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2016, 35 (S2): 0-0

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Mechanical response and failure characteristics of granite under different stress paths in triaxial loading and unloading conditions

LI Diyuan，SUN Zhi，LI Xibing，XIE Tao

2016, 35 (S2): 3449-3457 doi: 10.13722/j.cnki.jrme.2016.0815

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By carrying out triaxial loading and unloading tests for granite under different stress paths，the stress-strain curves of granite under different loading and unloading paths are obtained，and the failure characteristics，deformation characteristics and strength characteristics are analyzed. The results show that：(1) The relationship among lateral strain，volumetric strain and confining pressure is linear in the initial stage，and then is nonlinear obviously in the total stage of unloading confining pressure. The axial deformation of rock is not obvious，and the main deformation shows increasing of lateral strain. Volumetric dilatation and brittle failure of rock are observed apparently. (2) The deformation modulus decreases with the increasing of unloading ratio while the Poisson ratio rises up for unloading confining pressure tests. The degradation of deformation parameters cannot be observed obviously in the early unloading process，and then it changes in an exponential function. Loading axial pressure-unloading confining pressure tests have a more remarkable influence on deformation parameters than those of fixing axial pressure-unloading confining pressure tests. (3) Mogi-Coulomb criterion reflects the characteristics of the rock unloading failure strength more reasonable than Mohr-Coulomb criterion under high stress unloading tests. Compared with conventional triaxial test，the value of cohesion c decreases about 24.21% and internal friction angle increases about 16.71% in fixing axial pressure-unloading confining pressure tests，while the value of cohesion c increases about 10.25% and internal friction angle decreases about 6.44% in loading axial pressure-unloading confining pressure tests. It means that the internal friction angles is the key factor to control the failure of granite under fixing axial pressure-unloading confining pressure tests，and the cohesion is the key factor to control the failure of granite under loading axial pressure-unloading confining pressure tests.

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Acoustic emission(AE) characteristics of fine sandstone and coarse sandstone fracture process under tension-compression-shear stress

XIAO Fukun1，2，LIU Gang1，2，QIN Tao2，ZHAO Rongxin2

2016, 35 (S2): 3458-3472 doi: 10.13722/j.cnki.jrme.2016.0775

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The use of TAW–2000KN press，TYJ–500KN press and SH–II acoustic emission(AE) system，coarse sandstone and fine sandstone under uniaxial compression，Brazil splitting and variable angle shear experiment on crack propagation mechanics characteristics and AE in the process of research. The experiment results show that the tensile strength and shear strength of sandstone and coarse sandstone can be compared with that of the approximate equivalent shear strength ratio and the ratio of shear strength to shear strength is larger than that of the single axial compressive strength. The AE characteristics of the fine sandstone and the coarse sandstone are obviously different. The variation law of AE count curve of fine sandstone under the action of shear stress：①– I–②–II–③(the mark express region by“-”)，shear stress gritrock regularity of AE count curve：①–I–II– III–②. The characteristics of AE energy characteristics are as follows，fine sandstone：present the bending“厂”type，coarse sandstone：present the bending“S”type. The curves of stress-strain curves are completely consistent. Fine sand and coarse sand rock tensile failure process of AE characteristic differences，The variation law of the AE count curve of fine sandstone under the action of tensile stress：①–I–②–II–③–III，the action of tensile stress gritrock regularity of AE count curve：①–I–②–II–③–III；AE energy features for fine sandstone：local instability damage exists，the complexity of the path curve growth，coarse sandstone：a linear trend growth. From the point of view of failure analysis，the difference between the two types of rock is that the sound emission count and the slow growth of energy before the destruction of fine sandstone，the occurrence of a certain period of stability after the destruction. Coarse sandstone loading period，high count signal and low count signal alternately，failure and failure early stage of high count signal and low count signal mixed sparse. Fine sandstone and coarse sandstone uniaxial compression process of AE characteristics of different AE count features，fine sand：①–I–②–II–③，coarse sand：①–I–II–②–③；AE energy features for fine sandstone：present the bending“S”type，coarse sand：present the bending“Z”type. The RA value of AE and the average frequency can reflect the type of crack，tensile failure and shear failure are in line with the objective reality. The uniaxial compression damage form given crack types of positive feedback，it is shown the application of AE technology to determine the crack type effective and feasible.

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Limit state surface in strength parameter space and system reliability analysis

ZHU Yong，FENG Xiating，ZHOU Hui，ZHANG Chuanqing

2016, 35 (S2): 3472-3480 doi: 10.13722/j.cnki.jrme.2015.0142

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A fixed slip surface is needed when FOSM、PEM and FORM are used to calculate the reliability index of slopes. This process may lead to underestimate of the system risk of slopes. To solve this problem，a system limit state surface in strength parameter space is defined to illustrate the new system reliability analysis approach. This new approach is to approximate the system limit state surface based on the global minimum safety factor searching process. Then the safety factors of the simulation strength parameters can be calculated by Excel. The system reliability index can be obtained by statistical analysis of the simulated safety factors. A case study is taken to illustrate the approach. The results show that the new approach can evaluate the system risk adequately and efficiently.

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Mechanical properties deteriorating change rule research of red-layer soft rock under water-rock interaction

DENG Huafeng，ZHOU Meiling，LI Jianlin，FANG Jingcheng，XIAO Yao，ZHANG Hengbin，WANG Chenxiejie

2016, 35 (S2): 3481-3491 doi: 10.13722/j.cnki.jrme.2016.0810

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Red-layer soft rock is widely distributed in the Three Gorges Reservoir area. The deterioration of physical and mechanical characteristics of red-layer soft rock，caused by water-rock interaction，will directly affect the long-term deformation stability and safety for the slopes of reservoirs concerned. Therefore，considering the fact that the water level of hydro-fluctuation belt is rising up and down repeatedly，the immersion-air dry test for red-layer soft rock is designed and conducted. The results show that：(1) Under water-rock interaction，it is obvious that the strength and deformation parameters of the red-layer soft rock are deteriorating，and the rock samples tend to be soft gradually. At the meanwhile，the first 3 tests have a faster deterioration rate for the parameters，but the rate tends to be slowdown after 5 immersion-air dry circulations；(2) As the number of circulation times increased，the failure modes of the rock samples would also be changed obviously，its shear failure features with different confining pressure would be behaved obviously，and the number of controlled cracks would be decreased gradually while the secondary cracks would be increased；(3) Under water-rock interaction，the repeated change of water pressure and the immersion-air dry circulation would impose irreversible cumulative damage to red-layer soft rock，which would convert to loose and porous structure with micro cracks and developing pores from relatively compact structure. In macroscopic view，it would behave as the deterioration of compressive strength and shear strength，and the change of failure modes. Related research results can provide references for the study of the long-term deformation stability and safety for the slopes of reservoirs.

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Analysis on spreading mechanism of fractured rock grouting process based on Bingham fluid

GAO Shengyuan1，2

2016, 35 (S2): 3492-3500 doi: 10.13722/j.cnki.jrme.2016.0792

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Based on the standard joint surface profile of Barton model，geometry model of fracture was constructed，and the finite element model was established by using Navier-stokes equation and considering grout as Bingham fluid. Grout spreading process was simulated and the influence on grout spreading process from fracture roughness，fracture gap width and grout viscosity was acquired. Results show that，when grout viscosity is high，the energy loss is mainly caused by viscosity force. The equivalent gap width increases nonlinearly with grout viscosity. When fracture roughness is constant，the equivalent gap width increment curve has an inflection point. With fracture roughness increasing，the inflection point move forward gradually. A fitting formula was proposed between equivalent gap width and fracture roughness through multiple function fitting with a quite accuracy. Research result may provide some reference to fracture rock grouting theory.

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Action-effect study of medium under loading of explosion stress wave and explosion gas

YANG Renshu1，2，DING Chenxi1，WANG Yanbing1，CHEN Cheng1

2016, 35 (S2): 3501-3506 doi: 10.13722/j.cnki.jrme.2016.0066

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Using laboratory model test method with the material of PMMA，combining numerical simulation of LS-DYNA，action-effect on medium under loading of explosion stress wave and explosion gas was studied. The result showed that effect of explosion stress wave mainly led to formation of microcracks in the smash area，effect of explosion gas was the major impetus of crack formation in the crack area.Mechanics characteristic of medium in the elastic vibration area was compressive firstly and tensile secondly. The function of explosion gas dramatically increased peak values of stress(strain) and loading time of medium in the elastic vibration area，it proved that explosion gas had dynamic effect in addition to quasi-static effect. It indicated that the theory of rock blasting need further improvement and amendment，algorithm of numerical simulation which took the actual process of explosion stress wave and explosion gas into account need to be developed urgently.

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Simulations of crack propagation in rock-like materials using peridynamic method

ZHU Qizhi1，2，NI Tao1，2，ZHAO Lunyang1，2，YUAN Shuangshuang1，2

2016, 35 (S2): 3507-3515 doi: 10.13722/j.cnki.jrme.2016.0900

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By introducing the mathematical description of cracks into the continuum medium，numerical simulations are performed via the peridynamic method on crack propagation inside the specimen of rock-like materials. The case of one pre-existing fissure with different dip angles and that of three pre-existing fissures with different rock bridge angles are taken into account under the condition of uniaxial compression. It is seen that with the increasing of dip angle，the nucleation position of wing cracks is gradually moved to the ends of the pre-existing fissures. The emergence time and shape of the secondary coplanar shear cracks and the secondary inclined cracks change accordingly；there exists an obvious difference in the form of fracture coalescence for rock bridge with different dip angles，but all the cracks initiate at the ends of pre-existing fissure，then gradually propagate and coalesce，leading to a final failure of the specimen. Comparisons between the simulation results and the laboratory tests on sandstone specimens show that the peridynamic method，as a new nonlocal numerical technique，is quite suitable for simulating the problem of crack propagation，and presents a broad interest in investigating rock materials and rock structures.

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Analysis on fragmentation behavior of rocks in indentation tests by disc cutter

LIU Quansheng1，PAN Yucong1，LIU Jianping1，KONG Xiaoxuan2，SHI Kai3，LIU Qi2

2016, 35 (S2): 3516-3525 doi: 10.13722/j.cnki.jrme.2015.0532

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The rock loading system and acoustic emission monitoring system were employed to conduct the indentation tests on four rocks with different strengths，namely mudstone，granite，sandstone and cement mortar specimens with cubic dimensions，with or without lateral confinement. The complete load-penetration curves and acoustic emission parameters were analysed together，and the process，form and mode of the rock fragmentation by TBM constant cross section(CCS) disc cutter were studied. The load drop of the load-penetration curve for soft rock is not obvious and the rock fragmentation presents the failure characteristic of elastoplasticity，while the load drop is remarkable in accordance with the brittle rupture for hard rock indentation test. The rock fragmentation without lateral confinement can be regarded as obvious splitting fracture mode and the failure process of the confined specimen is controlled by the combined effect of both splitting fractures and lateral fractures. The curves of acoustic emission parameters are in good agreement with the load-penetration curves and can generally reflect the damage，degradation and fracture formation of the indented rock specimens. The indentation tests conducted on the rock-like material can reproduce the fragmentation process and failure mode of the natural rock at some extent，but due to the discordances of the strength and deformation properties between rock-like material and natural rock，the results obtained from similar material simulations should be further investigated.

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Discontinuous deformation analysis method based on the explicit time integration scheme

XU Dongdong，WU Aiqing

2016, 35 (S2): 3526-3534 doi: 10.13722/j.cnki.jrme.2016.0838

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Discontinuous deformation analysis method(DDA) is very suitable for modeling the mechanical behaviors of highly discrete rock block system. However，it need to integrate the global stiffness matrix and solve the matrix equation for the traditional DDA that adopts the implicit time integration scheme. This will result in the decrease of calculation efficiency，especially in solving the large-scale discontinuous problems. Therefore，an explicit version of two-dimensional DDA is proposed based on the explicit time integration scheme. There is no need to integrate the global stiffness matrix and solve the large-scale simultaneous algebraic equations in the solving process. Block elimination method is used to calculate the acceleration as the result of adoption of consistent mass matrix，which is simple and time-saving. The open-close iteration is still adopted to ensure the right arrangement of constraints. At last，the correctness and robustness of explicit DDA is confirmed by several classic numerical examples.

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Hydraulic fracture propagation analytical analysis meeting skew bedding

SUN Keming，ZHANG Shucui

2016, 35 (S2): 3535-3539 doi: 10.13722/j.cnki.jrme.2016.0096

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In order to study the laws of fracture propagation meeting skew bedding. The concentration stress solutions of arbitrary crack tip were obtained by complex functions，conformal transformation and coordinates transformation. Compared the stress state and strength at original fracturing direction with bedding，the hydraulic fracture propagation when fracture vertical minimum in-situ stress meet skew bedding were obtained based on the maximum tensile stress criterion.The indexes，namely the critical intensity ratio，show the difficulty of fracture turning to bedding，which decreases indicate that fracturing turned to bedding demanding the ratio of bedding and rock matrix strength have to be smaller. The critical intensity ratio was influenced by in-situ stress state，strength of the rock matrix and bedding and bedding orientation. It heightens when the difference of maximum or middle principal stress with minimum principal stress reduced and when the angle between bedding with fracture surface decreased. It lessens when rock matrix tensile strength and the angle between intersecting line of bedding and fracture surface with middle principle stress declined. The rules of analytical solution and experimental results compared have no difference.

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Experimental study on stress-seepage coupling properties of sandstone under different drainage conditions

WANG Wei1，2，CHEN Xi1，2，TIAN Zhenyuan1，2，ZHU Qizhi1，2，XU Weiya1，2，RUAN Huaining1，2

2016, 35 (S2): 3540-3551 doi: 10.13722/j.cnki.jrme.2016.0828

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Stress-seepage coupling is one of fundamental problems in rock mechanics. In order to investigate the hydro mechanical coupling properties of sandstone，a series of triaxial compression tests under drained and undrained conditions are carried out. Based on the experimental results，the following conclusions are obtained. The elastic modulus，peak strength，crack initiation stress and expansion stress increase with the increased confining pressure. Under drained condition，pore water pressure can weaken the effect of confining pressure，which leads to the decrease in mechanical properties of rocks. It appears that cohesion is more sensitive to pore pressure than internal friction angle. Under undrained condition，the peak stress of pore pressure appears around expansion stress，which indicates the initiation of microcracks in rocks. In the condition of the same initial pore pressure，peak stress of pore pressure increased with the confining pressure and under the same confining pressure，the change of pore water pressure is more obvious when the initial pore pressure is lager. The peak strength，crack closure stress，crack initiation stress and expansion stress under undrained condition are lower than those under the condition of drainage.

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Numerical study on stress wave propagation across filled joints

LIU Tingting1，2，3，LI Xinpin1，2，LI Haibo3，LI Jianchun3，LUO Yi1，2

2016, 35 (S2): 3552-3560 doi: 10.13722/j.cnki.jrme.2016.0829

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The discrete element simulations were conducted to investigate the wave transmission across a set of parallel filled joints. In addition，the equivalent medium model was used to analyze the wave transmission across multiple filled joints with small space. Firstly，the feasibility of UDEC was verified through the comparative analysis of results of numerical simulation and two theoretical methods. Subsequently，the numerical simulation was extended to investigate the wave transmission across a set of parallel filled joints. Moreover，the parametric analysis for the effects of filled thickness，joint space and number on transmission coefficients was carried out. The results revealed that the transmission coefficient decreases with increasing the filled thickness，which is not affected by joint space and number. However，the influence of joint number on transmission coefficient is related to joint space. Note that the influence of joint space on transmission coefficient can be divided into three different ranges by two critical values. Transmission coefficient tends to be stable when the joint space is large enough. And the stable value in exponential function with joint number. Finally，the equivalent medium model was used to analyze the wave transmission across multiple filled joints with small space. Then，the effect of relevant parameters such as incident wave frequency，filled material properties，filled thickness and joint number on wave transmission was carried out. The results show that the equivalent medium model can be used to describe wave transmission across multiple filled joints with small space.

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Model experiment study on the failure characteristics of weak surrounding rock mass above tunnel arch and the anchoring effect of bolts

CHENG Panpan1，XU Qianwei1，ZHU Hehua2，DING Wenqi2，CHEN Guozhong3，WU Yongbo3

2016, 35 (S2): 3561-3569 doi: 10.13722/j.cnki.jrme.2016.0902

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In order to study the failure characteristics of weak rock mass and the anchoring effect of rock bolts，a series of geomechanical model experiments were carried out to simulate tunnel excavation in rock mass of grade Ⅳ，which includes two modes，unsupported and supported with bolts. Subsequently，the evaluation laws of displacement，stress and the macroscopic failure forms of the surrounding rock mass were analyzed through a comprehensive comparison. According to the experiment results，the following conclusions can be drawn. (1)The damage of surrounding rock induced by tunnel excavation starts from tunnel arch foot，extending upwards gradually and collapsing into arch eventually. (2) Due to the anchor suspension and extrusion effect of bolts combined with the rock beam effect，the rock collapse zone can be reduced significantly. (3) The bolts can improve the strength and toughness of rock mass owning to the applied anchor force，which is conducive to enhance the bearing capacity and the deformation resistance ability of surrounding rock. (4) The bolts can make the surrounding rock obtain a stable equilibrium with high energy，which not only makes the stress distribution in rock mass more balanced，but also delays the rock entering into the “softening” stage. The conclusions gained can provide references for the stability evaluation of soft rock mass during tunnel construction as well as the design and construction of the supporting structures.

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Pseudo-dynamic analysis of anchored characteristics of layered rock slopes subjected to seismic loads

ZHOU Wei，LI Haibo，LIU Yaqun，CHAI Shaobo，LIU Jingsen

2016, 35 (S2): 3570-3576 doi: 10.13722/j.cnki.jrme.2015.1742

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Anchoring technology has played an important role in slope reinforcements in engineering practice. However，the failure mechanism of anchored slopes subjected to seismic loads is not fully understood at present. Therefore，the study of dynamic behavior of anchored slopes is of great significance for the optimal design of slope reinforcements. In this paper，the pseudo-dynamic method is used to simulate the input of acceleration-time history. Based on the upper bound theorem of limit analysis，the mathematical expressions of the required reinforcement force when the layered rock slope under seismic loads is in critical status and the factor of safety of it are then deduced. Finally，the parametric studies on the influence of the dip angle of bolt，the dip angle of joint surface，seismic acceleration coefficients，seismic amplification factor，joint cohesion，joint friction angle on the required reinforcement force when the slope is in critical status are discussed. The results indicate that the stability of layered rock slope is influenced to some extents by all the parameters mentioned above. In addition，with the increase of joint friction angle，the horizontal seismic acceleration coefficient and seismic amplification factor have greater effects on the required reinforcement force，while the dip angle of bolt，the dip angle of joint surface，the vertical seismic acceleration coefficient and joint cohesion have less influence on it.

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THE METHOD TO IDENTIFY CHARACTERISTIC STRESSES OF ROCK in different stages during failure process

GAO Meiben1，2，LI Tianbin1，2，MENG Lubo1，2，CHEN Guoqing1，2，CHEN Chao1，2，

2016, 35 (S2): 3577-3588 doi: 10.13722/j.cnki.jrme.2015.1645

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Accurate identifying each stage characteristic stresses of rock has significant importance on determining rock deformation and failure stage，mechanics，design parameters. In view of this，the “testing data+ strain stiffness” combing method has been proposed to identify those stresses. According to the trixial compression testing data of sandstone(30 MPa)，the operation process has been detailed，and the method has been verified. Then the following conclusions can be drawn：(1) The linear elastic feature is obvious in stress-strain curve，but the demarcation point of the linear elastic stage and the stable crack growth stage is not easy to be detected；(2) The tiny changes in stress-strain curve can be amplified by strain stiffness，which is better used to identify the rock deformation stages，and the strain stiffness curve can be divided into five stages：irregular fluctuation，regular fluctuation and nearly horizontal，irregular fluctuation and gradually decreasing to zero，extremely fluctuation，nearly zero.(3) The serious irregular fluctuations in strain stiffness are related to the events of the crack closure，initiation，expansion，coalescence，rock failure and block sliding；(4) The ratio of crack closure stress，crack initiation stress and damage stress to peak stress are 0.10，0.56 and 0.68 respectively. (5) Based on first derivative，objective and reasonable operation process，the method is an accurate in theory and semi-accurate in operation method. Finally，with the modern computer and data processing technology，the processing can be easily operated；providing a new approach to identify rock characteristic stress.

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Experimental study on overlying strata deformation based on distributed optical fiber sensing

CHAI Jing1，2，YUAN Qiang1，LI Yi1，2，ZHANG Dingding1，2，LIU Qi1

2016, 35 (S2): 3589-3596 doi: 10.13722/j.cnki.jrme.2016.0892

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In order to solve the difficulties of internal deformation measurement and movement characteristics describing in the overlying strata model test，a detecting method based on BOTDA distributed optical fiber sensing was put forward to study the optical fiber sensing representation of rock layers fracture and collapse. A similar material model with the size of 3 000 mm(L)×200 mm(W)×1 280 mm(H) was produced to simulate the caving process of overlying rock strata，three horizontal optical fibers and three vertical optical fibers were pre-embedded while the model production. Afterwards，the model test of strata movement by distributed optical fiber sensing was carried out and the results comparison were conducted by comparing the measurement results between the BOTDA and the optical fiber Bragg grating sensors，dial indicators and total station. The results show that the strata collapse has aroused a clear strain variation，its distribution reveals the caving status of overlying strata under different extracting stages，which represents the development of strata fractured lines，the change of caving angles，the evolution of rock internal stress and the process of strata caving from bottom to top of the model. It indicates that the BOTDA distributed optical fiber detection method has a good adaptability in this experiment，which can sense and reflect the rock deformation characteristics，and a standardization optical fiber installation procedure will help to further improve the testing reliability and quantification.

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Numerical simulation of air-water two-phase flow in inflatable slope

YU Wenfei1，SUN Hongyue1，SHANG Yuequan2，MEI Cheng1

2016, 35 (S2): 3597-3604 doi: 10.13722/j.cnki.jrme.2015.1643

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Based on the multi-phase porous flow theory and unsaturated soil theory，a new method was proposed to improve the stability of the slope. In this method，through filling the trailing edge of potential landslide area with compressed air，an unsaturated belt was formed. By cutting off water in seepage path，the underground water level was artificially lowered. To enhance the theoretical research，a two dimensional finite element model was employed to investigate the characteristics of air-water two-phase flow and study the law of groundwater level variation in unsaturated zone during the process of aeration. The results illustrate that it is feasible to intercept water with compressed air in a slope. An analysis on the expansion process in unsaturated zone indicates that the process of intercepting water can be divided into three stages：(1) The unsaturated zone near aeration point is formed and start to expand；(2) As the unsaturated zone extends over underground water level，an unstable two-phase flow is formed；(3) The unsaturated zone expansion is terminated and water intercepting method works smoothly. In the unsaturated zone，it is found that the pore-air pressure，pore-air velocity，pore-water velocity and volumetric water content fluctuate locally and these variations are related intimately. As the pore-air pressure increases with the time，the pore-air velocity increases while the pore-water velocity and volumetric water content decrease，and vice versa. This phenomenon can be ascribed to the interaction and lag between air and water.

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Sealing and healing of compacted bentonite block joints in HLW disposal

ZHANG Huyuan1，2，WANG Xuewen2，LIU Ping1，2，YAN Ming2，PENG Yu2

2016, 35 (S2): 3605-3614 doi: 10.13722/j.cnki.jrme.2015.1691

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Within the multi-barrier system for high-level waste(HLW) disposal，compacted bentonite blocks joints play as potential “hydraulic defects” with low strength. Block joint with a width of 2 mm were prepared and back-filled with different materials such as bentonite powder，bentonite sludge in plastic limit，and the mixtures of bentonite pellet-powder with a pellet ratio of 30%，50%，70% and 90%，respectively. This paper tends to evaluate the sealing and healing effects of the joints with different treatments by hydraulic and thermal conductivity tests in laboratory. The bentonite pellet-powder mixture with pellet size in 0.25–0.5 mm and 70% pellet content exhibits highest filling density and therefore possess high swelling potential. Tests data show that the hydraulic conductivity of specimens varies between K = (2.51–4.94)×10－10 cm/s，increasing with the decrease of initial bulk density of bentonite sealing material for joints treated by Rg = 70% pellet-powder，Rg = 90% pellet-powder，Rg = 50% pellet-powder，bentonite sludge in plastic limit，Rg = 30% pellet-powder and bentonite powder. The average thermal conductivities along joints vary between = 1.43－1.63 W/(m·k)，among which the highest is the joint treated by Rg = 70% pellet-powder. On the contrary，thermal conductivity along the direction perpendicular to the joint displays a little lower at the joint than the other parts. This study confirms that Rg = 70% bentonite pellet-powder mixture is the best sealing material among the three materials tested. With bentonite hydration and swelling，joints tend to be healed as a result of increase in dry density of sealing materials，and exhibit comparatively uniform hydraulic and thermal conductivity properties as compacted block.

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Stress and deformation laws and influence factors analysis of tunnel across the slope deformation zone

YIN Jing1，2，DENG Ronggui1，ZHONG Zhibin1，LI Kaitian1，SUN Chunping2

2016, 35 (S2): 3615-3625 doi: 10.13722/j.cnki.jrme.2015.0628

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The stress of the tunnel across landslide deformation zone is very unfavorable. In order to study the stress and deformation laws of the tunnel under sliding force，firstly，the model of elastic rock-the tunnel structure is built on the basis of the interaction between tunnel and soil landslide. The matrix transfer method is adopted to establish the calculation formulas of internal force and displacement of the tunnel. Secondly，the distribution characteristics of the tunnel internal force and displacement and the influence of some important parameters are analyzed by MATLAB programming. Finally，the physical model test is carried out to verify the theoretical results. The studies indicate that，when the across segment of tunnel is long，the internal force is almost zero in a certain range of middle tunnel，and the degree of tunnel bending deformation is small，mainly presented global displacement，which is mainly controlled by the vertical foundation coefficient，the value and distribution of sliding force. The stable rock mass outside the landslide has an anchor effect on the tunnel. The force and deformation state of tunnel is the worst near the boundary of the tunnel and sliding surface，where the tunnel is most prone to failure. The results of physical model test are in good agreement with the theoretical calculation results，which verify the correctness of the theoretical calculation method and results.

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Study on single crack propagation and damage evolution mechanism of rock-like materials under uniaxial compression

ZHAO Cheng1，2，LIU Fengming1，2，TIAN Jiashen3，MATSUDA Hiroshi4，MORITA Chihiro4

2016, 35 (S2): 3626-3632 doi: 10.13722/j.cnki.jrme.2015.1270

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Through laboratory test by employing the digital image correlation method(DICM)，the laws of crack propagation and mechanism of plastic deformation of rock-like material with single crack pre-existing with various inclined angles when subjected to static loading are studied. The results show that when the inclined angle = 15° and = 30°，the position of the maximum strain is near the inner crack tip point，the new crack propagation begins at the initial crack wing，and the tension stress is the main reason of the new crack generation and propagation. With the increasing of ，when = 60° and = 75°，the strain concentration is detected at the crack tip. The main propagation mode of new cracks is secondary cracks，and the shear stress play a dominant role. There are both wing cracks and secondary cracks when = 45°. The crack initiation stress increases as increasing. The sample shows there are the minimum compression strength and the fastest crack propagation speed when = 30°. The uniaxial compressive strength of the sample with secondary cracks is significantly higher than that sample with wing cracks.

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Single edge notched deep beam specimen to test I/II mixed-mode fracture toughness of rocks： numerical analysis and calibration

LUO Yi1，2，REN Li1，2，XIE Lingzhi1，2，LI Cunbao1，2，WANG Jun1，2，GAO Chao2

2016, 35 (S2): 3633-3643 doi: 10.13722/j.cnki.jrme.2015.1450

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A new specimen，namely the single edge notched deep beam(SENDB) specimen，which could test the mixed-mode fracture toughness of rock materials was proposed. The finite element method(FEM) was used to analyze and calibrate the mode I and mode II dimensionless stress intensity factors(i.e. YI and YII) and the dimensionless T-stress(i.e. T*) of the new specimen. Numerical results demonstrated that the SENDB specimen indeed could test the mixed-mode fracture toughness of rocks in a full range of mode mixities from pure mode I to pure mode II by different combinations of the crack inclined angle ，the crack length a and the half distance S between the two bottom supports. The dimensions of the new specimen significantly differed with the ones of the classic single edged notched beam(SENB) specimen，and the mixed-mode loadings can be introduced by an inclined crack in a SENDB specimen while for a SENB specimen mixed-mode loadings are introduced with asymmetry three points bend test(which can not introduce pure mode II loading) or four points bend test(which requires a complex loading fixture). In the aspect of the investigation on scale effect，the SENDB specimen is more suitable than the disc-type specimens，especially for very large size. Compared to the edge crack triangular(ECT) specimen recently proposed by other researchers，the SENDB specimen can conduct mixed-mode fracture tests within a large range of dimensionless crack length and dimensionless span distance. To successfully conduct a pure mode II fracture test，a relative small span distance and a relative long crack are recommended for SENDB，SCB and ECT specimens.

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Experimental study on conductivity of rough shale fractures using methane

PENG Huihua1，ZHOU Lei1，2，LU Yiyu1，2

2016, 35 (S2): 3644-3652 doi: 10.13722/j.cnki.jrme.2015.1488

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Hydrofracturing method is the main technique of shale gas exploitation. Researching the methane through rough shale fractures is of great practical significance in this field. In this work，experiment of CH4 through rough shale fractures was investigated under different gas pressure gradients and confining pressures from 1 to 10 MPa. The main results are shown as follows. The fracture conductivity of shale is lower than that of other rocks. The values of flow rate do not strictly follow a linear trend with pressure changes，and the growth rate decreases with the increase of confining stress， indicating that gas through rough shale fractures is non-linear flow. The effective stress increases with the increase of confining stress. While the hydraulic aperture，flow rate and permeability follow the opposite trend. When the confining pressure exceeds 4.0 MPa，the fracture closure reaches the maximum，and the flow rate keeps stable. Forchheimer equation provides a good description for the non-linear fracture flow process. When confining pressure increases，the pore structure and fluid property changed，and the seepage prefers to the linear flow. According to the engineering practice，critical Reynolds number was determined when 10% of nonlinear effect was considered.

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Recent studies on time-dependent behavior of rock strength and the effects of confining pressure

FU Jianxin1，2，3，SONG Weidong1，2，HASHIBA Kimihiro3

2016, 35 (S2): 3653-3661 doi: 10.13722/j.cnki.jrme.2015.1534

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To estimate long-term stability of deep underground structures，it is important to investigate the time-dependent behavior of rock. Loading rate dependency，creep and relaxation have been well examined under uniaxial stress state conditions，however，less in known of the effects of confining pressure. In this paper，recent experimental and theoretical studies on the time-dependency of rock were reviewed primarily focusing on the effects of confining pressure. Firstly，time-dependent behavior under confining pressure was compared to the uniaxial stress state，and the effects of confining pressure were discussed. Loading rate dependency，creep and the relation between them were examined with the aid of recent theoretical studies. The close relations among time-dependency，probability distribution of rock properties and scale effect were explained theoretically. Finally， equipment and practical testing methods used to investigate the time-dependent behavior under confining pressure were reviewed.

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Experimental study on mechanism for fracture network initiation under complex stress conditions

LIU Xuewei1，LIU Quansheng1，2，LIU Jianping1，WEI Lai1

2016, 35 (S2): 3662-3670 doi: 10.13722/j.cnki.jrme.2015.1544

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As one of the most common object in rock engineering，the fractures in the rock mass may appear initiation and propagation under the engineering disturbances. Fracture initiation and propagation will change the deformation and strength characteristics of rock mass obviously. Therefore，a series of uniaxial and biaxial compression tests are carried out for the fractured specimens through RMT–150C and lateral pressure-adding equipment. Combined with the characters analysis of fracture propagation path，failure modes，acoustic emission (AE) energy and the positions of AE events under different loading conditions，the mechanism of fracture propagation is researched. With the increase of lateral pressure，the ductility of stress-strain curves increases. The newly formed cracks propagate from the initial fracture tips under the whole conditions，while the propagation path changed hugely under the biaxial compression condition. The positions of AE events during the loading process match well with the macroscopical fracture propagation path. The ratios of AE events before fracture initiation and the whole loading process for the typical specimens are all above 80%，which proves that the fracture initiation and propagation is the result of microcracks development and damage accumulation in the specimen. The results are significant for simulating unstable process of engineering rock mass more effectively.

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Application of grey evaluation model based on classification degree and weight of classification of index to rock mass quality evaluation of underground engineering

ZHOU Shuda1，PEI Qitao2，DING Xiuli2

2016, 35 (S2): 3671-3679 doi: 10.13722/j.cnki.jrme.2015.1545

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Classification degree is usually used to measure the contribution of the evaluation indexes in distinguishing the sample classification. Based on the theory of classification degree and grey clustering method，the formula for determining the classification degree and weight of classification of index of the white nization weight function is modified. Compared with the traditional formula，the modified formula is suitable under any conditions，which is more reasonable in theory. On the basis，the evaluation indexes including rock quality designation，uniaxial compressive strengthen，rock mass integrality coefficient，strengthen coefficient of structural plane and seepage measurement of groundwater are chosen to establish the grey evaluation model for rock mass quality evaluation by modifying classification degree and weight of classification of index(GEM-MCD-WCI model). Based on the measured data of the first stage project in Guangzhou pump accumulator electricity station，the GEM-MCD-WCI model is adopted to predict the evaluation of rock mass quality. Compared with the traditional model，the prediction error of the GEM-MCD-WCI model is smaller. Furthermore，the GEM- MCD-WCI model is applied to predict the evaluation of the second stage project. The results show that the evaluation results of the model in the paper agree well with those of the catastrophe progression method and support vector machine method. Therefore，the proposed method provides a practical way to accurately evaluate the quality of rock mass in underground engineering.

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Effect of debris flow converging into river on the basis of physical simulation experiments

ZHU Dapeng1，2，QIN Liangkai3，HE Qiduo3

2016, 35 (S2): 3680-3688 doi: 10.13722/j.cnki.jrme.2015.1556

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As for prevention and cutting off the disaster chain induced by debris flow converging into river，taking the debris flow happened on August，14th at Hongchun Ditch，Wencuan County as the prototype，the physical simulation model is established，and 5 groups of 17 physical simulation tests are used to study the main factors that influence the debris flow flowing into river. The results are that，the intersection angle of 90°is the easiest condition to block the river. The more rapid the flow speed of the main river is，the stronger the ability of its scouring and carrying particles is and the smaller the volume of accumulation at intersection zone is. When the moisture content is close to 0.85，the accumulation volume reaches the maximum. Accumulation volume has a linear relationship with the total amount of disposable solid source，and the total amount contributes to a bigger growth rate on accumulation volume than other factors，such as intersection angle and flow velocity. Its easy to form the submerged dam below water if the source volume of debris flow is small. When the source volume of debris flow increases gradually，one part of debris flow forms into submerged dam，the other part remains its movement above water，and then the fine particles is taken away by the river while the coarse one remains at the intersection zone which leads to blocking the river partially or totally. Gravity of mixture in test and flow velocity by back calculation is in accord with the Hongchun Ditch debris flow basically，and it verifies the accuracy of the physical simulation experiment.

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Experimental study of deformation and seepage characteristics of raw coal under unloading axial stress

BIAN Guang1，2，3，ZHANG Dongming1，2，3，LI Minghui1，2，3，DENG Bozhi1，2，3，

2016, 35 (S2): 3689-3695 doi: 10.13722/j.cnki.jrme.2015.1562

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Based on domestic-developed triaxial servo-controlled seepage equipment for thero-fluid-solid coupling of coal containing methane，the deformation and permeation experiment on row coal was performed under different initial unload levels. The results show that，in the process of unloading axial stress，the relationship between axial stress and strain of coal contained gas is expressed by quadratic functions，and the resilience deformation of coal containing methane decreases with the increase of initial load level. The ascent rate of the penetration rate of raw coal increases with the decrease of axial pressure. In the process of unloading axial stress，the penetration rate of raw coal becomes mild with the increase of initial load level. And there is a better similarity of the change of gas permeability in linear elastic stage. Gas antireflective effect weakens with the increase of initial load level. The relationship between increment of relative permeability at unloading unit stress and the initial stress can be described by logarithmic function. In the process of unloading axial stress，the growth trend of anti-reflection rate gradually weakens with the increase of initial load level.

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Study on effects of unloading rate on macro-meso failure mechanism of brittle rock

CONG Yu1，2，FENG Xiating1，ZHENG Yingren3，WANG Zaiquan2，QIU Shili1

2016, 35 (S2): 3696-3705 doi: 10.13722/j.cnki.jrme.2015.1159

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Loading axial compression and unloading confining pressure tests and simulations of particle flow under different unloading rates have been performed，and effects of unloading rate on unloading failure process of brittle rock have been analyzed by multi-perspective macro-meso methods. The results show that，specimens show shear failure in the macroscopic，but show connective failure plane caused by tensile cracks propagation in the microscopic. The phenomenon of bond energy and strain energy simultaneously show the characteristic of negative growth，which could be known as failure precursor of brittle rock. There are several connective failure planes containing discontinuous joints，obvious secondary shear planes and larger distribution area of tensile cracks under high unloading rates. The growing rate of tensile cracks between peak point and inflection point of axial stress grows as unloading rate increases；there are higher shear cracks under low unloading rate. Growing rate of acoustic emission count rate before failure，count rate value around failure and count rate range after failure depend on unloading rate. An increase of unloading rate could cause bond energy，strain energy and friction energy to increase，but kinetic energy to decrease.

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Study on energy release process of high energy storage rock mass induced by excavation unloading

FAN Yong1，LU Wenbo2，ZHOU Yihong1，YAN Peng2，CHEN Ming2

2016, 35 (S2): 3706-3715 doi: 10.13722/j.cnki.jrme.2015.1287

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For the case of excavation of deep rock mass，based on the determination of energy storage limit，the energy release process of high energy storage rock mass induced by transient unloading of in-situ stress was studied by using local energy release rate and energy release coefficient indexes，and the relationship between energy release and damage of surrounding rock mass was analysed. The results show that，influenced by the excavation unloading，the strain energy of surrounding rock mass firstly decreases，then increases，soon reduces and stabilizes at last. Similar with the elastic case，the first decrease process of strain energy is mainly caused by elastic unloading wave and does not induce damage in surrounding rock mass. While the second decrease process is mainly caused by that the strain energy accumulated in the surrounding rock mass exceeds the energy storage limit，and is bound to induce damage in surrounding rock mass. Further study shows that with the increase of the distance from the excavation face，the energy release rate of surrounding rock increases first and then decreases. The closer distance from excavation boundary means the larger energy release coefficient，the shorter duration time of energy release，and the more drastic energy release. In addition，the bigger energy release rate and coefficient means the larger wave velocity drop and the more serious damage in surrounding rock mass. Therefore，damage degree of surrounding rock mass can be assessed and predicted by calculating the energy release coefficient.

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Through mechanism and experimental study of rock-plug blasting with single and double free faces

HU Yingguo，WU Xinxia，ZHAO Gen，LIU Meishan，ZHOU Xianping，LI Weichao

2016, 35 (S2): 3716-3724 doi: 10.13722/j.cnki.jrme.2015.1388

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Investigating the rock plug blasting technology is of great significance in engineering reconstruction or accident emergency rescue. At first，the through mechanism is analyzed by describing the stress field of the rock plug blasting with single and double free surfaces. Based on the secondary development of LS-DYNA，numerical simulation of the rock plug blasting with single and double free surfaces was implemented. Result reveals that the through depth of rock plug blasting with single free surface is little than that with double free surfaces，and the former is close to the half of latter. Experiment of rock plug blasting with single and double free surfaces was carried out three times. Results demonstrate that when the depth of rock plug blasting with single are 6.5 m and 8 m，the through depth are about 4.5 m and 6 m，But when the depth of the rock plug blasting with double free surfaces is 11 m，the rock plug could be through completely. Results of experiment and numerical simulation support each other，which reveals that the because of the suppress system and the tensile stress wave from the free surface，the through depth of rock plug blasting with single free surface is close to the half of that of the rock plug blasting with double free surfaces. Results expect to provide the reference of the similar engineering.

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Research on slate creep experiment and a modified H|M model in NaCl solution corrosion

JIANG Zongbin1，JIANG Annan1，LI Hong2

2016, 35 (S2): 3725-3733 doi: 10.13722/j.cnki.jrme.2015.1478

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Due to the status that lack of researches on seawater corrosion slate creep，with Dalian Metro as study object，the NaCl solution corrosion-creep experiment and model research are carried out. Firstly，the experiment of slate immersion in NaCl solution is performed. By contrast of SEM images and EDS elements from mesoscopic perspective，and combination of longitudinal wave velocity and pH value analysis，the test specimens corrosion characteristics with different immersion periods are revealed. Then，by RLW–2000 rock mechanics triaxial rheological system，creep experiment is carried out，and the test specimens creep curve and characteristics in immediate deformation，initial phase，stable phase and acceleration phase are analyzed from macroscopic perspective. The long-term strength，creep rate，and elasticity modulus change rule with different immersion periods are summarized. Finally，based on experiment results，introducing a five-component nonlinear viscoelasto- plastic rheological model(H|M-CD model) with consideration of chemical corrosion，and the model parameter recognition is realized by 1stOpt optimization software. The research results indicate that NaCl solutions corrosiveness has changed slates creep mechanics properties，with the increase of immersion time，the acceleration phases speed increases，and creep time shortens. The longer the immersion time is，the obvious the damage feature becomes. The model theory curve accords with experiment curve in three phases，and indicates that the model H|M-CD proposed above is capable to describe the whole creep process of corrosion slate. The research results provide reference and basis for long-term stability evaluation on slate rock engineering in seawater environment.

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Experimental research on shear creep properties of a swelling rock under different expansive states

FAN Qiuyan1，ZHANG Bo2，3，LI Xian4

2016, 35 (S2): 3734-3746 doi: 10.13722/j.cnki.jrme.2015.1494

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In order to study the effect of different expansive states on the shear creep characteristics of the swelling rock，the creep test without expansion，the expansion and creep completely coupled test，the expansion and creep incompletely coupled creep test，and the expansion and creep separately coupled test were carried out. The creep curves of all tests have similar regularities. The long-term strength under expansion is much smaller than that under no expansion，and the long-term strength under completely coupled expansion and creep is smaller than that under separately coupled and creep. In completely coupled expansion and creep situation，a function made by curve fitting is used to express the relationship between long-term strength and normal stress. In separately coupled expansion and creep situation，a function is used to express the relationship of the normal pre-stress and the long-term strength.

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Effect of unloading damage on deformation characteristics of jointed rock mass

WANG Ruihong1，2，JIANG Yuzhou1，LI Jianlin2，LIU Jie2

2016, 35 (S2): 3747-3755 doi: 10.13722/j.cnki.jrme.2015.1552

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The mechanical properties of jointed rock mass are significantly different under loading and unloading conditions. However，the current research on the damage characteristics of jointed rock mass under unloading conditions is relatively less，especially the influence of different unloading degree on mechanical properties of jointed rock mass is not considered. In order to understand the influence of unloading degree，joint dip angle and confining pressure on the deformation characteristics of rock mass，the repeated loading tests are performed in laboratory. The results show that with the increment of unloading value，the peak strength decreases. It has little effect on the rock mass ultimate strength when unloading degree is low. With the increase of unloading value，the reduction of the rock ultimate strength increases. The characteristics of brittle stress drop is obvious under the low confining pressure condition，whereas with the increase of confining pressure，the rock mass deformation from failure to residual strength increases and the influence of unloading degree on rock mass mechanical properties decreases gradually. The joint dip angle and unloading degree have great effect on the Poisson's ratio. The Poisson's ratio of jointed rock specimen is bigger than that of intact rock specimen，and it reaches a maximum value when the joint dip angle is 45°. The Poisson's ratio increases with the unloading degree，and the unloading degree is higher，the increase rate of Poisson's ratio is faster. The confining pressure，joint dip angle and the unloading damage degree are associated with the elastic modulus of jointed rock mass. With the increase of confining pressure，the value of elastic modulus increases but the increase rate decreases. The reduction degree of elastic modulus increases with the increase of unloading degree. Moreover，the impact of unloading degree on elastic modulus is different for rock specimens with different joint dip angles，in which the rock specimens with 45° and 60° joint dip angles are most deeply influenced.

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Experimental research of effect of water intrusion times on crack propagation in coal

CHEN Tian1，YAO Qiangling1，DU Mao2，ZHU Chenguang3，ZHANG Bo1

2016, 35 (S2): 3756-3762 doi: 10.13722/j.cnki.jrme.2015.1720

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Underground water has repeated intrusion on waterproof coal pillars and on underground reservoir boundaries. Therefore，researching the damaging effect of water intrusion times on crack propagation in coal gives meaningful advice to cope with problems，such as setting the width of water proof coal pillars and storing underground water in arid region of the West China. In this paper，coal samples were wetted by self-made humidifier and then were grouped into dry coal samples，coal samples under once water intrusion，twice water intrusion，third water intrusion and forth water intrusion. By acoustic emission testing，this research found the peak stress and elastic modulus decreased with the growth of water intrusion times but peak strain increased because of the rising water intrusion times. The stiffness-stress curve and accumulative AE counts combined with overall strain-stress curve could evaluate all phases of crack propagation. With the growing times of water intrusion，the stress thresholds of crack closure，crack initiation and crack damage declined linearly. Nevertheless，the percentage of three stress thresholds over peak stress did not vary with the change of water-intrusion times，with 15.52%，31.04% and 67.81% respectively. The experimental results can partly help set the width of waterproof coal pillars and of underground reservoir boundaries.

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Tests on hydro-mechanical coupling characteristics of fractured limestone in complete stress-strain process

ZHAO Yanlin1，2，FU Chengcheng1，WANG Yixian3，TANG Jinzhou1，ZHOU Zhihua1，WAN Wen1

2016, 35 (S2): 3763-3773 doi: 10.13722/j.cnki.jrme.2016.0866

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To clarify mechanical and permeability characteristics of fractured limestone in complete stress-strain process，the hydro-mechanical coupling tests on fractured limestone at various seepage pressures and confining pressures were performed，and the strength and deformation characteristics of fractured limestone under the hydro-mechanical coupling were studied. The six key permeability values in complete stress-strain process were defined. The results showed that the mechanical characteristics of fractured limestone are sensitive to seepage pressure，which reduces rock strength and deformation modulus，activating the lateral deformation of fractured limestone. The strength characteristics of fractured limestone can be characterized by the Mohr-Coulomb yield criterion under the hydro-mechanical coupling；The permeability values display four stages of decrease-gradual increase-rapid increase-small drop in complete stress-strain process，which roughly correspond to volumetric compression stage，elastic deformation stage，failure stage near peak strength point and residual strength，respectively. At low seepage pressure(about 2 MPa)，the correspondence above is perfect. However，at high seepage pressure(above 8 MPa)，there is a deviation from the correspondence above，i.e. permeability reduction stage is shorter than the stage of volumetric compression. A negative exponential equation can describe the relationship between permeability and volumetric strain in volumetric compression stage at low seepage pressure (about 2 MPa). At high seepage pressure(above 8 MPa)，a cubic polynomial can be used to describe the relationship between permeability and volumetric strain in volumetric compression stage.

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Model test research of similar materials for underwater tunnel lining in fluid-solid two-phase field

GUO Xuan1，HE Ping1，ZHU Kun1，ZHANG Xiaoxin2，WANG Mengshu1，ZHU Ying1

2016, 35 (S2): 3774-3784 doi: 10.13722/j.cnki.jrme.2016.0149

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The orthogonal model tests were carried out to solve the problem of material simulation and parameter determination for tunnel lining design in the fluid-solid two phase field. The similar materials were developed by quartz sand，steel fibers and industrial paraffin，which the quartz sand and steel fibers is the aggregates and the industrial paraffin is the bonding agent. The orthogonal model test optimized the ratio of materials，the loading temperature and the load effect's measurement. The experimental results show that the structure model of the similar material has good non-hydrophilicity，rapid prototyping，no need of maintenance，low cost，convenient preparation，less pollution and stable performance. The similar material is very suitable for the tunnel lining model test in the fluid solid two-phase field. The control module temperature is 62 ℃ under the similarity ratio of 1∶100. The standard ratio will be paraffin∶quartz sand∶steel fiber = 15∶90∶1. The lining similar materials are developed to satisfy both the boundary condition of the tunnel lining surrounding rock in the fluid-solid coupled two phases field and the failure mode is similar. The similar lining is applied in the model test， and the reasonable range of internal force change and failure law is obtained by comparing with the actual working conditions，which can satisfy the similarity principle of the mechanical parameters. The parameter measurement method of the similar test can provide the choice for the parameter comparison in engineering design.

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Study on collapse mechanism of expansive bedding layered slope

CHEN Zhimin1，2

2016, 35 (S2): 3785-3793 doi: 10.13722/j.cnki.jrme.2016.0946

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The collapse mechanism of the sandstone and mudstone bedding slope under the condition of drying-watering cycles and concentrated precipitation in Gulang，Gansu，was studied，which has great significance to the treatment of this kind of collapse. The collapse mechanism can be summarized as follows. The formation and connection of joints in the hard sandstone layer is caused by the repeated expansion and contraction of soft mudstone under drying-watering cycles. Under the influence of concentrated precipitation，the suspended sandstone is formed by the mudstone collapse. The overturning or sliding sandstone collapse appears when the limit equilibrium is broken. Considering the mudstones swelling and softening mechanisms，the mechanical models of crack，overturning and sliding stabilities for expansive sandstone and mustone bedding slope were established based on the confined swelling tests and direct shear tests in laboratory. The formula of anti cracking coefficient，overturning stability coefficient and sliding stability coefficient were deduced. These formula have been applied and verified in the practical project. The results show that，when the water content is less than its threshold，the shear strength of mudstone increases with the increasing of water content，and the swelling force caused by the water absorption expansion play a major role in the shear strength. When the water content exceeds the threshold，the shear strength decreases with the increasing of water content，and the decreases of ， of the mudstone caused by the water absorption play a major role. The anti cracking coefficient of the suspended sandstone is proportional to the square of the thickness of the sandstone，inversely proportional to the swelling force of the lower mudstone and the square of the weathering depth of the lower mudstone. The sliding stability coefficient of the suspended sandstone is inversely proportional to its thickness. The sliding stability coefficient is proportional to，it is negatively correlated with the dip of the sandstone and it is positive correlated with and.

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Reliability-based design approach of rock slopes using Monte Carlo simulation

PENG Xing1，2，LI Dianqing1，2，CAO Zijun1，2，TANG Xiaosong1，2，ZHOU Chuangbing1，2，3

2016, 35 (S2): 3794-3805 doi: 10.13722/j.cnki.jrme.2014.1210

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This paper develops a reliability-based design(RBD) approach for rock slopes based on Monte Carlo simulation(MCS)，and proposed a practical design framework that is comprised of four design modules. Under the proposed design framework，the design process of MCS-based RBD of rock slopes is transparent and accessible to geotechnical practitioners so that they can make assumptions deemed appropriate for a specific site and have flexibility to adjust the target failure probability and uncertainty model. The proposed approach and design framework are illustrated using the Sau Mau Ping rock slope in Hong Kong. Results show that：(1) The failure probabilities of possible designs obtained from a single run of MCS in the proposed approach agree well with those obtained using repeated runs of MCS for different designs，which validates the proposed approach. (2) The target failure probability and uncertainty modeling may affect the final designs significantly. Such effects can be taken into account in RBD of rock slopes through the proposed approach in a rational manner. (3) In design practice，overestimation of the variability of uncertain parameters or ignoring the negative correlation between them might lead to overestimation of standard deviation of safety factor and，hence，underestimation of reliability index，which subsequently results in conservative designs. On the other hand，ignoring the positive correlation between uncertain parameters might lead to overestimation of reliability index and unsafe designs.

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A preliminary study of the post-peak characteristics of shear stress-displacement curves of joints

WANG Shuilin，GUO Mingwei，WANG Wanjun，ZHENG Hong

2016, 35 (S2): 3805-3812 doi: 10.13722/j.cnki.jrme.2014.1336

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During shear test of joints，strength-weakening in post-peak part is observed in many types of shear stress-displacement curves. Aiming at the mechanical characteristics of rock fractures，a set of shear stress- displacement curves was analyzed，and the peak and residual strength parameters were obtained. The shear stress-displacement curve in the post-peak part was approximated in a stepwise way，and the strength-weakening process was simplified as a series of stress drop and plastic flow during the increase of shear displacement. The complete shear stress-displacement curves were modeled and compared with those obtained by lab tests. Furthermore，the internal relationship between strength-weakening and the shear stress-displacement curve in the post-peak part was studied，and the influence of dilatancy angle on the normal displacement was analyzed. The study helps to deepen the understanding of the mechanical characteristics of rock fractures.

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Experimental and numerical study of hydraulic properties of 3D crossed fractures

LIU Richeng1，2，LI Bo3，JIANG Yujing1，4，YU Liyuan2

2016, 35 (S2): 3813-3821 doi: 10.13722/j.cnki.jrme.2015.0456

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Fracture intersection plays a basic role in fluid flow and solute transport through fracture networks because they allow different fluids to mix and disperse along the flow paths. An artificial three dimensional crossed fracture model is manufactured and a high-precision experimental system of fluid flow test was established. Numerical simulations by solving the Navier-Stokes equations were performed to investigate the fluid flow behavior through crossed fractures with different widths. The results show that the flow rate is quadratically related with the tested pressure drop，following the famous Forchheimers law. The Reynolds numbers(Re) of the tested results agree well with those of numerical simulations and theoretical solutions，indicating that both the experiments and simulations are reliable. This work suggests that the suitable width of fractures in a fracture model should be 8 times larger than the maximum hydraulic aperture of all fractures. The critical Re for the onset of nonlinear flow through crossed fractures is in the range of 12.33–61.67.

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Statistical analysis of acoustic emission energy distribution during uniaxial compression of shale

JIANG Deyi，XIE Kainan，JIANG Xiang，CHEN Jie，YUAN Xi

2016, 35 (S2): 3822-3828 doi: 10.13722/j.cnki.jrme.2015.0699

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The energy release of brittle rocks failure under loading is critical process. In order to have a more clear understanding about the brittle rocks failure process and the rule of energy release，shale under uniaxial compression test has been carried in laboratory，and the loading rates were 0.01，0.1，0.5 mm/min respectively. During the whole loading process, acoustic emission(AE) parameters have been collected，and the probability density function(PDF) of absolute AE energy was calculated. PDFs critical exponents were estimated by the maximum likelihood estimation method. The results showed：(1) The PDF of absolute AE energy under different loading rate in seven orders of magnitude ranges conformed to the power law distribution. (2) The critical exponent r calculated by the maximum likelihood estimates method had an optimal range of stability，which characterized the power law distribution accurately. (3) The critical exponents of one span and the whole process were similar with each other，which allowed one use the AE information in the preliminary stage to study the energy release during final collapse.

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Scattering of SH-wave by an ellipse cavity in right-angle plane with beeline crack

DING Xiaohao，QI Hui，ZHAO Yuanbo

2016, 35 (S2): 3829-3836 doi: 10.13722/j.cnki.jrme.2015.0915

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The scattering problem of SH-wave by a shallowly buried ellipse cavity in right-angle space with a beeline crack was analyzed by using Greens function and complex function method with conformal mapping method. The conformal mapping method and image method were employed here to construct the scattering wave field function，which satisfies the condition of stress free on the straight boundaries. An essential solution to displacement field of an elastic right-angle plane containing an ellipse cavity that any point bore an anti-plane harmonic line source load was taken as Greens function. Beeline crack was constructed with crack-division technique，and expression of displacement and stress field were given while both crack and ellipse cavity exist. The dynamic stress concentration factor(DSCF) on the edge of ellipse cavity was given as an example and the results are analyzed and discussed. Results show that the crack length，angle，distance between the ellipse cavity and beeline crack have an effect on the distribution of DSCF of the ellipse cavity.

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Study of the failure of pillar-roof system in gypsum mines based on catastrophe theory

XIA Kaizong1，2，CHEN Congxin1，2，LIU Xiumin1，2，ZHOU Yichao1，2，JIANG Xuanwei1，2

2016, 35 (S2): 3837-3845 doi: 10.13722/j.cnki.jrme.2015.1064

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According to the failure characteristics of pillar-roof system in gypsum mines，and combined with the theory of the nonlinear mechanics，a simplified mechanical model of pillar-roof system was established. Then a cusp catastrophe model of pillar-roof system was build. The failure mechanism of pillar-roof system was analyzed，and the influence of geometric parameters on the stability of the system is analyzed. It is shown that：the stability of pillar-roof system is mainly affected by two factors，namely internal and external factors，and the internal factors indicate that modulus of elasticity of roof，pillar thickness，the width between pillars，pillar area，pillar height and pillar strength. The external factor refers to dead weight of roof and overlying strata. The displacement jump is only related to the internal factor. When regulating the stability of pillar-roof system，the order of these geometrical parameters are：pillar thickness，pillar area，the width between pillars and pillar height. The engineering application shows that the present internal geometric parameters of the mined-out area in Jingmen gypsum mine has reached the sufficient and necessary condition of instability，which consist with field investigation.

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Analysis on bending moment property of hard roof influenced by elastic，hardening and softening zone of coal seam

PAN Yue1，GU Shitan2，3，LI Wenshuai2，3

2016, 35 (S2): 3846-3857 doi: 10.13722/j.cnki.jrme.2015.1090

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It was usually considered that the yield soften state of coal seam was derived from coal wall to abutment pressure peak in coal seam and coal seam was in elastic state in front of the abutment pressure peak. The hardening state between the soft and elastic state was neglected. Given this above，the coal seam was divided into the softened zone near the coal wall，the hardened zone in front of peak abutment pressure and the elastic zone ahead again. Then expressions of abutment pressure in hardened and softened zone of coal seam were proposed and determination methods of abutment pressure in each section of coal seam were continuous. On the basis of reference [13]，expressions of deflection of hard roof supported by elastic zone，hardened zone and softened zone of coal seam were derived before periodic weighting. According to the expressions，cases of abutment pressure of coal seam to roof and corresponding bending moment distribution curve of hard roof were given by Matlab when the elastic，hardening and softening zone parameters were changed. From the above，the changeable parameters of any section of the coal seam could cause the change of abutment pressure in other sections. Pre-distance of bending moment peak of the roof was 6.04 m which had crossed the softening zone and was in coal seam hardening section under the assumption that the coal seam residual strength was 0. Compared the cases with abutment pressure and corresponding roof bending moment under the assumption that only supported by elastic and softening zones，the roof deflection，peak bending moment and pre-distance of bending moment peak of the former were significantly greater than the corresponding value of the latter. After the analysis of abutment pressure of coal seam and the corresponding roof bending moment data of the former，an important understanding was obtained that anti bending moment formed by abutment pressure of softening zone in coal seam was small，the corresponding peak value of bending moment and pre-distance of bending moment peak of the roof were large. The explanation was that roof and coal seam was a community which supported overlying load together. When the anti- bending moment caused by the abutment force of softening zone of coal seam was small，bending degree and bending scope of the roof would increase to resist its overlying load，which led that the roof peak value of bending moment and pre-distance of bending moment peak increase.

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Experimental study of the characteristics of strength and AE of Diorite porphyrite under complex loading and unloading path

FU Jianxin1，2，SONG Weidong1，2，TAN Yuye1，2

2016, 35 (S2): 3858-3867 doi: 10.13722/j.cnki.jrme.2015.1171

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Loading and unloading rock mechanics tests were tested using brittle rock from a typical deep mine. Mechanics and fracture characteristics of brittle rock under complex stress path were analysed. The AE ring count evolution characteristic in rupture process was studies using acoustic emission equipment. Studies have shown that，mechanical properties and deformation characteristics of rock have a close relationship with the confining pressure and its failure mode gradually transited from brittle fracture to ductile failure. Unloading operation amounted to apply a reverse rally on specimen surface that usually caused the rapid growth of radial displacement which named expansion phenomenon. Damage degree of unloading was more severe than loading and a large number of vertical cracks appear on rock surface so that rock damage form was composite tensile and compressive damage and acoustic emission count rate when the rock damaging of unloading was far greater than loading. The rock internal AE ring count evolution process was divided into three phases in the unloading process including calm before the peak period，active period and gentle period after peak. There were critical value of stress，strain and AE ring count in every period that got by a large number of laboratory tests and field monitoring.

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Study of slope stability based on blasting cumulative damage

FEI Honglu，YUAN Junhua

2016, 35 (S2): 3868-3878 doi: 10.13722/j.cnki.jrme.2015.1192

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The disturbance and damage of adjacent slope caused by blasting excavation，especially the accumulative damage caused by multiple blasting，will inevitably lead to the weakening of rock mechanics parameters，which is an important factor causing the failure of the slope. According to the damage model，the cumulative damage effect of rock slope under blasting load was studied by using the method of sonic wave test，which was used to reduce the shear strength parameters of the slope mass. Based on the strength reduction method and time history analysis method，the change law of slope safety factor under blasting load was studied by using finite element software ANSYS. The results show that the safety factor of the slope is reduced by 5.1%–12.6% under each blasting load，and the safety factor of the slope is decreased by 35.2% because of the cumulative damage，the effect of blasting damage on the safety factor of the slope is greater than that of the blasting load. With the reduction of slope strength parameters，the maximum displacement of the slope bottom node is also increasing under the loading of seismic wave，which is mainly because of the plastic displacement caused by the strength reduction of the slope. The influence of blasting vibration on weak slope is more obvious.

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Meso failure mechanism of rock mass and slope with intermittent joints

ZHOU Yu1，HAN Guang1，2，WU Shunchuan1，HU Nailian1

2016, 35 (S2): 3878-3890 doi: 10.13722/j.cnki.jrme.2015.1207

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The slope of Muliashi north open-pit copper mine in Zambia was selected as engineering background. Based upon particle flow theory and PFC2D(Particle Flow Code 2D) program，the rock block and joint were represented by bonded particle model and smooth joint model，respectively. The rock mass model containing two intermittent joints and rock slope model with bedding intermittent joints were constructed，and their failure mechanism were investigated from meso mechanical viewpoint. The failure research of rock mass with intermittent joints shows that the failure mode of rock bridge can be divided into four types such as mode I，mode II，mode III–a and mode III–b，which are essentially lead to by the dominated tensile microcracks between mineral grain bond. The failure research of rock slope with bedding intermittent joints shows that the microcracks caused by landslide primarily generate at the intermittent joint endpoint of bottom slope，and gradually develop towards top slope. The bottom shape of slide mass is relatively straight，while its tail shape is flexural and presents step-path failure. The fragmentized particle assemblies with relatively small volume primarily generate at middle and bottom part of slope，and then they generate at top slope with relatively large volume. During landslide，the particle contact force along rock bridge is relatively high，and the relationship between magnitude and count of microseismic events approximately obeys normal distribution function.

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Study of seismic response of different clear-distance vertical intersecting combination subway station structures

LI Jidong1，2，TAO Lianjin2，YOU Xinhua1，ZHANG Jinxi2

2016, 35 (S2): 3890-3897 doi: 10.13722/j.cnki.jrme.2015.1216

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Shaking table tests of subway station with different clear-distances were performed to study on the seismic response of these subway stations. The design of tests were presented，some results of seismic response about the subway station，which with different clear-distances，were provided and compared with the seismic response of single subway station. Experimental data indicate that：(1) With clear-distance increases，seismic response of upper structural model increases，and the lower structural model decreases，the relative horizontal displacement between upper and lower structural model. (2) With clear-distance increases，the strain amplitude at the top of sidewall and center pillar increases，the strain amplitude at the bottom of sidewall and center pillar decreases，and the strain amplitude of lower structure model all decreases. (3) With clear-distance changes，the range of strain amplitude at the bottom of upper structure model is greater than the upper，and the range of strain amplitude at the top of lower structure model is greater than the lower.

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Experimental study of shear displacement effect seepage characteristics of random surface cracks

LEI Jinsheng，LI Shen，WU Zenglin，YAO Qi，ZENG Youwei

2016, 35 (S2): 3898-3905 doi: 10.13722/j.cnki.jrme.2015.1343

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In order to analyze the seepage characteristics and motion laws of fracture surface in random single crack under the influence of axial compressive stress，shear stress and osmotic pressure，shear seepage stress coupling tests were carried out by using shear flow coupling test system. According to the relationship curves of shear load and tangential displacement，the relationship curves of the normal displacement and the tangential displacement acquired by the experiment，the influence of the shear load and the normal displacement on the shear load and normal displacement was summarized. The relationship curves of hydraulic opening and tangential displacement was acquired by using the cubic law and seepage quantity. According to the characteristics of the curves，the four parameters Logistic function was used to fit the curve，and a good result was achieved. Depending on that，the relationship between shearing expansive angle and stress in the process of shear flow coupling was proposed. What is more，a new method to locate the dangerous point in the shear dilatation stage which can be presented through the parameter of the function.

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Calculation method for multi-fracture propagation geometry of multi-stage fracturing in horizontal wells

CHEN Ming1，XU Yun2，3，WENG Dingwei2，3

2016, 35 (S2): 3906-3915 doi: 10.13722/j.cnki.jrme.2015.1365

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For the issue of multi-fracture geometry by multi-stage fracturing in horizontal wells，a multi-fracture propagation-path algorithm was proposed，by incorporating a 3D-fracture stress field calculation model based on displacement discontinuity method，different fracture boundary conditions and subcritical fracture growth law. The algorithm was validated by UFM. Multi-fracture propagation paths for multi-stage fracturing in horizontal wells were investigated by the algorithm，and the results show that later fractures curve toward or away from previous pressurized fractures，while later fractures keep straight paths affected by sand-filled fractures. The exterior fractures propagate dominantly，but the inner fractures were suppressed due to stress shadow effect. Later fractures deviate toward the previous pressurized fracture when the ratio of fracture spacing to fracture height is less than one，and the smaller the ratio，the larger the deviation angle，otherwise they deviate away from the previous pressurized fracture or propagate straightly. The smaller the ratio of fracture spacing to fracture height，or the larger the ratio of net pressure to principle stress difference，the larger the deviation angle for two simultaneous- propagation fractures. Increasing the ratio of fracture spacing to fracture height promotes uniform fracture-length distribution，while changing the ratio of net pressure to principle stress difference can not change fracture-length distribution for multi-fractures by multi-cluster fracturing.

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Shearing strength of single structural surface of grouted rock mass

ZHENG Zhuo，LI Shucai，LIU Rentai，ZHANG Shijie，LI Xia，WANG Xiaochen

2016, 35 (S2): 3915-3922 doi: 10.13722/j.cnki.jrme.2015.1445

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To evaluate grouting reinforcement strength of single fracture surface，shearing failure mechanism of structural surface and coupling effect between cohesion force and friction force was analyzed. Shearing tests was conducted for regular saw-tooth structural surface. Anisotropy of surface roughness and its characterization methods was analyzed. According to the relationship between shearing direction and micro asperity of the structural surface，a conception of cohesion controlling area and friction controlling area was proposed. Based on failure criterion for non-cohesion structural surface and mechanism of cohesion force，a formula was established for shearing strength on one single surface of grouted rock. Calculation shows cohesion force is influenced by the asperity of surface roughness. Grouting reinforcement increases shearing strength of structural surface along all direction，while the asperity of shearing strength still exists. Research results may provide a method for evaluation on grouting reinforcement of fractured rock.

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Model experiment of engineering protection on loess-mudstone interfacial landslide

LI Chi1，YANG Liu1，WULIJI Nashun1，YAO De2，WANG Xiaorong1

2016, 35 (S2): 3923-3929 doi: 10.13722/j.cnki.jrme.2015.1451

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Loess-mudstone interfacial landslide is one of the most prominent landslide hazards occurred in soil-rock contacting zones. A semi-similar material physical model testing on anchor rod retaining wall was conducted to investigate the sliding mechanism of rainfall induced loess-mudstone interfacial landslides and the feasibility of engineering protection in this paper. The sliding mechanism of interface is analyzed through monitoring the pore water pressure，earth pressure and the displacement of slope surface markers along different sections of inner loess strata and interface between loess and mudstone. The variation of displacement and earth pressure behind anchor rod retaining wall were summarized. The results indicate that the average displacement of anchor rod retaining wall is 5.45 mm after the during two rainfall period，is far less than the specification requirements. This study explores the anchor rod retaining wall can effectively prevent the sliding of slope at the slope toe，restrain the development of cracks within the slope，slow down the development of interface displacement，and prevent the loess-mudstone interface landslide. It also provides the scientific guidance for the engineering prevention from geologic hazards of rainfall induced loess-mudstone interfacial landslide.

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Mathematical model of coal seam methane displacement by injecting CO2/nitrogen

WANG Gongda1，2，3，REN Tingxiang2，QI Qingxin1，ZHANG Jian2，ZHANG Lang1

2016, 35 (S2): 3930-3936 doi: 10.13722/j.cnki.jrme.2015.1465

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In order to understand the physical mechanism of coal seam methane replacement by injecting CO2/N2，this paper analyses the flow mechanisms of methane and injected gas during replacement and the corresponding controlling factors. Based on Langmuir model，Langmuir-like sorption swelling model，P&M permeability model and variable Klinkenberg coefficient model，the sorption model，sorption swelling model of mixed gas were proposed，and the absolute and apparent permeability models of gas injection process were improved as well. Based on above equations，a coupling mathematical model of coal seam methane replacement by injecting CO2/N2was proposed by using mass conversation law. The proposed model reflects the adsorption-desorption，diffusion，Darcy flow and the additional flow from Klinkenberg phenomenon，and it can be used to calculate the gas content and pressure change，the injected and produced gas volume and the gas composition of the produced gas. This study provides theoretical foundation for the design of coal seam methane replacement by injecting CO2/N2.

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Stability analysis on structural plane effects and compatible reinforcement relating to Wudongde dam abutments

LIN Peng1，SHI Jie1，ZHOU Hua2，HU Qingyi2，CAO Quxiu2

2016, 35 (S2): 3937-3946 doi: 10.13722/j.cnki.jrme.2016.0783

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Multiple structural planes are found at the abutments of Wudongde arch dam. It is important for dam compatible deformation to ensure dam overall stability safety. Based on 3D nonlinear finite element，the effect of structural planes on the working performance and stability of Wudongde arch dam is analyzed. The reinforcement effect is discussed from the view of stress homogenization，compatible deformation and stiffness matching. The results show that under the influence of structural planes，the transverse displacement at the abutments increase obviously and local foundation rock deform incompatibly close to structural planes，as well as present stress concentration and local plastic zone. The reinforcement measures，i.e. consolidation grouting and concrete replacement，are able to improve the distribution of stress and deformation. The proposed compatible reinforcement procedure is a valuable tool for improving the reinforcement design and analysis of similar super high arch dams.

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Study of the characteristics and mechanism of surrounding rock deformation during the first layer excavation in Baihetan hydorpower station underground main powerhouses

LI Shuaijun1，FENG Xiating1，XU Dingping1，JIANG Quan1，LIU Guofeng1，FAN Yilin2

2016, 35 (S2): 3947-3959 doi: 10.13722/j.cnki.jrme.2016.0799

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The underground powerhouse cavern group in Baihetan hydropower station is in an extremely grand scale. Geostress in powerhouse area is relatively high and geological condition is quite complicated. The problems of surrounding rock deformation and stability are serious during the first layer of main power houses construction.. Based on deformation monitoring data after excavation of I layer，the deformation characteristic of the surrounding rock in main power houses are systematically analyzed，combining geological conditions and construction information. The mechanism of deformation characteristic is illustrated as well. Analysis shows that under the control of high ground stress and weak tectonic zone，surrounding rock deformation is relatively large after the I layer excavation in both riversides；Resulting from the larger ground stress in right bank than that in left bank，the larger expanding excavation span in right bank and more pervasive adverse geological structures development in right site area，surrounding rock deformation of main house in right bank is thus generally larger than that in left bank； Deformation in vault and downstream spandrel is generally larger than that in upstream due to the maximum principle stress direction；It is observed that there are usually weak tectonic zones or poor quality rock mass where the deformation is more pronounced；Surrounding rock deforms closely related to excavation. The deformation-time curves exhibit step-increase when excavates near the monitoring section. As for the tunnel section where rock mass quality is relatively good，the span of spatial effect is about the cavern span. However，for the tunnel section with weak tectonic zones，deformation keeps continuous increment following construction. Distance of spatial effect reaches approximately two diameters of cavern span. Rock mass deformation exhibits time-independent；Deformation velocity near tectonic zone is usually several times of that at quite good quality rock. To analyze and summarize the surrounding rock deformation characteristic and understand the mechanism is of significance for safety during construction period and for the prediction of rock stability for future construction stage.

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Settlement control study of shield tunnelling crossing railway station in round gravel strata

XIE Xiongyao1，2，WANG Qiang1，2，LIU Huan1，2，LI Jun1，2，QI Yong3

2016, 35 (S2): 3960-3970 doi: 10.13722/j.cnki.jrme.2016.0805

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There is a higher demand on settlement control for shield tunnelling crossing railway station. The Nanning metro line one crossing Nanning railway station is confronted with the challengeable soil of round gravel with high permeability. The piled raft foundation beneath the railway tracks as well as some other control measures to reduce settlement is first introduced. Then the FEM-based shield tunnelling deformation prediction are used to study the change rule of the settlement induced by shield tunnelling. In addition，a real-time remote automatic monitoring system is proposed. By the means of instant messaging(IM) platform，all the participants concerned the project can know the settlement as well as the tunneling situation timely. According to the variation of the settlement data，the engineers gave orders to the operators in the tunnel to adjust the key tunneling parameters. The numerical simulation results and filed monitoring data indicate that it`s essential to reinforce ground before shield TBM crossing the railway track. The piled raft foundation is suitable for round gravel with high permeability. The FEM is helpful to determine the monitoring ranges and settlement control standards. With the feed-back control mechanism，the Nanning metro line one crossing Nanning railway station realized the micro-disturbed construction and the maximum settlement was only -4 mm.

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The downhole pressure data acquisition system and its application in hydraulic fracturing in- situ stress testing

WANG Jianxin1，ZHAGN Ce1，GUO Qiliang1，LI Bing1，LIU Xiaoli2

2016, 35 (S2): 3971-3976 doi: 10.13722/j.cnki.jrme.2016.0816

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The downhole pressure data acquisition system has first been developed by the Institute of Crustal Dynamics. According to accurately recording the water pressure in a hydraulic fracturing test section，the system can not only eliminates the effects of hydraulic fracturing test system compliance and pore water pressure unevenness in the hole wall，but also greatly improves accuracy of the hydraulic fracturing system. The system has been successfully applied in practice，and its running stability and environmental suitability are satisfied to the requirements of further applications. Recently，two in-situ stress tests were successfully carried out by our work team，then the paper conducted a comparison of the two test results based on the data obtained by downhole and ground data acquisition system respectively. The results show that the test errors become larger with the test depth increasing. Moreover，both of two pressure gradients recorded by ground and downhole data acquisition systems are consistent during the pressure increasing stage，nevertheless，the pressure gradient obtained by ground data acquisition system is significantly greater than the one recorded by downhole system during pressure decreasing stage. The stress characteristics and in-situ stress values，especially reopen pressure，are smaller by ground system than those values obtained by downhole system.

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Time-space monitoring and stability analysis of high fill slope slip process at a airport in mountain region

YANG Xiaohui1，2，ZHU Yanpeng1，2，ZHOU Yong1，2，YANG Xiaoyu1，2，SHI Zhanbin1，2

2016, 35 (S2): 3977-3990 doi: 10.13722/j.cnki.jrme.2016.0097

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The stability problem of high fill slope is one of the hot issues in the field of geotechnical engineering at present，but the relevant theories have not been built up. The paper first execute spatial-temporal analysis to the process of slip deformation as well as its mechanism of high fill slope through monitoring sliding deformation process of #3 high fill slope of an airport in mountain region. According to the presumed position of potential sliding surface，back analysis is used to analyses strength parameter of landsilde slip layer，meanwhile finite element software is used to study the relationship between the slope stability and the original foundation treatment of high fill slope，compactness of fill body，fluctuation of groundwater level and reinforcement. The results include：(1) During creep of high fill slope in mountain region，the deformation with obvious lateral displacement mainly focus on settlement，the three-phase law of landslide deformation with time and the characters of cracks spatial evolution in different deformation periods are significant，and the characters are typical artificial loading back stepping landslide. (2) The sliping surfaces are easily generated in filled soil body or weak intercalation in original foundation soil body. The uprising of underground water level can reduce the soil cohesion and slope stability factor massively. (3) Increasing the compactness of filled soil body，lowering the groundwater water level，setting reinforced geotextile can effectively optimize stability of high embankment slope. But the stability of upper filling body is decided by the qualification of the original foundation treatment. (4) Combining the experience and monitoring，the deformation control recommendations and stability evaluation criteria of high fill slope have been proposed. The results can be referenced to high filling standard writing and engineering practice.

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Analysis for landslide caused by underground mining

FU Hua，CHEN Congxin，XIA Kaizong，DENG Yangyang

2016, 35 (S2): 3991-4000 doi: 10.13722/j.cnki.jrme.2016.0110

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Based on the description of rock deformation caused by underground mining，the distribution curves of rock maximum shear deformation and maximum tensile deformation were deduced，which can explained the reason of surface landslide. Combine with Chengchao iron monitoring results of surface deformation，the factors and features of landslide caused by underground mining were described detailedly. In order to describe surface deformation trend，finally，UDEC(Universal Distinct Element Code) was used to simulate the development of such rock deformation. It shows that，under the action of underground mining，the maximum shear deformation in rock can lead to the surface subsidence while the maximum tensile deformation can cause cracks through the rock. Under the combined action of above two factors，the landslide appears usually. After that，with Shallow cracks，deep cracks and unloading cracks generating，affected rocks can be divided into slip zone and unloading zone. Among them，deep crack can be seen as the dividing line between slip zone and the unloading zone. Influenced by surface landslide，under the further mining， the surface deformation degree is increased in the slip zone while the main deformation range of the surface is suppressed.

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Design scheme and optimum research of using the sequential riprap filling method plugging oversize deep water hole

REN Jie，DANG Faning，HUANG Jun，PAN Feng

2016, 35 (S2): 4001-4008 doi: 10.13722/j.cnki.jrme.2016.0796

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Oversize deep water holes have occurred in Goupitan and many other hydropower stations. Therefore， it’s of great engineering value for emergency rescue to research on the rapid plug of oversize hole. Based on the characteristic of the large-scale deep water hole，this paper proposes a sequential riprap filling method，which includes reinforced gabion，stone ballast，composite geo-membrane，mold bag concrete and clay woven bag. An analytical calculation method of evaluate the plug effect is proposed. Finally，the riprap filling project is calculated by using analytical calculation method and finite element method. The results show that the seepage discharge can meet the requirements after the completion of plugging. Therefore，the sequential riprap filling plugging method can be applied successfully in plugging large-scale deep hole. The clay woven bag plays an important role in the plugging process. In order to guarantee the plugging effect，more attention should be paid to the quality of the filling of the clay woven bags. Attention should be paid to avoid the occurrence of local vacancies in the clay woven bags，especially for the clay woven bags at the bottom of the slope. A method for determining the optimum thickness of the clay woven bags is proposed.

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Analysis of mechanism and mechanical characteristics of landslide disaster

YANG Guanghua1，2，3，ZHONG Zhihui1，3，4，ZHANG Yucheng1，2，FU Xudong3

2016, 35 (S2): 4009-4017 doi: 10.13722/j.cnki.jrme.2016.0804

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Landslide disaster mainly means that the sliding body suddenly produces massive soil sliding. Great sliding force could destroy construction，which would cause great losses. The variable-modulus strength reduction method is adopted to analyze displacement process before landslide sliding. It is found that the displacement of retrogressive landslide is more mutational than displacement of thrust load-caused landslide. The retrogressive landslide causes landslide disaster much easier. In contrast，thrust load-caused landslide has obvious warning displacement；therefore，the concept of plastic slope is proposed. Plastic slope can avoid or reduce landslide disaster. In addition，analysis results of calculation examples show that in retrogressive landslide or when the stress level in different part of sliding surface is very different，safety factor by the traditional limit equilibrium method has risk of overestimation. The above conclusions would give new research ideas to avoid or reduce landslide disaster.

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Hard roof fracturing form and dynamic disaster control in short island mining face

WANG Zhaohui，CHENG Zhanbo

2016, 35 (S2): 4018-4028 doi: 10.13722/j.cnki.jrme.2015.1571

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Stress concentration in hard coal seam and complicated roof boundary condition make it，referring to dynamic failure of the surrounding rock，easy to happen in ultra short island mining face with hard roof. For improving surrounding rock controlling condition in this kind of mining face，hard roof fracturing form，surrounding rock dynamic failure mechanism and its controlling measures were studied with field observation and theoretical analysis methods. The result shows that：fracturing of the main hard roof in advancing direction belongs to class II “O-X” failure form and only triangle broken block of the main roof affects mine pressure appearance intensity which means coal seam bears high static load and low dynamic load during the periodic weighting of the mining face. Local dynamic failure of the shallow coal body is main abnormal mining pressure appearance while intensive rock burst is unlikely to happen in short island working face. Dynamic failure of the coal body may be induced by dynamic impact of the hard roof，instability of the lateral main roof structure and dramatic horizontal principal stress relief induced by quick advancing speed. Finally，comprehensive measures including “pre-hydraulic fracturing of the hard top-coal”+”increasing cutting height and decreasing advancing speed“+”improving fore-poling support carrying capacity and extending fore-poling scale”were applied in 412 ultra-short island working face and dynamic failure phenomenon of the surrounding rock is controlled effectively.

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Experimental study and prediction on large section tunnel construction deformation of surrounding rock in soft ground

SU Daozhen，LUO Jianjun

2016, 35 (S2): 4029-4039 doi: 10.13722/j.cnki.jrme.2015.1600

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Considering landslides，distortion of steel arch and frequent arch changing occur easily for large cross section tunnels of carbide argillite in the course of construction，Selected multiple monitor sections near the entrances and exits of Xiaopanling tunnels for the field test. Conducted the convergence deformation test，vault subsidence test，bolt axle force test，sprayed concrete strain test，steel camber bearing stress test，secondary lining concrete strain test，secondary lining back surrounding rocks stress test respectively. The results show that the tunnel deformation stabilizes at 48 d and the deformation accumulation is large，the vault subsidence reached 334 mm，convergence value reached 318 mm. The study also shows that taking the excavation step of 0.5 m，adopting I20 steel bracing，and taking the radial grouting behind the tunnel lining，can effectively reduce the stress of surrounding rock deformation and lining structure. This study points out the effects of the network on veracity and advantages of deformation prediction of surrounding rock. This method has great guidance for the excavation of tunnel construction site.

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Research on influence of left bank slopes long-term deformation on dam body for Jinping I arch dam

CHENG Li1，LIU Yaoru1，PAN Yuanwei2，YANG Qiang1，ZHOU Zhong3，XUE Lijun3

2016, 35 (S2): 4040-4052 doi: 10.13722/j.cnki.jrme.2015.1659

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Gradually，most of the completed super high arch dams in China are stepping into operation. Experimental results and monitoring records demonstrate that excavating，impounding and other perturbations can quicken the creep deformation of rock slope in junction areas. This long-term deformation may seriously threaten the safety of arch dams. New analytical methods of dam body safety under long-term deformation of high-slope are proposed. The creep deformation of high-slope has been calculated and analysed by viscoelastic-plastic rheological constitutive models. The evaluating methods for long-term stability of arch dam based on boundary displacement method(BDM) and stiffness and strength reduction method(SSRM) are proposed while limit analysis is introduced to estimate the capacity of dam body bearing the long-term deformation of slope. Boundary constrains are replaced by exerting fixed displacements to simulate long-term displacement field in BDM. SSRM has a complete theory based on the internal relationships between the elastic-plastic model and the creep model with reducing stiffness and strength at the same time. The above methods are applied in evaluating the capacity of Jinping I arch dam bearing the long-term deformation of the left bank slope. The results indicate that the long-term deformation of the left bank slope is beneficial to Jinping I arch dam body in some extent. The yield zone volume and plastic complementary energy norm both decrease while the stress state improves when the creep deformation is stable. The dam body could bear more than 6 times boundary displacement. Hence, more attentions should be focused on the local stress concentration in the base surface damaging the long-term stability of Jinping I arch dam.

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Analysis of landslide mechanisms of the southern red bed slope in the No.2 opencast coal mine in eastern Shengli coal field

FAN Zhiyong1，ZHOU Yang1，LIU Xiaoyu1，LI Shihai1，ZHANG Xin2

2016, 35 (S2): 4063-4072 doi: 10.13722/j.cnki.jrme.2016.0837

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Sliding mechanisms have been studied for the series of the landslides of the southern red bed slope in the No.2 opencast coal mine in eastern Shengli coal field. The geological exploration is used to determine the distribution of the faults and the properties of the strata. By field survey and comparison of the four images photographed by an unmanned aerial vehicle，the deformation and failure characteristics of every landslide area are analyzed phenomenally. Using the monitoring data of the GPS，the deformation characteristics of the two large landslides are analyzed quantitatively. Combined with boreholes information，the slip face of the deforming area is obtained. Based on the generalization of the stratum structure and the effect of water，a physical model experiment is made to qualitatively explore the failure evolution mechanisms of the southern red bed landslide. The research shows that，the watertight property of the F68 fault，the different deformation between the sandstone layers and mudstone layers，and the distribution of lots of weak layers with low shear strength in the southern slope are the primary geological factors resulting in the series of the landslides，the increase of the rainfall intensity aggravates the deformation of the southern slope. In fact，Sandstone and mudstone belong to hard rock and soft rock respectively，and the mudstone softens easily when encountering water；because of the different deformation of sandstone and mudstone，the steep joints in the sandstone become open and then the surface water infiltrates easier；besides，the groundwater cannot dissipate in the F68 fault. All of the above reasons cause the ulceration at the toe of the slope and the formation of the fracture zones on the surface of the slope. Under the condition of the rainstorm，plenty of rainwater infiltrates and softens the weak layers，the higher seepage water pressureexists in the weak layers and the hydrostatic pressure forms in the fracture zones，consequently leading to the multistage “horizontal-pushing-type”landslides.

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Mechanism of gorge-type landslide disaster chain and its hazard evaluation

CHEN Yu，LI Tianbin，WEI Yongxing，CHEN Guoqing，LUO Kai，MA Chunchi

2016, 35 (S2): 4073-4081 doi: 10.13722/j.cnki.jrme.2016.0865

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High-speed rocky landslide has a great potential risk in the deep-cutting gorges by its unique characteristics，i.e. high speed but short travel distance，disaster chain effect，high potential energy. This paper，based on kinematics of Layue landslide-damming process，firstly concluded the failure mechanism of rocky high speed landslide occurred in gully terrain. And then analyzed its disaster chain effect，which could be outlined as follows：quake-rainfall coupled degradation of slope stability，rock slide in a topple-pull apart model，brittle rupture of the locked path，rock avalanche，riverbed ploughed and thither slope uplifted，blocking and dammming. Given the trait of high speed but short travel distance，this paper formulated that it’s the landslide intensity(volume，velocity，runout) determins the occurance of landslide-damming disaster while river features perform as influential factors. Eventually，based on the analytic hierarchy process to highlight the factors‘ weight function，this paper established the gorge-type high-speed short-runout landslide damming hazard evaluation model. Two case studies have shown that this hazard model can fairely well reflects the effect of rocky high-speed landslide damming disaster chain in deep-cutting gorges. Moreover，such model has a great significance and instructions for future mountainous engineering risk control and disaster prevention and mitigation.

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Study on transverse deformation and cracking property of shield-driven tunnel induced by adjacent excavation

YANG Yubing1，ZHOU Biao2，XIE Xiongyao2

2016, 35 (S2): 4082-4093 doi: 10.13722/j.cnki.jrme.2016.0893

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The left shield tunnel between two stations of Ningbo metro line No.1 was damaged as a result of adjacent excavation. Cracks，concrete spalling and chipping appeared in the reinforced concrete segments due to the large displacement and transverse deformation of tunnel. The damage and cracking characteristics of this tunnel was summarized according to results of the on-site inspection and measurement. The transverse deformation and cracking property of shield tunnel induced by the adjacent excavation was numerically and separately studied，and the tendency of cracking was also numerically predicted. The numerical prediction of the vertical convergence was lower than the field data，and the rigid body displacement was mainly induced by the dewatering inside the excavation pit. The transverse deformation mode of tunnel lining ring，“horizontal oval”，actually determines its cracking range. The crown and invert of tunnel were the most vulnerable positions. The relative maximum crack width appeared around these positions. These predictions were agreed well with the field observations. The macro cracks at the invert of tunnel would run through the depth of reinforce concrete segment and become penetrating cracks if the increment of vertical convergence reached up to 1% tunnel external diameter.

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Study on the shale creep properties of Goupitan hydropower station ship-lift base and its foundation treatment technology

XU Qianwei1，CHENG Panpan1，CAI Yongchang2，WANG Zhaokong3

2016, 35 (S2): 4094-4102 doi: 10.13722/j.cnki.jrme.2016.0909

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The second level ship-lift of Goupitan hydropower station is built upon the shale mass which has significant creep properties. In order to ensure the long-term stability and safety，a series of study have been carried out to investigate the creep characteristic of the shale and the long-term deformation of ship-lift foundation. Firstly，the creep model and its parameters are identified according to the results of in-situ rigid bearing plate creep test；Secondly，based on the analysis of model pile loading test results，the stress and deformation characteristics of the pile-rock interface and its ultimate friction resistance can be investigated respectively. Finally，with the help of numerical simulation，the long term settlement of ship-lift based on different types of foundation structure are analyzed and compared，and the pile-raft foundation is optimized as the recommended foundation scheme. The above results not only has a certain reference value for the selection of ship lift base，but also provides evidence for evaluating its long term stability and reserving the reasonable foundation deformation allowance.

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Geomechanical model test on global stability for Wujiagang bridge tunnel-type anchorages

JIANG Yuzhou1，WANG Ruihong2，ZHU Jiebing1，LIU Jinghua3，LI Cong1，WANG Ben1

2016, 35 (S2): 4103-4113 doi: 10.13722/j.cnki.jrme.2016.0911

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In order to reveal mechanism and the global stability of Wujiagang yangtze river bridge tunnel-type anchorages，the deformation characteristics and the potential failure mode of surrounding rockmass，a 3D geomechanical model test with the similar scale of 1∶40 for tunnel-type anchorage was carried out. Base on the similarity theory，the complex geological structures including anchor plug body and different rock mass are simulated. Through the overloading destructive model test，the deformation characters，the failure process，the pattern and mechanism of tunnel-type anchorages and surrounding rockmass are obtained. The test results show that the deformation characteristic curves at the rear surfaces of anchorages and surrounding rockmass present symmetrical bimodal shape，and those of the frontal surfaces present the shape of convex upward. The deformations at the rear surface are greater than those at the frontal surface. Because of the clamping effect，the amount of deformation in the surrounding rock range 1.0 to 1.5 times width of anchorages rear surface is large. After comprehensive analysis，the global stability coefficient of tunnel-type anchorages is considered to be 9.0.

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Research on stability of deformation body of Baishadiao under water level change in reservoir area

XU Kaimin，SHENG Qian，FU Xiaodong，HU Wei，ZHOU Yongqiang

2016, 35 (S2): 4114-4120 doi: 10.13722/j.cnki.jrme.2015.0895

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Coupling analysis of the seepage field-stress field is a hot and difficult problem in the study of stability for deformable body under water level change in reservoir area. The discontinuum-based discrete element method is a fully fluid-solid coupling analysis method，which can simulate the fluid flow between fractures of the impervious rock mass. Taking the Baishadiao deformable body at right bank of the Xiluodu hydropower station in Jinshajiang river as a case study，the mechanical properties of rock slope parameters are obtained with various tests；according to the reservoir operation curve of the Xiluodu hydropower station，based on full consideration of the regional geological condition of the bank slope，stability analyzing of the deformable body under reservoir water level change has been carried out with the discrete element method；the limit equilibrium analysis based on the calculation of seepage field is also carried out for a comparative analysis. The simulation result shows that with increase of the reservoir water level，the pore water pressure increases，and stability gradually decreases；at a water level of 600 m，instability failure of the deformable body is observed；compared with the limit equilibrium analysis，the discrete element method considers the dynamic flow of the water in the cracks and can reflect the actual situation.

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Monitoring method for coal-mass lateral deformation in deep mining and characteristics of step deformation

CHEN Shaojie1，2，WANG Huaiyuan1，ZHU Yan1，YIN Dawei1，QU Xiao1，LIU Yong1

2016, 35 (S2): 4121-4128 doi: 10.13722/j.cnki.jrme.2015.1553

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Coal-mass deformation，especially the lateral deformation，can be used as an important indicator to evaluate the stability of coal pillar. One high frequency and larger monitoring range of 3 000 m method was designed to monitor the lateral deformation of coal mass in Tangkou coal mine over 1 000 m mining depth. The monitoring results show that the movement of roof and the spatial structure around the strip mining panel cause the lateral deformation trend of coal mass. The lateral deformation becomes large when the station is in 30–40 m front of the working face. The prominent deformation appears when working face passes the station about 28–36 m. The deformation curves become flat successively when working face passes the station about 90 m. The maximum lateral deformation of 287 mm is smaller than that of other coal-mass in the same coal mine. The reasons are without influence of repeated mining，the small angle between roadway and the maximum stress and the bedding sandstone roof easy to break out. Some new characters as discontinuous，step and mutation of coal-mass lateral deformation in deep mining are monitored，which are caused by energy accumulation and release leads coal-mass discontinuous damage in deep mining. Those coal-masses show more plasticity and more elasticity，brittleness and burst tendency at the same time.

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Horizontal foundation surface excavation method under the protection of energy shaped and dissipation composite cushion

HU Haoran1，2，LU Wenbo1，2，XI Hao3，YAN Peng1，2，WU Gang3，HU Yingguo1，2，CHEN Ming1，2

2016, 35 (S2): 4129-4138 doi: 10.13722/j.cnki.jrme.2015.1005

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In order to improve the excavation efficiency of hydraulic structures horizontal rock foundation，an energy shaped and dissipation composite cushion is presented，and developed iron sand concrete with high wave impedance used as energy shaped structure construction material. It analyzed the composite cushion’s impact on damage properties at the bottom of blasting holes，and proved its feasibility to be used for foundation surface excavation by using blasting damage numerical simulation technology based on LS-DYNA secondary development. Furthermore，it verified the composite cushions actual effect by carrying out blasting field experiments in Baihetan hydropower station，where controlled surface over excavation and under excavation amount，and explosion damage depth were measured. The results showed that the composite structure enhanced rock fracture degree in horizontal direction and reduced the vertical damage depth at the bottom of blasting holes. Thus it effectively reduced the over and under excavation amount and controlled foundation surface fluctuation，helping to achieve a good rock foundation. Also，it could make full use of the excavation work face and achieve one-time forming of vertical blasting holes， which could realize rock foundation rapid excavation on a large scale.

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Source development and slope gradient effect of debris flow source in earthquake zone

ZHANG Shishu1，PEI Xiangjun2，ZHANG Xiong2，RAN Congyan1，MA Jingen1

2016, 35 (S2): 4139-4147 doi: 10.13722/j.cnki.jrme.2016.1134

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The geological hazard triggered by Wenchuan earthquake was characterized by great damage，huge volume and great quantity. It resulted in huge increasing of the potential material of debris flow in the earthquake area. Thus，the frequency and volume of debris increased after the earthquake. The investigation of the potential debris material along Duwen highway was conducted. The statistic of spatial distribution of debris was performed by GIS. The effect of gradient on debris erosion was analyzed. The results showed that，the hazard area and volume followed the model. The density of hazard was largest in the granitic area. The hazard mainly occurred on the slopes in the gradient range of 40°–50°，in the exposure range of 120°–150° and in the elevation range of 1 400–2 800 m. Meanwhile，it increased with increasing earthquake intensity and the distance to the surface rupture of the Wenchuan earthquake. The occurrence of the hazard followed the“hanging wall effect”and“topographic effect”. The maximum value of flow velocity of the debris was reached at slope gradient of 60° and the critical slope gradient for debris erosion was in the range of 42.4°–48.1°.

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Research on comprehensive evaluation of cavability of block caving based on MRMR

CAO Hui1，2，YU Shibo2，WANG He2，QIN Xiushan2，YUAN Ye2

2016, 35 (S2): 4148-4153 doi: 10.13722/j.cnki.jrme.2015.0689

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A reliable prediction of rock mass cavability is a critical factor in the successful caving of most orebodies. Aim to build a cavability assessment system of rock mass based on three-dimensional geological statistics method. Distance power inverse ratio method was used to digitize the three-dimensional geological information of drill. With the assistant of 3DMine，the three-dimensional digital model was built based on MRMR rock mass quality evaluation system. And then，the area distribution of cavability was evaluated from the aspects of macroscopic. Combining with engineering analogy and the predicted results of caving fragmentation，a cavability comprehensive evaluation of block caving is finished aiming at Don Javier mine. The results indicate that，the evaluation system was finally built. At last，the evaluation method was applied to Don Javier studies of the natural caving method. The result shows that，this evaluation system can satisfy the needs of rock mass cavability evaluation in block caving. The average value of MRMR is 56.4 from 1 800 m to 2 400 m of Don Javier Mine. And the cavability grade of orebody is defined as III medium. The initial undercutting area of production capacity reaches about 15 000 m2. The predicted caving fragmentation of Don Javier is from 0.06 m3 to 2.95 m3 and the results verify the evaluation of cavability.

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Study of influence of rainfall permeation on shallow stope stability by microseismic monitoring

PENG Fuhua1，2，LI Shulin3，LENG Xiuning4，CHENG Chao4，LIU Dongchun4

2016, 35 (S2): 4154-4163 doi: 10.13722/j.cnki.jrme.2015.1153

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The geological background，mining background and characteristics of ground pressure of Xianglushan Tungsten mine were briefly described. Aiming at the influence of rainfall permeation on stope stability since 2012，a typical case of stope collapse and the law of ground pressure activity influenced by rainfall permeation were quantitatively analyzed by micriseismic monitoring，the mechanism of stope collapse induced by rainfall permeation was briefly analyzed. The results show that，under the influence of rainfall permeation，microseismic events significantly increased，and the events of the sensors nearby the collapse exceed early warning value before stope collapse. A large-scale stress transfer and distribution appears after the stope collapse，and the stress transfers to perimeter of the ore body arch after stope collapse. A lot of rock fractures and collapses appear in the process of stress redistribution，and the rock mass tends to be stable after nearly two months of stress adjustment. The microseismic event level changes with the rainfall as a whole，and will lag behind. This means the ground pressure activity increases with the increase of rainfall，rainfall permeation is an important causes of stope instability. At last，the prevention and control measures of ground pressure disasters were put forward. This study has important significances for the quantitative assessment of the influence of rainfall permeation on shallow stope stability，and ensuring the safety in underground production.

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Mechanism and synergetic treatment technology of water inrush disaster in completely and strongly weathered granite tunnels

YUAN Jingqiang1，CHEN Weizhong1，2，HUANG Shiwu3，ZHOU Xiaosheng3，ZHOU Zenghui1，LIU Jinquan1

2016, 35 (S2): 4164-4171 doi: 10.13722/j.cnki.jrme.2015.1167

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Water inrush disaster in weathered granite regions with abundant water does tremendous harm to the construction of tunnels and surrounding environment. Combining with the treatment practice of water inrush disaster of Shanxin tunnel in Guangxi Zhuang Autonomous Region，the water inrush mechanism，character of disaster and countermeasures were studied by conducting geophysical and drilling exploration at field，laboratory experiments and theoretical analysis. It shows that the water inrush disaster happens suddenly and has strongly destructive influence with high evolution speed. The risk environment factor of water inrush disaster in weathered granite regions are disintegration of surrounding soil，interconnected channels of groundwater，abundant groundwater recharge，and banded valley topography. Meanwhile，unsatisfactory of grouting implementation，insufficient of outburst prevention thickness and disturbance of excavation is the dominant inducing factor to cause water inrush disaster. Under the influence of excavation disturbance and groundwater pressure，the advancing face loses stability because of seepage failure and evolves rapidly to form water inrush disaster，even inducing ground collapse and severe water losses，etc. Considering the safety of tunneling construction and ecological environment，general treatment principle of water inrush disaster is proposed，which emphasizes on giving priority to seal water by grouting combining with the drainage work. Further on，according to the different geological conditions caused by water inrush disaster，corresponding treatment scheme should be adopted with dynamic construction principle. In order to seal water and reinforce the completely weathered granite，the synergetic treatment technology is optimised，with composite curtain grouting and full-face curtain grouting. And the proposed synergetic treatment technology is adopted in the design of treatment of water inrush disaster and applied into practice.

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Rock burst mechanism and tremors law of high and thick strata of hard rock during repeated mining

WANG Shuli1，ZHANG Kaizhi2，JIANG Jinquan3，ZHU Guangli1，YU Hailing1

2016, 35 (S2): 4172-4179 doi: 10.13722/j.cnki.jrme.2015.1245

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Aiming at tremors with large energies during repeated mining induced by instability of super-thick strata，using 200 m red beds as an engineering project in Baodian Coal Mine，rock burst and tremors law of high and thick strata of hard rocks were analyzed. The tremors law show that micro-seismic events which energy below 104 J cut down observably compared to upper coal seam，on the contrary，strong rock burst which energy higher than 105 J effecting mining seriously increased observably. In generally the micro-seismic show out no obvious laws，but strong rock burst appearing at boundary sides observably larger than that in middle zone，and show the same laws in gob side compared with the coal side. Based on tremors law and analyzing characters of reds beds during the first fractured，putting forward two rock burst mechanism in different zone. First，in the middle of working face，because of subsidence space enlarged，vertical load will change suddenly caused shearing strength between rock blocks exceeding limits，finally break stable articulated and balance structure，formed type of shear and slip. Second，at boundary sides，the external expansion of strata movement line caused highly-concentrated stress area，and following cause compaction of fractured strata，finally induced rock burst，formed type of slip and backfill. Two mechanisms give a positive function to each other. The type of slip and backfill act predominant in strong rock burst.

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Research on blasting under the controlled of acceleration power spectrum density index

YAN Honghao，HUN Changhong，LI Xiaojie，ZHAO Tiejun

2016, 35 (S2): 4180-4186 doi: 10.13722/j.cnki.jrme.2015.1256

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In order to ensure that the land leveling blasting will never be a threat to the Intel company lithography platform operation，the acceleration power spectrum density control indexes for engineering blasting were studied. Based on the analysis of multiple project cases，the acceleration spectrum density control index was turned into the control of blasting vibration velocity，and the vibration peak velocity of 0.05 cm/s was forecasted. Considering the engineering cost，the deep-hole blasting method could be used in some areas. After blasting experiment，when the Ms–6，Ms–7，Ms–8 sections of the nonel tube detonators was used in the holes，and Ms–4，Ms–5 sections of the nonel tube detonators on the surface，the blasting vibration peak velocity was not greater than 0.02 cm/s. At this time，the lithography platforms were working properly. It showed that transition from the acceleration power spectrum density control to the control of the blasting vibration velocity index is feasible. This transformation could provide a blasting scheme design reference with the presence of precision instruments.

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Investigation of rock and soil deformation distributed detection based on spiral parallel line and time domain reflection technology

ZHANG Yangkai，JIA Shengyao，CAO Bo，LI Qing

2016, 35 (S2): 4187-4195 doi: 10.13722/j.cnki.jrme.2015.1309

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Aiming at some problems in the geological hazard monitoring methods for the rock and soil deformation caused by landslides，debris flow，etc，a new method for the monitoring of rock and soil deformation has been proposed. The method is a deformation distribution measurement technique which is composed of the spiral parallel transmission line and time domain reflection technology. The deformation distributed measurement and calibration system is designed. The tensile device of the system is used to stretch of the whole spiral line of 162 cm and stretch positioning of the spiral line of 500 cm，at the same time，the time domain reflection device of the system is used to test the spiral line，and using the partial least squares to model the measurement data of the two groups respectively. To gradually stretch the spiral line of 165 cm to 195 cm，centimetre by centimetre，once 1 centimetre is stretched，new reflection data of time domain is acquired.The maximum error of the tensile model is 0.3%. To gradually stretch the spiral line of 500 cm from the starting to the end，and to stretch the spiral line 2 cm every 10 cm，once 1 step is stretched，new reflection data of time domain is acquired. The maximum error of the tensile model is 2%. The experimental shows that the proposed method can accurately predict the tensile and tensile strength of the parallel transmission lines，and it solves the problem that the measured place not be changed and the changed place can not be measured. Whats more，it has a larger measurement range than the optical measurement method of slope.

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The slab instability of a stilling basin caused static effect of hydraulic jump

LUO Guanyong1，2，CAO Hong1，2，PAN Hong1，2

2016, 35 (S2): 4196-4204 doi: 10.13722/j.cnki.jrme.2015.1323

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Occurrence of a hydraulic jump can reduce the balance weight of a slab in a stilling basin. Ignoring them would result in a dangerous situation. In this paper，a slab failure case，which occurred in Guangzhou is examined carefully by numerical simulation. The method to locate a hydraulic jump and that to simulate the draining holes were addressed in details. The restoration and its effect is also discussed. It found that，(1) the occurrence of a hydraulic jump both reduces the balance weight of a slab and changes boundary condition for seepage flow significantly. (2) It is the ignoring the static effect of a hydraulic jump that makes the failure happen. (3) Draining holes in the slab reduce the water pressure difference between the top and bottom and eliminate the static effect. (4) For a slab with draining holes，stability analysis without taking into account the hydraulic jump static effect is acceptable for its result is on the safe side.

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Goaf group instability analysis based on rigid frame structure model method

JIANG Lichun1，2，XIAO Kang2，WU Aixiang3

2016, 35 (S2): 4204-4210 doi: 10.13722/j.cnki.jrme.2015.1356

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In order to study the overall stability of vertical goaf group under external load，a rigid frame structure model was developed by converting vertical goaf group into plane frame system. Based on the model，a goaf group instability judgment criteria and analysis method was presented. The method，together with numerical simulation method，was used respectively to analyze the overall stability of a vertical goaf group after completely mining the pillar of the uppermost level. The result shows that，after mining the pillar，the maximum tensile stress and vertical deformation of the uppermost roof surrounding rock mass both exceed the permitted threshold，which has led severe instability to the goaf group. Comparing with numerical simulation method，the conclusion of two methods has close values of internal rock mass both on maximum tensile stress and compressive stress，which shows similar variation trend. The field engineering proves that the gob roof rock mass of the uppermost level has been collapsed and the gob has extended to surface，which has verified the rigid frame structure model method in large part.

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Modification of reinforcement effect model of herbs root system in soil

WEN Wei，LI Guangfan，HU Wei，LIU Huijiang，XIANG Wen

2016, 35 (S2): 4211-4217 doi: 10.13722/j.cnki.jrme.2015.0704

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The herbs living in the slope is helpful to decrease the erosion of the rain to the soil，improving the resistance shear strength of the shallow soil and so on. The article has been analysis and assessment the WU.T.H and Waldron model separately that herbs rootss reinforced effect can be calculated by formulas. Obtained the advantage and disadvantage respectively. Based on the WU.T.H and Waldron model，introduced the depth of the coefficient，revised and improved the initial model of reinforcement soil，obtained the new interactive diagram of root and soil，the model can describe the whole shear process used by pressure，shear displacement，the depth of the coefficient and the root diameter. Introduce the parameters obtained by two roots-soil shear test to the modify model，concluded the results calculated by modified model less than the Waldron model，while the results calculated by modified model was most close to the test value. So，the modified model was better than the Waldron model.

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Micro-structure statistics analysis and reinforcement effect judgment of K2SiO3 reinforced soil based on SEM test

ZHOU Shangzhi1，YIN Xiaotao2，TANG Yan1，LIU Mingqun3

2016, 35 (S2): 4218-4226 doi: 10.13722/j.cnki.jrme.2015.0806

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Chemical reinforcement of soil often evaluates change of initial micro-structure under different sizes affected by strengthening material by means of all kinds of meso-tests，which reveals strengthening mechanism and estimates reinforced effect. Three types of SEM specimen such as clay without saturated by 5% concentration k2SiO3 solution，clay with saturated and dried once by the solution and clay with saturated and dried three times by the solution are prepared and respectively used to test under different SEM experiment conditions such as amplification 500 and 50 m，amplification 1 000 and 10 m and amplification 5 000 and 5 m. Phenomenological analysis of images，accumulation curve and distribution curve of ray segmentation，radar of different gray statistics(such as average，standard deviation and coefficient of variation) on sixteen subarea of images are compared and analyzed. Apparent enhancement of particle and flake edge in SEM images，sharpening of accumulation curve，elevation of distribution curve and reduction & homogenization of variation coefficient radar are all proved reinforcement effect. Clay with saturated and dried three times by 5% concentration K2SiO3 solution is integrated to be optimal reinforcement scheme，in which not only particle of soil is strengthened but also pore is partly filled. The reinforcement is comprehensive，whose homogenization is better than raw one，which does good to full play of integrity and is suitable for protection of cultural relics. If SEM test condition is designed to be amplification 500 & 50 m，shape factor of radar on variation coefficient of sixteen subarea in images increases with increasing of saturated & dried time and amplification，which do good to observe whole reinforced effect and micro-structure being particle. When amplification 5 000 & 5 m being set in SEM tests，the shape factor curve decreases with increasing of saturated & dried time and amplification，which is beneficial to observe pore partly filled effect and micro-structure being flake. During statistical analyzing of quantitative data existed in images，variation coefficient does better than average and standard deviation，which is suggested to use in image quantitative analysis.

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Study on cyclic shear characteristics of cement-soil under seismic loading

LI Pu，FAN Henghui，SHI Xiang，LIU Gang

2016, 35 (S2): 4227-4234 doi: 10.13722/j.cnki.jrme.2015.0944

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Based on the failure mechanism of cement-soil pile group under seismic loading，the dynamic cyclic shear tests of cement-soil were carried out by using GDS dynamic simple shear apparatus to study the effect of cement ratio and cyclic stress ratio on dynamic deformation，dynamic strength and degradation characteristics. The results indicated that the dynamic shear strain developed more slowly and the dynamic strength was gradually increased with the cement ratio increasing. However，the results of the increase of cyclic stress ratio were opposite. It was shown that the critical cyclic stress ratios were 0.267，0.286 and 0.327 for the cement-soil with cement ratio of 5%，10% and 15%，respectively. Using the failure criteria of turning strain and the method of normalization， the model between cyclic stress ratio and failure number was established. The degradation index of cement-soil reduced with the increase of cyclic stress ratio and cyclic number under cyclic loading，and the Semi-logarithmic model could more accurately describe the degradation characteristics of cement-soil.

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Centrifugal modeling of big sandbag cofferdam on coastal soft soil

CHEN Lingwei1，2，ZHOU Xiaowen1，GONG Biwei3，LI Bo3，TONG Jun3

2016, 35 (S2): 4235-4240 doi: 10.13722/j.cnki.jrme.2015.1547

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How to build a quick and safe cofferdam in sea is a difficult challenge in land reclamation engineering. A new method named“big sandbag cofferdam”is developed and applied in many projects. In this paper，a series of centrifugal model tests were conducted to investigate the behavior of the big sandbag cofferdam. The stress-strain of geotextile was get by using a flexible glue to paste the strain gauge. It was found that the big sandbags have a good integrity and strong adaption to ground deformation. The uneven settlement of soft foundation without wick drains was obvious，sandbags near the slope toe were in tension，and those under the road center were pressurized. For the cofferdam installed with wick drains，the magnitude of maximum tension of the sandbag was higher，and the distribution of tension in reinforcement was more localized under the toe of the cofferdam. The mobilization of the tension reaches around 86% of the tensile strength. The existence of wick drains increases the strength of the foundation during the period of cofferdam construction. It can contribute significantly towards the stability of the cofferdam.

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Fractal features and dynamical characters of the microstructure of paste backfill prepared from fly ash based binder

CHENG Haiyong，WU Aixiang，WANG Yiming，WANG Hongjiang，WANG Shaoyong

2016, 35 (S2): 4241-4248 doi: 10.13722/j.cnki.jrme.2015.1607

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There are not many indicators to quantify the effect of fly ash on promoting the development of objects and enhancing strength in paste in micro scale. Based on SEM and energy spectrum analysis experiment，paste micro structure research is conducted with the help of Fractal Theory and Reaction kinetics. Results show that combination of fly ash and cement hydrated products are beneficial to promote the produce of Ettringite of expansion phase. In a certain range，with the increasing input of fly ash，the production of Ettringite phase increase correspondingly，and the micro structure of paste is more and more compact. As the Box-counting Dimension increasing，the strength of paste increase dramatically at the beginning and remain stable at last. If the fly ash contains too much calcium，the production amount of Ettringite will be excessively and the Box-counting Dimension increase and then decrease，which acts as strength deterioration in macroscopic view. The established fly ash paste hydration reaction model divides its process into dissolution period，soakage period and setting and hardening period. Based on the two courses(named crystal nucleation and crystal growth)，into which the develop procedure of gel particles are analyzed，the formula of cementing crystal growth rate is obtained.

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Research on compressive strength of frozen sand-silty clay mixed soil with different mixture ratios

HUO Haifeng1，CHEN Ruiqing1，LEI Huayang2，LI Haonan1，LIU Zhuangzhuang1

2016, 35 (S2): 4249-4255 doi: 10.13722/j.cnki.jrme.2015.1641

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In order to study the influence of different mixture ratio on compression strength of sand-silty clay mixed soil，the unconfined compressive tests were conducted on frozen soil samples by means of controlling variables. The experiments indicate that different silty clay contents has remarkable influence on the unconfined compressive strength of frozen soil. Inhabitation of ice and appearance of cohesion，both contributed from increasing of fine soil， mutually interact and determine the strength. Once the ice in pore space fails to combine to a unit，the strength would drop dramatically. Meantime，the maximum unconfined compressive strength can be obtained when clay content is 60% and water content is16%. If the content is below the optimum content，the strength of the frozen soil continuously increases with the content increasing. Otherwise，the strength of the frozen soil gradually reduces with the content increasing. Moreover，the optimum clay content and water content will decrease when dry density increases. Finally，a reduction of unconfined compressive strength，47%，is captured for the mixed soil after 20 freeze-thaw cycles.

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Study on surface deformation induced by shield tunneling based on random field theory

CHENG Hongzhan，CHEN Jian，LI Jianbin，HU Zhifeng，LI Jianhe，HUANG Juehao

2016, 35 (S2): 4256-4264 doi: 10.13722/j.cnki.jrme.2016.0099

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Random field theory and numerical analysis method are combined to investigate the influence of the spatial variability of material properties on surface deformation caused by shield tunneling. Random fields of elasticity modulus are generated by Covariance Matrix Decomposition method to model the characteristics of spatial variability. Within Monte-Carlo framework，FLAC3D is used to analyze the influence of coefficient of variation and correlation distance of elasticity modulus on surface deformation. The results show the spatial variability of elasticity modulus has significant effects on both the values of greenfield settlement and the shapes of settlement trough. Depending on the relative size ratio between correlation distance and tunnel diameter，three surface deformation patterns are identified. The distribution of maximum surface settlement follows an approximate lognormal distribution. With coefficient of variation and correlation distance increasing，the more scattered the probability distribution of the maximum surface settlement，and the larger the probability of surface settlement exceeding the critical value.

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Experimental study on dynamic characteristics of dry rubber-sand mixture at large strains

LIU Fangcheng1，YANG Jun2，WANG Haidong3

2016, 35 (S2): 4265-4278 doi: 10.13722/j.cnki.jrme.2016.0193

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Rubber sand mixture(RSM) has been recognized useful widely in civil engineering as low cost material for energy absorbing and isolating，while little research has been done on dynamic shear modulus and damping ratio of it in large strains. Cyclic simple shear tests on dry RSM with seven rubber content and four vertical consolidation pressure are introduced in this paper，and general rules on dynamic shear modulus and damping ratio of RSM at large strain range 10－3–10－1 are introduced. Results on RSM dynamics properties at large strain indicate that：(1) Dynamic shear modulus of RSM decays relative to that of pure sand，and the decay coefficient decrease with the increase of rubber content as well as with the increase of shear strain amplitude. (2) Damping ratio of RSM is amplified comparing with that of pure sand，the amplification coefficient increases with rubber content while decreases with shear strain amplitude. (3) Vertical consolidation pressure affects little on shear modulus decay coefficient of RSM to pure sand versus rubber content，while influences significantly damping ratio amplification coefficient of RSM to pure sand versus rubber content，that is damping ratio amplification coefficient increases with vertical consolidation pressure. With the increase of shear strain amplitude，influence of vertical consolidation pressure on damping amplification attenuates. (4) Both dynamic shear modulus and damping ratio are influenced obviously by shear cycle numbers，and it seems that the effect decreases with rubber content.

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Experiment on shear resistance behavior of interface between slurry modified by calcined ginger nuts and soil mass of earthen sites

WANG Nan1，ZHANG Jingke1，2，SHAN Tingting1，GUO Qinglin2，ZHAO Linyi2，LI Zuixiong2

2016, 35 (S2): 4279-4286 doi: 10.13722/j.cnki.jrme.2016.0785

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To explore the shear resistance behavior of grout-soil interface in anchoring conservation of earthen sites and reveal the internal mechanical mechanism of anchorage system，calcined ginger nuts，fly ash，quartz sand and soil from earthen sites which are commonly used in anchoring engineering are selected as the main grout materials. Bonded samples were made by grout and undisturbed soil from earthen sites. Regarding the actual environment at which the anchor system survives，all the samples were buried and maintained in outdoor soil mass. The relationship between shear stress and displacement，strength parameters，and a new fitting formula were gained by direct shear test. The results show that slurry and soil fail to bond，interfacial shear strength should rely on sliding friction and particles interlock capacity. The mixing slurry of calcined ginger nuts with earthen sites soil presents the largest inner friction angle，which means that compatibility between slurry and soil is of important significance to improve shear strength of interface. Owing to the large variation of temperature and moisture and consolidation of grout-soil interface by PS solution，shear resistance of grout-soil interface is to some extent weakened. The experimental results reveal that anchor craft of earthen sites plays an important role in the improvement of shear strength.

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Analysis of spatial distribution characteristics of seabed sediments critical starting velocity in the northern South China Sea

TIAN Zhuangcai1，GUO Xiujun1，2，QIAO Luzheng1，JIA Yonggang1，2，YU Le1

2016, 35 (S2): 4287-4295 doi: 10.13722/j.cnki.jrme.2016.0800

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To study the space distribution characteristics of critical starting velocity of sediments in the northern South China Sea(SCS)，the 45 stances sediment physical property data of corresponding area has been collected and self-test，then calculating the critical starting velocity by choosing appropriate formula and evaluating the applicability of the results. According to the sediment space distribution and statistical results，112 stances sediment critical starting velocity values have been received by interpolation and drawn. The results show that sediments critical starting velocity is different in the space. The distribution of sediment particle size corresponds with distribution characteristics of critical starting velocity substantially and controls it. Compared with upper laminar flow field in the northern SCS，the degree of starting difficulty of the seabed sediments continental shelf in the winter and summer has been gained，which provides the basis to study the transformation mechanism of seabed sediment by ocean dynamics and change rule of seabed sediment in the northern SCS.

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Investigation of laterally loaded pile based on the hydraulic gradient model test

YUAN Bingxiang1，CHEN Rui2，YANG Xueqiang1，LUO Qingzi1，PENG Tao2，WANG Yixian3，CHEN Wenwu4

2016, 35 (S2): 4295-4301 doi: 10.13722/j.cnki.jrme.2016.0802

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A hydraulic gradient test device was used to conduct a model experiment and to study the pile-soil interaction. In this model test，the seepage field and gravity field simulate the in-situ stress field，the deformation pictures of soil are captured with the use of a high resolution camera，and the soil displacements are obtained using the particle image velocimetry technique. The mechanical properties of the model pile and the distribution characteristics of the displacement field of soil around the laterally loaded pile are visually studied. The laterally loaded pile was studied at the hydraulic gradient of i = 0，i = 5 and i = 10. As the hydraulic gradient increases，the displacements of the pile and the sand particles decreased，the influence zone of the pile shrank，and the depth of the rotation point of the pile was uplifted. The underlying reason for the changes is that the seepage increased the stiffness of the soil. As a result，the relative stiffness ratio between soil and pile increased，leading to a stronger pile-soil interaction.

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A method for determinting the mechanical parameters of marine layersusing pressuremeter test

WANG Mingyuan1，SHAN Zhigang1，WANG Hanwu2，DI Shengjie1，CHENG Yonghui2

2016, 35 (S2): 4302-4309 doi: 10.13722/j.cnki.jrme.2015.1639

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For obtaining the exact mechanical parameters of marine layers，a new method was proposed based the pressuremeter test，its difficulty and the corresponding solution were also described clearly. The method for calculating design parameters from pressuremetertes was modified using the in situ contrast experiment on the land. Furthermore，the results from pressuremetertes in the sea were also compared with that ontained from vane shear test and standard penetration test. The research results can provide the calculation method for the marine structures foundation design on one hand，and can rich marine strata exploration methods on the other hand.

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Researches on the durability of the SH-(C+F+CaO) slurry applied to reinforce the cracks in earthen sites

CHEN Wenwu1，2，LIU Jian1，2，GONG Shuya1，2，YANG Guang1，2，WANG Dongyang1，2，LIN Gaochao1，2

2016, 35 (S2): 4310-4317 doi: 10.13722/j.cnki.jrme.2016.0871

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In order to explore the the grouting material which is suitable to reinforce the soil cracks in Northwest region site，We try to use a new material which is a mixture of SH-(rammed earth clay + fly ash + CaO)(SH- (C+F+CaO)).Through a serial of tests ，learn about its Slurry shrinkage deformation and aging strength. The durability of the slurry is evaluated through the temperature and humidity cycle test，the freeze-thaw cycle test，water stability test，stability test and the alkali resistance test. The shear characteristics of slurry-soil interface is estimated through the indoor simulation fracture grouting.The test results indicate that SH-(C+F+CaO) material has less shrinkage deformation，strong aging strength and good durability，and especially suitable for the Northwest region-specific alkaline environment. However，sodium sulfate weaken the material strength，so the material should be used with caution in the area of high concentration sodium soil sites. The shear strength of slurry-soil interface is strong as well as the undisturbed samples. The study shows that this material is suitable as northwest earthen crack grouting material.

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Microstructure research on cement stabilized clays

LIAO Yilei1，2，ZHANG Zixin1，2，XIAO Shihui3，LIU Kuan4，YANG Xiaorong3

2016, 35 (S2): 4318-4327 doi: 10.13722/j.cnki.jrme.2016.1292

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The micro structure of cemented soils，which is made from different original soils as well as with various cement contents，is investigated by ESEM method. Then，the data of pore such as the diameter，shape index and orientation angle are quantitatively analyzed via image processing technology. Comparing these data got from the loaded samples and unloaded ones，the connection between the strength of cemented soil and bearing mechanism is explored. The results show that the performance of pore diameter and pore shape is different before and after loading. Under the lowest cement content(5%)，shear contraction happens after loading，while pore diameter reducing and coefficient of pore shape increasing. However，shear dilation happens under the highest cement content(20%)，while pore diameter increasing and coefficient of pore shape reducing. During the loading process，under the interaction of internal stress，particles of cemented soils will directionally slide or rotate whether the cement content is lower or higher. Furthermore，pore axis direction of cemented soils is also changed，and orientation angle changed from uniform into concentration，and pore directional characteristic is obvious.

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Water migration regularity of self weight collapsible loess ground

SU Lihai1，2，YAO Zhihua2，HUANG Xuefeng3，LI Ning1，QU Yaohui4

2016, 35 (S2): 4328-4337 doi: 10.13722/j.cnki.jrme.2015.1512

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On basis of a large-scale in-situ soaking test in a self weight collapsible loess ground located in Lanzhou City，Gansu Province，volumetric water content recorded in real-time by TDR water meters was analyzed to research water migration morphology in the self weight collapsible loess ground with heavy section. The results show that，infiltration zone and saturated zone similarly take on a elliptical shape in the self weight collapsible loess ground，which would be associated without water injection hole. Water migration is not downward with permanent infiltration angle. The phreatic line is basically linear in advance，then becomes elliptical infiltration. The vertical penetration is faster than the radial penetration. When the moisture penetrates into the deeper soil layer，that vertical penetration will decrease and the radial penetration will increase which would be associated with joint and fissure. Vertical-horizontal ration of wetting front is larger at the beginning of soaking test. With the increase of soaking time，the vertical-horizontal ration decreases rapidly. After the infiltration front reaches 15 m，the vertical-horizontal ration decreases gently. The vertical diffusion coefficient shows a decreasing form of basic power function，and the radial diffusion coefficient shows a variation of“small-big-small”. The mathematical expressions of vertical and radial diffusion coefficient with change of soaking time are given. Analysis results would provide a test foundation to know water migration regularity of self weight collapsible loess ground and some scientific basis for collapsible deformation in self weight collapsible loess area.