The mechanical parameters of samples with asymmetrical flaw geometry are lower than that of samples with symmetrical flaw geometry. And then，on the basis of AE behavior of sandstone samples containing a single hole and fissure during loading，the AE distribution is significantly affected by flaw geometry，which is mainly due to significant differences of crack coalescence modes of sample containing different holes and fissures. Finally，by photographic measurement techniques，the failure modes of sandstone containing different holes and fissures are analyzed，and the crack coalescence process of sample containing a single hole and fissure and its effect on microscopic stress-strain curve are also investigated.

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FULLY COUPLED THERMAL-HYDRAULIC-MECHANICAL MODEL AND FINITE ELEMENT ANALYSIS FOR DEFORMATION POROUS MEDIA

JIA Shanpo1，RAN Xiaofeng2，WANG Yuezhi2，XIAO Taoli1，TAN Xianjun3

2012, 31 (s2): -3556
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[PDF 698 KB] (2295)

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With the application of continuum mechanics and mixture theory，a coupled mathematical model and governing equations of full coupled relation between temperature，seepage and stress fields for porous media are established. The solution process for coupled problem of three fields is studied by using finite element method and the corresponding computer code is developed with MATLAB with the ABAQUS solver. A typical example of application is presented to verify the validity of the code. Then，the coupled process of wellbore is studied and the influence laws of pore pressure，temperature and stress are discussed between different coupled fields. The results show that the coupled processes have significant effects on wellbore stability. The presented method can provide references for the influence of multi-field coupling on geological environment and coupled thermal-hydraulic- mechanical-chemical process analysis of underground engineering.

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MICROSCOPIC CHARACTERISTICS ANALYSIS OF BRITTLE FAILURE OF DEEP BURIED MARBLE

LIU Ning，ZHANG Chunsheng，CHU Weijiang，WU Xumin

2012, 31 (s2): -3565
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[PDF 1472 KB] (821)

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The failure process of brittle material is closely related to the propagation of crack. The microscopic structure characteristics directly determine the macroscopic mechanical behavior. But currently limited by the test instrument，the brittle failure mechanism can't be fully understood，and the test method must be combined with numerical method. Firstly，the uniaxial and triaxial compression tests were finished by mechnical testing system(MTS)，and the acoustic emission(AE) signal was monitored. According to the test data，the failure characteristics of deep buried marble were analyzed in detail and the development evolution law of internal cracks and its influence on macroscopic mechanical properties were made clear. Particle flow code was introduced，and the particle and cement parameters were confirmed by completed uniaxial and triaxial compression tests. The brittle failure of rock was simulated by bonded-particle model(BPM). The numerical simulation results show that the PFC can accurately reproduce the crack propagation and failure characteristics of deep buried marble and show the valuable microscopic mechanism that can't be monitored and obtained in the actual test process. The PFC method can be relied on to describe failure characteristics and complex mechanical behavior of brittle rock.

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DEFORMATION CHARACTERISTIC ANALYSIS OF TUNNEL SURROUNDING ROCK IN JOINTED MASS

XU Chongbang1，2，3，XIA Caichu2，SONG Erxiang3

2012, 31 (s2): -3570
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[PDF 333 KB] (762)

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Jinjishan Tunnel is the first multi-arch tunnel with bidirectional eight-lane in China. There were developed joints and crushed rock in tunnel surrounding rock，and the characteristics of joint distribution has significant effect on the stability of tunnel surrounding rock. The data of joints in several cross-sections of mid-drift and other outcrop areas of the tunnel are collected，and joints distribution of the main tunnel by using statistical analysis method is predicted. On the basis of this，simulation calculation for the deformation process of Jingjishan tunnel surrounding rock is made with the self-programmed computation program of analyzing initiation，extending and connecting of rock fractures，and the simulation results show that affections of two joints distribution features on surrounding deformation and the displacement of tunnel surrounding rock be dominated by vertical displacement，and the maximum displacement is at the lateral arch shoulder. The results provide the basis for strengthen and construction methods of tunnel.

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RESEARCH ON STABILITY OF FAULT f5 REPLACEMENT TUNNEL AND ITS INTERSECTION TUNNEL AND DESIGN OF SUPPORTING STRUCTURE IN JINPING I HYDROPOWER STATION

QU Xing1，LI Ning1，ZHOU Zhong2，SUN Hongchao3

2012, 31 (s2): -3578
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f5 Fault is the largest fault in the dam area of Jinping I hydropower station。In order to improve the quality of rock mass of dam abutment，adits f5–1，f5–2 and 4 inclined shaft were used to replace the fault f5. Based on the extensive research，the necessity of replacement grid setting was discussed. 3D finite element method was employed to simulate natural topography and geological conditions and excavation. The stability of replacement grid was evaluated by stress and deformation，and compared with measured data. The results show that the adits f5–1and f5–2 meet the stability requirement of the construction period，but supporting force in local tunnel is insufficient. For adit f5–2，two kinds of reinforced measures，prestressed anchor bolt，steel arch centering，thick shotcret and lining in advance，were adopted，these measures can makes the adit to meet stability requirements. Taking the other factors into consideration，it is believed that lining in advance is more reasonable. For cross parts of adit and inclined shaft，inclined shaft were excavated after lining before and after 10 m of cross parts of adit were completed，the maximum compressive stress of lining is less than 6.5 MPa and the maximum tensile stress is less than 1.7 MPa. For cross parts of adit f5–1 and force transmission tunnel # 5，first proposed in # 5 tunnel applied lining，then consolidation grouting on the thinner rock pillar，last for the construction of the adit. The numerical analysis results provide a scientific basis for the design of lining in replacement tunnel，and has guiding meaning to the other similar projects.

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MESOSTRUCTURAL INVESTIGATION ON MARBLES UNDER UNIAXIAL CONPRESSION AT HIGH TEMPERATURES

WU Gang1，2，ZHAI Songtao3，LI Yushou2，WU Xueping3

2012, 31 (s2): -3585
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Exploring the effect mechanism of high temperature on rock，which will has important significance for solving the problems of high temperature rock engineering. The measurement of surface element distribution，the surface morphology and mesostructural analysis have been tested for Xuzhou marbles that failed under uniaxial compression at different temperatures (20 ℃，200 ℃，400 ℃，600 ℃，800 ℃ and experienced 400 ℃，600 ℃ and 800 ℃) using S–3000 N scanning electron microscopy made by Japan's Hitachi Ltd. A rational explanation in the mesoscopic level has been given on the characteristics of deformation，strength and failure of marble which experienced different temperatures. The test results show that the particles of Xuzhou marble are relatively thick，typical cleavage crack，cracks in part particle or between the particles at 20 ℃，while there are apparent fragmentations on the port surface，the particles become smaller，forms are more structured，and slender cracks exist in some areas at 800 ℃；The mesostructure of marbles that failed under uniaxial compression is quite different at high temperature and after high temperature. Generally the atomic percentage of marble doesn?t change significantly before 800 ℃；When temperature reaches 800 ℃，the weight percentage of elements of marble takes place more change. The weight percentage of Ca declines sharply and that of Si raises rapidly which indicate that the structure of marble perhaps occurs phase transition from crystalline to amorphous and results in the plummeting of the mechanical index of marble at 800 ℃.

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VISCOELASTOPLASTIC CREEP SOLUTIONS TO DEEP CIRCULAR TUNNELS CONSIDERING INTERMEDIATE PRINCIPAL STRESS AND SHEAR DILATANCY

YU Dongming，YAO Hailin，DUAN Jianxin，ZHAN Yongxiang

2012, 31 (s2): -3592
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[PDF 269 KB] (679)

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The excavation and supporting of a deep circular tunnel is a complex mechanical process related to time. To describe this process，the surrounding rock of the tunnel is supposed to a viscoelastoplastic combination model of a Burgers body and Drucker-Prager criterion. At the instant time that the excavation and supporting were finished，the surrounding rock of the tunnel performs as a elastoplastic material. Under this condition，the influence of intermediate principal stress was considered，and the stress field under the combined action of the primary rock stress and supporting force could be obtained. With the assumption of constant stress field，the surrounding rock exhibits creep properties of time-dependence. Furthermore，the analytical solution to the creep displacement of the surrounding rock was deduced considering shear dilatancy for the deep-buried circular tunnel. A practical engineering instance was given and the regularities that the supporting force and dilation angle of the surrounding rock affect the creep displacement in deep circular tunnel were analyzed. The results show that the change of dilation angle could produce significant influence on the creep displacement，while the supporting force could not completely control the sustained increase of displacement of the surrounding rock with time in the deep circular tunnel.

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PROPAGATION LAW OF OBLIQUE INCIDENCE OF STRESS WAVE ACROSS A VISCOELASTIC JOINT

LIU Libo，LI Jianchun，LI Haibo，LIU Tingting

2012, 31 (s2): -3598
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[PDF 271 KB] (1055)

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The study of stress wave propagation in rock mass is an important topic in rock mechanics. Based on the assumption of displacement and stress discontinuity，for the visco-elastic behavior of filled joint，the transmission and reflection coefficient equations of P-wave and S-wave in the frequency domain are respectively derived. By numerical calculation and parameter analysis，the impact of parameters on the law of stress wave propagation is studied，such as the incident angle，the incident wave frequency and joint stiffness. Reasonable parameters selections of incident wave and filled joint have significant effects on the determination of transmission and reflection coefficient.

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STABILITY ANALYSIS OF DEPOSIT LANDSLIDE BASED ON IMPROVED DYNAMIC PROGRAMMING ALGORITHM

SHI Chong1，2，YOU Lin3，XU Weiya1，2，HUANG Wei1，2，ZHANG Yulong1，2

2012, 31 (s2): -3606
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[PDF 741 KB] (674)

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Based on graph theory，investigation of the most dangerous sliding surface and safety coefficient calculation in slope stability analysis is transformed into solution of shortest path problem in mathematics. The dynamic programming algorithm is improved to build a limit equilibrium finite element method(FEM)，in which the basic equation is given and the stress along the sliding surface is computed so as to avoid the computing iterative procedure because of given safety coefficient when auxiliary function is introduced. Then the improved method is applied to analyze the stability of landslide deposit at left bank，Xiluodu hydropower station. The safety coefficient is estimated based on the fracture appearance，landslide development and creep deformation under nature condition，then the deformation and failure mechanism is studied. According to monitoring data of hole with clinometer. The sliding surface of limit equilibrium finite element method is compared with reality，so the accuracy of this improved method is verified and stability under rainfall condition is discussed. At last，a analysis procedure is put forward based on limit equilibrium FEM，which is proved more suitable for stability analysis of deposit landslides.

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EXPERIMENTAL STUDY OF INFLUENCE OF WATER-ROCK CHEMICAL INTERACTION ON MECHANICAL CHARACTERISTICS OF SANDSTONE

WANG Wei1，2，LIU Taogen1，2，LU Jun1，2，WANG Rubin1，2，XU Weiya1，2，JIAN Bo3

2012, 31 (s2): -3617
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[PDF 608 KB] (721)

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In order to investigate the influence of water-rock chemical interaction on the mechanical characteristics of sandstone，the corrosion tests are firstly carried out on the standard specimens of red sandstone taken from the site of Taoyuan hydropower project. The variations of relative qualities of samples with time are obtained as well as the variations of pH values of chemical solutions. Then，a rock triaxial testing machine is used to conduct triaxial compression tests on the red sandstones specimens soaked in six chemical solutions. The effect of chemical solutions with different pH values and ion components on the mechanical characteristics of red sandstones is studied and the influences of chemical solution on strength and deformation characteristics of red sandstones are investigated. The results indicate that the change in rock mass is related to chemical solution. There are obvious differences between different chemical solutions. As to the pH values of chemical solutions，the pH value of solution with the initial pH value equal to 13 decreases very slightly. But the pH values of other solutions finally tend to reach a regular value about 7.9. The corrosion degree is evaluated by measuring the variation of pH values for all solutions and the variation of mass of soaked specimens. According to the results of triaxial compression tests，the mechanical characteristics of rocks are related to the kinds of the chemical solutions. The pH values and ion components have a great impact on the mechanical characteristics of the red sandstone. The peak strength，residual strength and elastic modulus of the rock after corrosion are likely to decrease to a certain degree for different solutions. The failure modes of the samples under different chemical erosions with the same confining pressure have no significant discrepancy. Results obtained from laboratory tests could provide experimental data for the constitutive modelling of sandstone under chemical corrosion.

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STUDY OF ACOUSTIC EMISSION CHARACTERISTICS OF BEISHAN DEEP GRANITE UNDER DIFFERENT STRESS CONDITIONS

CHEN Liang1，LIU Jianfeng2，3，WANG Chunping1，WANG Lu2，3，WANG Xiyong1，WANG Ju1

2012, 31 (s2): -3624
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[PDF 602 KB] (1245)

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The foundational mechanical behavior and acoustic emission(AE) characteristics of intact Beishan granite under different stress conditions are investigated，with the MTS815 Flex Text GT rock mechanics test system and PCI–II AE test system. The obtained direct tensile strength is 9.53 MPa，which is 1/17 of the average uniaxial compressive strength. Under the tensile stress condition，the AE events appear much later and mainly concentrate at the failure stage，since there is not a closing process of original microcracks. At the post-peak strength，the constantly increasing AE events indicate that the granite specimen does not break immediately and still has a certain tensile strength. Under compressive stress condition，AE events appear at initial loading stage，and increase continuously with loading stress，representing the initiation and propagation of the stress-induced microcracks. With the increase of confining pressure，the granite exhibits a more significant ductile at the peak stress，and a nonlinear mechanical behavior at the same time，with a progressive propagation of the microcracks(damage)，which leads to more intensive accumulated AE events. The significant ductile characteristics especially before the failure stage are obviously different from those of other common granite. The achievements of the work about mechanical behavior and AE characteristics of intact Beishan granite under different stress conditions are essential to the further study on the damage evolution mechanism of Beishan granite under different stress conditions.

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STUDY OF RELATIVE LIMIT DISPLACEMENT MODEL OF PRIMARY SUPPORT IN TWIN-TRACK TUNNEL CONSIDERING EFFECT OF MULTI-FACTORS

LIU Fangbiao1，WU Shunchuan1，2，GAO Yongtao1，2，LI Jian1，XIONG Feng3

2012, 31 (s2): -3631
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[PDF 444 KB] (702)

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Relative limit displacement U0/U of tunnel primary support is an important judgment index of surrounding rock and support system stability. U0/U values defined by related standards range for different surrounding rock grades and embedded depth，making surrounding rock stability judgment more flexible. To get more exactly value of U0/U under various tunnels and mechanical parameters，finite difference method(FDM) is adopted to research correction factor K4 showing the influence of pan length B on [BQ]，and modified rock quality index [BQ]－B is established. Multi-nonlinear regression technology is used to fit the relation among U0/U，[BQ]－B and embedded depth h in twin-track tunnel. Then the model of relative limit displacement of primary support under multi-factors is founded. As the influence of multi-factors on U0/U has been considered synthetically and the quantitative value for U0/U is defined in the model，the model makes up for deficiencies of current standards and provides new methods and thoughts for exact surrounding rock stability judgment. Besides，the functional relations are helpful for information programming and application. Observed data from Shanping highway tunnel has been adopted to verify the applicability that the model founded to deep-buried soft rock，hallow-buried loess and deep-buried hard rock tunnel，providing reference for similar tunnels.

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RESEARCH ON TYPE OF TUNNEL-LANDSLIDE SYSTEM AND TUNNEL DEFORMATION MODE

WU Honggang1，WU Daoyong1，2，MA Huimin1，ZHANG Hongli1

2012, 31 (s2): -3642
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[PDF 1925 KB] (900)

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While constructing tunnels of highway or railway in the mountainous area，the situation that tunnels pass through the landslide site often occurs. These tunnels usually suffers deformation and crack diseases because of landslide. Generally，tunnel excavation and landslide creep are considered separately，which can not well explain the interaction between them. The spatial position relationship of tunnel and landslide controls the nature and scale of the disease，and it is the main factor that decides the interaction model of tunnel-landslide system. It confirms the force mode of tunnel in the landslide，and the force that acts on tunnel is the fundamental reason of tunnel deformation. Therefore，the position relationship of tunnel and slip plane of the landslide determines the stress mechanism and deformation characteristics of the tunnel. According to the position relationship of the tunnel and the slip plane，tunnel-landslide system has been divided into three types，which are parallel，orthogonal and oblique systems. With typical engineering examples，different systems have been divided into more subtypes. Then the stress mode and deformation characteristics of each type have been analyzed，the interaction law of the tunnel-landslide system is got ultimately. The results show that，the stress and deformation of different systems have great differences generally，and the tunnel-landslide system interaction decreases with the increase of the distance between tunnel and landslide.

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STUDY OF STABILITY AND SUPPORTING MEASURES OF CHAMBER ARCH CROWN FOR LARGE SPAN UNDERGROUND CAVERNS

XIANG Xin1，2，WANG Yifeng1，MENG Guotao3，JIANG Yali4，LU Kang4

2012, 31 (s2): -3649
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[PDF 1114 KB] (1243)

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The proposed hydropower station which is located on lower reaches of Jinsha River is characterized by the large scale and complex arrangement. The height of cylindrical throttled surge chamber is about 100 m，and the diameter reaches 50 m. The stability and supporting measures of chamber arch are the noteworthy factors needed to be considered. In order to analyze potential stress-type failure，deformation and collapse caused by structure planes of tailrace surge chamber arch crowns under complex geological conditions，engineering geological analysis and three-dimensional numerical simulation(3DEC) are adopted to study the stress concentration arrange，stress concentration degree and risk of high stress failure，and the effects of interlayer fault zones on stability of surrounding rock are demonstrated. The results show that the overall stability of cavern satisfies the engineering requirements，and the relatively stress concentration degree(30–44 MPa) of arch crown doesn?t cause prominent issue of high stress failure. However，bedding fault zones reduce the stability of surrounding rock distinctly，thus large sliding deformation occurred along the bedding fault zones and shear yield occurred in NNE direction from surface to 7 m superficial zone. After strengthened reinforcements including system supporting and concrete replace are adopted，sliding deformation of bedding fault zones is reduce obviously，and interlaminar band security reserve is improved.

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A RHEOLOGICAL DAMAGE MODEL OF SANDSTONE AND ITS APPLICATION TO ENGINEERING

WANG Wei1，2，LU Jun1，2，WANG Haicheng1，2，SUN Shaorui3

2012, 31 (s2): -3658
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[PDF 874 KB] (675)

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Common method of describing the rheological damage is usually limited to the accelerated rheological stage，and damage in the decay and steady rheological stages are not considered，which contradict lots of experimental results. In order to better describe three stages of rock rheology，a rheological damage constitutive model for sandstone is proposed by using the damage theory and by introducing the concept of the whole process of damage into Burgers rheological model based on the Mazars damage evolution law. The validity of the model is verified and the parameters are determined by fitting the triaxial rheological test data. Then，the model is applied to the Phoenix Mountain Tunnel project by using the fast lagrangian analysis of continua in three- dimention(FLAC3D). The field monitoring data are compared to the model prediction using the proposed rheological damage model and the rheological model without damage. Results show that the numerical prediction using the proposed model agrees well with the field measurements and describes well the damage and rheological properties of surrounding rocks of the tunnel. Accordingly，the rheological damage model considering the whole process of damage is reasonable.

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USING GRAPHIC METHOD TO REPRESENT NATIONAL STANDARD FOR ROCK MASSES CLASSIFICATION BQ

SHEN Yanjun1，XU Guangli2

2012, 31 (s2): -3665
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[PDF 368 KB] (812)

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The National Standard for Engineering Classification of Rock Masses(GB50218—94)，as a general rock masses classification standard，can be suitable to all kinds of rock engineering；it uses the method combining the qualitative description with the quantitative calculation to evaluate the rock masses quantity，and has been extensively applied to different rock-mass projects. Yet because the qualitative description content is relatively complex，the grading criteria is fairly rough；and when using the quantitative index BQ formula，it is necessary to consider two corresponding limiting conditions，the practicality of the BQ is effected to some extent. For the purpose of solving these problems，a graphic method is put forward to represent the national standard rock masses classification BQ，the intact rock uniaxial compressive strength Rc and the integrity index Kv of rock masses are chosen as the Y-axis and the X-axis，respectively；and the two limiting conditions are also considered into this method to draw the broken line graph. Using this graph，the rock masses classification can be determined conveniently，rapidly and accurately as the results of different rock engineering examples. Besides，in view of the local inconsistence conditions between the qualitative descriptions and the quantitative indices，some optimizations to the qualitative grades of the intact rock uniaxial compressive strength Rc and the integrity index Kv of rock mass are done according to the graphic results，the coincident degree between the optimized qualitative grades and the BQ value has been increased 3%–12% comparing with the original grades and the BQ values. At last，the choosing approach of two grade indices and the influence of modified factors to the graphic results have also discussed and analyzed by the chart. This research can provide some references to the latter modified and optimized to the national standard BQ.

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SECURITY AND STABILITY RESEARCH FOR SALT-ROCK GAS STORAGE CAVERNS GROUP BASED ON STRENGTH REDUCTION METHOD

JIA Chao，LI Peng，ZHANG Qiangyong

2012, 31 (s2): -3672
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[PDF 1412 KB] (593)

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Strength reduction theory is introduced into security and stability research of the underground gas storage caverns group，and critical failure criterion of caverns is put forward. In the static analysis，critical failure criterion is transfixion of equivalent plastic strain among caverns. In the long-term rheological analysis，critical failure criterions include transfixion of equivalent plastic strain among caverns and the limiting shrinkage state of caverns? volume. Rock material strength parameters are reduced by reduction factor(F) step by step and the general safety factor of caverns is obtained when the calculated results just reach critical failure criterions. Jintan salt-rock underground gas storage is taken as an example. Numerical model is created by using the software of fast lagrangian analysis of continua in three-dimention(FLAC3D) and the model is analyzed both in static state and long-term rheological state based on strength reduction theory. The general safety factors of caverns are obtained in different conditions. In the static analysis，equivalent plastic strain among caverns develops continually with the increasing of the reduction factor and the general safety factor of caverns is 2.25. In the long-term rheological analysis，the key failure factor of the caverns transforms gradually from volume shrinkage to transfixion of the equivalent plastic strain among caverns. With the same numerical model parameters and internal pressure as the static analysis，the general safety factor of caverns is 1.83 after the system operates for 50 years. The relationships among safety factor，pillar spacing，pressure condition and failure mode are discussed. It is useful for safe operation and stability evaluation to other similar salt-rock underground gas storages group.

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VOLUME SHRINKAGE RISK ANALYSIS OF SALT ROCK CAVERN GAS STORAGE BASED ON RELIABILITY METHOD

JING Wenjun1，CHENG Lin2，YANG Chunhe1，3，XU Yulong1，ZHANG Yujun1，SHI Xilin1

2012, 31 (s2): -3680
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[PDF 256 KB] (668)

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Effective volume reduction resulted by cavern shrinkage is one of the common risk types in the operation phase of salt cavern gas storage. Cavern shrinkage risk will lead to damage or collapse of cavern wall rock，even serious accidents. Aimed at the possible cavern shrinkage risk during operation phase of salt cavern gas storage，volumetric shrinkage formula of steady state creep phase is derived on the condition of spherical cavern with constant internal pressure in the limitless and ideal salt rock. Combined with the cavern shrinkage risk classification of salt cavern gas storage，the limit state equation of cavern volume shrinkage is created. On the assumption that every random variable in the limit state equation follows normal distribution，probability of risk occurrence under different levels is calculated using reliability analysis. Then the change regularity of stress-difference between grostress and internal pressure and risk probability of every level is analyzed. Lastly，the elastic deformation，initial creep deformation and accelerated creep deformation are taken into consideration and the calculations result is discussed. The research results can provide theoretical reference for the operation management of salt cavern gas storage.

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GEOMECHANICAL MODEL TEST OF CHAIN FAILURE AND STABILITY ANALYSIS OF UNDERGROUND GAS STORAGE CAVERN IN SALT ROCK

LIU Yaoru1，LI Bo1，YANG Qiang1，GUAN Fuhai2

2012, 31 (s2): -3687
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[PDF 464 KB] (666)

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It is very important to study whole stability and failure mechanism of gas storage cavern in layered salt rock for safe operation. The geomechanical model has been constructed with small blocks and low strength binder. Small blocks are used to simulate the deformation characteristics of salt rock，and the low-strength adhesive to simulate the strength property of salt rock. Mudstone interlayer is simulated with dewatered gypsum slices. The natural gas injection-production cycles are simulated for 4-cavern group under different internal pressures. The displacement and strain of the surrounding rock and the cavern group are automatically recorded by the displacement meters and the strain gauges buried in the model. Cavern stability under different gas production processes，the failure pressure of the caverns and the impact of mudstone interlayer on stability are analyzed. The result shows that the injection-production of single cavern have large influence and mudstone has little influence on the stability and chain failure of cavern group.

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EXPERIMENT RESEARCH ON DAMAGED ZONE EVOLUTION OF DENSE STORAGE GROUP IN SALT ROCK

CHENG Lijuan1，2，LI Zhongkui1，XU Bin1，YANG Qiang1

2012, 31 (s2): -3695
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[PDF 7249 KB] (539)

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The evolution rule with the increasing pressure difference of rock pillars? damaged zone of different storage spaces is studied by geomechanical model test. The followings are completed mainly：(1) Firstly，several key techniques related to the experiment model test are studied，including model material，generation system of crustal stress，loading and unloading system of cavity pressure and measurement techniques. And a new method to generate trapezoidal-distribution stress with spherical particle is put forward. (2) Secondly，three experiment schemes are planed and accomplished. Last but not least，numerical simulation of the model test is carried out and the results are contrasted with that of the model test. The conclusion is that the stability of the rock pillar between pressurized caverns is the determinant factor for preventing the chain breaking of cavern group.

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TEST STUDY OF UNFROZEN WATER CONTENT IN ARTIFICIAL FROZEN SILT

LIU Bo1，2，LI Dongyang1

2012, 31 (s2): -3702
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[PDF 306 KB] (722)

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How to determine the unfrozen water content in frozen soil is still a key and difficult problem in geocryology. For measuring the unfrozen water content in frozen silt in laboratory，silt samples are taken into isothermal air to melt by natural convection after being frozen at a negative temperature with the temperature-time history recorded. Based on Newton?s law of convection exchange，a analytical model reflecting the variation of the temperature with time throughout whole process is formulated. Some important parameters such as the convective heat transfer coefficient，freezing point and length of melting time are then obtained by fitting the temperature-time history of the tests. On the relationship between ice mass and quantity of heat absorbed in process of thawing，a thermal model of the unfrozen water content in practically frozen state is presented. The results indicate that the unfrozen water content in silt in practically frozen state is about 3.75% when temperature is －4 ℃. Based on the unfrozen water content obtained by this method，the process of the sample melting is then back analyzed. It shows that the analytical results match well with the measured temperature，and feasibility of the proposed analytical model and test method is proved.

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ENGINEERING PRACTICE AND ANALYSIS OF LIMIT ROOF DIAMETER IN BUILDING SUMP OF SALT CAVERN FOR GAS STORAGE

QU Dan?an1，2，3，SHI Xilin2，LI Yinping2，YANG Chunhe1，2，MA Hongling2，ZHANG Guimin2

2012, 31 (s2): -3709
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[PDF 949 KB] (854)

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According to the analysis of an engineering case of building sump of Jintan salt cavern，some problems existing in the engineering case are discussed. The experience and lesson are summarized，and some ideas and suggestions are proposed. Then，some key factors that should be considered in the design progress of solution mining are discussed. The necessity of determining limit diameter of cavern roof is expounded. And a method of calculating limit exposed diameter of cavern roof is presented. With this method，the limit roof diameters of some salt caverns are studied basing on simulation test. The limit roof diameters of salt caverns with different lateral solution angles and cavern heights are obtained，and their laws are studied.

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CALCULATION METHOD FOR GAS LEAKAGE MASS FROM UNDERGROUND GAS STORAGE CAVERNS IN SALT ROCK

YANG Shigang，FANG Qin，ZHANG Yadong，MA Linjian

2012, 31 (s2): -3715
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[PDF 327 KB] (714)

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To analyze and evaluate the hazard of the leakage accident from underground gas storage caverns in salt rock，a prediction method for the gas leakage mass is firstly established on base of the existing models for calculating gas release rate of gas transmission pipelines and pressure drop of vessels. The analytical results were then validated by comparison with the existing test data. Furthermore，the factors influencing on the gas leakage rate of the underground gas storage cavern in salt rock were discussed. The results indicate that the release rate decreases with increase of the length，and increases with increases of the operating pressure as well as the pipeline diameter. Finally，the gas leakage rate and mass varying with time were evaluated by the proposed method.

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STUDY OF SYNTHETIC ROCK SALT SIMILAR MATERIALS FOR SOLUTION MINING TEST

REN Song1，REN Yiwei1，JIANG Deyi1，CHEN Jie1，YANG Chunhe1，2

2012, 31 (s2): -3724
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[PDF 308 KB] (561)

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The mechanical property of rock salt similar model is derived from the similarity theory in order to obtain the similarity criteria of the mechanical parameters. Considering the four factors，i.e. pressing strength，water ratio，salt particles with different diameters and insoluble in salt，Chongqing Beibei salt mine is chosen to make a materials proportion test. The results show that Chongqing Beibei salt filtered into 16 mesh size without gypsum powder when putting it in the 105 ℃–110 ℃ oven for 24-hour drying，under 100 MPa pressing strength while keeping the pressure for 30 minutes，then the synthetic rock salt that can meet the requirement of uniaxial mechanical similar model of Jintan rock salt was produced. This study makes a research on the dissolution characteristics of synthetic rock salt produced by the best materials proportion whilst dissolve angle is 90° and 180° in regular temperature as well as in 60 ℃，70 ℃ and 80 ℃. The results show that the dissolution rate of molded rock salt was 0.75 times as quick as that of natural rock salt when the angle was 90º and remains 0.81 times under 180° angels in regular temperature. What?s more，the dissolution rate of molded rock salt was 0.88，0.74 and 0.78 times as quick as that of natural rock salt whilst temperature was 60 ℃，70 ℃ and 80 ℃ respectively. The similar material proportion can be used for the making of large-size synthetic rock salt to simulate the rock salt cavity formation process，thus it has an important effect on the cavity simulation study.

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RESEARCH ON THERMAL CONDUCTIVITY OF SALT ROCK AT TEMPERATURE RANGE FROM -20 ℃ TO 50 ℃

MA Cong，TAN Yuehu，LI Erbing，YANG Meng

2012, 31 (s2): -3730
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[PDF 834 KB] (685)

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To study the thermal conductivity of salt rock at temperature ranges from －20 ℃ to 50 ℃，a mathematical model of inverse heat conduction problem is established which is based on the analysis of test results of heat conduction for salt rock samples at the initial temperature of －20 ℃，0 ℃，20 ℃，45 ℃. According to information on the boundary conditions and the test results of the internal temperature distribution field，using implicit finite difference scheme and combining Matlab numerical solution procedures to solve the inverse problem，the function expression of thermal conductivity coefficient is defined. The function expression is applied into finite element procedure to simulate temperature field. Compared with the experimental results，the two fit well. The results show that the relationship between the thermal conductivity of salt rock at temperature ranges －20 ℃ to 50 ℃ and absolute temperature yields is parabolic，and the thermal conductivity drops when the temperature rises. The determination of thermal conductivity of salt rock at temperature range from －20 ℃ to 50 ℃ would provide certain guiding significance for study of temperature effects of variety of mechanical properties of rock salt as well as actual project application in salt rock storage caverns.

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THEORETICAL ANALYSIS OF MECHANICS BEHAVIOR OF CYLINDER STORAGE CAVERN IN ROCK SALT CONTAINING INTERLAYER

WANG Wu1，2，XU Hongfa1，TONG Quan1

2012, 31 (s2): -3739
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[PDF 389 KB] (560)

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Salt caverns are created by the method that circulating fresh water into the salt formation to dissolve the salt，so the cavern?s ratio of radius to height is small and the cavern can be simplified into a hollow cylinder. The intermediate zone of the cavern was sectioned to take as research object. Considering the fact that the salt deposit in China is characterized by more interlayer，an equivalent calculation model was established to discuss the stress distribution function near the layer，based on the method of equivalent relative displacement on contact surface between rock salt and interlayer and actual state. Where assuming the contact surface is smooth，and thus the elasticity solutions of the thick-walled cylinder could be used to calculate stress distribution，then local internal pressure near the interlayer are increased and decreased to adjust the relative displacement until equivalent to actual state. The contrast between the numerical simulation and analytic solution shows that two results on stress distribution considering effect of interlayer is basically the same，in which maximum error of radial stress ?r and circumferential stress on cavity surface are less than 6.8% and 2.7% respectively. The analytic result meets require of storage cavern design analysis.

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RESEARCH ON PERMEABILITY TESTING OF ROCK SALT UNDER DIFFERENT PERMEABILITY PRESSURES

WU Zhide1，2，ZHOU Hongwei1，3，DING Jingyang1，RAN Lina2，YI Haiyang1

2012, 31 (s2): -3746
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[PDF 931 KB] (1130)

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Rock salt cavern is widely used for nuclear waste disposal，petroleum and natural gas storage and CO2 sequestration. The permeability of rock salt is too low to be obtained easily by experiments. The permeability of three different rock salt samples are obtained through the steady-state method. The permeability calculated by pseudo-pressure method and considering Klinkenberg effect are compared. The results show that：(1) The permeability and porosity of rock salt are extremely low，and the porosity is between 0.3% and 3%. The permeability of pure rock salt is about 10－20 m2，greater than that of impurity rock salt，which is between 10－20 and 10－21 m2. (2) During the permeability experiment，when the inlet pressure is 1–5 MPa，Klinkenberg effect is obvious. When the inlet pressure is higher than 5 MPa，the rock salt is damaged and the permeability increases. (3) By comparing the results，the method of considering Klinkenberg effect is more ideal than pseudo-pressure method in rock salt permeability calculation.

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EXPERIMENTAL AND THEORETICAL RESEARCH ON YIELD AND FAILURE CHARACTERISTICS OF ROCK SALT

MA Hongling1，YANG Chunhe1，LI Yinping1，GUO Enhong2，SHI Xilin1，LIU Jianfeng3，4，5

2012, 31 (s2): -3756
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[PDF 1715 KB] (788)

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The scopes of yield zone and failure zone of surrounding rock are the important factor in design of the space between underground gas storages in rock salt formation. Accurate description of yield and failure property is helpful for reducing the space between storages and building more storages in a limited rock salt zone. Based on the uniaxial compression tests and axial compression tests，yield property and failure characteristics were analyzed and surrounding rock is divided into elastic zone，plastic zone and failure zone. Experiment results show that yield function is a linear curve and Tresca yield criterion can be used to describe the yield characteristics of rock salt. The second invariant of plastic strain was used as harden parameter to analyze the harden property of rock salt，and the result shows that rock salt is a isotropic hardening material. In terms of yield，rock salt acts like metal，in terms of failure，it?s like rock. Shear failure and split failure were observed in compression tests. Split failure observed in axial compression test was analyzed based on the theory of thick cylinder. Failure property was confining pressure dependent，and when confining pressure is equal or greater than 5 MPa，the rock salt would never break even the axial strain move to 20%. A non-broken criterion was imported into Mohr-Coulomb criterion and a new failure criterion was built which contain tensile failure criterion，shear failure criterion and non-broken criterion. Based on the failure criterion，the stress space was divided into three parts：tensile failure zone，shear failure zone and non-broken zone. The constitutive model was modified and state parameters were self-defined in FLAC3D. A simple model was constructed to verify new yield function and modified failure criterion. Elastic zone，plastic zone and failure zone were found in the surrounding rock，which is the same as the surrounding rock zones divided above.

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CALCULATION AND ANALYSIS FOR FAILURE RISK PROBABILITY OF GROUND SETTLEMENT ON AREA OF SALT ROCK UNDERGROUND GAS STORAGE

ZHANG Ning1，ZHANG Qiangyong2，XIANG Wen2，LI Shucai2，JIA Chao2，LIU Jian2

2012, 31 (s2): -3762
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[PDF 509 KB] (638)

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During the operation of salt rock underground gas storages，ground settlement would be generated due to the volume shrinkage of salt rock caverns，and that would made a negative impact on the facilities on the ground(such as buildings，bridges，roadbed，etc.). In order to assess the impact，the method for calculating the failure probability of ground settlement in the area of salt rock underground gas storage was established. Firstly，the volume shrinkage of the salt rock caverns was obtained by numerical calculation. Then the SRAKA SCHOBER mining method was used to obtain the surface settlement caused by the volume shrinkage，and the performance function of the risk was established. Finally，the failure risk probability of ground settlement can be calculated by Monte Carlo method based on random variables. The method was applied to the Jintan underground gas storage in salt rock，the impact of the facilities on the ground settlement was effectively accessed，and the theoretical basis for the safety control of the salt mine zone was also provided.

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EXPERIMENTAL RESEARCH ON FAILURE MODES AND MECHANICAL BEHAVIORS OF GAS-BEARING SHALE

LI Qinghui1，2，CHEN Mian1，JIN Yan1，WANG F P2

2012, 31 (s2): -3771
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[PDF 898 KB] (1812)

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Testing system MTS 815 is used to carry out triaxial compression tests for specimens from Barnett，Haynesville，Eagle Ford in North American，and Longmaxi shale in South China. Their failure modes and mechanical behaviors under different confining pressures are obtained correspondingly. The similarities and differences between them are analyzed in detail. Splitting failure and splitting-shear mixed failure modes are the main failure modes for shale samples under low confining pressures，while shear failure modes predominate under higher pressures. The types of shale，burial depth，coring direction and confining pressures are all factors affecting the mechanical behavior of specimens. More quartz and carbonate contained specimen tends to be more brittle. In addition，the peak strength and Young?s modulus of shale are proportional with confining pressure，especially when the confining pressure is higher than 30 MPa. The peak strength of Barnett shale is higher than Haynesville，but lower than Eagle Ford. Shale samples from South China，compared with that from North America，have higher strength and Young?s modulus，while lower Poisson?s ratio. The brittleness characteristics of shale samples from China is similar to that from America.

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STRESS EVOLUTION AND INDUCED ACCIDENTS MECHANISM IN SHALLOW COAL SEAM IN PROXIMITY UNDERLYING THE ROOM MINING RESIDUAL PILLARS

BAI Qingsheng1，2，TU Shihao1，2，WANG Fangtian1，2，YUAN Yong1，2

2012, 31 (s2): -3778
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[PDF 454 KB] (673)

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Mining in shallow coal seam，which in proximity underlying the room mining residual pillars，is mainly affected by the upper residual pillars and the active mining induced stress. According to the problems of huge ground pressure and support yield accidents during mining in the No. 3–1–2 seam in the Shigetai Coal Mine，integrated research methods of theoretical analysis，numerical simulation and field testing were undertaken for the mechanism of mining induced stress evolution and support accidents. The result shows that，in contrast with Mohr-Coulomb criteria，the strain-softening criteria is accurate to capture the mechanism of deformation and destruction of the residual pillars in the room mining goaf，under the condition of the lower longwall mining induced stress. In the conditions that the residual pillars were stable in the room mining goaf，and the mining face was underlying these stable pillars，as a result of the residual pillars concentrated stress and the mining induced stress，the roof of the underlying seam slicing and falling nearby the edge of the residual pillar，and this big loading results in support yield. Blasting the upper pillars was carried out before and during excavated the No. 3–1–2 seam，the roof pressure transfers into the distant rock(coal) in the front of the working face. This measure effectively reduces the concentrated surrounding rock stress in the lower longwall face，and enables mining safely in the shallow seam in proximity underlying the room mining residual pillars.

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DETECTION TECHNOLOGY OF TUNNEL LEAKAGE DISASTER BASED ON DIGITAL IMAGE PROCESSING

LIU Xuezeng1，SANG Yunlong2，SU Yunfan3

2012, 31 (s2): -3786
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[PDF 811 KB] (1256)

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Focused on area of tunnel leakage disaster，a complete set of image processing algorithms，consisting of denoising，sharpening，image segmention，and improving algorithm，are developed for inspecting leakage disaster. By pre-processing，gray translation，segmentation threshold and pattern correction，finally，area of leakage disaster is got. Then，the calibration relation between pixels and actual shot size is got with outdoor tests. And as a convenient，low-costing，visual and highly efficient detection method，tunnel leakage recognition system is developed.

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TEST RESEARCH ON PIECEWISE SEEPAGE CHARACTERISTICS OF ROCK FRACTURE UNDER MULTISTAGE LOADINGS

GUO Baohua，SU Chengdong

2012, 31 (s2): -3794
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[PDF 511 KB] (811)

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The piecewise seepage characteristics of closed tensile fracture and loading history effect were investigated at room temperature using cylindrical rock samples of coarse-grained marble，sandstone，limestone and fine-grained marble with self-developed radial flow system. The results show that fracture seepage can be divided into three phases of islands flow，transitional flow，and groove flow according to different contact states and watershed distributions. Flowrate per head follows an exponential function with the normal stress，and it will be significantly lower in the subsequent loading process at the same normal stress. The relationship between flowrate per head and mechanical aperture was well simulated by the power function，in which the range of index is 1.93–2.60，so that sub-cubic law could be used to describe seepage in contacted rough rock fracture；flowrate per head is significantly lower at same mechanical aperture in subsequent loading process. Moreover，there is a piecewise linear relationship between equivalent hydraulic aperture and mechanical aperture，therefore，the modified cubic law can be established in each appropriate phase. The results have some theoretical significance for calculation of rock fracture seepage.

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TEMPERATURE FIELDS ANALYSIS OF ABSORBING SECTION OF TUNNEL HEATING SYSTEM USING HEAT PUMP IN COLD REGION

ZHANG Guozhu1，2，3，XIA Caichu1，2，SUN Meng1，2，ZOU Yichuan1，2，ZHAO Fei4

2012, 31 (s2): -3802
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[PDF 543 KB] (738)

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In order to prevent freezing damage in cold regions tunnels，tunnel heating system using heat pump was introduced for the first time at Linchang tunnel in Inner Mongolia Autonomous Region of China. The tunnel heating system consists of the heating section，absorbing section，heat pump，collector，and distributor line. This system can be used for heating lining and drainage system in tunnel portal. Absorbing section exacts geothermal energy from the surrounding rock of the central part of the tunnel and consists of surrounding rock outside of the heat exchanger pips and fluid in the pipes. The heat transfer model of surrounding rock is obtained considering lining structure and heat resource. The analytical solution can be obtained using the superposition principle，Laplace transform and finite integral transfer method. The heat transfer model of liquid is based on energy conservation method. Back analysis method is used to determine the thermal physical parameters. The outlet temperature can be obtained by the iterative method. Accuracy of the analytical solution is examined by comparing the calculated results with measured results. It is found that the calculated values well agree with those measured in the field. The results of temperature field theory solutions can provide theoretical guidance for the system dasign.

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MECHANISM OF SLOPE FAILURE INDUCED BY UNDERMINING —A CASE STUDY OF JIWEISHAN ROCKSLIDE IN WULONG

Li Tengfei1，2，LI Xiao1，LI Shouding1，HE Jianming1，MA Chaofeng3，4

2012, 31 (s2): -3810
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Landslide geohazards induced by underground mining at home and broad were summarized，and the current status of studies were analyzed. Common characteristics of these geological disasters were generalized. To reinforce the understanding of mechanism of undermining-induced landslides，taking Jiweishan Rockslide in Wulong for example，large-scale three-dimensional numerical model was built with the Continuum-based Discrete Element Method. The GPU technology that could accelerate the velocity of the circulations was used in the process of operation. Landslide failure process induced by undermining was modelled. The influence of rockslide stress field and displacement field caused by undermining were analyzed，and the formation mechanism and movement trend were investigated. The conclusions are as follow：the failure mechanism of Jiweishan Rockslide is part of the key block in front of the landslide collapsed，the sliding body at back of the landslide slided，and the karstificated belt was suddenly broken with shear rupture that had triggered the rockslide. Failure pattern was testified concretely with variation analysis of stress and deformation. This study shows that Jiweishan Rockslide was induced by underground mining.

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PHYSICAL SIMULATION STUDY OF PRINCIPAL STRESS DIFFERENCE EVOLUTION LAW OF SURROUNDING ROCK OF DEEP MINE ROADWAYS

NIU Shuangjian1，JING Hongwen2，YANG Dafang3

2012, 31 (s2): -3820
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[PDF 907 KB] (687)

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In the engineering background of a failure deep mine roadways of in Shandong Yuncheng Mine，its excavation unloading whole process is physically simulated by the large scale(1.0 m×1.0 m×1.0 m) three-dimension test system. The failure patterns and range of surrounding rock of deep mine roadways with no support are obtained by the method of model thin section. Using the independent development testing elements for three-dimensional stress，the actual loading-unloading stress paths and stress states of surrounding rock in different depths of deep mine roadways are revealed，and the evolution law of deviatoric stress inside and outside of the broken rock zone are mainly studied. Based on the results of the failure patterns and range of surrounding rock，the evolution mechanism of deviatoric stress is initial explored.

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MODEL TEST STUDY OF SURROUNDING ROCK LOAD RELEASING DURING SUPER-LARGE SECTION TUNNEL EXCAVATION

ZHAO Yong1，LI Shucai2，ZHAO Yan2，3，LI Liping2

2012, 31 (s2): -3830
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[PDF 1968 KB] (828)

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Against the background of the Liangshui tunnel of Lanzhou—Chongqing line and based on 3D large-scale geomechanical model test of excavation and support on large cross-section tunnel，the process of surrounding rock load releasing during tunnel excavation is studied. New similar material is developed according to the field geological condition，which is proved by the laboratory tests to be similar to original rock materials on mechanical properties and meets the test requirement. Construction methods of excavation and support on different sections are various and the load releasing processes of surrounding rock on full-face excavation and bench-cut excavation are compared firstly. Through analyzing the test data，the features and differences of load releasing processes with different excavation methods are revealed. There are great differences in load releasing processes at different locations of the same section using the same excavation method. Meanwhile，the load releasing process at the same locations of the same section are various when different excavation methods are used. Secondly，the phenomenon of first load concentration occurs in front of tunnel face affecting by the excavation. The degree of first load concentration is related with the excavation method and section form. High degree of load concentration in front of tunnel face would aggravate the crowding-out effect，which is unfavorable to surrounding rock stability. Lastly，by comparing the load releasing processes of support excavation and non-support excavation，it is known that support can response the first load concentration effectively，reduce the load releasing amount，and optimize the load releasing process of surrounding rock in construction.

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STUDY OF INFLUENCE OF ROCK STRUCTURE ON SURROUNDING ROCK MASS STABILITY OF UNDERGROUND CAVERNS IN HARD ROCK REGION WITH HIGH GEOSTRESS

LU Bo1，DING Xiuli1，WU Aiqing1，DONG Zhihong1，XIAO Pingxi2，PENG Shixiong2

2012, 31 (s2): -3846
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Guandi underground powerhouse is typical deep cavern groups in hard rock region. The challenge is that the geostress in the powerhouse area is high and discontinuities are well developed at the same time. The major principal stress is 25–35 MPa，no regional fault or major weakness zone have been found，but shear zones and joints are well developed. Failure phenomenon of the surrounding rock mass during the excavation of the underground cavern groups has been reviewed thoroughly. Rock structures and failure modes of surrounding rock mass have been studied in full length. The influence of geostress and rock structure on the stability of surrounding rock mass have been investigated in detail. The results show that the rock masses are fresh and belong mainly to class II and have a relative high strength，and so a high strength-stress ratio. The surrounding rock masses has strong ability to resist stress-induced failure. The influence of rock structure on rock masses is relatively stronger than that of geostress. Local instabilities and large deformation of some locations are all controlled by adverse geological discontinuities. In general，the characteristics of the rock structures of machine hall，transformer chamber and surge chamber are similar. This results in the similarity of the deformation characteristics and failure modes of the surrounding rock masses. The three cavers have certain differences in rock structures. Rock structures have different influences on the surrounding rock masses in different caverns，and also the failure modes. Jointed hard rock may assume time-dependent deformation under high geostress and this is another adverse influence of rock structures on rock masses. So，in hard rock regions with high geostress where the strength-stress ratio is high and joints are well developed，the influence of rock structure on surrounding rock masses must be fully considered.

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ANALYSIS OF SEISMIC DAMAGE OF SEGMENTS AND JOINTS AT THE JUNCTION OF SHIELD TUNNEL AND SHAFT

ZHAO Wusheng1，HE Xianzhi2，CHEN Weizhong1，TIAN Hongming1，YUAN Kekuo1

2012, 31 (s2): -3854
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[PDF 464 KB] (879)

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Models for elastic，flexible and rigid joints were established. Considering the interaction between structure and soil，failure mechanism and influential factors of segments and joints at the junction of shield tunnel and shaft were studied under different working conditions based on cross-river tunnel at Weisan Road in Nanjing. The results show that segments and joints bear large internal forces and small displacements using rigid joints，while flexible joints result in smaller internal forces and larger relative displacements. The corresponding response of elastic joints is between those of flexible joints and rigid joints. The mechanical parameters of soil and slip between contact faces significantly influence the seismic response of segments and joints. The conclusions are in good agreement with seismic damage data，which can provide references for seismic design of similar projects.

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DISCRETE ELEMENT ANALYSIS OF FAILURE PROCESS OF HARD ROCK WITH A PRE-EXISTING CIRCULAR OPENING

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

2012, 31 (s2): -3863
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[PDF 2076 KB] (690)

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Based on the theory of particle flow code，the failure process of tuffaceous sandstone with a pre-existing circular opening is simulated by numerical experiments under uniaxial，biaxial and triaxial compressions. And the impact of different loading modes is analyzed from the view of peak strength，microcrack and energy. The results show that the failure of rock specimen starts around the opening regardless of loading modes. The deformation of opening under uniaxial compression is different from that under biaxial and triaxial compressions. And a macro-crack is formed on the side of rock specimen under uniaxial compression. Peak strength of rock specimen under triaxial compression is larger than that of biaxial compression at the same confining pressure. And the difference of peak strength between biaxial and triaxial compressions increases with the increase of confining pressure. Crack-initiation stress decreases with the increase of confining pressure under biaxial compression，while crack-initiation stress increases with the increase of confining pressure under triaxial compression. The change process of strain energy can reflect the failure process of rock specimen. And its peak value is greatly influenced by confining pressure. The change process of dissipated energy can reflect the extent of slip and friction between microscopic particles. And its change law is related to loading modes and confining pressure.

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EXPERIMENTAL RESEARCH ON GOB-SIDE ENTRY RETAINING SUPPORTED BY FILLING TWO MATERIALS

CHENG Yunhai1，2，JIANG Fuxing2，LI Haiyan3

2012, 31 (s2): -3868
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[PDF 555 KB] (660)

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Gob-side entry retaining by filling has two shortcomings in high stress or encountering overlying strata violent movement，i.e. rigid material filling easily lead to packing wall stress concentration，even fractured or failure，caused fire or CO，CH4 leakage，and flexible material filling easily lead to roof cave-sink too large and even the occurrence of roof fall. In order to solve the problems，filling method was improved in Huaheng coal mine. Based on the study on the overburden stratum movement process and structure morphological characteristics above gob-side entry retaining，we calculated the amount of compression of the filling body，and two strength grades of roadway supports of gob-side entry retaining were design：the upper filler is high expansion to firmly seal the gap，and adapting impact load of the main roof movement；the lower filler strength support specific roof. Based on mechanical model established，the lower filler strength is calculated；Based on structure model established，the lower filler strength is calculated. Mineral pressure observation showed that the design of gob-side entry retaining met the application requirements.

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DISTRIBUTION CHARACTERISTICS OF OIL WELL WATER INJECTION EXPLORED BY IN-SITU STRESS MEASUREMENT

YANG Wuyang

2012, 31 (s2): -3875
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Water injection oil displacement through oil well stratum fracturing can enhance oil recovery factor，and the determination of stratum aquifer distribution after water injection is important basis for appropriately designing injection production well network. The natural electromagnetic wave in-situ stress measurement has been applied to detect the distribution features of stratum water injection in Zhouzhuang well G1. The voltage value obtained through measurement is converted into in-situ stress. Research results show that in-situ stress value has a certain correlation with the water abundance，low in-situ stress value is corresponding to abundant water，high in-situ stress value is low water abundance or have no water. Water injection influence scope and water abundance plane distribution features have been analyzed based on the horizontal and vertical distribution of in-situ stress and aquifer thickness in water injection section. The test result of the exploration shows that existing two water abundance low in-situ stress value zones trending near NS direction at 40 m east and 50 m southwest of well G1. The correctness of the result has been proved by afterwards oil production，this method provides a effective technical means for old oil well potential tapping.

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STUDY OF BLASTING VIBRATION CHARACTER OF SOFT ROCK ROADWAY EXCAVATION IN COALMINE

WANG Haibo，ZONG Qi

2012, 31 (s2): -3881
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[PDF 561 KB] (695)

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Based on testing and analysis of blasting vibration and excavation damage zone(EDZ)，blasting vibration effects of coalmine soft rock roadway excavation and its impact on roadway loose circle radius are researched. The vibration testing and wavelet analysis results indicate that level-radial direction value of blasting vibration velocity is the largest of three directions，velocity of vertical direction is the minimum，so，the level-radial direction velocity can be taken as safety criterion for roadway excavation blasting vibration；main frequency of blasting vibration are more than 100 Hz，80% of the blasting energy concentrated in the range of 100 to 150 Hz，and there are two distinct “sub-band”. Loose circle radius testing and analysis indicate that the loose radius of stabilized roadway is about 1.8 m，and about 10% of it was caused by blasting vibration. Based on this，length of bolt should be lengthened for improving safety and reliability of supporting. According to the research results，technical measures for reduce the vibration effect of coalmine soft rock roadway blasting excavation are given from the blasting parameters and charging structure.

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DETECTION，STABILITY ANALYSIS AND DISPOSAL OF LARGE SHALLOW GOAF：A CASE STUDY

WANG Desheng1，ZHOU Qingzhong2，CHEN Xucheng1，LU Guodong2

2012, 31 (s2): -3888
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[PDF 714 KB] (783)

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Based on the exploration and laser scanning of 3D space in the field，the stability and predictive analysis of the shallow and weak roof large goaf at Shouyun mine are made by using FLAC3D numerical simulation. Studies have shown：the limit state of crushing destruction is achieved at the two corners of roof plate，and gradually expands into a deep extension of the arch. There is the central tensile stress distribution clearly in the roof，but tensile failure will not be caused. Displacement of surrounding rock mass is eminent，but the overall of the goaf is stable. Numerical simulation research also shows that a certain size roof window will yield the limit state of shear failure near the fault F53. A relief window is formed by a fan-shaped deep holes blasting that is 13 layer of 132 deep holes? milliseconds blasting，the goaf collapsed gradually from the south to north on its own，an overlying rock protection layer of sublevel caving is formed by filling empty areas. The large goaf is handled safely.

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ABNORMAL STRATA STRESS RESULTED FROM GOAF SQUARE OF LONGWALL FACE BASED ON MICROSEISMIC MONITORING

KONG Linghai1，2，QI Qingxin1，2，JIANG Fuxing3，OUYANG Zhenhua1，2

2012, 31 (s2): -3896
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[PDF 776 KB] (796)

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Fracture instability and sink are the fundamental reason of strata pressure behaviors. Microseismic monitoring technology is applied to strata fracture monitoring of the goaf square period(i.e. length of the goaf sides of longwall face are equal) in longwall face. Relationships among microseismic events，strata movement and strata pressure behavior are conducted to reveal the physical mechanism of large energy microseismic events and abnormal strata pressure of surrounding strata during goaf square. Comprehensive comparative studies，statistics of dynamic changes of working resistance of support and collapse of coal wall of longwall face，have shown that mining influence range is larger than normal mining；and energy release of strata reaches a maximum value. The results prove that long wall face will occur abnormal strata pressure during goaf square can be used to guide prevention of mine dynamic disaster as coal bump，coal and gas outburst and water inrush of strata.

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EXPERIMENTAL STUDY OF SHEARING FAILURE PROPERTIES OF SANDSTONE UNDER ACIDIC CONDITIONS

XU Jiang1，2，WU Hui1，2，CHENG Lichao1，2，LIU Jing1，2，ZHOU Wenjie1，2

2012, 31 (s2): -3903
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[PDF 1138 KB] (720)

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The fine sandstone from the Xujiahe group of Three Gorges reservoir area is selected as object. The effect of various acid solutions with different pH values on sandstone under shearing load is investigated by using the independent development of meso-shear test equipment for coal rock. Simultaneously，temporal and spatial evolution law of microcrack of sandstone sample under the shear loading is researched by image processing technology. The relationship between the crack initiation and the degree of sandstone erosion was investigated. The results show that there is obvious correlation between the shear stress and crack evolution of sandstone at different time points，and process from surface crack?s initiation to the unstable failure of the samples was completed in a relatively short time. In the process of rupture failure of sandstone，it almost produced intergranular fracture in the mineral grain boundaries and cements，and transgranular fracture only produced in highly concentrated region of stress. Furthermore，as the increase of acidic strength of solution and time of erosion，the erosion degree and the deformation of sandstone increased，while the shear strength reduced and the width of crack corresponding increased，crack situation was more complex. Therefore，chemical solution is an important factor which affects the rock?s strength and deformation attenuation.

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SUPPORT TECHNOLOGY TO DEEP LARGE-SCALE SOFT SURROUNDING ROCK OF ROADWAY IN PINGDINGSHAN COAL MINE

GUO Jianwei1，2，LIU Quansheng3，YANG Zhanbiao2，LIU Bin3

2012, 31 (s2): -3910
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[PDF 565 KB] (679)

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A typical deep roadway with large-scale soft surrounding rock is researched here to study the stability of surrounding rock in Pingdingshan coal mine. With the laboratory experiment，the complex geological condition in deep rock roadway was determined. Discrete element method was adopted to simulate the deformation and failure of surrounding rock. The failure mechanism of surrounding rock was revealed. Technologies of spray layer which resisted bending and cracking and floor heave control were proposed. The main reason for instability of soft surrounding rock in deep rock roadway is the lower rock strengthen and the high geostress. The tensile failure appeared at vault and two side-walls and in the middle of floor at first. Then，the shear failure appeared at spandrel and two base angles. The failure zone extended into the deep area until the roadway is instable. According to the in-situ monitor data，it is concluded that stress in anchor and cable tended to be stable after supporting for two months，as well as the horizontal convergence，vault subsidence and floor heave. It means that the supporting technology works and the stability of soft surrounding rock in deep rock roadway is controlled.

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ANALYSIS OF SURROUNDING ROCK DISPLACEMENT CHARACTERISTICS DURING CONSTRUCTION IN GUANDI UNDERGROUND POWERHOUSE CHAMBERS

GAO Chunyu1，2，DENG Jianhui1，2，WEI Jinbing1，2

2012, 31 (s2): -3919
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[PDF 750 KB] (723)

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Based on the monitoring data of Guandi hydropower station underground powerhouse chambers during the construction period，displacement characteristics of surrounding rock are analyzed. Taking the generator chamber for example，research focuses on the structure face impact of the displacement and variation of the displacement-time curve. The research results show that the displacement of the rock mass is normally less than 20 mm. The larger displacement positions concentrate in the rock-anchored beam site and the middle and upper positions of generator chamber upstream side walls. Excavation exposed the larger displacement magnitude positions are controlled by the fault zone. The maximum displacement of construction period is 61.49 mm. The opening displacement of the structure face is the main displacement of the measuring point. Anchor bolts and anchor ropes restricted the rock displacement well. Displacement generate mainly during the excavation period，and display a typical characteristic step rise with the excavation process. When excavation completed，the surrounding rock mass deformation reduce quickly. The time characteristic of the surrounding rock displacement is not noticeable. The stability of the cavities is good.

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SAFETY ANALYSIS FOR SOFT ROCK TUNNEL FLOOR DESTRUCTION BASED ON DIFFERENT YIELD CRITERIONS

WANG Weiming，ZHAO Zenghui，WANG Lei

2012, 31 (s2): -3927
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[PDF 539 KB] (860)

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For a long time，stability evaluation of underground tunnel is unreasonable and unscientific. Safety factor of cave cannot be got by classical finite element method and it is difficult to judge the stability of tunnel by the criterion of stress，displacements of tunnel perimeter or size of plastic zones of surrounding rocks. Therefore，strength reduction technique is conducted to solve the stability factor of tunnel floor. Ultimate analysis is essentially a strength problem，so different strength criterions would cause different results. In view of this，relationship of strength parameters of different yield criterions are put forward and conversion expressions of the shear safety factors between classical Drucker-Prager(D-P) criterion and extended D-P criterion were obtained based on plane strain assumption. Considering that floor heave is caused by the general shear failure by compression effect of rock mass of tunnel walls，stability safety factors and potential failure surface of soft rock tunnel floor were analyzed according to the damage criterion of displacement catastrophe based on strength reduction finite element method，and results were compared with respect to different yield criterions. The results show that，theory conversion methods of safety factors have higher accuracy. Relationship of safety factors solving by different criterions are DP1＞M-C＞generalized D-P＞DP2＞DP4＞DPM-C＞DP3，which shows result of DP1 is in unsafe side and the results of DP2，DPM-C，DP3 are in good agreement with each other. Grid density and dilatancy angle have great influence on the results convergence.

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GEOMECHANICAL MODEL EXPERIMENT OF GLOBAL STABILITY OF LIZHOU ARCH DAM ON MULI RIVER

CHEN Yuan1，ZHANG Lin1，2，YANG Baoquan1，DONG Jianhua1，HU Chengqiu1

2012, 31 (s2): -3935
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[PDF 532 KB] (611)

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The global stability of Lizhou arch dam is studied by overloading model test in the 3D geomechanical model，the complex geological structures including faults，interlayer shear zones，fissure zones and large fissures affecting the global stability are considered and simulated. Through the overloading destructive test，the deformation characters，the failure process，pattern and mechanism of dam，rocks and structure planes in foundation and abutment are obtained. The controlling factors and weak regions impacting the stability are revealed. And the overloading safety factors of dam and foundation at each destructive stage are determined as follows：the crack initiation overloading factor K1 = 1.4–2.2，the nonlinear deformation overloading factor K2 = 3.4–4.3，the ultimate overloading factor K3 = 6.3–6.6. Furthermore，comparing with other similar projects，the safety factor of Lizhou dam is within the statistical range of overloading test safety factors. While local parts of rocks and structure planes in middle and upper abutments are damaged seriously，their reinforcements should be paid more attention to improve the global stability of Lizhou arch dam.

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EXPERIMENTAL RESEARCH ON MECHANICAL CHARACTERISTICS OF WEAK STRUCTURAL PLANE(ZONE) UNDER HIGH PORE WATER PRESSURE

LI Tianyi，XU Jin，WANG Lu，RAN Jie

2012, 31 (s2): -3941
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In order to study the strength and deformation characteristics of the weak structural plane(zone) with high stress and high pore water pressure，a series of triaxial tests coupling water and rock for two weak structural planes(zones) from a large hydraulic engineering are realized on MTS815 Flex Test GT rock mechanics test system. The results show that：the variation of the intensity parameter f of the weak structural planes(zones) is very little following the change of pore water pressure，while strength parameter c decreases rapidly with the increase of pore water pressure，and with a pore water pressure more than 2 MPa，c can disappear entirely；the shear strength of the weak structural plane(zone) lessen with the increase of pore water pressure，and the shear strength of the weak structural plane(zone) with 4 MPa pore water pressure will be reduced by more than 30% under 10 MPa normal stress. The deformation properties of the weak structural plane(zone) weakened dramatically when pore water pressure increases，and the deformation modulus E of the weak structural plane(zone) with 4 MPa pore water pressure reduces 34.2% under 10 MPa confining pressure. The research results show that：we should consider the influence of pore water pressure after the completion of the project when we select the value of the mechanical characters of weak structural plane(zone) in rock. For general engineering，the shear strength of weak structural plane(zone) can be forecasted with effective stress principle；for large engineering with high water head，we should make it with the undisturbed sample test.

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RESEARCH ON QUANTIFICATION INDEX OF ROCK MASS IN RIVERSIDE UNLOADING ZONE CLASSIFICATION

SUN Yunzhi1，2，HUANG Runqiu3

2012, 31 (s2): -3949
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[PDF 472 KB] (856)

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Rock mass unloading in riverside is a familiar geological phenomenon in hydroelectric project slope，it has important significance with regard to stability of rock mass slope，as well as relevant rock engineering problem. Unloading zone quantitative classification is always high lightened by hydroelectric project survey and design，it is common to use quantitative index to reflect rock mass structure characteristics despite of many other index used for unloading zone quantitative classification. According to hydroelectric engineering practice，this paper discussed the problem how to classify quantitative index for rock mass unloading zone in riverside，and proposed to use width of opening fissures，total width of opening fissures and ratio of wave velocity as quantitative index for rock mass unloading zone in riverside.

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IN-SITU STRESS FIELD ANALYSIS BASED ON MULTI-SOURCE INFORMATION INTEGRATION

YIN Jianmin1，LI Yongsong1，2，CHEN Jianping2，AI Kai1，MAO Ning1

2012, 31 (s2): -3958
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[PDF 459 KB] (577)

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Based on data mining and feature extracting of the source data of the in-situ stress field?s characters，and combined with the technology of multi-source information integration，the analytical method of multi-source information integration for in-situ stress field is proposed. And the method is organized by three gradational steps：the first time of multi-source information integration for the source data of the in-situ stress field?s characters→calculation of multi-source information integration→the second time of integration，feedback information integration. The calculation of multi-source information integrationis is carried out combining with uniform design and hybrid algorithm of simulated annealing and particle swarm optimization. This method is applied to simulate the in-situ stress field of Baihetan hydropower station，and the calculated results are consentaneous with the testing results. Meanwhile，the rock-core disking phenomenon when drilling and spalling phenomenon in the testing tunnel during excavation is compared with calculated results. It is shown that the proposed analytical method of multi-source information integration for in-situ stress field from the two sides of stress?s magnitude and azimuth，is reasonable and practicable.

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EXPERIMENTAL STUDY OF MECHANICAL CHARACTERISTICS OF SANDSTONE UNDER DIFFERENT LOADING PATHS

HAN Tielin1，CHEN Yunsheng1，SONG Yongjun2，LI Weihong1，YU Zhao1

2012, 31 (s2): -3966
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[PDF 864 KB] (668)

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Triaxial compression for sandstone sample under three paths，i.e. axial loading and radial constant，axial loading and radial unloading，axial constant and radial unloading are realized on WDT–1500 reactive material testing machine. The mechanical characteristic of sandstone comparatively from deformation property，strength property，failure feature and its mechanism are analyzed and researched. The test results show that strength of sandstone is reduced，but deformation of radial and its expansion of capacity under the same principal stress increase significantly under axial loading and radial unloading，axial constant and radial unloading relative to axial loading and constant radial，and especially under axial loading and radial unloading the expansion of capacity is largest；the deformation property and strength property of sandstone under these three stress paths are mainly influenced by initial axial pressure and initial radial pressure，but the influence of the unloading speed of radial pressure on mechanical characteristics of sandstone is not clear. The failure characteristics of samples under axial loading and constant radial present shear failure，but the failure characteristics of samples often present mixed tensile-shear failure under axial loading and radial unloading，axial constant and radial unloading.

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DAMAGE STRENGTH DETERMINATION OF MARBLE AND ITS PARAMETERS EVALUATION BASED ON DAMAGE CONTROL TEST

WANG Bin1，ZHU Jiebing1，YAN Peng2，HUANG Shuling1，WU Aiqing1

2012, 31 (s2): -3973
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[PDF 1073 KB] (708)

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In order to obtain the reliable damage strength and the evolution regulation，an experimental scheme of synchronic testing of stress-strain curves，AE activity and velocity of P wave is proposed and carried out. Compared with the results from three different methods，besides AE and P velocity testing method，the characteristic strengths can be objectively obtained from stress-volumetric strain (including crack volumetric strain) curves. By defining the irreversibly accumulative crack strain as damage parameter from loading and unloading volumetric curves，the characteristic strength and deformational modulus evolvement process are obtained based on damage-controlled testing. The results show that the deformation modulus，crack-damage strength and peak strength are all decreasing with damage growing；however，once the damage reach to a certain degree，the damage strength promptly decrease earlier than peak strength，and the peak strength keeping on increasing with damage growing and then decreasing gradually. By further analysis，the internal friction angle and cohesion evolvement law during failure process are discovered，that is，cohesion decreases rapidly with damage growing and reach to residual；but internal friction angle experiences increasing firstly then decreasing slowly，among which the increasing period happens to the moment of most cohesion loss. All the experimental results play a significantly theoretic role in discovering the failure mechanism of brittle rock.

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RESEARCH ON MEASUREMENT METHOD FOR STRESS OF ROCK EXCAVATION SURFACE UNDER EXTRA-HIGH STRESS

AI Kai，YIN Jianmin，LIU Yuankun，LI Yongsong，WANG Jie

2012, 31 (s2): -3980
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[PDF 541 KB] (647)

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For the limitations of current in-situ stress measuring methods when they are carried out in high in-situ stress conditions( ＞0.5)，a new goestress measurement method called based on partly restoration slot relief method is proposed to measure in-situ surrounding rock stress in high stress condition，and its feasibility is illustrated by theoretical model. This new method was applied at an experimental tunnel in Jinping II hydropower station，China；and the measured maximum stress is 80 MPa. When the test is carried out，it is not need to obtain intact rock core，meanwhile，the instruments of extra-high pressure is not requried. The device of this method is light weight，the operation is easy and quickly. It can be used to measure in-situ rock stress in high stress condition. it provides measured stress for prevention of the cavern rockburst and slope treatment.

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RESEARCH AND DEVELOPMENT ON HIGH PERFORMANCE ANCHOR CABLE DYNAMOMETRIC SYSTEM BASED ON VIBRATING-WIRE SENSOR TECHNOLOGY

WANG Qingbiao1，2，3，JIANG Jinquan2，SUN Yanqing3，QI Yinshan3，ZHANG Jun2，YIN Fali2，LI Zhiguo2

2012, 31 (s2): -3987
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[PDF 500 KB] (786)

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Outstanding anchor cable dynamometric system is urgently needed in anchor engineering of pre-stressed anchor cable so as to control tension during the process of anchor cable construction and monitor long-period variation of anchoring force. A breakthrough research has been made on the development of high performance anchor cable dynamometric system based on vibrating-wire sensor technology through theoretical research，laboratory study and field engineering experiment research. Here are the research results：(1) The newly-built mathematical model can improve the accuracy of vibrating-wire sensor and make error compensation for temperature. (2) The matching technique of string and operating diaphragm was adopted so that lag was decreased and accuracy of process was improved. (3) The low excitation circuit technology has been put into use that the inconformity of frequency was solved and the resolution of measuring instruments was enhanced. (4) The techniques of piston-conveying pressure and force conversion technology has been used to solve the vibrating-wire sensor problems of wide range，partial load effect，accuracy and long-term stability，which can be used to develop vibrating-wire sensors characterized with wide range，high-accuracy，high resolution and long-term stability. (5) Supporting detecting equipments，can directly display the physical quantity without additional errors but more accuracy. The newly developed anchor cable dynamometric system has achieved international leading level at aspects of accuracy，wide range，partial load，stability，reliability and environmental suitability that it can offer technical support for real-time monitoring of stress condition of pre-stressed anchor cable.

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CHARGE-INDUCED TECHNIQUE OF ROCKBURST PREDICTION AND ITS APPLICATION

PAN Yishan，ZHAO Yangfeng，LI Guozhen

2012, 31 (s2): -3993
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Using the experimental system for collecting the charge-induced signal of coal and rock，the research is made on the characteristic of charge induction during the deformation and fracture process of coal and rock. Using the self-designed charge-induced instrument，field test is done in coal mine. The experimental results show that the charge-induced signal generates during the deformation and fracture of coal and sandstone. The higher the stress in the coal or rock is，the stronger the deformation and the failure are，and the stronger the charge-induced signal is. The strongest charge-induced signal generated near the peak stress of coal or rock and the strong signal generated when coal damage. The higher compressive strength of the coal is，the stronger the charge-induced signal is and the longer the signal duration is. The primary principles of charge generation in the process of coal or rock deformation and fracture are friction and crack-tip charge separation because of micro-rupture. Field practice shows that there is a certain relationship of the charge induction value and the stress in the coal. The charge-induced amplitude is small in the stable period in the face，but the amplitude is large in the event of impact. The impact danger can be predicted by the charge induction method，but still the charge induction method is at an experimental stage. Charge induction forecasting techniques also need to continuously be validated and improved in the field. The reliable technical support is provided for the non-contact forecast to the mine dynamic disaster.

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DEVELOPMENT AND PRELIMINARY TEST OF EQUIPMENT OF MESOSCALE TEST IN URBAN UNDERGROUND ENGINEERING

QIN Weimin，REN Weizhong，ZHOU Zhengming

2012, 31 (s2): -4000
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Aiming at a series of environmental protection problem brought by urban construction including highway tunnel，subway and tunnel construction，the development of mesoscale physical scale model test equipment is carried out. The test equipment mainly consists of bench system，measuring equipment，and tunnelling system，which belongs to separate component. Because of the characteristics design of tunnelling system，influence on surrounding environment by physical simulation of different construction methods are respectively achieved in three aspects including tunnelling，underground excavation and pipe culverts shield pushing. After the materials formation ratio test，the test methods and processes of geologic strata material are selected. The preliminary test of tunnelling model shows that the value of surface subsidence predicted by Peck formulas is too small，and its transverse settlement trough shape has a certain gap by comparing with Gaussian curve，so it is not appropriate for prediction of surface subsidence by Peck formulas in this type of soil mechanics test. According to some of the questions found in preliminary tests of tunnelling simulation，some follow-up research prospects are given by the researchers.

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2012, 31 (s2): -4001
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2012, 31 (s2): -4006
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2012, 31 (s2): -4060
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