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2010, 29 (08): 0-0 doi:

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RELIABILITY ANALYSIS OF SLOPE USING STOCHASTIC
RESPONSE SURFACE METHOD AND CODE IMPLEMENTATION

LI Dianqing1，2，ZHOU Chuangbing1，2，CHEN Yifeng1，2，JIANG Qinghui1，2，RONG Guan1，2

2010, 29 (08): 1513-1523 doi:

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This paper aims at proposing a stochastic response surface method(SRSM) for reliability analysis involving correlated random variables. The Nataf transformation is adopted to effectively transform the correlated nonnormal random variables into the independent standard normal variables，which facilitates the collocation points associated with the correlated random variables and reliability computation using the SRSM. Explicit polynomials are derived for fourth-order to sixth-order Hermite polynomial chaos expansions of any number of random variables. A C#-language based computer program WHUSRSM (Wuhan University SRSM) is developed. An example of reliability analysis of rock slope stability with plane failure is presented to demonstrate the validity and capability of the proposed SRSM. The results indicate that the proposed SRSM can evaluate the reliability of rock slope stability involving correlated random variables efficiently. The proposed SRSM has a higher accuracy than the conventional first-order reliability method；and its efficiency is higher than Monte Carlo simulations. Moreover，the convergence in Hilbert space of the SRSM can be ensured in any case. The mean of factor of safety for slope stability can be accurately estimated by the proposed SRSM with different orders. However，the orders of the SRSM should be selected carefully to accurately estimate the probability of rock slope failure. The calculation of factor of safety and the reliability analysis can be conducted separately within the framework of the SRSM based on reliability analysis. Slope stability analysis would be investigated systematically with the results associated with factor of safety as well as probability of failure. These results can provide a basis for extending the application of the SRSM to reliability analysis of rock slope stability.

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STUDY OF RELATIONSHIP BETWEEN EVOLUTION OF POST-PEAK STRENGTH PARAMETERS AND STRESS-STRAIN CURVES OF GEOMATERIALS

WANG Shuilin，WANG Wei，WU Zhenjun

2010, 29 (08): 1524-1529 doi:

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CREEP TEST AND RHEOLOGICAL MODEL SELECTION OF MARBLE
OF JINPING I HYDROPOWER STATION

ZHANG Ming，BI Zhongwei，YANG Qiang，CHENG Lijuan，LI Zhongkui

2010, 29 (08): 1530-1537 doi:

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The creep tests on marble specimens from the underground powerhouse of Jinping I hydropower station of China are carried out to meet the demand of long-term stability analysis of the caverns during the construction and the operation periods. Two common rheological models，Hooke-Kelvin model and Burgers model，and their parameters determination are described with comparative discussion for the model selection. The least squares fitting to the testing results with the model curve is recommended to gain the model parameters. The creep testing system and the testing procedure are introduced briefly. It is manifested by the uniaxial creep tests and the biaxial creep tests that the considered marble shows time-dependent behavior to some extent under certain stress states. The deformation gradually approaches to corresponding constant after the early stage of creep attenuation，which accords with the creep characteristic of the Hooke-Kelvin model. The measured strains with respect to the loading time are close to the Hooke-Kelvin model curve. Therefore，the Hooke-Kelvin model is recommended to describe the rheological properties of marble. As for the Burgers model，the analysis shows that it is unsuitable for modeling the viscoelasticity of hard rock like marble. The creep behavior during relatively longer testing time，e. g. 150 hours or so，needs to be examined if the Burgers model is adopted. The fact that the deformation of the underground powerhouse caverns of Jinping I hydropower station finally tends to become steady after excavation can be better explained by means of the Hooke-Kelvin rheological model. The Hooke-Kelvin rheological model and the model parameters obtained from creep tests may also be served as the fundamental data in the later long-term stability analysis of the surrounding rocks of the underground powerhouse caverns in the periods of construction and operation.

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STUDY OF MECHANICAL MODEL FOR WEAKENING PROCESS OF DISCONTINUOUS JOINT ROCK BRIDGE

XIA Caichu1，2，XIAO Weimin1，2，LIU Yuanming3

2010, 29 (08): 1538-1545 doi:

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According to direct shear tests performed on artificial discontinuous intermittent joints，the mechanical mechanism of weakening process of discontinuous joint rock bridge during shearing is described，i.e. tensile failure of micro-unit rock bridge under shear loads results in the mechanical properties weakening of rock bridge. And the development law of weakening zones in rock bridge is also investigated. Based on the above analysis，assuming that rock bridge micro-unit strength is of Weibull random distribution and the minor principal stress of rock bridge micro-unit is adopted as the random distribution variable，model for explaining the weakening process of rock bridge is set up；and a parameter ，which is named as the degree of weakening，is defined to characterize the degree of rock bridge weakening during shearing. And then，based on direct shear tests，rock bridge weakening mechanical model that takes shear displacement as random distribution variable is derived from analogy method. Finally，the change laws between the degree of rock bridge weakening and parameters m， are analyzed . The results show that the new model can properly reflect the weakening and failure process of rock bridge during shearing.

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MODEL TEST STUDY OF SECTIONAL METRO TUNNEL WITH FLEXIBLE JOINTS ADAPTING LARGE DEFORMATION OF GROUND FISSURES

HUANG Qiangbing1，2，3，PENG Jianbing1，2，3，MEN Yuming2，3，LI Ke4

2010, 29 (08): 1546-1554 doi:

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Ground fissure is a special urban geological hazard in Xi¢an；and metro tunnels should be divided by special deformation joints and connected with flexible joints to adapt the large deformation of active ground fissures. Based on the Xi¢an metro tunnel orthogonally passing through active ground fissures，by means of large-scale model tests with a geometric proportion of 1∶5，the adaptability of sectional metro tunnel with flexible joints to active ground fissures is studied. The test results show that the flexible joints prevent tunnel from stress concentration and protect tunnel structures under the influence of active ground fissures；and the sectional tunnel with flexible joints can adapt the large deformation of active ground fissures. To some extent，the special deformation joint with the same dip angle as active ground fissure has certain effect on pressure and displacement of surrounding rock，but affects the safety of tunnel lining structure less. Meanwhile，the oblique special deformation joint can absorb over 20% of the total displacement of active ground fissure. In active ground fissure zones，tunnel can be divided into a few sections and connected in series to eliminate the influence of large deformation of active ground fissure on tunnel lining to the maximum. The watertight belts are undamaged at the top and bottom of lining and mangled on the bilateral wall affected by the vertical displacement of ground fissure，so the bilateral wall of flexible joint should be intensified in waterproof design. The conclusions provide an important reference for structure and waterproof designs of metro tunnel under the influence of active ground fissures.

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STUDY OF CREEP MECHANISM OF ARGILLACEOUS SOFT ROCKS

FAN Qiuyan1，YANG Keqing2，WANG Weiming3

2010, 29 (08): 1555-1561 doi:

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Based on the analysis of existing research results of rock creep mechanism，the mudstone in Nanning Basin is taken as the mainly research object；and its creep property is deeply discussed by a series of tests under unconfined uniaxial compression and confined uniaxial compression. Especially，the creep changes of meso- and micro-structure are researched combining with scanning electron microscope(SEM) images of mudstone. It¢s indicated that the creep mechanism of the argillaceous soft rock is the result of the interaction between the damage effect and hardening effect. It is reasonable to explain and illustrate the mechanism of three creep phases by using the comprehensive curves，which include the creep curve，the damage effect curve and the hardening effect curve：at the first stage，hardening effect is much stronger than the damage effect and the creep mainly obeys the decay law of hardening effect at this stage；at the second stage，the damage effect is stronger than the hardening effect，and the creep mainly obeys the constant-rate law of the damage effect at this stage；at the third stage，the hardening effect disappears and the creep obeys the acceleration law of the damage effect. The creep mechanisms of the argillaceous soft rock and the metal materials are different in terms of magnitude of objects and the mechanism.

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ACOUSTIC EMISSION TEST ON DAMAGE EVOLUTION OF SURROUNDING ROCK IN DEEP-BURIED TUNNEL DURING TBM EXCAVATION

CHEN Bingrui1，FENG Xiating1，XIAO Yaxun1，MING Huajun1，ZHANG Chunsheng2，
HOU Jing2，CHU Weijiang2

2010, 29 (08): 1562-1569 doi:

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Diversion tunnels of Jinping II hydropower station，which is located at high stress zone，Southwest China，encounter many geological disasters，such as rockburst，water bursting，collapse of tunnel and so on during construction. It is very important to master damage evolution of surrounding rock and to design effective supporting measures to prevent or relieve geological disaster. Therefore，acoustic emission(AE) test was carried out and law of damage evolution of marble was studied. Different damage of surrounding rock comes up in 10 m range before free face during TBM working；and main damage or cracking is developed in 7 m range；3 m location is the most severe after free face. Damage range of surrounding rock is about 9 m in direction of tunnel axis. Relaxation，damage and disturbed zone are distinguished by evolution law of AE events，energy release and mechanism of damage evolution. Relaxation and damage range of surrounding rock are 3，3–9，and 9–22 m far from tunnel wall，respectively. Mechanism of damage evolution is illuminated by AE and mechanical characteristics before and after peak strength of rock mass. The influences of sensor types and arrangement，environmental noise and geological conditions on testing result are discussed；and the directions to improve testing result are also pointed out.

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IN-SITU MONITORING OF DISPLACEMENTS AND STABILITY EVALUATION OF SLOPE BASED ON FIBER BRAGG GRATING SENSING TECHNOLOGY

PEI Huafu1，YIN Jianhua1，ZHU Honghu1，HONG Chengyu1，FAN Youhua2

2010, 29 (08): 1570-1576 doi:

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A new type of in-place inclinometer based on fiber Bragg grating(FBG) sensing technology and the related analysis method are presented. Based on the linear relationship between the wavelength change of FBG and strain，the strains at different measuring points on the new in-place inclinometers are obtained. Using the classical beam bending equation and finite difference method，the displacements of the inclinometer can be calculated. This new type of in-place inclinometer overcomes certain disadvantages of the conventional in-place inclinometer，such as low accuracy，poor durability，and complex operation. Laboratory calibration results verify the reliability of the new in-place inclinometer and its analysis method. For a cut slope along the Panzhihua—Tianfangcun highway，three new FBG in-place inclinometers were placed in three vertical boreholes in the same cross-section of the slope, ensuring that the inclinometers passed through the potential slip surface. Then the field monitoring started. Monitoring data derived from the inclinometers are collected and analyzed. An optimal model is adopted to calculate the position of the potential slip surface and the factor of safety of the slope，which is well compared with the results obtained from Bishop¢s method. It is shown that the method presented provides a new and reliable approach for assessment of slope stability based on slope monitoring data.

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STUDY OF ANCHORAGE MECHANISM OF GRANULAR MIXTURE

MA Gang，ZHOU Wei，CHANG Xiaolin，ZHOU Chuangbing

2010, 29 (08): 1577-1584 doi:

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The mesoscopic numerical simulation method is employed to study the anchorage mechanism of granular mixture in geotechnical engineering. 3D random distribution particle model of granular mixture is built based on random simulation technique；the form factor is used to control the surface irregularity of the granules. In addition，nonlinear contact algorithm is presented based on modified augmented Lagrangian algorithm and is employed to simulate the interaction between granule and rockbolt. The mechanical properties of granule obey Weibull probability distribution；mesoscopic damage softening model is employed to describe granule deformation and breakage. The numerical models for triaxial shear test of granular mixture and anchored granular mixture are built；triaxial shear test is carried out based on displacement loading. The numerical simulation results show the anchorage mechanism，i. e. anchorage body intimately contacts the rock particles to produce the frictional resistance，and supporting structure forms the radial resistance the anchors and their adjacent rock granules form the anchorage zone. The numerical calculation results show that anchorage can significantly increase the shear strength and integrity of granular mixture. The peak principal stress difference can increase by 37.8%–88.8%，the initial modulus can increase by 37.4%–93.2%，and the internal friction angle can increase by 13.3%–24.2%.

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EXPERIMENTAL STUDY OF EFFECT OF TEMPERATURE ON PERMEABILITY CHARACTERISTICS OF LIGNITE

HU Yaoqing，ZHAO Yangsheng，YANG Dong，KANG Zhiqin

2010, 29 (08): 1585-1590 doi:

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By adopting the triaxial permeability test system MDS200，which was made by Institute of Mining Technology of Taiyuan University of Technology，some experimental researches are conducted on the permeability of lignite collected in Inner Mongolia Autonomons Region，China，under the condition of different volumetric stresses and different temperatures. The results indicate that，with the increase in coal burial depth，in other words，with the increase in volumetric stress，the permeability of lignite tends to decrease as a whole；under the condition of unchanged temperature and volumetric-stress，with the increase in pore pressure，the permeability of lignite has a tendency towards declining at first and then rising again. The critical point of the pore pressure is about 2 MPa. Under the condition of unchanged volumetric stress and pore pressure，with the increase in temperature(within 100 ℃)，the permeability of lignite decreases at first，then rises and decreases at last. During this process，the lowest temperature is 50 ℃，while the highest temperature is 80 ℃. When the temperature is below 50 ℃，with the increase in pore pressure，the permeability has a downtrend；when the temperature is above 50 ℃，the permeability has a uptrend.

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RESEARCH ON ROCKBURST PRONENESS AND ITS MICROCOSMIC MECHANISM OF GRANITE CONSIDERING TEMPERATURE EFFECT

ZHANG Zhizhen1，2，GAO Feng1，2，LIU Zhijun2

2010, 29 (08): 1591-1602 doi:

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Experiments on granite under uniaxial compression at high temperatures of 25 ℃–850 ℃ and after high temperature 25 ℃–1 200 ℃ were conducted；and the fracture surfaces were observed by scanning electron microscope (SEM) to study the effect of temperature on rockburst proneness. The results show that：(1) Two critical temperatures are found when the rockburst proneness index of samples changes with temperature from 25 ℃ to 850 ℃. The first is from 150 ℃ to 250 ℃；and the second is between 500 ℃ and 600 ℃. The rockburst proneness index increases substantially from the room temperature to the first critical temperature，and it decreases little between the first and the second critical temperatures；above the second critical temperature，it decreases largely. (2) While the samples are refrigerated after high temperature，the rockburst proneness index decreases generally with the temperature increases. The rockburst proneness is strong from 25 ℃ to 200 ℃；it is moderate between 200 ℃ and 800 ℃；above 800℃，it becomes weak. (3) Effective impact energy index and residual energy index are reasonable while the other three indices are unsuitable for incomprehensive information. (4) Four typical stress-strain curves were analyzed to get the relation with the rockburst proneness，and the corresponding relation among the heating mode，the temperature stage and these curves. (5) Based on the macroscopic and microcosmic characteristics of failure samples，it is indicated that the failure mechanism in turn is tension failure，tension-shear failure and shear failure as the rockburst proneness lowers，and it has the tendency that transforms from brittle fracture mechanism at low temperature to ductile fracture mechanism at high temperature.

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INFLUENCE OF HIGH PORE WATER PRESSURE ON CREEP PROPERTIES OF ROCK

SHE Chengxue，CUI Xuan

2010, 29 (08): 1603-1609 doi:

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Three types of loading modes are designed in which a high pore water pressure is applied；and creep tests are performed respectively to study the influence of pore water pressure on creep properties of rock. Firstly，with the normal marble samples，the triaxial tests in the three loading modes are performed to get the axial and lateral creep deformation curves as well as the failure patterns of the rock samples. Then the analyses and comparisons of the test results of axial，lateral，shear and volumetric strains as well as failure patterns are performed. Finally，based on the analysis and comparisons，the influence of high pore water pressure on the creep and failure of rock is analyzed. The research shows that the effects of the pore water pressure on creep of rock are obvious with the influential coefficient of pore water pressure less than 1，but approaching to 1. Under the action of high pore water pressure，the strength，strain and the time of creep to failure are lessened greatly. Though the samples are all in shearing failure，the failure under high pore water pressure is more sudden. There might be no definite equivalent strain under which the tertiary stage of creeps under different loading conditions begin to occur. And the pore water pressure has no effect on the volumetric strain before failure occurs. The results can be applied to guide the establishment of the nonlinear creep constitutive model of rock under high pore water pressure. And it is also useful for guiding the design and construction of rock structures under high pore water pressure.

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THREE-DIMENSIONAL NUMERICAL TEST OF ELEMENT SAFETY DEGREE OF ROCK CORE DISCING AND FEED-BACK ANALYSIS OF GEOSTRESSES

JIANG Annan1，2，ZENG Zhengwen2，TANG Chun¢an3

2010, 29 (08): 1610-1617 doi:

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Rock core discing is a kind of unique phenomena that occurs in environment with high geostresses. Both practical observation and theoretical analysis state that there is an inner relation between geostresses and the degree of rock core discing. Because it is difficult to measure geostresses in above environment，it has remarkable meanings in estimating geostresses by rock core discing. There is a complex mechanical process in rock discing，whose calculation formula and theory are very immature. The paper simulates how different geostresses affect the degree of rock core discing，stating that different geostresses induce different failure patterns of rock core，and the discing can be induced by the action of either shearing or tension. Then the paper proposes a calculation method of safety degree of elements located in potential failure surface of rock core combining elastic finite element method and Mohr-Coloumb criterion with tension limitation. The element safety degree distribution of potential surface can be displayed by element safety degree method，and can reflect the relation between geostresses and discing thickness. Based on the relation，the observation of rock core can be used to feed-back analyze original geostresses. By simulation based on element safety method，corresponding to different vertical stresses while the horizontal stresses being fixed，the safety of element degree distribution and the failure pattern of rock core are gotten. Using the method to analyze the geostress and rock core of Bakken formation in Williston Basin in USA，the results of calculation and observation are identical，which shows the method is feasible.

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EXPERIMENTAL STUDY OF MECHANICAL PROPERTY OF SANDSTONE UNDER PORE WATER PRESSURE AND CONFINING PRESSURE

XU Jiang，YANG Hongwei，PENG Shoujian，JIANG Yongdong，ZHANG Yuan

2010, 29 (08): 1618-1623 doi:

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Testing study is made on sandstone under two types of triaxial compression experiments with rock mechanic system MTS815. Based on the Mohr-Coulomb criterion，under the condition of non-pore water pressure and different confining pressures，the influence of confining pressure on the parameters such as peak failure strength ，axial strain ，shear strength t and normal stress s is analyzed；under the condition of pore pressure and constant confining pressure，the influence of pore water pressure P on the parameters such as peak failure strength and the corresponding axial strain ，effective peak intensity ，effective confining pressure ，effective shear strength and effective normal stress is analyzed. The following conclusions are drawn：(1) Under the condition of pore water pressure，with the increase of the effective confining pressure，the effective peak failure strength increases. Under the same confining pressure，however，with the increase of the pore water pressure，the effective peak failure strength reduces. (2) Under either the condition of non-pore water pressure or pore water pressure，both unary quadratic equation and linear equation are fit for the stress-strain relationship；and the corresponding intensity curve is in good agreement with the Mohr-Coulomb criterion. (3) The effective shear strength reduction factor can well demonstrate the influence of the pore water pressure on the effective shear strength.

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EXPERIMENTAL INVESTIGATION INTO DEFORMATION CHARACTERISTICS OF ANTHRACITE UNDER THERMO-MECHANICAL COUPLING CONDITIONS

FENG Zijun1，WAN Zhijun2，ZHAO Yangsheng1，LI Genwei2，ZHANG Yuan2，WANG Chong2

2010, 29 (08): 1624-1630 doi:

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By utilizing the self developed “600 ℃ 20 MN servo-controlled rock triaxial testing machine with high temperature and high pressure”，the investigation into deformation characteristics of anthracite specimen with 400 mm in length and 200 mm in diameter was carried out at constant stress corresponding to the in-situ stress at the depth of 500 m (axial pressure is 12.5 MPa and confining pressure is 15 MPa)，increasing temperature from room temperature(20 ℃) to 600 ℃ at a rate of 10 ℃/h. The study results indicate that the process of temperature-dependent deformation of anthracite can be divided into three stages，i.e. thermal dilatation stage with temperature rising from room temperature to 200 ℃，slow volume compression stage from 200 ℃ to 400 ℃ and serious volume compression stage from 400 ℃ to 600 ℃. The critical temperature range of anthracite deformation mechanism transition from brittle to ductile is from 400 ℃ to 450 ℃. Temperature and pressure are the main factors which influence the brittle-ductile transition of coal mass. The principle of transition condition is temperature-pressure equivalent，i.e. higher critical temperature needs lower transition pressure. The deformation of coal mass is significantly influenced by thermo-mechanical coupling and pyrolysis gas，while the main factor at a high temperature is pyrolysis gas.

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EXPERIMENTAL STUDY OF ELECTRICAL CONDUCTIVITY OF MAIN ROCKS IN STRATA OF HUAIBEI AND HUAINAN COALFIELD UNDER UNIAXIAL COMPRESSION

WANG Hua1，2，JI Hongguang1，CHENG Hua2，WANG Jin¢an1

2010, 29 (08): 1631-1638 doi:

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The test equipment of litho-electric experiment under loading was designed. Through experiments a convenient and effective coupling electrode material，the over-saturated clay，was found. The changing rule of the electrical conductivity of main rock specimens in the coal-bearing strata in Huaibei and Huainan Coalfield(HHC) in relation to changes of current，voltage and stress was also studied experimentally. And resistivity-stress regression equations of different rock masses were fitted with much high correlation coefficient. Research results show that：(1) within the range of elastic deformation，the electrical conductivity of the coal-bearing rocks in HHC increases with the enhancive stress，i.e. the rock resistivity decreases with increasing stress；(2) the electrical conductivity of the weak sandy mudstone is more susceptible to the variation of stress than the hard sandstone and diorite；(3) there exists a good correlation between the resistivity of the rock and stress；(4) under certain conditions of stress，the electrical conductivity of the weak sandy mudstone will be enhanced with the increase of the voltage and the current，thereby the resistivity is reduced，while the electrical conductivities of the hard sandstone and diorite are to some extent unaffected by voltage and current. In measuring and testing released zone of surrounding rock of roadway by high density resistivity method in mines in HHC，measured apparent resistivity section or resistivity inversion section is combined with the resistivity-stress regression equations obtained from litho-electric experiment to analyze the development of released zone of surrounding rock of roadway. The technology has been successfully applied to engineering practice.

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EXPERIMENTAL STUDY OF MECHANICAL CHARACTERISTICS OF COAL SPECIMEN IN PROCESS OF UNLOADING CONFINING PRESSURE IN GEOSTRESS FIELD AND ANALYSIS OF GAS SEEPAGE CHARACTERISTICS

HUANG Qixiang1，2，YIN Guangzhi1，2，JIANG Yongdong1，2

2010, 29 (08): 1639-1648 doi:

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Based on the briquette specimens of the outburst coal seam of typical coal and gas outburst mine of Datong in Songzao，the experimental study of unloading confining pressure of briquette specimen is performed by means of mechanical testing machine MTS815. The results are shown as follows：(1) unloading confining pressure with displacement control leads to the dilatancy and damage of briquette specimens，unloading confining pressure with load control leads to the failure of briquette specimens；(2) if the confining pressure is unloaded by means of displacement control，within a certain range of initial confining pressure，the axial stress of briquette specimens drops with decreasing confining pressure，and the velocity of axial stress drop rises，the nonlinearity of curve of unloading confining pressure is more significant when unloading confining pressure in yield phase than that in elastic phase；the nonlinearity is more and more obvious with the increase in initial confining pressure；(3) if the confining pressure is unloaded by means of load control，within a certain range of initial confining pressure，the axial strain of briquette specimens rises with decreasing confining pressure，the velocity of axial strain rise increases，the increase in axial strain is more significant when unloading confining pressure in yield phase than that in elastic phase. The increasing failure is more and more obvious in yield phase with the increase in initial confining pressure；the work of testing machine done in the process of unloading confining pressure can be calculated and analyzed according to axial strain. Based on the test results，combining with the test results of permeability of briquette specimens in the complete stress-strain process，the permeability curve of briquette specimens in the process of unloading confining pressure is deduced. Based on these results，using damage theory and Mohr-Coulomb theory，the formula for calculating the damage of briquette specimens containing gas in the process of unloading confining pressure is derived. The study results have a reference value for predicting gas emission and failure in the process of unloading confining pressure.

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CENTRIFUGE EXPERIMENTAL STUDY OF DEFORMATION CHARACTERISTICS OF OVERLYING SAND INDUCED BY FAULT RUPTURE

LUO Guanyong1，NG C W W2，CAI Qipeng2

2010, 29 (08): 1649-1656 doi:

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Ground deformation induced by fault rupture gives a potential threat to the safety of infrastructures，pipe line systems and tunnels. In this paper，two centrifugal tests with different bedrock faulting displacements were conducted to investigate the static permanent responses of a sandy soil overlaying an active normal fault with a dip angle of 90°. Emphasis was placed on the results of engineering concerns：(1) the range of the significant distortion zone；(2) the characteristics of the ground deformation；and (3) the fault rupture propagation pattern in soil. Through analysis of the displacement vector and the deviatoric strain obtained by geotechnical PIV technique，the following conclusions are drawn：(1) the range of significant distortion zone does not increase linearly as the increase in bedrock displacement，especially on the foot wall block；(2) the fault rupture brings more disturbance on the hanging wall side than on the foot wall block；and (3) the fault rupture propagates toward the hanging wall block in a bending line. The propagation angle of the principal fault rupture through soil equals the dilation angle of the soil under the mean confining pressure. When approaching the upper part of stratum，the rupture bends towards the hanging wall block with a larger angle.

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RESEARCH ON DYNAMIC FRACTURE TOUGHNESS AND TENSILE STRENGTH OF ROCK AT DIFFERENT DEPTHS

MAN Ke1，2，ZHOU Hongwei1

2010, 29 (08): 1657-1663 doi:

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According to the standard test method suggested by ISRM and Standard for Test Method of Engineering Rock Mass(GB/T50266–99)，the dynamic fracture toughness and uniaxial tensile strength of the basalt specimens at different depths are measured. It is observed that there may be a certain relation between dynamic fracture toughness and tensile strength. From the point of view of rock failure mechanism，the essential reason for existing relation between dynamic fracture toughness and tensile strength is analyzed. Rock failure is due to the microcrack unstable propagation. The growth，propagation and coalescence of microcracks in rocks induced by tensile stresses lead to the failure of rock. It provides an easy method to estimate the dynamic fracture toughness by the tensile strength value according to the certain relation between dynamic fracture toughness and tensile strength. It will greatly simplify the dynamic fracture toughness test.

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QUANTITATIVE STUDY OF STRUCTURAL PLANE DIRECT SHEAR TEST RESULTS INFLUENCED BY SAMPLE PREPARATION ERRORS

ZOU Zongxing，TANG Huiming，LIU Xiao，YONG Rui，NI Weida

2010, 29 (08): 1664-1669 doi:

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How to obtain reasonable shear strength parameters of structural planes is one of the important topics in rock mechanics. Direct shear test is widely used to determine the shear strength parameters of rock joints. Sample preparation errors have great effects on shear strength obtained from the test. Great deviation between test results and true values will be generated unless the test results are amended. However，this kind of preparation errors can not be avoided under the current situation. So，it is significant to study the test results influenced by sample preparation errors. Normal and shear stresses correction formulae are deduced in this paper. In addition，the influence of parameters a and b on test results is also interpreted. Quantitative analysis shows that test results are sensitive to climbing angle a，while b has little effect on the test results，which is so tiny that it could be ignored. Two methods are put forward to amend the results，and an instance is also cited.

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STUDY OF BROKEN ROCK MASS STRENGTH BASED ON V. RQD VALUE AND HOEK-BROWN CRITERION

LIU Shuxin1，2，LIU Changwu1，YUAN Shaoguo2，ZHOU Xiaoming1

2010, 29 (08): 1670-1676 doi:

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After being cut by some sets of structural surfaces，the large broken rock mass remains certain strength under different confining pressures. Due to the lack of quantitative description of rock structures，those parameters such as m and s values are difficult to be determined by Hoek-Brown strength criterion. Based on the defects of traditional RQD concept，by introducing the concept of 3D V.RQD under different threshold values，a kind of computer simulation method of V.RQD value was established. Then，combining RMR rating criteria and Hoek-Brown strength criterion，by discussing the influence of the threshold range of 3D V.RQD，some important laws which can lead to change of rock quality parameters such as m and s values and Hoek-Brown strength envelope as well as the rock deformation modulus E0 were achieved. As a result，an important quantitative relation between V.RQD value and broken rock mass strength was resolved. The conclusions show that the V.RQD value，one of the rock quality indices，may become a new and practical way to accurately estimate the strength of broken rock mass.

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STUDY OF HYSTERESIS AND DAMPING EFFECTS OF ROCK SUBJECTED TO CONSTANT AMPLITUDE CYCLIC LOADING

XIAO Jianqing1，2，FENG Xiating2，DING Dexin3，JIANG Fuliang3

2010, 29 (08): 1677-1683 doi:

[PDF] 322 KB (1305)

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The nonlinear elastic hysteresis behaviour of granite is studied based on experimental results under constant amplitude cyclic loading. It is found that the strain phase is lagging behind the stress phase in unloading while lagging，coincident or leading in loading. The results of further analysis show that the difference of damping effect during loading and unloading can result in the malformation of the strain-time curve. It becomes a nonstandard sine curve wide at the top and narrow at the bottom. And the accumulation of plastic deformation leads to the average strain level rising gradually and the strain phase being leading of stress phase. Then，according to the relation between strain phase and stress phase，the potentially existing shapes of hysteresis loop are explored. The hysteresis loop is oval-shape if the strain phase is always lag behind the stress phase，crescent-shape if the strain phase is leading of the stress phase during loading and long eggplant-shape if the strain phase is lagging，coincident and leading of the stress phase in one cycle. While the rock is treated as a visco-elastoplastic material，the calculating method of dynamic elastic modulus and damping ratio is discussed；and the improved formulae are proposed. Based on the experimental data，the evolution of dynamic elastic modulus and damping ratio is analyzed. It is shown that the development of dynamic elastic modulus is closely related with the stress level and the developing curve may be linear or inverted-S shape. The shape of evolution curve of damping ratio，which can be U shape or L shape，greatly depends on the dynamic elastic modulus as well as the area of the hysteresis loop.

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EXPERIMENTAL STUDY OF PROPAGATION OF DIRECTIONAL CRACKS WITH SHAPED CHARGE UNDER BLASTING LOAD

LI Qing，LIANG Yuan，REN Keke，ZENG Jia，ZHANG Xi

2010, 29 (08): 1684-1689 doi:

[PDF] 347 KB (1288)

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In order to make further analysis of crack propagation for blasting fracture，the paper gives a method to research dynamic mechanical characteristics by the transmitted dynamic caustics. The results indicate that the zone of fracture shows typical tensile fracture. The experiment finds that the trend of the dynamic stress intensity factors，the crack expanding lengths and velocities is almost the same with time. The lengths of blasting main cracks are achieved during 60–200 μs. The ultimate values of dynamic stress intensity factors are smaller than 1.5 MN/m3/2. The tough value of blasting cracks is about 0.3 MN/m3/2. “Gas wedge effect”of the high-pressure gas jet is the main driving force of radial compression cracks，playing a key role in the crack propagation of the cumulative energy orientation cracks under the directional blasting，while restraining the development of the non-cumulative energy directional radial compression crack. It is analyzed the fracture characteristics of the double-point jet with the double-seam thread jet in further，and found that the results of directional fractures and the fine fracture surfaces both can be achieved. Technical ideas are brought forward that both the double thread jet and the multi-seam thread jet cumulative cartridge should be utilized in the directional fracture blasting. The multi-seam thread jet cartridge can be applied to deep-hole presplitting explosion，such as deep-hole presplit blasting，to improve the speed of seam gas drainage and prevent mine gas and coal outburst in high gassy and low permeability coal seam.

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STUDY OF MECHANICAL CHARACTERISTICS OF SECONDARY LINING OF LARGE-SECTION LOESS TUNNEL

LI Pengfei1，ZHANG Dingli1，ZHAO Yong1，2，ZHOU Ye1，3，FANG Qian1，ZHANG Xuan1

2010, 29 (08): 1690-1696 doi:

[PDF] 318 KB (1487)

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Taking Humaling tunnel in Lanzhou—Chongqing railway as project background，contact pressure between the primary lining and secondary lining of large-section loess tunnel was acquired by means of in-situ monitoring；development law over time and spatial distribution along the tunnel ring of the contact pressure were discussed. Loads on the secondary lining were calculated according to code for design on tunnel of railway. Internal force of the secondary lining under calculation loads and monitoring loads was solved individually by load-structure model；and a comparative analysis was conducted. The study method and conclusions can provide references to analyze the mechanical characters of lining in soft ground and establish a scientific and reasonable design method of tunnel.

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MONITORING AND BACK ANALYSES OF SLOPE FAILURE PROCESS AT A LANDFILL

ZHAN Liangtong，GUAN Renqiu，CHEN Yunmin，LIU Zhao

2010, 29 (08): 1697-1705 doi:

[PDF] 499 KB (1549)

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The landfill studied in this paper is one of the earliest sanitary landfills with composite liner system installed in China. A slope failure took place in the landfill as a result of successive heavy rainfalls in June 2008. A field monitoring program was carried out to record the slope failure process. The monitoring items include surface horizontal displacement，deep lateral displacement，and leachate level within the slope. On the basis of the monitoring results，back analyses were carried out to access the slope stability，as well as to determine interface shear strength of the composite liner system. This paper also report the emergency measures taken for preventing further catastrophic failure of the huge landfill. The field monitoring and theoretical analyses came to the following conclusions. The high leachate level，which was found to be closely correlated with the measured displacement rate observed in the landfill is a major factor leading to the slope instability. The measurement of deep lateral displacement indicated that the slip took place along the weak interface of the composite liner system at the bottom of landfill. The significant lateral movement of waste body resulted in a displacement-softening effect on the interface strength of composite liner system，and hence the shear strength along the liner was in between the peak and residual strength. Drawdown of leachate level by pumping from vertical wells was found to be the most effective and workable emergency measure.

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EXPERIMENTAL STUDY OF LOESS STRUCTURAL PROPERTIES BASED ON SOIL DEFORMATION

TIAN Kanliang1，2，ZHANG Huili3

2010, 29 (08): 1706-1712 doi:

[PDF] 190 KB (885)

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The mechanical properties of soil are affected by its structure，which is the intrinsic determinant of its strength and deformation. Loess is a kind of typical structural soil. Its special structure is an important reason for the occurrence of brittle fracture and collapse. The structural properties of loess is determined by link structural strength and friction structural strength；and the variation of link structural strength and friction structural strength of loess should be quantitatively studied to quantitatively describe the structural properties of loess. Therefore，some new and reasonable structural parameters of loess are proposed based on soil deformation，such as the link structural deformation potential parameter ，the friction structural deformation potential parameter and the structural deformation potential parameter mp. The variation of the structural properties and the structural parameters of loess is studied through the confined compression tests of intact loess and man-made cement structural loess；and the effect of the moisture，pressure，density and cement content on the loess structural properties is revealed. Finally，the rationality of these structural parameters based on soil deformation is discussed.

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IN-SITU PROTOTYPE TEST STUDY OF COMPOSITE FOUNDATION OF RIGID PILE WITH CAP

LEI Jinbo1，2，CHEN Congxin2

2010, 29 (08): 1713-1720 doi:

[PDF] 316 KB (1079)

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In order to realize the working properties of the composite foundation of rigid pile with cap，the character laws were researched intensively by in-situ prototype test at the highway around Suzhou，such as Q-S，the settlement difference between load plank and pile，distribution of surface earth pressure，section settlement for composite foundation of rigid pile with cap. The results indicate that the composite foundation of long pile with cap is easier than the composite foundation of short pile with cap in controlling the settlement and enhancing the soil carrying capacity；the composite foundation of short pile with cap is easier than the composite foundation of long pile with cap in exerting the soil carrying capacity under the design load；the soil under pile caps is different from the soil beside pile caps in the load capability and its exerting extent；the vertical deformation is approximately same between the pile with cap and soil under pile cap；and the whole effect of the cushion can be ensured，because the pile cap can afford the rigid plank action and diffuse the stress on the top of pile. The test and analysis results are helpful to establish the calculation model of composite foundation of rigid pile with cap，consummate the theory of working properties of composite foundation of rigid pile with cap，and optimize the engineering design.

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STUDY OF DYNAMIC TORSIONAL IMPEDANCE OF RADIALLY INHOMOGENEOUS SATURATED SOIL CONSIDERING
PILE CONSTRUCTION EFFECT

ZHANG Zhiqing1，WANG Kuihua2，GENG Cuizhen1，LI Qiang3

2010, 29 (08): 1721-1728 doi:

[PDF] 307 KB (898)

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Based on Biot¢s dynamic consolidation theory，the torsional vibration of radially inhomogeneous saturated soil surrounding a pile is theoretically investigated. At first，the radially inhomogeneous soil is divided into inner annular disturbed and outer semi-infinite undisturbed regions，and the inner disturbed region is divided into many thin concentric annular zones. Then，the dynamic governing equation of saturated soil undergoing axisymmetric torsional deformations is derived in cylindrical coordinates. By utilizing the properties of modified Bessel function，the vibration displacement solution with undetermined constants of the soil layer is obtained and the solution holds for each thin concentric annular zone. Under the boundary and continuity conditions of the radially inhomogeneous soil layers，the torsional impedance of saturated soil is derived by means of transfer of shearing rigidity. Finally，the influence of changes of soil parameters caused by pile construction effect on torsional impedance of the soil is analyzed within the low frequency range；and several available solutions are compared with the present solution. The results show that：(1) The greater the hardening extent of the soil is，the higher the real stiffness and damping of the soil are；(2) The greater the softening extent of the soil is，the lower the real stiffness and damping of the soil are；(3) Within the two times of the radius of the pile，the larger the width of the inner region is，the higher the real stiffness of the hardening soil is and the lower the real stiffness of the softening soil is；(4) When the excitation frequency is relatively low，the material damping of inner region has negligible influence on the real stiffness of the soil.

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2010, 29 (08): 1729-1729 doi:

[PDF] 95 KB (688)

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2010, 29 (08): 1730-1731 doi:

[PDF] 122 KB (785)

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