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2010, 29 (S2): 0-

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THREE-DIMENSIONAL SEEPAGE NETWORK SEARCHING OF FRACTURED ROCK MASS AND STEADY SEEPAGE FIELD ANALYSIS

李海枫，张国新，朱银邦

2010, 29 (S2): 3447-3454

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Combining with percolation theory，the composition characteristic of fractured rock seepage network is analyzed according to the statistic data and seepage characteristic of discontinuity in practical engineering；and the similarity problem of three-dimensional block cutting technology and percolation theory in fracture classification is also studied. The identification module for water-block characteristic on seepage fractures plane is added based on three-dimensional block cutting technology；and three-dimensional seepage network searching algorithm is formed finally to solve the problem that three-dimensional seepage network is difficult to be established. According to Louis formula and generalized Darcy law，a program named 3D-Network-Seepage.f90，which can solve the problem of three-dimensional seepage network searching in fractured rock and analyze steady seepage，is developed by this algorithm. Combining with a classical example，this method is proved that it not only can form objective and valid seepage network，but also reflects the laws of water movement on fracture plane and the actual flow trend in fracture network. However，this method is expected to be proved in practical project in the future.

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IMPROVED CONSTITUTIVE RELATION OF ROCK MASS BASED ON TWO-PARAMETER NEGATIVE EXPONENTIAL DISTRIBUTION

胡秀宏1，2，伍法权1，孙强2

2010, 29 (S2): 3455-3462

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The functional relationship between discontinuity occurrence and ground stress is established. This improved constitutive relation can quantify the anisotropic property of rock mass mechanics which is controlled by the discontinuity occurrence and ground stress direction by introducing surplus shear stress ratio h. The research results show that when the direction of ground stress changes，the value of h will change accordingly and further lead the curve of stress-strain of rock mass to alter at the same time. Based on this improved constitutive model of rock mass，the stress-strain curves of rock mass of Xiaowan hydropower station foundation in Yunnan Province are calculated；and the anisotropic characteristics of rock mass under different stresses are revealed.

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STUDY OF CONSTITUTIVE MODEL FOR SINGLE INFILLED JOINTED ROCK MASS

XIAO Weiguo1，DUI Guansuo1，ZHU Yuping1，CHEN Tielin1，REN Qingwen2

2010, 29 (S2): 3463-3468

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According to the previous direct shear test results of infilled joint，the influence of the ratio of infilled thickness to asperity height on mechanical parameters of joint is detailly studied. On the basis of analyzing several kinds of shear strength models for jointed rock mass，the constitutive model for increment-type stress and displacement of infilled joint rock mass is proposed by using the elasto-plastic theory；and the hardening and softening characteristics of joint shear stress-displacement curve are especially studied. Through the comparison of shear curves of existing test sites，the results indicate that the proposed model curve agrees better with the experimental data，which identifies the correctness of the model.

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EXPERIMENTAL STUDY OF DYNAMIC MECHANICAL PROPERTY OF DAGANGSHAN GRANITE

ZHU Zeqi，SHENG Qian，LENG Xianlun，ZHU Fuguang

2010, 29 (S2): 3469-3474

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Taking the Dagangshan granite specimens for example，the conventional(static) triaxial compression tests and dynamic triaxial compression tests are both carried out to analyze the relationships of some important parameters such as compressive strength，Young¢s modulus，Poisson¢s ratio and their corresponding ultimate stress with strain rate. The research results show that under different confining pressures，with the increase in strain rate，lateral failure strain keeps invariant within the range of 0.002–0.004，axial failure strain increases a little and compressive strength of the granite increases significantly. The results also show that the increase in Young¢s modulus tends to reduce with the confining pressures，and the Poisson¢s ratio has no evident relation with the increase in strain rate. Based on the static complete stress-strain curves and damage mechanical analysis of Dagangshan granite，it is found that the brittle rock damages mainly are lateral damage types. Through regression analysis，damage evolution equation of the Dagangshan granite under static triaxial compression is set up. The rate-correlation between dynamic damage and static damage is further established according to damage theory. Considering the correlation between dynamic strength and initial Young¢s modulus，the experiential dynamic damage constitutive model for rock is established，which can be used as a basis for analyzing the attenuation law and strain wave spreading of rock mass under earthquake loads.

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STUDY OF UNLOADING DILATANCY PROPERTY OF ROCK AND ITS CONSTITUTIVE MODEL UNDER HIGH CONFINING PRESSURE

HUANG Wei1，SHEN Mingrong1，2，ZHANG Qingzhao1

2010, 29 (S2): 3475-3481

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Based on the unloading test of rock specimen under high confining pressure，the dilatancy property of rock mass is studied. The study results show that the deformation modulus at initial dilatancy point where the largest compression volumetric strain can be used as elastic modulus at elastic stage. Based on the unloading test，the complete stress-strain curve for rock is composed of four phase：elasticity，unloading yield，post-peak brittleness and residual ideal plastic phases. According to the characteristics of each stage，the constitutive model for that corresponding stage can be obtained. Finally，complete constitutive model for rock mass under unloading can be established. Through data fitting method，the model curves of different unloading tests are obtained，which has been verified to well fit the experimental curves.

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EXPERIMENTAL STUDY OF GAS PERMEABILITY OF OUTBURST COAL BRIQUETTES IN COMPLETE STRESS-STRAIN PROCESS

JIANG Changbao1，YIN Guangzhi1，2，LI Xiaoquan1，CAI Bo1

2010, 29 (S2): 3482-3487

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Based on the briquette specimens of the outburst coal seam K1 of typical coal and gas outburst mine of Sanhui a mine of Tianfu Coal Industry Co.，Ltd. in Chongqing，the experimental study of gas seepage law of outburst coal briquettes in complete stress-strain process under continuous loading is conducted by fluid-solid-heat coupling with triaxial servo-controlled seepage system of coal containing gas. The study results show that gas flow is tightly related with the damage deformation of the outburst coal briquettes during the complete stress-strain process. Gas flow firstly decreases gradually with the increase in axial strain，but it starts to rise after the yielding point of the complete stress-strain process of outburst coal briquettes；and the increasing rate of gas flow also enlarges after the peak point. On the other hand，the gas flow decreases primarily when the coal sample is volume compressed and then reverses to increase after the sample starts on dilatancy. The increasing range of gas flow enlarges after failure phase. The relationship between gas flow and axial strain can be expressed as a quadratic function and the gas flow decreases with the increasing confining pressure.

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EXPERIMENTAL STUDY OF TEMPORAL AND SPATIAL DISTRIBUTION CHARACTERISTICS OF ACOUSTIC EMISSION DURING ROCK FRACTURE BASED ON SINGLE-LINK CLUSTER METHOD

LIU Jianpo，LI Yuanhui，TIAN Jun，ZHAO Xingdong，LIU Hongtao，GAN Huaiying

2010, 29 (S2): 3488-3497

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Based on acoustic emission(AE) locating technique and single-link cluster(SLC) method，the experimental study of change characteristic of spatial correlation length of AE events during the fracture process of rock specimens under uniaxial compression is conducted. The color separation of AE events by link¢s length distribution of SLC frame can be used to study the cluster concentration degree of AE events. The results show that the two factors influencing the change in spatial correlation length are as follows：stress release，which leads correlation length to decrease，and stress field transferring，which leads correlation length to increase. According to the changes in spatial correlation length，the rock specimens can be classified into three types：(1) the specimens show no significant plastic deformation before failure. The spatial correlation length of AE events present a trend of accelerate growth which features as power law. It reaches the maximum value before rock failure. (2) The specimens show remarkable plastic deformation before failure. In plastic deformation stage，the spatial correlation length can either increase or decrease which depends on combination of the two above mentioned factors. (3) The specimens show clear cracking localization during loading. The spatial correlation length shows a sharp decrease when macro cracks generate. The link¢s count in SLC frame shows fractal characteristics. It can reflect the spatial evolutional process of AE events，which is consistent with the results acquired by spatial correlation length. The increase in spatial correlation length reflects the long-range transfer of stress field process. The difference between spatial correlation length and its previous value during the plastic phase has important significance for predicting rock failure.

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EXPERIMENTAL STUDY ON DEFORMATION AND SEEPAGE PROPERTIES OF OUTBURST COAL SAMPLES UNDER CYCLIC LOADING

LI Xiaoquan1，2，YIN Guangzhi1，3，CAI Bo1

2010, 29 (S2): 3498-3504

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Based on the typical coal and gas outburst K1 coal seam of Sanhui mine which belongs to Tianfu Coal Industry Co., Ltd.，the seepage experiments of outburst coal samples under cyclic loading，constant gas pressures and different confining pressures are conducted by self-developed fluid-solid-heat coupling triaxial servo-controlled seepage system of coal containing gas. The research results show that plastic deformation of coal sample is produced under cyclic loading. With the cyclic number，its elastic modulus and permeability both tend to decrease which is the most obvious in the first cycle. The permeability of coal samples gradually increases in unloading process and decreases in loading process. Closed rings are formed in the permeability-strain curves in the two above processes，corresponding to a closed hysteresis loop formed in axial stress-strain curve，which indicates that permeability changes is closely related to the damage deformation of coal sample. What¢s more，permeability rate is positively correlated with damage variable. The variation is more obvious in the previous cycles and tends to be stable after the later cycles.

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ANALYSIS OF ENERGY CHARACTERISTICS AND DEFORMATION PARAMETERS OF ROCK MASS UNDER CYCLIC LOADING

LIU Jie1，LI Jianlin1，ZHANG Yudeng2，ZHU Ting1，YANG Shanshan1，LI Yingxia1

2010, 29 (S2): 3505-3513

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Using RMT–150C rock mechanics test system，experimental tests of different kinds of rock materials under cyclic loading with the test condition of different stress levels and loading rates are carried out. Based on the division of stress and strain curves under loading and unloading conditions，the energy dissipation rate during unloading process is defined；and energy conversion during rock damage process is explored. Meanwhile，change laws of the deformation parameters such as the elastic modulus，Poisson¢s ratio and residual strain are also analyzed quantitatively. The research results indicate that the higher the stress level and loading frequency are，the stronger the lithology is，the greater the hysteresis loop area，doing work the process of loading and the release elastic energy during the unloading process are；besides，the rock is softer，the energy conversion rate is higher. Before rock mass does not reach the peak value of compressive strength，the higher the stress level is，the greater the elastic modulus is，which shows that within the range of the rock mass compressive strength，with the higher loads，the deformation ability of rock mass under the same load increment weakens significantly when the gap and micro defect are compacted. Meanwhile，it can be given that fatigue strength will reduce when the frequency increases to a certain level. As a whole，the axial and lateral relative residual strains of rock decrease gradually with the increase in cycle numbers.

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ELASTIC WAVE VELOCITY AND MECHANICAL PROPERTIES OF SANDSTONE UNDER DIFFERENT WATER CONTENTS AT LONGYOU GROTTOES

SHAO Mingshen1，LI li2，LI Zuixiong3

2010, 29 (S2): 3514-3518

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To study the impact of water environment change on weathering and damage of Longyou grottoes，the experimental research on the mechanical property and the elastic wave velocity of sandstone under different water contents is conducted. The change laws of stress-strain curve and mechanical properties such as peak stress，elastic modulus are also analyzed. The analysis results show that the water content has obvious effect on stress-strain curve and mechanical properties of sandstone：strain softening behavior weakens，peak stress and elastic modulus decreases exponentially with the increase in water content. Elastic wave velocity test results indicate that the uniaxial compressive strength is linear with elastic wave velocity，and the elastic wave velocity decreases abnormally to a very low value at the water content of about 1.5% due to expansible clay minerals. The water content has a little impact on anisotropy. Therefore，it can be concluded that dry and steady environment is of benefit to the conservation of Longyou grottoes.

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STUDY OF MECHANISM OF ROTARY PENETRATION

SONG Ling1，2，LI Ning1，LIU Fengyin1

2010, 29 (S2): 3519-3525

[PDF] 678 KB (891)

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Based on the cutting mechanism，besides the mathematical model for torque and axial force being established，the mathematical model for torque and axial force on the probe，changing with the penetration velocity，the rotary velocity of the probe and the physico-mechanical parameters of rock and soil masses，is also developed by analyzing the forces on cutting edges of probe. In addition，the validity of the mathematical model is proved according to the data from laboratory experiment. The influence factors on the torque and the axial force of probe unit are analyzed；and the theoretical basis of rotary penetration technique，which is made clearly，is that the values of axial force and torque of the probe unit only depend on mechanical property of rock and soil masses when the running mechanical parameters of machine，probe diameter，materials and form of the probe are all the same. Moreover，the axial force of rotary penetration test is compared with that of static cone penetration test to fundamentally explain the reason why rotary penetration test can be applied to rock mass.

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STUDY OF RELATIONSHIP BETWEEN FAILURE PROPERTIES OF SURROUNDING ROCK AND DIRECTION OF GEOSTRESS

ZHANG Yihu，LU Yiran，ZHOU Huoming，ZHONG Zuowu

2010, 29 (S2): 3526-3535

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Considering practical engineering needs，the classification standard of spalling is established；and a related method for speculating the principal stress direction by the development position and development degree of spalling is proposed. Meanwhile，combining laboratory tests，biopsy scanning and other means，the generated mechanism of tensile crack on spalling face is deeply studied；and a related method for determining initial geostress directions by extended direction of tensile crack is also given. Finally，taking a hydropower project in southwest China for example，on the basis of the investigate and research results of spalling and tensile crack at dam site，principal stress direction and its variations are speculated，which forms the effective complement to geostress test and provides strong support for the later engineering designs.

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DEFORMATION CHARACTERISTICS OF ROADBED FILLING OF SOFT METAMORPHIC ROCK BEFORE AND AFTER SOAKING IN QINLING—BASHAN MOUNTAINOUS REGION

YANG Lingyun，WANG Xiaomou，ZHANG Zhe，LIU Peng

2010, 29 (S2): 3536-3541

[PDF] 585 KB (718)

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In order to study the deformation characteristics of roadbed filling of soft metamorphic rock before and after soaking in Qinling—Bashan mountainous region，the conventional compression tests and other compression tests under cyclic loading and different soaking loadings on three different lithological roadbed fillings of soft metamorphic rocks are conducted by using large-scale compression apparatus. The research results show that both the water infiltration and the applied cyclic loading can increase the deformation of soft rock filling；and the deformation of different lithological soft metamorphic rock filling induced by water infiltration and cyclic loading is different. Moreover，the wetting deformation increases and the total compression deformation of roadbed filling decreases with the soaking load. By comparing the results of conventional compression tests with those of compression tests under cyclic loading，it is found that cyclic load increases the deformation of soft metamorphic rock roadbed filling. Therefore，the analysis indicates that the roadbed soaking and traffic loading are the two important factors affecting the deformation of soft metamorphic rock roadbed，which cannot be ignored. The above conclusions have certain guide significance for the highway construction of Qinling—Bashan mountainous region，where the soft metamorphic rock is used as roadbed filling.

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RESEARCH ON PERMEABILITY COEFFICIENT OF ROCK MASS BASED ON UNDERWATER PUMPING TEST AND ITS APPLICATION

(School of Civil Engineering and Architecture，Wuhan University，Wuhan，Hubei 430072，China)

2010, 29 (S2): 3542-3548

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Hydraulic boundary conditions of borehole pumping test for underwater rock mass are analyzed. Based on the principle of superposition of potential field，the conditions are divided into horizontal recharge condition and vertical recharge one. The theory of horizontal recharge is the same as that of land-based artesian water borehole pumping recharge. For the vertical recharge，the calculating formula for the borehole water flow is derived with some appropriate assumptions and simplifications；and the theoretical calculating formula is deduced and applied to obtain the permeability coefficient theoretical formula for underwater rock mass pumping test. Using this permeability coefficient calculated by the theoretical formula，the in-situ pumping tests for underwater rock mass are simulated by numerical methods. The calculating results are close to the test results. For the convenience of comparison，the permeability coefficient calculated by land-based formula is used to simulate the in-situ pumping tests. The calculating results show that compared with the permeability coefficient formula based on the land-based seepage theory，the permeability coefficient calculated by the theoretical formula is more reasonable，more realistic；and it can better reflect the seepage characteristics of underwater rock mass pumping test than those by land-based formula. Finally，according to the permeability coefficient calculated by the formula，the numerical method and empirical formula are used to predict the water inflow during constructions of a submarine tunnel. The results of water inflow obtained from the two methods are nearly the same，which can provide references to the selection of design plan and the construction of submarine tunnel.

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SYNTHETIC ADVANCED FORECAST TECHNIQUE BASED ON GEOLOGICAL LOGGING FOR TUNNEL FACE AND GROUND PENETRATING RADAR

WANG Zhenyu1，CHENG Weifeng1，LIU Yue2，ZHANG Yuhao3

2010, 29 (S2): 3549-3557

[PDF] 1790 KB (714)

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Synthetic advanced forecast technique based on geological logging for tunnel face and ground penetrating radar(GPR) is proposed and put into practice in the case of a certain deep and long tunnel project. On the basis of regional engineering geology data analysis，the forecast scheme and time are optimized depending on tunnel face geological logging. Meanwhile，according to the occurrence of adverse geological body which has been partially exposed and the location of single side wall which has been seen，the border and influence length of adverse geological body on the two side walls and apex of arch are calculated through trigonometric functions. When getting close to special geological sections，more accurate short-term forecasts have been obtained using GPR to detect faults and underground water storage situations based on radar-wave reflection amplitude，phase and frequency. For a wide range of adverse geological body，the reliability of forecast can be improved with the strategy of continuous forecast，which is useful for the confirmation and feedback of the forecast. This synthetic geologic forecast method is applied to the tunneling construction passing through faults and water inflow sections，and gives a satisfied effect.

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STUDY OF HIGH-PRECISION MEASUREMENT OF THIRD-ORDER ELASTIC MODULUS FOR ROCK

TIAN Jiayong1，MAN Yuanpeng2，QI Hui2

2010, 29 (S2): 3558-3561

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Based on the acoustoelastic theory of rock，velocity variation of longitudinal and transverse ultrasonic waves propagating along the thickness direction of plate rock samples under biaxial loading condition is measured by the pulse echo method to investigate the third-order elastic modulus for rock. The test results indicate that sensors of transversal wave and longitudinal wave are set at the relative surface of the central portion of rock specimen to measure the transversal wave and longitudinal wave at the same position，which not only can weaken the biaxial loading end effect，but also overcome the influence of rock anisotropy on the measured results. Furthermore，time difference between multi-echo signals is measured by pulse-echo method to overcome the influence of couplant and measured circuit on the travel-time difference of echo signals. The pulse-echo method can implement the high-precision measurement of third-order elastic modulus for rock，which provides technical support for the measurement of in-situ crustal stresses.

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INFLUENCE OF LOW-FREQUENCY VIBRATION ON DESORPTION CHARACTERISTICS OF COAL SAMPLES

LI Shugang1，ZHAO Yong1，ZHANG Tianjun2，XU Hongjie2

2010, 29 (S2): 3562-3568

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The excited and testing system of gas adsorption and desorption is developed to study the influence of low-frequency vibration on gas desorption characteristics of coal sample. The test results show that the amount and velocity of gas desorption increase，and the velocity of attenuation becomes fast with the decrease in vibration frequency；the attenuation coefficient and desorption intensity of coal sample gradually decrease with time. Using related knowledge about the theory of gas desorption velocity and vibration to analyze the test results. It is shown that low-frequency vibration can lead the porosity of coal to weakening，permeability to decrease and diffusion rate to slow down，all of which are no advantage for the coal gas desorption. With the effects of disturbances，adsorpted accompanying molecules can obtain desorption energy，but the gas desorption capacity is small because of the decrease in diffusion rate and desorption velocity；without the effects of disturbances，the porosity of coal sample doesn¢t change. Although the adsorpted accompanying molecules cannot obtain desorption energy，the desorption velocity and gas desorption capacity are larger than those in the effect of vibration because of the larger diffusion rate and permeability. Therefore，the weakening of the porosity of coal samples and increased molecular mean free path under low-frequency vibration can lead to slow diffusion of molecules. Meanwhile，lots of tiny porosity layers are formed at the vibration face，which increase the adsorption sites inside the coal samples；and then slow down the coal gas desorption.

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ANALYSIS OF FAILURE MECHANISM OF BADONG RED BED SOFT ROCK GENTLY INCLINED BEDDING SLOPE

LU Haifeng，CHEN Congxin，YUAN Conghua，YU Hongdan，SHEN Qiang

2010, 29 (S2): 3569-3577

[PDF] 630 KB (659)

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Based on series of experiment researches on the engineering geological properties of Badong red beds，the formulae of stability coefficient on different positions of potential sliding surface are established by the mode of plane sliding which is most commonly used for this kind of slope. Combining with the calculation of the examples，the analysis of influence of excavation on slope stability is conducted and the shear rheological process of weak intercalation on the potential sliding surface is analyzed. The research results show that the failure of Badong red bed soft rock gently inclined bedding slope begins at the excavation of slope foot，and intends to potential sliding surface. The process starts from constant rate creep，gradually to accelerated sliding，which comes with the interaction of many factors，such as disintegration of rock mass，crack growth and water infiltration softening the potential sliding surface. On the basis of grasping the failure mechanism of this kind of slope，the related recommendations on the reinforcement means and construction managements are proposed and the research results have significant referenced values for the similar slope.

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STUDY OF TRIAXIAL CREEP MECHANISM OF MICA-QUARTZ SCHIST BASED ON MICROSCOPIC TEST

CHEN Wenling1，2，3，ZHAO Fasuo1，2，3，GONG Hujun4

2010, 29 (S2): 3578-3584

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Firstly，the mineral composition of mica-quartz schist samples is determined through visual measurement by polarizing microscope and energy spectrum analysis. The mineral composition of mica-quartz schist is divided into three parts such as hard part，soft part，and defects such as voids and cracks. For these three parts，the hard part is the force skeleton，the other two parts fill in it. Quartz is the hard part，white mica is the soft part in the mica-quartz schist sample. Secondly，in order to study the microstructure changes of mica-quartz schist during triaxial creep process，the polarizing microscope tests and electronic microscope scanning tests are conducted to observe the radial slices and axial slices of mica-quartz schist for three triaxial creep stages，which are no force stage，the upcoming accelerated creep stage and damage stage. According to the test results，the microstructure changes of mica-quartz schist are divided into four kinds，which are closure of open crack，position adjustment of hard part，position adjustment of soft part and micro-damage. At the same time，the micro-damage style of white mica and quartz are summarized separately. Thirdly，through analyzing the reasons for microstructure changes of mica-quartz schist，the creep mechanism is interpreted. It is observed that in different stress levels，and through different loading time of the same stress level，several microstructure changes of above-mentioned four changes of mica-quartz schist will generate，therefore there show attenuation creep stage，constant creep stage and accelerated creep stage，respectively. Lastly，three characteristics of this triaxial creep mechanism for mica-quartz schist based on microscope test are summarized.

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DETECTION OF LIMESTONE WATER-CONDUCTING CHANNELS IN COAL MINE BY PARALLEL 3D ELECTRIC METHOD OF SURFACE BOREHOLES

WU Rongxin1，LIU Shengdong2，ZHANG Pingsong1，XIAO Yulin1

2010, 29 (S2): 3585-3589

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It is put forward that the parallel 3D electrical method of surface boreholes can be used to detect the limestone water-conducting channels；and it is also a new geophysical prospecting means for the prevention of limestone water disaster in coal mine. Generally，three boreholes are set on the ground and an electrode cable is imbedded in each borehole to detect the objective strata. After the observation system of the parallel electric method is correctly connected，the AM mode of data-collecting is adopted by this method. Coordinate of each electrode in borehole is edited；and electrical resistivity tomography of AM data is conducted to obtain the 3D resistivity changes among the three boreholes. Based on the electrical property differences between water-rich area and normal strata，the possible resistivity manifestation of water-rich area is analyzed. Combining with the existing data such as stratigraphic column，water gushing in roadways，grouting materials，etc.，the distribution ranges of aquifer region and water-conducting channel are found out. The exploration case for detecting water-conducting channels in Xieqiao coal mine of Huainan mining industry by using this method is conducted. The detection results show that this method can be used to well find out the limestone water-conducting channels in water inrush area. It provides a good guidance to the work of grouting and water plugging in limestone strata，which leads to dimish the water inflow of Dongfeng well yard greatly and the threat of limestone water inrush have been well removed.

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COUPLING STUDY OF MICROSEISMIC MONITORING AND NUMERICAL SIMULATION FOR TECTONIC ACTIVATION

JIANG Fuxing，LIU Weijian，YE Genxi，LI Wei

2010, 29 (S2): 3590-3597

[PDF] 1322 KB (786)

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Microseismic monitoring technology is applied to the catastrophe process monitoring of geological anomalous bodies，such as faults，karst collapse columns and high angle fractured zone long wall face. It provides dynamic information including propagation，growth and failure of the channel for warning the underground water inrush hazard of dangerous working face. Coupling analysis of displacement field and stress field of surrounding rock at the working face by numerical simulation method and the activation information of geological anomalous bodies such as faults，karst collapse columns and high angle fractured zone obtained by microseismic monitoring technology is conducted to reveal the mechanism of tectonic activation and mutation induced by mining. According to the coupling analysis results，combined with the distribution of faults，karst collapse columns and high angle fractured zone at tested working face，some targeted water proof and control projects are implemented. The analysis results prove that the coupling analysis method of microseismic monitoring and numerical simulation can be used to study the tectonic activation and can provide guidance for water proof and control of mining project.

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PRELIMINARY ANALYSIS OF EARTHQUAKE OCCURRENCE BACKGROUNDS OF Ms≥8.0 CATASTROPHIC EARTHQUAKES IN MIDDLE AND EAST PARTS OF CHINESE CONTINENT

TAN Chengxuan1，QIN Xianghui1，WANG Ruijiang2，LONG Changxing1，DENG Naigong1，SUN Ye1，ZHANG Chunshan1，SUN Weifeng1

2010, 29 (S2): 3598-3607

[PDF] 5335 KB (687)

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The earthquake occurrence backgrounds of Ms≥8.0 catastrophic earthquakes in the middle and east parts of Chinese Continent are discussed from aspects of tectonic landform，geological mass features and its physico-mechanical properties，present GPS displacement field，active fault，contemporary tectonic stress and energy field，and so on. Preliminary results show that earthquake，which is triggered by a sudden release of the concentrated geo-stress and energy in the interior of the earth，is one kind of activities in local or regional crust；and that the location of earthquake is always the active tectonic zone or weak belt in the crust，such as active fracture belt，etc.；and that the geo-stress and energy are always concentrated in the evolution process of active fracture belt in the crust while the active fracture belt passing through and being blocked by the special geological environments，such as tectonic landform，rigid crystalline basement，etc.. When the concentrated geo-stress and energy exceed the strength of rock or rock mass，the rock or rock mass will be broken，so an earthquake will be triggered. Active tectonics and geological mass features and physico-mechanical properties are necessary conditions for earthquake occurrence，and geo-stress and energy concentration are sufficient conditions for earthquake occurrence. At last，the key region which should be paid attention to for a mid-long term in the middle and east parts of Chinese Continent and the working suggestions are proposed.

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STUDY OF OPTIMAL LENGTH-DIAMETER RATIO OF ROCK SPECIMEN BASED ON NUMERICAL TESTS

YIN Xiaotao，GE Xiurun，LI Chunguang，WANG Shuilin

2010, 29 (S2): 3608-3608

[PDF] 1433 KB (661)

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The uniaxial and triaxial compression tests of rock are virtually realized by particle flow method. Numerical compression tests of rock specimens with seven kinds of length-diameter ratios，i. e. 0.5，1.0，1.5，2.0，2.5，3.0，4.0，under four different confining pressures are conducted to analyze the influence of the ratio and confining pressure on the failure process，failure shape，stress-strain curve and energy transfer. The study results show that the test data scatterness of optimal length-diameter ratio of rock specimen by mechanics index are larger than those calculated by energy analysis method；and the test result rule by energy analysis method is good and stable. Besides，the optimal length-diameter ratio of 3.0 is strongly recommended.

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EXPERIMENTAL STUDY OF CORROSION OF GLAUBERITE SALT ROCK

LIU Zhonghua1，2，XU Suguo1，HU Yaoqing1，FENG Zengchao1，LIANG Weiguo1，ZHAO Yangsheng1

2010, 29 (S2): 3616-3621

[PDF] 932 KB (743)

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The glauberite salt rock samples are scanned at various corrosion time by the μCT225KVFCB-type high-precision micro-CT test system. According to the different ray attenuation coefficient changes in the whole corrosion process，the corrosion damage law of glauberite salt rock is studied from the perspective of meso- structure. The research results show that the density damage and pore ratio of the glauberite salt rock samples increase gradually，but the total specific surface area declines linearly with corrosion time. Meanwhile，the change in specific surface area of corrosion route way is particular，and it increases at first and then decreases. These research results have a very important significance for studying the output capacity，production efficiency and ground settlement of in-situ corrosion mining of glauberite salt rock deposit.

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IMPERMEABILITY OF OVERBURDEN ROCK IN SHALLOW BURIED COAL SEAM AND CLASSIFICATION OF WATER CONSERVATION MINING

(西安科技大学教育部西部矿井开采及灾害防治重点实验室，陕西西安 710054)

2010, 29 (S2): 3622-3627

[PDF] 1001 KB (673)

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According to simulation model tests and water conservation of overburden rock in shallow-buried coal seam，it is revealed that the cracks of overburden rock induced by mining are mainly composed of upward cracks and downward cracks；the impermeability of overburden impermeable layer depends on the interpenetration of mining crack zone. The calculation formula of the developing height of upward crack zone is analyzed；and the developing depth of downward crack zone is also measured by simulation. Based on the relationship among developing degree of mining crack，mining height and impermeable layer，the impermeability criterion is put forward by the ratio of impermeable layer thickness to mining height. The water conservation mining is divided into 3 types，i. e. nature water conservation mining，controllable water conservation mining and special water conservation mining，which provide scientific basis for shallow buried coal seam mining.

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PORE PRESSURE MONITORING AND SLOPE STABILITY ANALYSIS OF A WASTE LANDFILL

ZHANG Wenjie1，2，LIN Weian2，CHEN Yunmin2

2010, 29 (S2): 3628-3632

[PDF] 1145 KB (674)

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Field monitoring is used to determine the pore pressure in a landfill；and the distribution of leachate level is obtained by analyzing the monitoring results. To determine the shear strength parameters of buried waste at different depths of the landfill，the triaxial test is conducted；and the influences of pore water pressure and poreair pressure on slope stability of the landfill are analyzed quantitatively by using limit equilibrium method. The research results show that the leachate level is high，and there is perched groundwater in the landfill because of the existence of intermediate cover. The triaxial tests demonstrate that the shear strengths for solid waste at different buried depths are different，and the effective cohesion of the buried waste decreases with buried depth，whereas the effective internal friction angle increases with buried depth. The leachate level can obviously influence the safety factor of landfill slope. The perched groundwater has a great influence on stability，whereas the pore air pressure has a minor impact on it.

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STUDY OF SAFETY THRESHOLD OF SURROUNDING ROCK DAMAGE DEGREE OF ANCHORAGE TUNNEL FOR SUSPENSION BRIDGE BASED ON DISPLACEMENT RULE

LI Gaohui1，2，WU Congshi2，DENG Longbo1

2010, 29 (S2): 3633-3640

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Based on the blasting excavation in tunnel-type anchorage of Aizhai suspension bridge，the characteristic curves of displacement and rock damage degree D of tunnel-type anchorage are obtained by numerical analysis according to the finite element models established under different damage degrees. The results show that the anchorage slides along the direction of cable tensile forces and uplifts vertically under cable tensile forces. There are two inflection points in the curve of displacement and rock damage degree when D = 0.1 and 0.4. When D = 0.2，the curve is a typical mono-peak one. Displacement field of surrounding rock nearby the anchorage has uniform distribution；and the efficiency of sharing and transferring cable forces by anchorage tunnel surrounding rock is higher. When D≥0.3，the curve of displacement and rock damage degree transforms into a typical double peak curve. Displacement field of the anchorages exhibits a mutual independence to a certain extent，and the displacement contours of the anchorages are separated with each other when the cable being overloaded. When D≥0.6，anchorage displacement increases greatly and its field separates completely. Based on the above conclusions，D = 0.2 and 0.6 can be considered as the safety threshold of damage degree of surrounding rock Dcr and critical value of anchorage failure Dur，respectively.

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APPLICATION OF GROUND PENETRATING RADAR TO DISEASE DETECTION OF KUNLUN MOUNTAIN TUNNEL

KANG Fuzhong1，QI Falin2，HE Shaohui1，JIANG Bo2

2010, 29 (S2): 3641-3646

[PDF] 1288 KB (739)

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Opening and operation of Qinghai—Tibet Railway line has almost been 4 years. In order to obtain the actual operating state of the tunnel，Kunlun Mountain tunnel，one of the permafrost tunnels in the cold plateau region，is detected by soundness diagnosis testing method. In order to keep the normal operation of the tunnel，the ground penetrating radar is used to detect tunnel damage during the absence of train. The detection results show that the general appearance of tunnel lining is in poor quality in the cold plateau environment，and the phenomena of fall-block and seepage appear at both ends of it. The lengths of detected line for empty defect behind the lining reaching serious and very serious level are 59 and 61 m separately，both of which take up the total tested length of 0.70% and 0.72%，respectively；the detected length of backfill undense defect as serious level is 10 m，taking up 0.12% of the total detected line length. Furthermore，test data also indicate that the tunnel in plateau-frozen atrocious environment is more prone to occur disease due to temperature and frost force；and the durability of tunnel is affected seriously. The detected results can provide reliable basis for normal operation and disease management of the tunnel in the future.

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RESEARCH ON SEEPAGE OF HIGH PRESSURE HYDRAULIC TUNNEL WHEN REINFORCED CONCRETE LINING CRACKING

BIAN Kang1，2，XIAO Ming1，2

2010, 29 (S2): 3647-3654

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Based on the elastic damage theory and seepage theory of equivalent continuum media，a method for evaluating the seepage of high pressure hydraulic tunnel after the lining cracking is presented. Changes in crack width of reinforced concrete under different water pressures are considered as the main factors of permeability changes of the lining. The situations of the internal water exuding from the tunnel when water fills the tunnel and the outer water infiltrating into the tunnel when the tunnel is empty are studied respectively. The influences of consolidation grouting under high pressure and the situation when faults get touch with the lining are considered. The comparison between monitoring data of Huixu tunnel under high pressure and results from numerical calculation shows that the seepage of tunnel has a close relation to the crack width of lining and the existence of remarkable seepage channel nearby the tunnel. If there is no remarkable seepage channel nearby the tunnel，when water fills the tunnel or the tunnel is empty，the monitoring results agree better with the computation results. Otherwise，if the remarkable seepage channel which combines the concrete cracks with faults，the difference between monitoring and computation results will become larger. The research results provide an effective thought for the seepage discharge calculation of water flowing into and flowing out of the tunnel at different periods.

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STUDY OF INFLUENCE OF GROUNDWATER SEEPAGE ON REINFORCEMENT EFFECT OF TUNNEL SURROUNDING ROCK IN SATURATED WATER-BEARING SAND LAYER

JI Xiaoming1，TAN Wen2

2010, 29 (S2): 3655-3662

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Based on analyses of engineering mechanics，seepage and deformation characteristics of tunnel surrounding rock，a two-medium model for the influence of seepage velocity in saturated water-bearing sand layer on high-pressure jet grouting pile reinforcement effect is presented；and the formula of critical hydraulic gradient of high-pressure jet grouting pile reinforcement failure is given. The reinforcement mechanism of double liquid compound grouting in saturated water-bearing sand layer is put forward. The engineering examples show that chemical grouting is enough to reinforce saturated water-bearing sand layer and can avoid grouting failure，after using chemical grouting to effectively decrease the strata permeability. This grouting system is successfully applied to the reinforcement of tunnel surrounding rock in water-bearing sand layer；and the results have great referential value to the similar projects.

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EFFECT OF WENCHUAN EARTHQUAKE ON EARTHQUAKE DAMAGE AND DYNAMIC RESPONSE ANALYSIS OF UNDERGROUND POWERHOUSE OF YINGXIUWAN HYDROPOWER STATION

ZHANG Yuting1，2，XIAO Ming1，2，LI Yujie1，2

2010, 29 (S2): 3663-3671

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Yingxiuwan hydropower station is the nearest hydropower project to the epicenter of Wenchuan“5.12”earthquake. This hydropower station has been put into operation for several decades. It was severely affected by the earthquake，and its earthquake response intensity amounted to 11 degrees. Firstly，according to the in-situ investigation after the earthquake，the earthquake damage of underground powerhouse is analyzed. The following results are obtained：(1) The general stability of Yingxiuwan underground powerhouse is favorable. However，a certain local deformation is observed at the sidewall area of the main powerhouse，which lead to local failure in the main powerhouse causing crane to be unable to operate. (2) The paint on the bus bar opening sheds off and the surrounding rock in the traffic opening slightly cracks. Then，according to the data of Wenchuan earthquake monitored by Wolong strong motion station，which is the nearest station to the epicenter，the dynamic response analysis was conducted by FLAC3D. The calculation results show that the transverse deformation increments of the upstream and downstream sidewalls are 5.4 and 1.0 cm，respectively，in a short time；and the tensile stress at sidewall area exceeds surrounding rock¢s tensile strength，which causes tensile crack. Comparison of the monitoring data and calculating results show that the dynamic response analysis results agree with the regularity derived from the in-situ earthquake damage investigations. Therefore，the investigated earthquake damage can be explained through numerical analysis；and it provides references to the postseismic reinforcement and rebuilt work of hydropower projects as well as relative researches.

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CENTRIFUGAL MODEL TESTS FOR RESPONSES OF SHALLOW-BURIED UNDERGROUND STRUCTURES UNDER SURFACE BLASTING

MA Liqiu1，2，3，ZHANG Jianmin2，3，HU Yun2，3，ZHANG Limin4

2010, 29 (S2): 3672-3678

[PDF] 1495 KB (701)

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Shallow-buried circular structures under surface blasting were investigated by using Tsinghua University 50 g-t geotechnical centrifuge，and the dynamic responses of structures were studied under the conditions of different explosive charges，different buried depths of structures，different materials of overburden layer and different water contents of soil. The results showed that：(1) The crater ejecta significantly affected by the Coriolis acceleration；(2) The peak strain at the bottom of the structure was about one third of that at the top part；(3) The more water the soil layer contained，the greater the strain response of the structure was；(4) The sandy soil as covering material was helpful to the blast-resistant of structure. These results can provide references to reinforcement of existing structure and design of underground structures.

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APPLICATION OF EFFICACY COEFFICIENT METHOD TO INSTABILITY RISK EARLY-WARNING OF TUNNEL SURROUNDING ROCK

WANG Yingchao1，2，3，SUN Hongyue1，SHANG Yuequan1，ZHANG Yun1

2010, 29 (S2): 3679-3684

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In order to judge the dangerous situation of tunnel surrounding rock accurately，corresponding engineering measures can be performed duly to prevent the instability disaster of tunnel surrounding rock. The efficacy coefficient method is used to evaluate the stability of surrounding rock and execute instability risk early-warning of tunnel surrounding rock. Uniaxial saturated compressive strength，rock quality designation，integrity coefficient of rock mass，strength coefficient of structural plane，groundwater index and the angle between tunnel axis and main structural plane are selected as evaluation indices. The weight coefficients of evaluation indices are determined by expert evaluation method，and the early-warning model of instability risk of tunnel surrounding rock is established. The dangerous situation of surrounding rock is divided into five warning limits，i.e. huge warning，serious warning，medium warning，light warning and no warning. Then，the early-warning model of tunnel surrounding rock is applied to Xihualing tunnel of Zhuji—Yongjia highway in Zhejiang Province. The results show that the efficacy coefficient method conforms to reality and is implemented easily when it is applied to the forecast of the instability risk early-warning of tunnel surrounding rock. This new method can be used to perform stability evaluation and instability risk early-warning of tunnel surrounding rock，which has high engineering application values.

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EXPLICIT ANALYSIS OF GROUND REACTION CURVE IN TUNNEL EXCAVATION

LEE Yulin，LEE Wenyuan

2010, 29 (S2): 3685-3692

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For design of support system of tunnel，the convergence-confinement method is a simplified analysis theory. Obviously，the confinement loss used by the theory is an important influential factor. According to the relationship between the confinement loss and tunnel advancing effect，the advancing effect function is proposed. The analytical solution for the elastoplastic response of circular tunnel excavation in rock mass is considered. The explicit analysis method taken into account the increment method of confinement loss is particularly proposed by using the spreadsheet for the computation of stress and displacement distribution around circular tunnel. The analysis contains the calculation steps of increment of confinement loss，elastic limit of confinement loss，plastic radius，radial stress and displacement in plastic zone. The results obtained by the finite element analysis and the explicit analysis are approximately consistent in the ground reaction curve.

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INVESTIGATION ON SHEAR CREEP EXPERIMENTS OF SANDSTONE WITH WEAK PLANE IN XIANGJIABA HYDROPOWER STATION

ZHANG Zhiliang1，2，XU Weiya1，2，ZHAO Haibin3，JIAN Bo3

2010, 29 (S2): 3693-3698

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The compressive zone was revealed in the excavation of left bank dam foundation of Xiangjiaba Hydropower Station. The quality of sandstone in the zone is poor，and its significant creep deformation is harmful to hydraulic structures. Shear creep experiments were carried out for the sandstone with weak plane by using CSS–3940YJ rock shear rheology testing machine. The results show that large creep deformation of the sandstone occurs in the experiment. Before the damage，the shear strain reaches 1.73%–8.05%. The rock is of significant ductility characteristics，and it is typical soft rock. The normal stress enhances the ductility of rock. At a constant normal stress，the creep rate of the rock increases with the increase in shear stress level. Based on large amounts of experimental data，the creep rates at every moment are calculated by difference methods，and the power function is used to fit the rate curve. The analysis shows that the time required for creep stability of rock increases with increase in shear stress level. It is found through the analysis of the fracture that the internal microcracks of rock expand with the increase in shear stress level and time until coalescence resulting in shear failure of the rock. The achievements offer important referential value for the research on dam foundation of Xiangjiaba Hydropower Station.

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EXPERIMENTAL STUDY OF RHEOLOGICAL MECHANICAL PROPERTIES OF ARCH DAM ABUTMENT ROCK AND ITS LONG-TERM STABILITY ANALYSIS

JIANG Yuzhou1，2，XU Weiya1，WANG Ruihong3，WANG Rubin1，ZHANG Zhiliang1

2010, 29 (S2): 3699-3709

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In order to understand the rheological properties of alteration rock specimen of two banks of Xiaowan hydropower station，triaxial compression rheological experiments on alteration rock specimens are carried out by the rock servo-controlled rheological testing machine. The test results show that the rheological properties of alteration rock are very significant，and the rheological deformation of specimens is large. Based on the triaxial rheological experimental results，the variation law of axial strains of alteration rock specimens with time is investigated. At the same time，the variation tendency of axial rheological rates under different stress levels is discussed in detail；the rheological failure mechanism is analyzed；and the triaxial rheological law of alteration rock specimen is obtained. Cvisc rheological model is used to fit the rheological test curves，and the constitutive relationships of Cvisc model and its parameters are obtained. Based on the optimal rheological model of rock，the rheological mechanical behaviors of rock mass on two banks are simulated by using 3D nonlinear numerical method. Throughout the analysis of the calculated results，the long-term stability of arch dam and abutment are estimated by studying the displacement and stress. The results show that the rheological effect of Xiaowan hydropower station is very remarkable. The rheological deformations of arch dam and two banks are larger than the elastoplastic deformations. Considering the rock rheological behavior，the stress field will redistribute with the increase in time；and the phenomenon of local stress concentration will decrease. The abutment rock mass expresses explicit rheological characteristics at the beginning of loading，and then，the rheological rate and rheological deformation of arch dam and abutment tend to stability.

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STUDY OF MODEL TEST OF SEEPAGE CHARACTERISTICS AND FIELD MEASUREMENT OF COARSE AND FINE TAILINGS DAM

YIN Guangzhi1，2，JING Xiaofei1，WEI Zuoan1，2，LI Xiaoshuang1

2010, 29 (S2): 3710-3718

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Taking the materials of the coarse and fine tailings from two tailings pond in Yunnan Province for example，the dam model experiment and field measurement were performed to study the seepage laws of coarse and fine grained tailings dam. The research results show that：(1) The reasons for that the seepage line of fine tailings dam is lower than that of coarse tailings dam are two aspects：① the permeability of fine tailings is lower than that of coarse tailings；② the fine tailings are deposited on the geotechnical fabric and formed a non-watertight layer，and it plugs the geotechnical fabrics drainage pore and make the effect of water drainage be lower obviously. (2) The sedimentary laws of coarse and fine tailings on the tailings beach were the same，i.e. the fine tailings are at front and the coarse tailings are at back in a same horizontal plane，on the top，there are coarse tailings and at the bottom were fine tailings. But the gradient of coarse tailings beach is steep which is about 1.0%–2.5%，and that of the fine grained tailings beach is only about 0.3%–0.9%. (3) From the whole water penetrability of tailings dam，the relative permeability is put forward. The relative permeability of fine tailings dam is only 25% of coarse tailings dam in same external conditions. (4) Because the water penetrability of fine tailings is lower and the height of seepage line is higher，the head pressure of fine tailings dam is large to make the dam failure. The research results are of significance for similar tailings dam engineering.

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A NEW METHOD FOR SEARCHING SLIDING SURFACE OF THREE-DIMENSIONAL HOMOGENEOUS SOIL SLOPE

DENG Dongping，LI Liang，ZHAO Lianheng

2010, 29 (S2): 3719-3727

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Two random curves are generated through a stochastic method：One is mother line，by which and slope line cross-section size on sliding direction of three-dimensional sliding body surrounded is the largest；and the other is standard line，by which and slope line cross-section size on perpendicular sliding direction surrounded is the largest. The three-dimensional sliding surface is generated through standard line moving on the mother line or mother line moving on the standard line. So sliding body is easily divided into n×m vertical stripes in the generation process of three-dimensional sliding surface，and it facilitates calculation of micro-components of stripes in formula of three-dimensional factor of safety and to generate graphic of three-dimensional sliding surface. In this process，in order to improve the accuracy of random search，the approximate mother line and approximate standard line are used instead of random mother line and random standard line respectively. Then the most dangerous sliding surface is found by searching arbitrary three-dimensional sliding surface generated by approximate mother line and approximate standard line. Examples of three-dimensional homogeneous slopes show that results computed by this method are smaller than those of previous studies，so it is safer and also proved that this method is practicable. At the same time，by studying the impact of length of sliding body on stability of slope，it shows that stability of three-dimensional slope is better than that of two-dimensional slope；with increasing length of the sliding body，stability problems of three-dimension tends to those of two-dimension. In addition，according to the analysis of the shape of standard line and comparison of mother line and two-dimensional sliding surface，it proves that it is feasible to simplify three-dimensional sliding surface to be two-dimensional arc.

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BACK ANALYSIS OF STRENGTH PARAMETERS OF SLIDING SURFACE OF ZHENGGANG LANDSLIDE DEPOSIT BODY

SHI Chong 1，2，ZHANG Yu1，2，SUN Huaikun2，3，NING Yu3

2010, 29 (S2): 3728-3734

[PDF] 1686 KB (2)

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The determination of strength parameters of slope sliding surface is one of the difficult problems in geotechnical engineering. According to engineering geological condition of Zhenggang landslide deposit body in Gushui Hydropower Station and the fact of slope stability controlled by rainfall conditions，grid control technology and Kriging interpolation method are used to establish 3D model of sliding block models. Then，a reasonable assumption is proposed according to the stability characteristic of landslide deposit body，shear strength parameters are inversely calculated with three-dimensional limit equilibrium methods. It shows that these parameters can reflect the overall stability and landslide failure mode，which are well coincide with field exploration，the effectiveness of back analysis method is also proved. Based on the analysis，the proper management ideas for treatment of landslide deposit body are presented. The inverse calculation method for shear strength parameters can provide useful references to similar projects.

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RISK ASSESSMENT OF COLLAPSES AND LANDSLIDES CAUSED BY 5.12 WENCHUAN EARTHQUAKE—A CASE STUDY OF DUJIANGYAN—WENCHUAN HIGHWAY

ZHUANG Jianqi1，2，CUI Peng1，GE Yonggang1，ZHU Yingyan1，LIU Yinghui3，PEI Laizheng1，2

2010, 29 (S2): 3735-3742

[PDF] 713 KB (2)

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Dujiangyan—Wenchuan highway，the serious quake-hit area，was selected as the investigative object to assess the risks of collapses and landslides caused by “5·12” Wenchuan earthquake along the highway，and the sensitivities of collapses and landslides to their impact factors were analyzed by the method of information acquisition analysis. Then，based on remote sense image interpretation and field investigation data，the risks of these geo-hazards were assessed by GIS. The results show that collapses and landslides easily occurr under the following natural conditions：(1) slope gradient：＞35°；(2) slope aspect：east，southeast and south；(3) surface roughness：＞1.15；(4) the distance to the main fault：5–20 km；(5) land use type：forest，woodland and shrub forest；(6) stratum and lithology：proterozoic diorite，plagiogranite，basalt and andesite，carboniferous limestone and marl and Silurian gray green phyllite and limestone，especially the proterozoic basalt and andesite. The hazard assessment results were given in terms of overlaying the information value of each factor，and then the assessment results were divided into five grades：high intense risk zone，higher risk zone，moderate zone，light risk zone and no risk zone. It is found that the moderate，higher and high intense risk zones account for 70.34% of the study area，the high intense risk zone accounts for 19.15%，and no risk zone only accounts for 11.81%. The high intense and higher risk zones mainly distribute in the areas from Yingxiu to Caopo River and the light risk zone and below light risk zones mostly locate in the section of Caopo River—Wenchuan. The presented results provide a scientific basis for the prevention，elusion and mitigation of geo-hazards and support the recovery and reconstruction of Dujiangyan—Wenchuan highway.

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STRUCTURAL STABILITY OF U-STEEL SUPPORT AND ITS CONTROL TECHNOLOGY

XIE Wenbing1，JING Shengguo2，WANG Tao2，REN Youkui2，ZHANG Nong2

2010, 29 (S2): 3743-3748

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To control strong deformation of surrounding rock around soft rock roadway with high stress，improving stability of support structure is important besides increasing support strength. The cause of U-steel support instability and support bearing characteristics during working are analyzed by theoretical analysis and laboratory experiment and field test. The technique of steadying support resistance，the principle of support structure compensation and its technique are proposed. The results show that the main reasons of support structure instability are low intensity connector，irrationality structure connector，poor interaction relation between surrounding rock and support，unstable support structure，etc. The corresponding technique，such as connector with high strength and rational structure，is adopted according to the main reasons of the support structure instability. The support bearing capability is unstable after support slipping，and in order to keep a high support resistance during support bearing，the support connector should be re-tightened after support slipping. Though the working resistance can be improved greatly by U-steel backfilling or U-steel back grouting，because of the instability of support structure，the support can still lose its stability. The device of steadying structure is rationally laid out to structural compensate for U-steel support according to the deformation characteristics of surrounding rock and the structural instable type of U-steel support，and it greatly improves the bearing capacity of the whole support and its structural stability.

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APPLICATION OF SUBLEVEL FILLING METHOD TO SOFT ROCK STRATA IN LAIXIN IRON MINE

LI Wenxiu1，LIU Xinqiang2

2010, 29 (S2): 3749-3754

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Because of complex geological conditions，weakness and crushing of ore and rock mass and developmental underground water，Laixin iron mine is one of the mines which is difficult to exploit in China. Under the self-weight stress，the tensile failure appears in the roof which leads to roof falling. By comparing with rectangle-shaped mining room，the diamond-shaped mining room can adapt to the stress transferring law. Then，the sublevel filling mining method with the diamond-shaped mining room is proposed based on the practical engineering；and the stress distribution，deformation characteristics and distribution of plastic zones are calculated by the 2D– software. The numerical results show that the diamond-shaped mining room is a stable structure. Tensile stress and plastic zone are not formed in roof and surrounding rock of the diamond-shaped mining room；and the sublevel filling method is feasible in soft rock strata in Laixin iron mine.

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ANALYSIS OF MONITORING AND MEASUREMENT OF SMALL CLEAR SPACING HIGHWAY TUNNEL WITH EIGHT LANES

JIANG Kun1，2，XIA Caichu1

2010, 29 (S2): 3755-3761

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In order to guarantee security when tunnel construction and study the stability of tunnel surrounding rock，some site monitoring and measurements have been performed in Kuiqi tunnel #2. Based on the analyses of measured data，the distribution characteristics and variation laws of the ground settlement，crown settlement and convergence around the tunnel，the displacement of the interior of surrounding rock，bolt axial forces and pressure of surrounding rocks and preliminary support are all studied. The study results are drawn to provide the basis for modifying and optimizing the design and construction scheme. This study will offer some useful references for the design，construction and monitoring of tunnels in the similar geological conditions.

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STUDY OF BUILDING SAFETY DURING SHALLOW-BURIED LARGE-SPAN TUNNEL UNDERPASSING

QIN Weimin1，ZHAO Rongsheng2，WANG Hao1，KONG Wentao3

2010, 29 (S2): 3762-3768

[PDF] 1848 KB (2)

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Wucun tunnel in Xiamen City is shallow-buried large-span tunnel with soft rock，which underpass intensive buildings. The research work of combining numerical simulation with on-site monitoring is conducted in the process of tunnel construction. According to the results of finite element analysis and on-site monitoring data，combining with construction measures，comprehensive research are carried out on the safety of building during the construction. The research results show that the strength of completely decomposed granite can be improved by full-face curtain grouting，but it has little effect on uplifting the above building. Nevertheless，surface grouting has obvious effect on controlling the settlement of the above building，and the accumulative settlements of most monitoring points are less than 30 mm，which meet the design requirements. Because of the insufficient grouting equipment，the building can not be overall uplifted by surface grouting，which leads new cracks to appear and make the original cracks alive. CRD(center cross diagram) method is adopted to underpass the building，and its construction order should be CRD1→CRD2→CRD3→CRD4，which has certain effectivemess on the control of the above building settlement.

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SEEPAGE-DAMAGE-STRESS COUPLING ANALYSIS OF HYDRAULIC TUNNEL LINING IN HYDRAULIC FRACTURING PROCESS

BIAN Kang1，2，XIAO Ming1，2

2010, 29 (S2): 3769-3776

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Based on the elastic damage theory and linear-elastic fracture mechanic theory，seepage-damage-stress coupling model for hydraulic tunnel lining in hydraulic fracturing process is established. The finite element iteration method with incrementally variable elastic damage stiffness is applied and the influence of damage on the seepage during the process of inner water pressure gradually increasing is considered in the model. It can be better to simulate the damage evolution and the fracture formation and propagation process of hydraulic tunnel lining in the process of filling the hydraulic tunnel by the pressure water，in the coupling circumstance of stress and seepage field. The project example calculation results show that the calculation results can reasonably reflect the cracking rule of hydraulic tunnel lining under high inner water pressure. When the coupling model is applied，the influence of damage evolution and crack propagation of the lining on the seepage field can not be ignored. Moreover，because of the influence of inner water exosmosis，the force bearing condition of the lining，to a certain degree，will also be improved.

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CAUSE ANALYSIS OF CRACKS OF SHOTCRETE LAYER AROUND THE DOWNSTREAM HANCE IN UNDERGROUND POWERHOUSE OF JINPING I HYDROELECTRIC POWER STATION

LIU Jianyou1，2，WU Faquan1，ZHAO Zhenhua3，LI Shengqing3，QI Shengwen1，LIU Tong1，DONG Jinyu1

2010, 29 (S2): 3777-3784

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Monitoring results show that a lot of concrete shotcrete layer has fell and cracked around the underground powerhouse of Jinping I hydroelectric power station，and then many shotcrete layer are spalling with the crack development. Meanwhile，displacement of surrounding rock and bolt stress in the downstream hance of the powerhouse increases particularly. The cause analysis of deformation and failure of surrounding rock and the crack and spallig of concrete shotcrete layer around the downstream hance of the powerhouse is conducted by detailed field geologic survey and numerical calculation according to the force condition of underground powerhouse. The research results indicate that high level of stress concentration formed by high geostress and eccentric compression are the major factors which lead the concrete shotcrete layer at corresponding position to crack and spall；and the excavation of main transformer chamber and universal development of the fourth discontinuities aggravate the process.

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IN-SITU MONITORING AND ANALYSIS OF 3D SLOPE DEFORMATION IN TWIN-ARCH TUNNEL

ZHOU Dingheng1，CAO Liqiao2，YANG Hongwei3，SHI Zhan4，MA Yongfeng5

2010, 29 (S2): 3785-3791

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Based on the engineering practice of a twin-arch tunnel，the monitoring of surrounding rock deformation during the tunnel construction is carried out. The change characteristics of 3D slope deformation in twin-arch tunnel with time and its spatial distribution law，and the slope deformation characteristics induced by different excavation procedures are analyzed. The analysis results indicate that：(1) The deformation of tunnel slope presents obvious 3D characteristics；(2) The slope deformation can be great influenced by tunnel excavation；(3) The excavations of the upper bench in the left and right carven have a great effect on the slope deformation during the construction of twin-arch tunnel；(4) The longitudinal influence area induced by the excavation of the upper bench of the left carven and the down bench of the right carven is about 2 times of tunnel span；and the influence area induced by the excavation of the upper bench of the right carven and the down bench of the left carven is about one half of the tunnel span. These presented conclusions can provide references for the design，construction and site monitoring of twin-arch tunnels in similar conditions.

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STUDY OF INFLUENCE OF SKEW HORIZONTAL ADIT TUNNEL CONSTRUCTION ON MAIN TUNNEL LINING STRUCTURE

LUO Yanbin1，CHEN Jianxun1，WANG Mengshu2

2010, 29 (S2): 3792-3798

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For the influence of skew horizontal adit construction on the main tunnel lining structure，the Tianhengshan highway tunnel engineering of Harbin by-pass city expressway is taken as an example and the actual measurement and 3D finite element simulation are adopted to study the deformation regularity and the stress characteristics of main tunnel lining structure during the horizontal adit construction stage．The research results are shown as follows：(1) the construction of horizontal adit leads the main tunnel lining near intersection to occurre deformation and stress concentration，and the influence range in acute angle side of intersection is 1.82D(D is main tunnel span)，in obtuse angle side of intersection is 1.32D；(2) the lining deformation mainly is arch settlement，and secondly is side wall expansion；(3) the excavation of horizontal adit destroys the original arch effect of main tunnel，so as to create the stress concentration on the lining at the intersection；(4) with the excavation depth increment of horizontal adit，the deformation and stress of the main tunnel lining structure gradually decrease and tend to be stable；(5) The safety factors of main tunnel lining structural strength are greater than design values of 2.0 on both sides of the intersection；(6) the deformation and stress concentration at the intersection acute angle side are greater than that of the obtuse angle side，but the safety factor of the former is less than that of the latter．The research results can be used as reference for the design and construction of other similar engineering.

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GROUND MOVEMENT ANALYSIS OF SOFT SURROUNDING ROCK DURING HIGHWAY TUNNEL CONSTRUCTION IN MOUNTAINOUS AREAS

LI Wenxiu1，ZHENG Xiaoping2，WEN Lei1，LIU Lin1，LIU Xiaomin1

2010, 29 (S2): 3799-3804

[PDF] 703 KB (4)

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Based on the soft surrounding rock practical engineering situation of Hanjiazhuang tunnel of Baofu highway in Taihang mountainous areas，the stochastic medium theory is applied to analyze the ground movement induced by tunnelling excavation in mountainous areas. In the project，the passing through zone of the tunnel has soft surrounding rock，big transformation and big-span tunnel. Because of big transformation and high construction difficulty in tunnelling engineering of soft surrounding rock，more deep study is needed for characteristics of big-span roadway. For the natural slope safety and normal usage of the tunnel，it is extremely important to estimate the ground movement induced by tunnelling construction. The ground movement is viewed as a stochastic process and the stochastic medium theory is applied to predict and analyze the ground movement in cross section due to tunnelling construction. By comparing the theoretical results with the practical engineering examples，the construction technological scheme applied to the safety in the tunnelling engineering is proposed.

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safety design of tunnel lining IN Fire

CAI Xiaolin1，SWOBODA G2，CHEN Wensheng1，WU Congshi1

2010, 29 (S2): 3805-3811

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Based on the consideration of the nonlinear and nonlinear load-temperature curves of tunnel lining concrete and steel，the internal loads of lining before and after fire can be obtained by finite element numerical simulation；and the lining capacity in fire is got by the temperature spread analyses and nonlinear structural analysis model. The stress releasing coefficient of mechanical property of lining，which decreases with the temperature，and the interaction between tunnel lining and surrounding rock，is considered in the calculation model. The calculation is associated with the time increment history，in other words，the variation of mechanical parameters of materials at different fire time is considered. Besides the safety design results of a tunnel section in fire within Austrian region is put forward，the influence of high temperature load on the lining is also considered in the calculation. The calculation results can be better to help to explain the mechanical behavior of tunnel lining under high temperature. It can be convenient for the tunnel structure design check in fire and set the code for fire safety design of tunnel lining. The calculation results can also provide the reference to the design and study of tunnel lining in fire safety aspects.

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JUDGMENT METHOD FOR STABILITY OF UNDERGROUND CAVERN BASED ON CATASTROPHE THEORY AND MONITORING DISPLACEMENT

MA Sha1，XIAO Ming2

2010, 29 (S2): 3812-3819

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Based on monitoring displacement and catastrophe theory，a new rapid and simply quantitative criterion is proposed to assess the stability of surrounding rock. The nonlinear dynamic-cusp catastrophe model is established. According to the instability catastrophe criterion(catastrophe feature value D≤0)，catastrophe displacement rate is calculated. The stable displacement rate is determined and the ratio of displacement rate is calculated by using stability criterion(D＞0). According to the method，the judgment quantitative criterion for main power house (or main-transformed cavern) is put forward，which is that the stability displacement rate，catastrophe displacement rate and the ratio of displacement rate are 0.4(or 0.2) mm/d，9.0(or 2.5) mm/d and 18%(or 14%)，respectively. The judgment quantitative criterion is applied to assess the surrounding rock stability of large-scale project. The rationality and effectiveness of the judgment method and quantitative criterion are validated，which can provide reference for the similar project.

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THEORETICAL ANALYSIS AND MODEL TEST STUDY OF SLOPE HORIZONTAL DISPLACEMENT OF GRILLAGE FLEXIBLE SUPPORTING STRUCTURE WITH PRESTRESSED ANCHORS

ZHOU Yong，ZHU Yanpeng

2010, 29 (S2): 3820-3829

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Based on the influence of excavation process，the free segment of anchor is regarded as spring，and the grillage flexible supporting structure with prestressed anchors is simplified as a vertical continuous beam，in which the bottom is regarded as hinge and the upper part is supported by anchor springs located at different positions. Then，a simplified calculating method of the horizontal displacement of slope of this kind of supporting structure is proposed. The calculating model and sketch are given out，and the relative parameters are determined. Taking a foundation pit for example，the calculation results and analysis of the horizontal displacement of slope show that the middle-top horizontal displacements of foundation pit are larger，and grillage flexible supporting structure with prestressed anchors has obvious effect on strictly controlling the horizontal displacement of foundation pit. In addition，in order to deeply understand the working performance of grillage flexible supporting structure with prestressed anchors，the laboratory model test is carried out based on geometric similarity rule. The comparison of the measured results of displacements and the theoretical calculated results indicates that the general trend agrees well，but there are large difference between the two values，and the model test justly obtains the distribution law of horizontal displacement and the anchorage effect of prestressed anchors. The calculation method of the horizontal displacement of slope is a simplified and approximate method，in which all the calculated parameters are easily determined，so the method is operable and feasible in the initial estimation of the horizontal displacement of slope.

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EXPERIMENTAL STUDY OF SIMILAR SIMULATION OF TAILINGS DAM-BREAK

YIN Guangzhi1，2，JING Xiaofei1，WEI Zuoan1，2，LI Xiaoshuang1，JIANG Changbao1

2010, 29 (S2): 3830-3838

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Based on self-developed large-scale simulation test system of tailings dam-break and the design data of tailings pond belonging to Yuxi Mining Co.，Ltd. in Yunnan Province，the hydraulic characteristic and dynamical effect of slurry after tailings dam-break are simulated by simulation test. The results show as follows：(1) There are some essential distinctions of movement characteristic between tailings dam-break and normal reservoir failure or typical debris flow；(2) The height of tailings dams has a significant effect on inundated height of slurry in downstream，and the peak of submerged height of slurry after tailings dam-break decreases with the increasing impact distance of slurry；(3) When the slurry barges up against bend groove，there is a climbing phenomenon at the concave bank by centrifugal force；(4) In the process of the slurry flowing，the characteristics of slurry impact force curves in each cross section of downstream presents the front-end steeper and the back-end relative smoother，and the peak value has arrived before peak of slurry height；(5) As the tailings dam height increases，the peak submerged height and the impact force strength show increasing trends，and the time of slurry arriving at the same section in downstream is contraction. So the disaster of downstream is more seriously. The results can provide some references to study the characteristics of slurry evolution and impact force strength deeply，and also can guide the mining enterprises to prevent and control the disaster of tailings dam-break.

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MODEL TEST AND NUMERICAL SIMULATION OF DRIVING PROCESS OF OPEN-ENDED JACKED PIPE PILES

ZHOU Jian1，2，CHEN Xiaoliang1，2，ZHOU Kaimin1，2，WANG Guanying3

2010, 29 (S2): 3839-3846

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With the outstanding economic performance，open-ended jacked pipe piles have been widely used in engineering construction field，and plugging effects will be developed during the installation of open-end pipe piles，which have significant influence on the characteristics of pile while jacking into soil. The mechanism of soil plug formation and particles movement were analyzed by the meso-scale through physical model tests and numerical simulations. The container that consists of four steel sheets and one toughened glass side and aluminum semi-model pile were used to simulate the installation of open-end jacked pipe pile in sand. During the pile jacking into the sand，the courses of soil plug formation were observed from the transparent glass side and the processes can be divided into three stages，and the mechanisms of soil plug formation at three stages were revealed respectively. Based on the results of model test，the parameters of numerical model were determined by the biaxical test in PFC2D；and with the established numerical model and procedure in PFC2D，the driving process was simulated，which could consider both squeezing effects and plugging effects simultaneously. The behaviours of the numerical model are consistent with the results of physical model test. It indicates that PFC2D is capable of simulating the process for pile jacking into sand. In the research work，the courses of soil plug formation and displacement field of sand particles were analyzed. The particles within 5–7 times of particle diameters away from the ektexine of pipe pile will bring out large displacements and rotations，while beyond the thickness of 10–15 times of diameters，the particles will not be influenced almost. Furthermore，the analysis of porosity and contact numbers indicates that the bearing capacity of soil plug is mainly dependent on the lower part.

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APPLICATION OF SELF-BALANCE DEEP LEVEL LOAD TEST IN PEBBLE BED AREA

YU Qingquan1，GONG Weiming2，LIANG Shuting2

2010, 29 (S2): 3847-3851

[PDF] 891 KB (5)

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There are intensive distribution pebbles with high bearing capacity in Urumqi，Therefore，the lateral friction is usually ignored，but the tip resistance is attached importance during pile foundation design in the region. However，it is difficult to accurately obtain the mechanical properties of tip soil by traditional deep load test. The self-balance load test method was used according to the advantage of testing tip resistance. Based on the test results and the corresponding codes，the tip resistant normal value and the tip resistant characteristic number were obtained. Besides，the design project has been optimized according to the achievements of the test. The experience for similar projects of deep level plate load in pebble bed area using self-balance load method was obtained.

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fractal behavior in crushing of rockfill material

SHI Xiusong，CHENG Zhanlin

2010, 29 (S2): 3852-3857

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Four groups of triaxial test with high confining pressure on Qipei hydropower station bedding material are carried out. Based on the test results of particle size distributions，the fractal model is established，and its fractal behavior in crushing is studied. The results show that particle size distributions after particle breakage of these two kinds of rockfills possess good fractal behavior；fractal dimensions vary from 2.612 7 to 2.723 2；and the fractal dimensions of bedding material after crushing are less than those of average line. The fractal dimensions increase with the increasing confining pressure in the same density. The increasing trend has stage characteristics：its growth rate keeps slow under low confining pressure；while the grain breakage increases with confining pressure，its growth rate becomes sharp under low confining pressure. The fractal dimensions increase with the density under the same confining pressure. The magnitude of fractal crushing dimensions reflects the particle sizes of breakage and the uniformity of the particle size distributions. The larger the fractal dimension is，the more the quantity of particle breakage is. Besides，there is a close relationship between fractal dimension and Marsal index of particle breakage.

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APPLICATION OF PARTICLE IMAGE VELOCIMETRY TO DEFORMATION ANALYSIS IN CENTRIFUGAL TESTS

ZHANG Min1，2，NG Charles W W3

2010, 29 (S2): 3858-3864

[PDF] 1669 KB (3)

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Since the technique of particle image velocimetry(PIV) can be controlled remotely and in real time，it is applied to the measurement of soil deformation in centrifugal tests. Soil model is divided into a number of fine elements. The displacement of each element can be traced by recognizing the texture of the soil element. A system is configured to measure slope deformations in centrifugal tests. After processing the test images with error correction，soil deformations can be achieved. The precision and accuracy of this method is estimated as 0.04 and 0.02 mm，respectively，based on the analysis of PIV theory. Two examples are used to illustrate the function of the system. One is to measure the slope deformation when the centrifugal acceleration is increased. The other is to measure the deformation induced by the rise in groundwater table. The analysis gives reasonable results in the two examples and illustrates the capability of the system for measuring displacements in the entire slope field at different moments. It is verified that the system is an important tool for studying the physical process.

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EXPERIMENTAL STUDY OF CENTRIFUGAL MODEL OF BUCKET FOUNDATION BREAKWATER ON SOFT SOIL FOUNDATION UNDER STATIC LOAD

JIANG Minmin1，2，CAI Zhengyin1，XU Guangming1，GU Xingwen1

2010, 29 (S2): 3865-3870

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The stability and mechanism of a new bucket foundation breakwater under horizontal static load are studied with the centrifugal model tests. By applying horizontal static load on bucket foundation breakwater until ultimate limit state，the displacement of structure and pore pressure response in foundation can be obtained. Test results indicate that the displacement of structure under design load is very small；load-displacement curve has an inflexion under 2.2 times design load；when load is greater than 2.2 times design load，displacement of the structure develops fast with increasing load. Under about 3 times design load，the structure approaches the ultimate limit state，the breakwater moves toward the harbor ward side，the harbor ward base cylinder sinks while the seaward base cylinder raises，and the breakwater rotates toward the harbor ward side. In addition，the pore pressure of foundation increases in landward and decreases in seaward under horizontal static load，excess pore pressure in bucket is larger than that of outside the bucket in landward；under low load level the minus excess pore pressure in bucket is larger than that of outside the bucket in landward，while under high load level the minus excess pore pressure in bucket is smaller than that out of the bucket.

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STUDY OF INFLUENCE OF PARAMETERS OF INTERMEDIATE PRINCIPAL STRESS AND PRINCIPAL STRESS DIRECTION ON ANISOTROPY OF INTACT CLAY

GUAN Linbo，ZHOU Jian，ZHANG Xun，XIE Xinyu

2010, 29 (S2): 3871-3877

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There was lack of knowledge about the anisotropy of soft intact clay since most studies were performed on cohesionless soils. A hollow cylinder apparatus(HCA) is used to study the anisotropy of typical Hangzhou intact clay to investigate the influence of the parameters of intermediate principal stress and the principal stress direction on anisotropy. It is revealed that the anisotropy of intact clay is greatly affected by the value of the parameters of intermediate principal stress b，and is hardly affected by the principal stress direction. The intact clay is transversely isotropic along the depositional plane when b equals zero. When b equals 0.5，the characteristic of anisotropy is different. Regardless of the direction of the principal stress，the radial strain and the tangential strain of the sample always equal in magnitude and opposite in direction. Meanwhile the volumetric strain of intact clay is equal to the value of the second principal strain. Apparent dilatancy and strain softening are observed when samples fail at small rotation angle. Shrinking is significantly noticed in the beginning of failure with the increase of the rotation angle，while strain softening gradually vanishes. All these phenomena are not observed in b equaling tests. Test results also present that the intact clays have the lowest compressibility along the direction of deposition and the highest compressibility along the direction of rotation angle 50°.

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CONSOLIDATION PROCESS ANALYSIS OF RECLAIMED SOIL FOUNDATION BY VACUUM PRELOADING AND FINITE ELEMENTS STUDY

SUN Liqiang1，YAN Shuwang1，HE Hongjuan2，LI Wei3

2010, 29 (S2): 3878-3884

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Through the analysis of the formation of the reclaimed soil foundation and its consolidation process，it was proposed that the reclaimed soil foundation was unconsolidated；and there was initial excess pore water pressure in it. Settlement would be generated during the plastic vertical drains(PVDs) installation，and the field data showed that it reached 1/3–1/2 of the total settlements. So it couldt be considered as the consolidated soil. It was suggested that in the finite element analysis the load included vacuum loading and effective self weigh of the reclaimed soil. The delivery of negative vacuum pressure in the PVDs was studied. Nonlinearity constitutive relation was adopted and a program was compiled to analyze the behavior of the reclaimed soil foundation consolidation with plane strain finite element method(FEM). An actual project was calculated using this program，and comparing to the field measurements data，it is found that the method reflected very well the developing trend of settlement and pore water pressure for the projects.

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EXPERIMENTAL RESEARCH ON POST GROUTING UNDER SUPER-LONG AND LARGE-DIAMETER BORED PILE TIP

CHENG Ye1，2，GONG Weiming1，ZHANG Xigang3，DAI Guoliang1

2010, 29 (S2): 3885-3892

[PDF] 609 KB (4)

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For the reason of construction，some deterring factors will be brought out such as residue and mud cake for bored pile. Post grouting under pile tip can reduce the deterring factor，and the bearing performance of the bored pile will be improved. Effect on the bearing performance of the super-long and large-diameter bored pile by post grouting under the pile tip was studied by a series of tests including the static loading test，CT test and coring test. The self-balanced method was adopted in the static loading test. The bearing performances of the same pile before grouting and after grouting were compared. In the same field，the bearing performances of the piles were compared. Dimensions of the piles were the same，one had been post grouted under the pile tip and the other had not been post grouted. According to the results of the static loading tests，the resistance of the pile tip was raised，and the friction of a finite scope of pile side above pile tip was also raised. So the whole bearing capacity of the pile was raised. By the post grouting under the pile tip，not only the bearing capacity of the whole pile was raised，but also the rigidity of the pile was raised which make the settlement of pile be easier to control. CT test and coring test both approved the effect of post grouting under pile tip. The effect of post grouting would be better when the grout was injected in the sand layer.

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NUMERICAL ANALYSIS OF DEFORMATION AND FAILURE OF REINFORCED SAND WITH GOODMAN INTERFACE ELEMENTS

PENG Fangle1，2，CAO Yanbo1，2，Nozomu KOTAKE3，SIDDIQUEE M S A4

2010, 29 (S2): 3893-3904

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The plane strain compression tests of dense sand reinforced with a smooth brass plate are simulated numerically with a finite element method(FEM). Considering the slippage at the interface between the sand and the reinforcement，Goodman joint elements are used as interface elements in the numerical simulation. In the finite element analysis，the effects of the following factors for sand are also taken into account：(1) correlation of confining pressure；(2) anisotropy of strength；(3) nonlinear characteristics of pre-peak strain-hardening and post-peak strain-softening；(4) dilatancy；and (5) strain localization and forming characteristics of shear zone. The results indicate that the strain-stress relationship obtained by the proposed finite element analysis is generally in good agreement with that of plane strain compression tests. It is found that the maximum stress ratio and pre-peak stiffness in the finite element analysis are quite close to the results of tests. In addition，the results also indicate that the progressive failure of reinforced sand with a development of shear zone can be reasonably examined by the proposed finite element analysis，and the interaction between sand reinforcement at the interface can be well understood.

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NUMERICAL ANALYSIS OF PROGRESSIVE DEFORMATION AND FAILURE OF REINFORCED SAND SLOPES

CAO Yanbo1，2，PENG Fangle1，2，Nozomu KOTAKE3，Fumio TATSUOKA4

2010, 29 (S2): 3905-3915

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The results from the laboratory model test on reinforced sand slope were simulated numerically by the nonlinear elastoplastic finite element method(FEM) considering the strain localization；and they were compared with the results from the unreinforced sand slope. Then，the elastoplastic finite element analysis of a reinforced sand slope with facing plates was also performed numerically to understand the effect of facing by adding the facing plates into the finite element model for reinforced sand slope. In the finite element analysis，strain localization(or shear banding)，strain-hardening，strain-softening，strength anisotropy and pressure dependency were considered for sandy soil. It was found that the presented finite element analysis could properly simulate the local stress-strain distribution and development of shear bands within the slopes，which could better understand the progressive failure characteristics of reinforced sand slopes，reinforcing mechanism of strips and the facing effect.

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APPLICATION OF STRENGTH REDUCTION FEM TO REINFORCED GABION RETAINING STRUCTURE IN STEEP SLOPE

HUANG Xiangjing1，2，XU Guilin1，3，CHEN Runxia4

2010, 29 (S2): 3916-3922

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According to the first expressway reinforced gabion retaining structure in China(reinforced earth engineering of Daqing—Guangzhou expressway section of Lanxi interchange AK0+939.38–AK1+079.71，BK0+296.55–366.18 in Hubei Province)，the stability of steep reinforced gabion slope is evaluated by using strength reduction finite element method(FEM) on the platform of the finite element software Phase2 V6.0. Based on the results of limit equilibrium slice method，the effect of selected element on the results of strength reduction method is analyzed. A new method to determine the internal failure surface of reinforced earth structure by using FEM to calculate tension distribution of reinforcements is proposed. The influences of cohesion，internal friction angle，tension，earthquake force，gravity density and vehicle load on factor of safety are discussed. Thus，it can be effectively used to guide the specific engineering designs.

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REASONABLE REINFORCEMENT POSITION AND SHEAR STRENGTH MODEL OF REINFORCED SALINE SOIL WITH WHEAT STRAW AND LIME

LI Min1，CHAI Shouxi2，DU Hongpu3，WEI Li2，SHI Qian1

2010, 29 (S2): 3923-3929

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Triaxial compression tests of reinforced saline soil with wheat straw and lime，reinforced uniformly at upper，lower and whole positions，were carried out to research the effect of reinforced position on stress-strain and shear strength characteristics. Moreover，strength model of reinforced saline soil with wheat straw and lime was discussed by WU model theory. The results show as follows：(1) Shear strength and anti-deformation capacity of lime soil in three reinforced positions are improved. (2) Reinforced position is related to the increase in cohesion，but has little effect on the internal friction angle. (3) Shear strength of reinforced saline soil with reinforcement in lower position is larger than that in whole and upper positions；and the reinforcement of lower position is helpful to the reinforcement function. (4) Strength model of reinforced soil with wheat straw shows that strength of reinforced soil is closely related to the distribution pattern of wheat straw. The research results are of important guidance for understanding the reinforcement mechanism of reinforced soil with natural fiber material.

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CALCULATION FOR UPPER AND LOWER LIMITS OF DYNAMIC SHEAR MODULUS RATIO AND DAMPING RATIO UNDER DIFFERENT PROBABILITIES

YUAN Xiaoming1，SUN Rui1，CHEN Hongjuan2

2010, 29 (S2): 3930-3940

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：By using experimental results，the upper and lower limits of the nonlinear curves of the dynamic shear modulus ratio and damping ratio for conventional soils under different probabilities are investigated. The method and formula for calculating the probabilistic zones of the two dynamic parameters for the cohesive and cohesionless soils under the typical shear strains are presented. The approach is that the experimental results are ordered by the standard way，and the distribution form of variability of two dynamic parameters is obtained by the frequency distribution diagram，the tests of normality diagram and the SAS software. According to different distribution forms，the probabilities of the upper and lower limits of the two parameters under typical shear strains are calculated. The results indicate that the relation between the upper and lower limits of the two dynamic parameters and their probabilities can be described by the Boltzmann equation，in which the parameters depend on the soil type and the shear strain. For all probabilities，the ranges of the shear modulus ratio for different shear stains are obviously different while the most ones appear at 10－4–10－3 of the shear strain. For the same probability，the range of the damping ratio increases with increasing shear strain. The proposed formula for calculating the probabilistic zones of the two dynamic parameters lays a foundation for the reliability theory in soil dynamics and earthquake engineering to some extent；and it also can directly supply the technical support to the risk evaluation of a seismic design and seismic safety of engineering structures.

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FIELD MEASUREMENT AND NUMERICAL SIMULATION OF GROUND DEFORMATION INDUCED BY PNEUMATIC CAISSON CONSTRUCTION

WANG Hailin1，2，PENG Fangle1，2，XU Zhengliang3，LI Yaoliang4，BAI Tinghui5

2010, 29 (S2): 3941-3951

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Characterized by unmanned excavation and remote controlling，the new pneumatic caisson(NPC) method has advantages in deep excavation such as deep shield tunnel shafts and some underground construction close to the existing structures or facilities. When adopted in urban areas，it is very important to control the ground deformation during a caisson construction. For this purpose，based on a shaft construction employing the NPC method in Shanghai，field measurement of ground deformation was conducted. Based on the particular construction sequence of pneumatic caisson，a kinematic mechanical model was proposed for evaluating the influence of NPC construction on the surrounding strata. This model was imbedded into a finite element method(FEM) program. In the numerical analysis，the soil was assumed as an elastoplastic material；and the Hardening-Soil(H-S) material model was applied. By comparing the FE predicted results using the proposed model and the field measurement，the accuracy and reliability of this model were verified；and the distribution pattern of soil movements induced by NPC construction was analyzed. It is found that its influence zone on the surface is about 1.5 times sinking depth of caisson. Finally，a ground surface settlement calculation mode during NPC construction in Shanghai soft ground is proposed and compared with that caused by other braced excavation methods.

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FINITE ELEMENT ANALYSIS OF UPPER BOUND SOLUTION OF SHALLOW-BURIED TUNNEL STABILITY IN UNDRAINED CLAY

YANG Feng，YANG Junsheng，ZHANG Xuemin，ZHAO Lianheng

2010, 29 (S2): 3952-3959

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The investigation of stability and failure mechanism of shallow-buried tunnel in undrained clay has important significance to tunnel design，construction and theoretical progress. Based on the existing finite element upper bound theory，the triangular elements with constant strain rate was adopted to discrete computational domain，and the velocity discontinuities were set up on all the adjacent borders of the triangular elements，while the Mohr-Coulomb criterion was linearized using circumscribing polygon to form a linear programming model. Then，a computer program using Matlab for finite element upper bound solution was compiled. The more accurate results of stability factors of shallow-buried tunnel in undrained clay ground were obtained by using the computer program of finite element upper bound solution with discretization of computational domain of finite element mesh. And the reliability of the obtained results was verified by comparing with the existing data in literature. The characteristic of the failure mechanism during occurrence of plastic flow was analyzed，and the influential factors of tunnel stability factor were discussed. The regulation of failure mechanism evolution for different parameters was also summarized.

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STUDY OF LONG-TERM PERFORMANCE OF REINFORCED EARTH RETAINING WALLS BY FIELD TEST

WANG Chengzhi1，2，3，LUAN Maotian1，3

2010, 29 (S2): 3960-3966

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In order to discuss the long-term performance of reinforced earth retaining walls in high grade highway of mountainous area，the field test is conducted on the stepped geogrid reinforced soil retaining wall. It is found that the foundation vertical pressure of reinforced earth retaining wall is nonlinear along the reinforcement length at early stage；but as time progresses，the pressure eventually becomes a straight line stress distribution and the value gradually reduces. The testing lateral pressure of the panel is nonlinear along the height，and the value is less than the active lateral earth pressure，which is associated with the lateral displacement of the wall and reduces with the change in time. The tensile strain is similar to Assmann energy method in the middle of the wall，but it is far from the Assmann energy method at the top and bottom. The distribution of tensile strain along reinforcement is trapezoidal type with small value at both ends and large value at the middle，and the value of the tensile strain gradually reduces. The potential fracture plane is similar to 0.3H method in the upper；but at the lower wall，the potential fracture face moves to the reinforced retaining body and the change in displacement with time is little. The position of the maximum lateral displacement of each step is at the middle，and the maximum lateral displacement of the wall is at the lower wall.

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EXPERIMENTAL STUDY OF UNSATURATED PERMEABILITY OF WEAK EXPANSIVE SOIL OBTAINED FROM WUHAN—SHIYAN HIGHWAY SLOPE

YE Weimin1，2，ZHANG Yawei1，MEI Zhengjun1，CHEN Bao1，ZHOU Xiuhan3，XIE Qiang3

2010, 29 (S2): 3967-3971

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Based on the instantaneous profile method，the unsaturated permeability of the weak expansive soil from Wuhan—Shiyan highway slope has been tested by using a self-developed permeameter. The influences of suction(or water content) on unsaturated permeability are analyzed. The test results show that the coefficient of unsaturated permeability of specimen is between 4.5×10－10 and 3.0×10－9 m/s，and it does not change linearly with suction. At the initial stage，the coefficient of permeability decreases with reduction in suction，whereas it reverses when suction is lower than a certain value.

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ANALYSIS OF ARCH DAMS ABUTMENT STABILITY UNDER COMPLICATED GEOLOGICAL CONDITIONS AND STUDY OF INFLUENCE OF DENSE JOINTS

YANG Baoquan1，ZHANG Lin1，2，CHEN Jianye1，HU Chengqiu1

2010, 29 (S2): 3972-3978

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According to the geological defects in abutment of Xiaowan arch dam，the plane geomechanical model test based on overload method was carried out to research the abutment stability of typical elevation 1 210 m. In the test，the main fault，altered zone，soft rock zone and the two groups of joints tending to SN and EW were simulated，and the displacement and strain of the dam，the abutment displacement，the failure process，failure modes，as well as the overloading safety coefficient were obtained. So the dam abutment stability could be evaluated. As the result of geomechanical model test was an experimental method，which was based on the principle of geometric similarity and the mechanical similarity reduced the scale of dam and foundation，the model can not simulate the dense joints contained in abutment rock. In order to analyze the influence of the dense joints，the nonlinear finite element method was adopted to research abutment stabilities with and without dense joints. The results show that the impact of displacement of dam and abutment is about －8%–10%，and the impact of overload safety coefficient is about －9%. Therefore，even the model test could not simulate the dense joints contained in dam abutment，the impact of the dense joints in the abutment at elevation 1 210 m of Xiaowan arch dam is small，and the results of the model test are reliable.

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TRIAXIAL EXPERIMENTAL STUDY OF MECHANICAL EFFECT OF SLOPE PROTECTION WITH VEGETATION FIBRIL

ZHANG Feng1，2，LING Xianzhang1，2，WU Liquan3，WANG Lina1，2，ZHU Zhanyuan1，2，4，WU Hao1，2

2010, 29 (S2): 3979-3985

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To investigate the shear strength parameters of silty clay influenced by the water content and vegetation fibril content，the conventional triaxial consolidated undrained(CU) experiments on the soil sampled from Pingtou Village slope at Wuyi County in Zhejiang Province were carried out through. The experimental results show as follows：(1) With the increase in axial strain，the deviatoric stress increases，and the relation curves of deviatoric stress and axial strain present as hardening type. With the increase in confining pressure，the shear strength increases. (2) The water content of soil has great impacts on shear strength of the silty clay. The relationships between cohesion and water content present as parabola type. The cohesion would approach the maximum value when the water content is 19%；whereas with the increase in water content，the internal friction angle decreases linearly. (3) The vegetation fibril could improve the shear strength of silty clay，but it is related to the values of water content and vegetation fibril content. When the water content is 19%，the cohesion is improved greatly；and when the vegetation fibril is 5%，the cohesion approaches the maximum value. The internal friction angle is less influenced by the vegetation fibril. All results are meaningful to providing the quantitative information for prevention and treatment of Pingtou Village slope，as well as providing the necessary engineering design reference for protection of other slopes with vegetation fibril.

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EXPERIMENTAL STUDY OF UNDRAINED STRENGTH PROPERTY OF SATURATED SILTY CLAY AFTER TRAFFIC LOAD

HUANG Bo1，2，DING Hao1，2，CHEN Yunmin1，2，BIAN Xuecheng1，2

2010, 29 (S2): 3986-3993

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To investigate the effect of drainage condition，disturbance of construction and overconsolidation effects on the static undrained strength of the soil，a series of postcyclic undrained triaxial strength tests are carried out on samples of a silty clay(obtained along Beijing—Tianjin speed line). The results show that the generated excess pore pressure and residual shear strain of the specimens after long-term traffic load both can be regarded as the characterizations of damage degree of soil structure，and they all have their threshold values. If the pore pressure or shear strain after cyclic load exceeds its threshold value，the strength attenuation of the specimens will be caused. Apparent reductions in the threshold values are observed as the post cyclic strength by comparison of the reconstituted and intact specimens. Moreover，the soil strength of reconstituted one is lower than that of intact one at the same effective confining stress，which means that the construction disturbance should be paid more attention. Good drainage condition will enhance the bearing capacity of normally consolidated foundation. The traffic load and drainage conditions have little effects on the post cyclic shear strength of the foundation with the application of preload treatment.

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HANSBOS CONSOLIDATION SOLUTION FOR SAND-DRAINED GROUND UNDER VACUUM PRELOADING

ZHOU Qi，ZHANG Gongxin，WANG Youyuan，DENG Zhiyong

2010, 29 (S2): 3994-3999

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The Hansbos consolidation theory for sand-drained ground was extended to the condition of vacuum preloading，in which the distribution pattern of negative pressure along the sand drain was considered，and then it was compared with the existing Dong Zhiliangs solution and Indraratnas solution to verify its correctness. The results show that the relation of the radial consolidation degree Ur obtained by the three analytical solutions is that the new solution＞Dong Zhiliangs solution＞Indraratnas solution. When Th≤0.5，the relative error among the three analytical solutions is relatively large，but the absolute error is small；and then the error decrease gradually with time(Th＞0.5). The new solution is more close to Dong Zhiliangs solution than Indraratnas solution；and its form is simple，which is advantaged to engineering practice. When the well resistance of sand drain isnt considered，the three analytical solutions can be simplified to Hansbos solution under vacuum preloading.

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APPLICATION OF DYNAMIC DRAINAGE CONSOLIDATION METHOD TO REINFORCEMENT AND TREATMENT OF DEEP AND THICK SILT FOUNDATION OF LARGE AREA

LIU Yongjian，LI Zhangming，ZHANG Lijuan

2010, 29 (S2): 4000-4007

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Based on silt ground treatment project of Taishan petrifaction storage area of Nansha，Guangzhou，the basic principle，design parameters and construction technology of dynamic drainage consolidation method(DDCM) for improving the mud ground with high water content and large void ratio are discussed. By using field test methods，the pore water pressure，the soil pressure and the layered settlement are measured；the standard penetration test，vane shear test，static cone penetration test and the load experiment have been used to monitor and test the construction process and consolidation effect. According to the experimental data，the laws of pore water pressure，soil pressure and settlement of soft soils under dynamic loading are analyzed. The test results show the correlation among the variation in vertical settlement，soil pressure and excess pore water pressure is significant. With the dissipation of pore water pressure，the shear strength of soil improves and the post-construction settlement reduces，and the soils reach over-consolidated state. The research results reveal that it is obvious to treatment the large area of deep and thick silt foundation with the new construction technology of “static-dynamic combination，the tamping is light first and then becomes larger with energy adds gradually，fewer time and more cycles，consolidation by layer”；combining mesh drainage system which is composed of the horizontal drainage body，the plastic vertical drainage board and micro-fracture system of soils，the physico-mechanical properties are improved obviously，and physico-mechanical properties are better than expected. DDCM has extensive perspectives for soft ground improvement engineering.

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STUDY OF CREEP CHARACTERISTIC OF TERTIARY ARGILLACEOUS ROCK IN LOESS AREA

WANG Zhongwen1，YUAN Zhiqiang1，LI Bin2，ZHU Jiebing3，WANG Huabin1

2010, 29 (S2): 4008-4015

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Time-dependent behavior of rock mass is one of the important factors influencing the deformation and long-term stability of slope. The large scale incised-rock landslide in the loess area is progressively deformed under the influence of deadweight and groundwater，etc. This kind of landslides was finally formed after creeping，cracking and shearing，on the basis of the previous surface due to the preliminary creeping behavior of argillaceous rock. It aims to study the creeping behavior of argillaceous rock after the analysis of physico-mechanical properties，in which the Liujiaquan landslide was taken for example in Jintai District of Baoji. The analysis of clay minerals in argillaceous rock shows that the rock is mainly composed of mixed-layer illite-montmorillonite and illite. It also noted that the rock is formed in the latest period of geological time，and characterized with lower strength，light cementation and expansibility. Compared with the results of quick shear test，it is found that the value of friction coefficient reduces by 66% and the value of cohesion by 80% in the process of rheological shearing. Meanwhile，the displacement increases with time，and the deformation behavior is identified to be nonlinear viscoelastic in low loading and linear viscoplastic in high loading. It can be concluded that the creeping behavior is the main property of argillaceous rock in the process of preliminary landsliding in the studied area. In addition，the generalized Kelvin and Bingham models were combined to describe the rheological properties. The calculation curves of the model and experimental points could well fit the decay creep stage and steady state creep stage of the argillaceous rock. Hence，the suitability of selected models was proved. Finally，the parameters of rheological constitutive model of argillaceous rock were identified using genetic algorithm. Comparing the curves fitted by genetic algorithm with experimental data，it is found that the fitting results and the test results are matched very well. The genetic algorithm can be used to identify the rock rheological model parameters.

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CONSTRUCTION TECHNOLOGY AND PILE QUALITY ANALYSIS OF SUPER-LONG ROCK-SOCKETED PILE CROSSING A HUGE-THICK GRAVEL LAYER

ZHANG Zhongmiao1，2，ZHANG Qianqing1，2，LUO Jiacheng3，LIN Xin4

2010, 29 (S2): 4016-4026

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An engineering project of the super-long rock-socketed bored piles crossing a huge thick gravel layer with about 40 m depth was conducted at a 350 m high-rise building in Wenzhou area. The selection of drilling machine，the drilling method in different soil layers，the construction technology in crossing a huge thick gravel layer，the preparation of mud and the bore hole cleaning technology were presented to discuss details of the construction technology of the over 100-meter super-long bored piles. Moreover，the pile diameter and the ultrasound test were used to analyze the quality of drilled hole and pile shaft，respectively. In addition，a large tonnage static load test was conducted to capture the bearing capacity and the settlement of test pile. Some key findings indicate that the varying drilling processes，the high quality mud and the variable drilling methods can be adopted in different soil layers during the construction of the super-long bored piles. During a super-long pile construction in a gravel layer，the mud leakage and the borehole collapse can be solved by adjusting the property of mud，whereas the bits with variable diameter and the pump suction reverse circulation drilling can be adopted to improve the drilling efficiency. The static load test shows that the percentage of the super-long pile settlement at the pile head caused by the pile compression is over 90% within the working load. It can also be concluded that the thickness of the sediments at the pile end has an influence on the settlement of the super-long pile.

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EXPERIMENTAL STUDY OF SETTLEMENT-TIME REGULARITY OF POST GROUTING PILE GROUP FOUNDATION DURING CONSTRUCTION PERIOD

ZOU Li1，WU Xingxu1，MA Jianlin1，PENG Shengying2

2010, 29 (S2): 4033-4037

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Beijing—Shanghai high-speed railway field tests on post grouting of pile group foundation have been carried out. By analyzing the long-term settlement measured data of post grouting and non-grouting pile group foundation，the settlement development laws of post grouting and non-grouting long pile group foundation in deep soft soil have been researched. The stable time of settlement of pile group foundation are analyzed，and the influence mechanism of the post grouting effect on pile group settlement and its development laws are discussed. The conclusions are that both pile shaft grouting and pile end grouting have obvious function on the control of the settlement of long pile group foundation in deep soft soil；and the control effect of pile end grouting is superior to pile shaft grouting. For shortening time of consolidation settlement，the effect of pile end grouting is more stable. The development laws of settlement of all shaft grouting and end grouting pile group foundation have been changed obviously. Compared with corner pile grouting and side pile grouting，all pile group grouting is more beneficial to control the settlement and accelerate settlement stabilization.

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STUDY OF INTERACTION BETWEEN HIGH ARCH DAM AND ABUTMENT EXCAVATED SLOPE

LIU Yaoru，HUANG Yuequn，YANG Qiang，CHANG Qiang

2010, 29 (S2): 4038-4042

[PDF] 568 KB (1)

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In southwest district of China，a number of high arch dams are being built or going to be built. Due to the complicated geological conditions and features of high arch dams and slopes，the interaction between dams and abutment excavated slopes has become an important issue in this area. On the basis of elastoplastic theory，the analysis method of structure stability using plastic complementary energy as parameter is proposed；and under specified loading conditions，elastoplastic constitutive relation makes the structure whose plastic complementary energy is minimum tend to be stable. It points out that an elastoplastic structure is not stable if it cant satisfy simultaneously equilibrium condition，kinematical admissibility and constitutive equations under the prescribed loading. If the plastic complementary energy equals 0，which means that the stress field can satisfy equilibrium condition and constitutive equation at the same time，then the structure is stable；if the plastic complementary energy is greater than 0，then it means the structure is unstable. Based on Drucker-Prager criteria，a perfect elastoplastic incremental analysis method is considered in nonlinear finite element computation，which has good convergence for both small and large loading step sizes；then above method is used to study the interaction between slope and dam of Jinping I. Plastic complementary energy curves varying with strength reduction are provided to show the interaction between slope and dam. The results show that the push force coming from the arch dam is of some benefits to the slopes stability to some extent；and the slope structure strength reduction has little influence on arch dam until the strength reduction rate is larger than 1.5.

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DISPLACEMENT BACK ANALYSIS OF CREEP PARAMETERS OF ENGINEERING ROCK MASS IN LARGE-SCALE UNDERGROUND CHAMBERS

WU Guojun1，CHEN Weizhong1，2，JIA Shanpo3

2010, 29 (S2): 4043-4049

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Back analysis of creep parameters of engineering rock mass is a most important research subject of stability analysis of rock mass in large-scale underground engineering. According to the dynamic monitoring data of Jinping II underground powerhouse，an analytical model is established which can objectively reflect construction and excavation sequences；by using a finite element program of displacement back analysis combining a new exact penalty method and the Nelder-Mead algorithm，creep parameters of rock mass of Jinping II underground powerhouse are studied. The results show that it is desirable that the calculated displacements are very close to the measured ones，and most of errors are within 8%；the reasonable stress and displacement distributions of rock mass considering creep after excavation are presented. The research achievements can provide theory basis for deeply researching the long-term stability and reliability of large-scale underground chambers.

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NUMERICAL SIMULATION ANALYSIS OF LARGE DEFORMATION OF DEEP SOFT ROCK ENGINEERING BASED ON SOLAR DECOMPOSITION THEOREM

HE Manchao1，2，GUO Hongyun1，2，CHEN Xin1，2，ZHANG Chun1，2，HAN Liuping1，2

2010, 29 (S2): 4050-4055

[PDF] 733 KB (6)

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There are two types of theorems in large deformation analysis of deep soft rock engineering，i.e. polar decomposition theorem and solar decomposition theorem，which the deformation gradient F is decomposed into addition of deformation and rotation by a co-moving coordinate system method. However，there is no finite element methou(FEM) software including solar decomposition theorem up to now，except the finite element software on large deformation analysis for soft rock engineering at great depth，briefly called Large Deformation Engineering Analyses Software(LDEAS) including a solar decomposition increment module. The finite element equations based on solar decomposition theorem were given；according to the functional expression between geostress and depth proposed by Hoek-Brown，the solar decomposition increment module was adopted to analyze the large deformation of a tunnel excavated at six different sets of designed depths to find the relation between deformation and depth. The results indicate that：the deformation of surrounding rock increases with increasing depth；the maximum value of relative displacement between floor and roof is much larger than that of the sidewall shrinkage；and each of them has a good linear relationship with depth；the increasing rate of relative displacement between floor and roof is larger than that of the sidewall shrinkage.

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IN-SITU TEST OF GLASS FIBER REINFORCED POLYMER ANCHOR ON HIGHWAY SLOPE REINFORCEMENT

LI Guowei1，2，LIU Chaoquan3，HUANG Zhihuai1，4，CAI Yeqing5

2010, 29 (S2): 4056-4062

[PDF] 620 KB (6)

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Glass fiber reinforced polymer(GFRP) anchor is a new composite reinforcement material composed of resin and glass fiber；and it has good corrosion resistance and mechanical properties. The tensile，creep behaviors and temperature effect of GFRP were measured in laboratory by strength test，temperature test and creep test. According to test data，the feasibility of GFRP applied to permanent reinforcement engineering is discussed. The tests show that the GFRP anchor is brittle material whose elastic modulus is approximately 40 GPa and yield strength can reach to 400 MPa. The thermal stability of GFRP is similar to HRB335 steel applied to engineering within working temperature range and under working load conditions. GFRP can not take place sustained creep deformations under design load for anchor. Guangdong—Jiangxi highway K3+728–904 right slope reinforcement adopted GFRP anchor frame beam structure as permanent reinforcement engineering. Through in-situ monitoring of GFRP anchor stress，deformation of reinforced slope and whole displacement，the reliability of permanent GFRP anchor reinforcement structure is discussed. The monitoring data show that the stress variation of GFRP anchor corresponds with the loading variation of slope reinforced by GFRP anchor；There is no stress relaxation under the long-term effect of loads，and GFRP anchor could still undertake some additional loads；Its stress distribution of GFRP anchors is different from that of steel anchors because of the difference in elastic moduli，and GFRP anchor is more suitable to soil slope reinforcement which usually has larger deformation than rock slope.

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AN EQUIVALENT 1D DYNAMIC CONTINUUM MODEL FOR ROCK MASS WITH PARALLEL JOINTS

LI Jianchun1，2，LI Haibo1，Guowei MA3，Jian ZHAO2

2010, 29 (S2): 4063-4067

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Based on viscoelastic theory，an equivalent one-dimensional dynamic continuum model is proposed for rock mass with parallel joints. The model includes two portions，one is the viscoelastic medium model and the other is the concept of“virtual wave source(VWS)”. The time retardation and attenuation of longitudinal wave propagation across jointed rock mass are considered in the viscoelastic medium model；and the concept of VWS is adopted to account for the wave reflections between joints. The parameters in the equivalent viscoelastic model are derived analytically based on existing solution for longitudinal wave propagation across a single rock joint. The proposed model is then verified by applying identical incident waves to the discontinuous and equivalent dynamic media at one end and receiving output waves at the other end，i.e. by comparing two results from the displacement discontinuity method and the present equivalent medium method. The results show that the proposed model can simplify the simulation of stress propagation effectively.

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Study oF anisotropic constitutive model of columnar jointed rock massES based on Cosserat theory

ZHU Zhende1，2，QIN Tianhao2，WANG Shihong3，WANG Lianguo4，SUN Linzhu1

2010, 29 (S2): 4068-4076

[PDF] 1726 KB (6)

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According to anisotropic mechanical properties of Baihetan columnar jointed rock masses，triangular and quadrangular prism generalized models were introduced. Based on microscopic media of a group of jointed rock masses，Cosserat extended constitutive equation was obtained by using Cosserat theory and Goodman equivalent superposition principle. Triangular and quadrangular prism columnar jointed constitutive models were established. At last，by using FLAC3D，Cosserat anisotropic constitutive model was applied to tunnel excavation numerical simulation of Baihetan columnar jointed rock masses. Variations in stresses and strains at different excavation stages and influences on engineering were comparative analyzed under isotropic and anisotropic conditions. Comparing with isotropic constitutive model，stresses in three directions of Cosserat anisotropic constitutive model have larger differences；it can reflect engineering reality better；and it is more important for design optimization of engineering.

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A NEW DEFINITION FOR INITIAL YIELD OF STRESS-STRAIN CURVES AND ITS APPLICATION

BAI Bing1，LI Xiaochun1，TANG Lizhong2

2010, 29 (S2): 4077-4081

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Through combining the path dependent hardening parameter and the definition of initial yield，a new definition method of initial yield is proposed. The key idea of this method is to apply the failure point to define the initial yield point on each stress-strain curve，in which the calculation of path dependent hardening parameter is prime. As an application of this new definition，a group of loading-unloading stress-strain curves of coal samples under confining pressures of 15–50 MPa are used to determine their initial yield points；and then the subsequent yield loci in q-p space are drawn，which reveal a new phenomenon that the slope of each q-p locus increases with hardening parameter. This is an important phenomenon for coal hardening plasticity；and it needs further studies.

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STUDY OF UNLOADING TESTS OF ROCK BURST AND PFC3D NUMERICAL SIMULATION

WU Shunchuan1，2，ZHOU Yu1，GAO Bin1

2010, 29 (S2): 4082-4088

[PDF] 1712 KB (6)

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According to rock burst hazard of Zhangjiakou—Shijiazhuang highway tunnel，laboratory unloading tests of rock burst were conducted. Based on particle flow theory and PFC3D，a loading-unloading code was developed by using Fish language embedded in PFC3D to carry out numerical simulation of laboratory unloading tests of rock burst. This approach reproduces the damage processes and mesoscopic fracture phenomena of unloading rock burst under different stress conditions；and it provides an effective means for discrimination of rock burst occurrence. The results are drawn as follows：(1) The rock burst of calcite dolomite of study area is an instantaneous type and its intensity level is IV. The ends of the specimen fully collapse while the central exposed surface of the specimen strips by slices accompanying with particles ejection. (2) The whole rock burst process of laboratory test can be divided into four states including quiet state，local particles ejection state，developing state and final eruptive state based on the variation in stress environment. (3) Fracture mechanism of particles bond during instantaneous rock burst is pertaining to tension type principally. (4) The load grade，stress-step curve and failure pattern of rock burst in simulation are consistent with laboratory unloading tests correspondingly. Therefore，PFC3D numerical simulation method can be substituted for some laboratory unloading tests of rock burst for its validity，lower experiment expense and convenience；and it also provides a new effective way to study rock burst.

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STUDY OF GEOTHERMAL EXTRACTION SCHEME OF HOT DRY ROCK IN TIBETAN YANGBAJING REGION

ZHOU Anchao1，ZHAO Yangsheng1，GUO Jinjing2，ZHANG Ning1

2010, 29 (S2): 4089-4095

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Deep melted rock mass structure at depths of 5–15 km of Tibetan Yangbajing region in China was analyzed in detail；and the temperature field distribution of hot dry rock(HDR) geothermal field was calculated by finite elements(FE). The calculation results show that the estimated HDR geothermal resource of Yangbajing region is 5.4×109 MW·a；and it will become Chinese huge potential HDR geothermal resource. Based on the detailed studies of the continental dynamics environment of formed HDR geothermal field of Tibet，the tectonic characteristics of south slope of Tanggula Mountain and Dangxiong—Yangbajing Basin，and in-situ stress size and orientation，the extraction scheme of HDR geothermal resource was proposed. That is considering fault sliding zone near the high temperature melted rock region as artificial reservoir；the vertical injection wells are arranged in the low site along the lean direction of the fault while the lean production wells in the high site. An artificial reservoir with the volume of 3×1011 m3 could be obtained，which is 360 times larger than that in Cornwall of British. Then the designed artificial reservoir features，seepage analysis of the heat exchange area，project implementation and investment analysis were investigated. The results indicate that a power station of 104 MW for 100 years can be built by using a set of geothermal extraction system mentioned in this plan；and it will bring forth great economic and social benefits.

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PRELIMINARY STUDY OF THEORETICAL SOLUTION TO STRESS RELAXATION EFFECT FOR UNDERGROUND ENGINEERING

WANG Zhechao1，CHEN Weizhong2，QIAO Liping3，ZHANG Lewen1

2010, 29 (S2): 4096-4101

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Creep and stress relaxation of geo-materials are the two frequently observed time-dependent phenomena in geotechnical engineering. For underground structures，the interaction between support system and surrounding rock or soil mass is influenced not only by the creep of rock or soil mass，but also by the stress relaxation. Based on a modified nonlinear creep model，a theoretical solution to an equivalent creep problem is proposed to describe the stress relaxation of circular caverns embedded in viscoelastic geo-materials. The dimensionless expression is also presented. Two types of soils are employed in case studies. The results show that the stress relaxation characteristics of geo-materials can be described by the parameters in the creep law；the design for long-term stability of lining without consideration of stress relaxation in rock or soil mass is safer than that in practice. In the view of energy conservation，stress relaxation can be considered as a decreasing process of concentrated ground stress，which is induced by excavation of caverns. The process is dependent on the initial condition and mechanical properties of material and influenced by time and space. Furthermore，the evolution of inner microstructure is reverse to that of creep. The study results can not only be applied to engineering applications directly，but also be helpful in understanding of rheological behavior of geo-materials.

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STUDY OF FRACTAL CHARACTERISTICS OF ELECTROMAGNETIC EMISSION DURING COAL AND ROCK MASS FRACTURE

YAO Jingming1，YAN Yongye2，SHUI Guohong1，YAO Junwei1，LI Shengzhou1

2010, 29 (S2): 4102-4107

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To improve accuracy of forecast of coal and rock mass dynamic disasters by using electromagnetic emission (EME)，the EME fractal characteristics of coal samples during uniaxial compression test are studied by laboratory experiments and fractal theory. The results show that the EME impulses have fractal characteristics；and the fractional dimension has a positive power exponential relationship with the impact energy exponent of coal samples. When the loaded coal samples are at the stage of consolidation，the fractional dimension of EME is small；at the stage of elasticity，the fractional dimension of EME has a little increase and remains at a stable level；at the stage of plasticity，the fractional dimension of EME increases greatly；close to main fracture，the fractional dimension of EME decreases gradually；at the main fracture，the fractional dimension of EME decreases gradually；and at the stage of residual deformation，the fractional dimension of EME firstly increases and then decreases，and general trend of the fractional dimension is declining. Based on the above studies，the rock burst has been forecasted accurately and successfully in working face 7249. The practice shows that the EME method which calculates the fractional dimension is feasible to forecast the dynamic disasters in mines.

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GRANITE DEFORMATION CHARACTERISTICS IN DRILLING PROCESS AT 4 000 m HYDROSTATIC PRESSURE AND HIGH TEMPERATURE

FENG Zijun1，ZHAO Yangsheng1，ZHAO Jinchang1，WAN Zhijun2，DONG Fuke3，ZHANG Yuan2

2010, 29 (S2): 4108-4112

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The stability of borehole will influence the construction progress of deeply drilling hole into the hot granite reservoir so as to extract hot energy from hot dry rock. However，the stability of borehole is subjected to the deformation of surrounding rock. The 600 ℃ 20 MN servo-controlled rock triaxial testing machine with high temperature and pressure developed by China University of Mining and Technology was utilized to investigate the deformation characteristics of surrounding rock of drilling hole at high temperature and pressure. The experiment on the deformation characteristics of granite in the process of drilling at 4 000 m in-situ hydrostatic pressure and different high temperatures was carried out. The results indicate that：(1) A clear creep process occurs in the process of drilling hole in granite at constant pressure and temperature，while the axial and lateral deformations appear the whole initial and secondary creep processes. (2) The axial and lateral strains increase with temperature rising in the process of drilling at 4 000 m hydrostatic pressure and different high temperatures；and there exists a critical temperature which ranges from 150 ℃ to 300 ℃. (3) Tertiary creep of granite deformation clearly happens at 300 ℃ in the process of drilling hole at 4 000 m hydrostatic pressure；and creep damage occurs at 500 ℃.

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STUDY OF RELATIONSHIP BETWEEN STRENGTH PARAMETERS AND ICE EXPANSION FORCE OF GRANITE UNDER LOW TEMPERATURE

LI Yunpeng1，2，WANG Zhiyin1，2

2010, 29 (S2): 4113-4118

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The strength parameters of rock under low temperature have a certain relationship with the ice expansion force. Based on thermodynamic properties of ice，the mathematical relationship between varying low temperature and ice expansion force is created. Considering that the surrounding rocks near the underground liquefied natural gas(LNG) storage caverns lie in 0 ℃–－50 ℃ environment for a long time，the compressive strength laws of dry and saturated granite at varying low temperature are studied under different confining pressures by using the triaxial compression test results of dry and saturated frozen granite samples. According to Mohr-Coulomb criterion and generalized Mises conditions(including Drucker-Prager criterion)，the relations among the rock strength parameters，temperature and ice expansion force are established under varying low temperature conditions. The results show that：The ice expansion force of rock pore has a relationship with the mechanical parameters and the volume expansion coefficient of ice changing with low temperature；and the ice expansion force gradually decreases with reducing temperature. The internal friction angle and cohesion of frozen granite are relative to varying low temperature and ice expansion force；and their values in frozen state are always greater than those in dry conditions at the same temperature. The results and the strength conditions can be used for researching and evaluating the long-term stability of surrounding rocks of underground LNG storage caverns.

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APPLICATION OF WEIGHTED MAHALANOBIS DISTANCE DISCRIMINANT ANALYSIS METHOD TO CLASSIFICATION OF ROCK MASS QUALITY

YAO Yinpei1，2，LI Xibing1，2，GONG Fengqiang1，2，PENG Kang1，2

2010, 29 (S2): 4119-4123

[PDF] 349 KB (6)

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Distance discriminant analysis method is one of classification methods according to multi-index performance parameters；and it has been applied to classification of engineering rock mass quality. However，the traditional Mahalanobis distance discriminant method treats with the importance of all parameters equally，and exaggerates the role of parameters which changes a little. The weighted Mahalanobis distance is used in discriminant analysis method to distinguish the importance of each parameter to improve the classification of rock mass quality. In the concrete application，firstly based on the principal component analysis scheme，a new group of parameters and their corresponding percent contributions of the parameters of rock mass quality are calculated；and the weighted matrix is regarded as the diagonal matrix of the contributions rates. Setting data to standardization，then the weighted Mahalanobis distance can be calculated to classify rock mass quality. The new method is used in practical project and compared with the artificial neural network method and Mahalanobis distance discriminant analysis method. The results show that the weighted Mahalanobis distance method has a higher discriminant ability；and prediction results are in better agreement with the fact. It is an exact and effective classification method of rock mass quality.

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CONFIGURATION OPTIMIZATION OF PRESSURE-DISPERSIVE ANCHORS IN SOFT-HARD INTERBED OF SEDIMENTARY ROCK

LU Li1，2，ZHANG Siping1，2，ZHANG Yongxing1，2，LIN Weixun1，2

2010, 29 (S2): 4124-4130

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Three-dimensional numerical models which contain soft-hard interbed and pressure-dispersive anchors are built to study configuration optimization of anchors. The pressure-dispersive anchors with rundle configuration are obtained by changing the quantity of steel strand on each unit anchor；then the numerical analysis of optimization is carried out. Comparing the stress distribution along fixed anchor length and the loading-displacement curves of different unit anchors，the best optimization scheme is selected. The results show that the rundle optimization scheme with nonuniform unit anchors can coordinate every unit anchors in soft and hard rock to reach the ultimate bearing capacity at the same time. In addition，the traditional pressure-dispersive anchors with uniform unit anchors have a disadvantage that the unit anchor in the soft rock will fail at first. Finally，a suggestion of the optimization scheme of pressure-dispersive anchor adopted in soft-hard interbed is summarized.

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POST-PEAK DILATANCY AND ITS EVOLUTION OF HARD ROCK FRACTURES UNDER NORMAL AND SHEAR LOADS

BAI Zhengxiong，CHEN Yifeng，ZHOU Chuangbing，LI Dianqing，RONG Guan

2010, 29 (S2): 4131-4138

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The dilatancy and its evolution of fractures under normal and shear loads are essential to understanding deformation behavior，coupled hydromechanical behavior and anchorage mechanism of fractured rock masses. Although the dependencies of joint dilatancy on plasticity，normal stress and scale effect have been demonstrated in the literature，the evolution of dilatancy remains an open issue for rock fractures. Existing studies commonly adopted a constant dilatancy angle between 0 and 20 or the internal friction angle to characterize the dilatancy behavior. As a result，the normal deformation of rock fractures induced by dilatancy may either be underestimated at small shear displacements，or be overestimated at relatively large ones. The post-peak dilatancy behavior and its evolution are better modeled by the formulae for peak dilatancy angles of rock fractures proposed by N. Barton and a mobilized dilatancy evolution model in negative exponential form. The proposed model have been validated by a number of existing laboratory shear tests；and it may provide a useful expression for investigating the deformation，seepage flow and reinforcement behaviors of jointed rock masses.

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ANALYSIS OF FIELD MEASUREMENT AND THEORETICAL CALCULATION ON ROCK PRESSURE IN SHALLOW-BURIED TWIN TUNNELS WITH SMALL SPACING

GONG Jianwu1，XIA Caichu2，LEI Xuewen1

2010, 29 (S2): 4139-4145

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Based on the code for design of road tunnel(JTG D70–2004)，the analysis has been carried out on the rock pressure of shallow-buried twin tunnels with small spacing；and the calculated model and theoretical calculation of rock pressure have been put forward by considering the construction processes of twin tunnels. The distribution law and influence factors of tunnel rock pressure have been discussed through calculation examples；the unsymmetrical characteristic of rock pressure distribution in shallow-buried twin tunnels with small spacing is pointed out，i.e. the vertical contact pressure at the inner side of twin tunnels is greater than that at the outer side，while lateral contact pressure at the inner side is less than that at the outer side. Meanwhile，the comparison analysis has been made between theoretical values from model and monitoring data from practical tunnel engineering. The results show that the calculated model and theoretical method proposed are rational and practicable. It is proposed that the unsymmetrical characteristic of rock pressure should be taken into account for the design of tunnel structure and support. The experience and conclusions can be referred to the analysis of rock pressure and the design of tunnel structure.

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SIMULATION ANALYSIS OF DYNAMIC PROCESS OF ENTRAINMENT OF PATH MATERIAL BY DEBRIS FLOW

FAN Yunyun1，WANG Sijing2，3，WANG Enzhi2，LIU Xiaoli2

2010, 29 (S2): 4146-4152

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The unconsolidated surface material along the way may have a shear failure and slide with the land during the motion process，as a result，the entrainment of path material on the surface is formed. In order to carry out the simulation of dynamic process of entrainment along the way and study the influence of this entrainment on dynamic process of debris flow，the back analysis is made to study a typical historical debris flow with its erosion along the way，by combining debris flow dynamic model theory and the method of finite volume discretization based on the approximate Riemann solver of HLL scheme. The calculation has considered the entrainment action during the dynamic process of debris flows and reappears the whole process. The calculation results which are identical to actual disaster-caused area confirm the effectivity of the dynamic model theroy and the numerical solution. At the same time，compared with the results which have no consideration of entrainment，it is can be seen that the entrainment action can increase the motion volume of debris flow and enhance the motility so that the dynamic process of debris flows would be greatly influenced；and as a result，the debris flow will be more destructive and harmful.

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EXPERIMENTAL STUDY OF DYNAMIC MECHANICAL PROPERTIES OF ROCKS

ZHANG Ying，LI Ming，WANG Kehui，CHU Zhe

2010, 29 (S2): 4153-4158

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To understand the dynamic mechanical properties of rocks，a series of dynamic shock compression tests were carried out by using 50 mm Hopkinson pressure bar apparatus，with strain rate range from 25.4 to 193.4 s－1. Wave shaping technique was used to smooth pulse load；dynamic stress-strain curves were obtained. Experiment data show that the strength of rock has an obvious strain rate effect. The value of strength increases with increasing strain rate. Compared with static strength of 120 MPa，the maximum dynamic strength is enhanced to 365 MPa at strain rate of 193.4 s－1. With the increase in dynamic load，specimen experiences a process of the generation of internal damage，micro flaw，macro crack，fracturing to nubbins and crushing to pieces. The results are valuable for military structure design.

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RESEARCH ON ENERGY PROPERTIES OF ROCK CYCLICAL IMPACT DAMAGE UNDER CONFINING PRESSURE

XU Jinyu1，2，LU Xiaocong1，3，ZHANG Jun3，WANG Zedong1，BAI Erlei1

2010, 29 (S2): 4159-4165

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Dynamic mechanical performance experiments were carried out for three types of rocks under different confining pressures and cyclical impact loadings by using split Hopkinson pressure bar with confining pressure device. The stress-strain curves of specimens under cyclical impact loadings were obtained. According to theoretical analysis，a determinant criterion of damage degree of rock was established；and the accumulative specific energy absorbency was defined to describe energy properties of rock dynamic damage. The studies of the relationships among damage degree of rock，accumulative specific energy absorbency and confining pressure under cyclical impact loadings show that accumulative specific energy absorbency could well describe the damage degree of rock. When the confining pressure increases gradually，the incremental tendency of damage becomes slow along with the accumulative specific energy absorbency，i.e.，the higher the confining pressure is，the more energy for rock to reach the same damage level is needed. The formulae of rock damage degree and accumulative specific energy absorbency are put forward under confining pressures. When the damage threshold is reached，the growth rate of accumulative specific energy absorbency of sandstone is the largest along with the increase in confining pressure，the rate of sericite quartz schist is the smallest，and the rate of plagioclase amphibolite is between ones of sandstone and sericite quartz schist.

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ANALYSIS OF DYNAMIC EFFECT OF ROCK FAILURE UNDER UNDERGROUND INTENSIVE EXPLOSION

WANG Derong1，LI Jie1，FAN Xin2

2010, 29 (S2): 4166-4172

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Dynamic effect of rock failure under underground intensive explosion is investigated by some results of underground explosion tests. The change laws of physico-mechanical characteristics including uniaxial compressive strength，velocity of longitudinal wave and porosity are studied；and the effects of explosion source parameters including initial loading density and pressure waveform on rock failure are analyzed. The state equations of rock in explosion near region，shear-crashed region and nondestructive loading region after explosion are established respectively. The results show that：In the near region of intensive explosion，the uniaxial compressive strength of rock decreases at the scale distance of 35–40 m/kt1/3. The parameters of explosion source have relatively great influence on dynamic failure effect of rock. The parameters such as radius of failure zone，expanding velocity of powder chamber wall and maximum particle velocity increase with the initial loading intensity of explosion source. The development and distribution of cracks are controlled by loading ratio.

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laboratory Experimental study of slaking characteristics of red-bed soft rock

WU Daoxiang1，2，LIU Hongjie1，WANG Guoqiang1

2010, 29 (S2): 4173-4179

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Taking red-bed soft rock along Tangkou—Tunxi section of Tongling—Huangshan expressway for example，according to the characteristics of softening and slaking with water，two representative rock samples (sandstone and mudstone) along the expressway are chosen to perform laboratory tests of slaking；and changes in grain contents of rock samples in slaking process are analyzed. On this basis，the comparative analysis of slaking characteristics of those representative samples is made；and the slaking characteristics of those samples are divided into four grades，i.e. strong slaking，medium slaking，feeble slaking and nonslaking. The results indicate that the types of red-bed soft rock and its cement，and the content of clay mineral are the main inner determinants of slaking of red-bed soft rock；the slaking characteristic gradually decreases as the grain diameter of slaking substance reduces；in order to obviously reflect the rate and degree of slaking of those samples，changes in grain contents of slaking substances greater than 5 mm and less than 0.25 mm should be selected as the evaluation objects. At last，thorough study of slaking mechanism of red-bed soft rock is made.

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EXPERIMENTAL STUDY OF ROCK COMPRESSION-DAMAGE-FAILURE PROCESS

SONG Weidong，MING Shixiang，WANG Xin，DU Jianhua

2010, 29 (S2): 4180-4187

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The mechanical properties of rock have an significant influence on the stability and deformation rule of surrounding rock. The triaxial compression test and the post-peak cyclic loading and unloading test on rock samples were carried out to discuss the deformation and failure characteristics of surrounding rock exceed the peak strength and to study the deformation mechanism and failure characteristics of rock samples. The results show that：(1) Under uniaxial compression or low confining pressure conditions，rock has brittle softening characteristics. As the confining pressure increases，the failure state gradually changes to the compression-shear and plasticity yield damaged state. (2) Rock in post-peak area has a significant volume expansion；and the Poissons ratio ( = 3/1) in post-peak area remains a constant. (3) Soft rock under cyclic loading and unloading has obvious slip friction characteristics in the post-peak area. After rock samples broken，3 and 1 show a good linear relationship throughout the post-peak deformation stage. (4) When soft rock reaches the peak strength，the rupture and slip will occur，and the peak point is the mutational site.

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STUDY OF FIELD MEASUREMENT OF MINING-INDUCED COAL FRACTURE FIELD AND ITS APPLICATION

PENG Yongwei1，2，QI Qingxin1，3，4，WANG Yougang1，5，DENG Zhigang1，2，LI Hongyan3，4，LI Chunrui1，2

2010, 29 (S2): 4188-4193

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The borehole camera method，single scan line method and sampling window method are used to study the mining-induced fracture field under high-strength mining conditions，based on the 3207 workface in Tiandi Wangpo coalmine. On this basis，the influences of mining-induced coal fracture field on mining-induced stress and gas pressure distribution are investigated by using COMSOL Multiphysics software. The relationship of gas pressure with mining-induced fracture distribution is discussed；and the reasonable layout of drilling holes under mining-induced fracture conditions is also analyzed.

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STUDY OF MESO-MECHANISM OF SEEPAGE FAILURE IN TUNNEL EXCAVATION PROCESS

NI Xiaodong1，2，WANG Yuan1，2，LU Yuguang1，2

2010, 29 (S2): 4194-4201

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Seepage failure is a main disaster in the process of tunnel excavation. The study of seepage failure mechanism is important to predict it and to decrease the probability of this kind of disaster. Taking advantage of discrete element method(DEM) comparing with the traditional numerical modeling on dynamic simulation and characteristic simulation of dispersed particles，the PFC2D based on DEM is adopted to establish the 2D numerical seepage model in which rock is built by bonded particles. The whole process of seepage failure under different hydraulic gradients due to tunnel excavation is simulated by using PFC2D and computational fluid dynamics(CFD). Propagation of microcracks and permeability changes can be real-time reflected during the excavation. Simulation results show that it is applicable to use particle flow code(PFC) to simulate seepage failure process of rock；and it has certain guiding significance on tunnel excavation.

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ERROR ANALYSIS AND FEASIBILITY RESEARCH ON PERMEABILITY EXPERIMENT OF BENTONITE

CAO Shengfei1，2，QIAO Lan1，LIU Yuemiao2，JIANG Yinhua1，MA Like2，XIE Jingli2

2010, 29 (S2): 4202-4206

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In deep geological disposal for high-level radioactive waste，the buffer and backfill materials between waste tank and surrounding geological body play an important role as hydraulic barrier. The engineered barrier made by densely compacted bentonite is used to prevent the groundwater infiltrating and the radioactive waste diffusing. The research on bentonite can provide essential parameters for the deep geology disposal of nuclear waste. Through six groups of bentonite variable head permeability experiments，the relationship between permeability coefficient and time is analyzed and the permeability curves of bentonite samples and time are obtained. Then according to the physical and chemical conditions of bentonite，the variable head permeability principle and the environmental conditions of experiments，the reasons about the relationship of the permeability coefficient with time and the accuracy of the data are analyzed. Finally，the measurement errors and feasibility of variable head permeability experiment are analyzed，according to the reasons of measurement errors；and it provides an improved method to test the permeability of compacted bentonite.

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EXPERIMENTAL STUDY OF EFFECT OF ROCK TARGETS PENETRATED BY HIGH-VELOCITY PROJECTILES

SHEN Jun1，XU Xiangyun1，2，HE Xiang1，FENG Shunshan2，YANG Jianchao1

2010, 29 (S2): 4207-4212

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In order to study the penetration effects of high-velocity projectiles on rocks，the model experiments of high-velocity projectile penetrating rock targets are carried out by using high-velocity ballistic gun，which the highest experimental velocity reaches 1 450 m/s. The relationship between penetration depth and velocity is obtained. The empirical equation of penetration depth is established when the bullet speed is lower than the terminal speed；and the equation has a good compatibility with experimental results. The damage types of model experimental targets are analyzed；the results show that various damage types of targets are generated under different projectile velocities for a given bullet and target. The penetration performance，terminal velocity and mass loss of projectile under high impact velocity are investigated；and the elements which affect the terminal velocity and mass loss of projectile are analyzed. It can be used to predict the main parameters such as penetration depth，acceleration，mass loss rate and so on；and it also provides an effective reference to the design of projectile head and protective engineering. The results show that unweathered hard rock can be used as materials in protective engineering after comparing the experiments of concrete plate targets.