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2016, 35 (S1): 0-0

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Analysis of influence of geometric parameters of columnar joints on tunnel stability by DDA

HAO Xianjie，FENG Xiating，CHEN Bingrui，JIANG Quan

2016, 35 (S1): 2593-2602 doi: 10.13722/j.cnki.jrme.2014.1407

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The complexity geometric features of columnar joint bring great difficulties for the evaluation of tunnel stability and failure pattern. Taking the plumose joint inside column as an example，on one hand，the mechanical properties is weakened for the existence of this type of joint，which leading to the increase of joint density，and on the other hand，the inlay characteristic of this type of joint is also very obviously，which could enhance its mechanical properties. Based on the in-situ investigation of the geometric distribution of columnar joints，the impact of these geometric features on the stability of columnar joints is studied using DDA and the failure pattern of columnar joints is discussed. The research results shows that：(1) When the angle of joint between the column and horizontal joint inside column is 90°，the tunnel stability is the worst，and when the angle is less than 20°，the tunnel stability is well. (2) The effects of joint space on the stability of underground tunnel mainly include two aspects，the ratio of joint spacing and the absolute value of the joint spacing. For the joint spacing ratio，with the ratio increased，the tunnel is more stable，and vice versa. For the absolute value of joint spacing，with increasing of it，the stress acting on the block is decreased，and the tunnel is more stable. (3) The joints inside the columnar joints are so well developed that the columnar will first break inside the column，and then it will break between columns. At last，the small columnar would collapse under the effect of gravity and excavation disturbance. In addition，for the crosswise joints are so well developed，large scale of collapse would happen in severe cases. The columnar joints at arch would also break under the tangential stress.

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End effects on strengths of rocks under true triaxial compression

YOU Mingqing

2016, 35 (S1): 2603-2607 doi: 10.13722/j.cnki.jrme.2015.0054

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Many true triaxial strength criteria for rock have been proposed；however，the true triaxial test data for evaluating the criteria are rare and also needed to verify. Strengths and deformation of Yamaguchi marble and Orikabe monzonite tested by Kiyoo Mogi exhibit strange phenomena：strength does not increase after an increase of 3 while 2 keeps a constant；2 has larger influence than 3 on the bearing capacity in ductile deformation. The abnormal strength property of Laxiwa granite is also discussed. A reasonable conclusion is that specimens compressed under high 3 are endured large axial deformation which may induce significant end effects from platens in 2-direction. The genuine effect of 2 on strength does not enhance with 3 after friction correction.

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Study of true triaxial strength of rock and modified method of Mohr-Coulomb criterion shape function

ZHANG Shihuai，WU Shunchuan，WU Haoyan

2016, 35 (S1): 2608-2619 doi: 10.13722/j.cnki.jrme.2015.0119

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Based on particle flow theory and PFC3D software，a bonded particle model(BPM) for Lac du Bonnet granite is generated and periodic boundary condition is applied. True triaxial tests are conducted by distortion of the periodic space. Constant mean stressand constant Lode angleare maintained. A new method for modifying Mohr-Coulomb criterion shape function is proposed. The three-dimensional failure envelope of sample is determined to study the limitations of Mohr-Coulomb criterion from three aspects：triaxial plane，biaxial plane， plane. The limitations of Mohr-Coulomb criterion are as follows. (1) Uniaxial tension strength predicted by Mohr-Coulomb criterion is higher. (2) Mohr-Coulomb criterion ignores the impact of the intermediate principal stress on strength of rock. (3) In the range of ，strength prediction made by Mohr-Coulomb criterion is smaller. According to the results of numerical tests，impacts of the intermediate principal stress on strength of rock are researched. Results show that，there is a general increase inat the low level ofuntil a plateau is reached. Then value of decreases at a higher level of. After taking impacts of the intermediate principal stress into account，Mohr-Coulomb criterion shape function is modified as a function of mean stress，which can predict the strength of triaxial compression and extension more accurately by comparingobtained from the fitting formula and the modified Lade-Duncan criterion. The research method and conclusion of this paper can provide a useful reference to the study of rock strength and have some practical significance for the engineering project.

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Experimental study on coal strain induced by methane sorption/desorption and effect of pore features

ZHU Jie，ZHANG Min，CHUAN Lijing，TANG Jun，ZHAO Fei

2016, 35 (S1): 2620-2626 doi: 10.13722/j.cnki.jrme.2015.0132

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The mechanical behavior of coal adsorbing/desorbing methane is an important issue in the mechanism of coal and gas outburst. The sorption/desorption deformations of coal samples，from No. 9 coal seam in Zhaogezhuang Mine of Kailuan Mines，under different gas pressures of sorption were observed by means of the test system for sorption-induced strain. Using mercury intrusion porosimetry(MIP) and nitrogen adsorption(NA) methods，the reasons for strain differentia of coal samples were analyzed. The experimental results show that methane sorption/desorption results in anisotropic swelling/shrinkage，and it takes a long time for coal strain to stabilize. Coal shrinkage increases quickly at the start of desorption period，and then it increases slowly. Gas pressure of sorption is greater，the more significant shrinkage of coal deformation due to gas desorption. Micropore amount and pore continuity in the coal samples are the important factors that control coal sorption/desorption deformation，the strain rate and residual strain of coal shrinkage.

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Development of nonlinear elasto-plastic constitutive model for rock based on Hoek-Brown yield criterion and its numerical implementation

SHU Cai1，2，SHI Feng1，2，HU Guozhong3，WANG Hongtu1，2

2016, 35 (S1): 2627-2634 doi: 10.13722/j.cnki.jrme.2014.1525

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In order to deal with the singularity of Hoek-Brown(H-B) yield criterion，a nonlinear elasto-plastic model based on the Hoek-Brown yield criterion was developed，where the stress was updated in the principal stress space and was mapped into general stress space，and the nonlinearity of elastic deformation was also taken into account. This method can serve as an accurate implementation of the Hoek-Brownyield criterion model. For the validation of the model，the user defined material(UMAT) code was redeveloped in Ls-dyna with Fortran programming language. With the building of 3D geometry of uniaxial compressive test model and Brazilian test model，the exact solution of the model based on H-B yield criterion including failure mode was implemented by deleting of elements whose effective plastic strain is up to a given value. Finally，the numerical results were compared with the experimental test and showed good agreement，which indicates a high accuracy of the presented model.

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Relations between macro- and meso-scopic mechanical parameters of granite based on actual distributions of mesocompositions

XU Jinming1，HUANG Dayong1，2，ZHU Hongchang1

2016, 35 (S1): 2635-2643 doi: 10.13722/j.cnki.jrme.2014.1448

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Rock is generally composed of various meso-compositions. The type and interaction between these compositions may affect the macro mechanical properties. Taking the Beishan granite as an example，the video images photographed during the laboratory test and the threshold segmentation technique were used to determine the actual types and locations of the various compositions. The particles and cements of the compositions were then assumed as disks and parallel bonds in simulation. The meso-scale mechanical properties were characterized with seven parameters，including the elasticity modulus，stiffness ratio and frictional coefficient of the particles，and the elasticity modulus，stiffness ratio，average normal and tangential strengths of parallel bonds. Macro-scale mechanical properties were characterized with three parameters，including the elasticity modulus，Poisson's ratio，and peak stress of the specimen. The particle flow code and the pixel and particle loops were combined to establish the particle flow model based on the actual compositions. Thirty-two orthogonal simulation tests were then conducted using the seven meso-mechanical parameters in a four level. The macro-meso mechanical relations and the adjustment method in calibrating the meso-mechanical parameters were thereafter proposed. It shows that the digital image processing techniques may be efficiently used to develop a particle flow model reflecting the actual distributions of the multi-compositions；there are good agreements between the elasticity modulus-modulus，Poisson's ratio-stiffness ratio，and peak stress-strength respectively in the macro- and meso-scales. A good correlation exists in the elasticity modulus-stiffness ratio-Poisson's ratio in the macro- and meso-scales. Because the distributions and mechanical features of the meso-compositions control the deformation/failure process，the results presented herein may provide references both in determining the meso-parameters and in estimating the macro parameters of rock materials.

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Research on long-term creep failure of brittle rock based on micromechanics

SHAO Zhushan，LI Xiaozhao

2016, 35 (S1): 2644-2652 doi: 10.13722/j.cnki.jrme.2014.1496

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Creep property is an important basis for evaluating long-term failure of rocks. Based on the model of micromechanics and law of crack growth in brittle rocks，combining the definition of damage in micromechanical and macroscopic scale，the linkage between microcrack growth and macroscopic strain is established，and the theoretical expression of stress-strain relationship and three independent stages of creep are derived. Relationships between stress and strain under different confining pressures are studied and the creep properties under step axial loading are analyzed，which both agree well with the experimental results. The rationality of micromechanical model is verified by the experimental results. The creep failure time and steady-state creep rate are studied at different constant stress states，which provides the important help for the evaluation of service life and design of underground structure under high geostatic stresses.

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Triaxial unloading creep experimental study of sandy mudstone

HUANG Xing1，LIU Quansheng1，2，3，KANG Yongshui1，PAN Yucong1

2016, 35 (S1): 2653-2662 doi: 10.13722/j.cnki.jrme.2014.1528

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In order to reveal the rheological mechanical characteristics of deep soft ground，triaxial creep tests unloading the confining pressure step by step with constant axial pressure of sandy mudstone are carried out. The axial，lateral and volumetric creep law of weak rock and the deviatoric stress–strain relationship in the process of unloading rheological are studied. The main conclusions are as follows. (1) The instantaneous deformation，creep deformation，ratio between creep and instantaneous deformation，proportion between creep and total deformation under each unloading step increase with the deviator stress，and the increment of creep deformation is larger under the lower confining pressure. (2) With the confining pressure unloaded gradually，vertical tensile micro cracks are induced in the internal of rock，micro cracks initiation and propagation will lead to larger lateral deformation at the confining pressure unloading transient，and will extent time-dependently in the creep process corresponding to the stress level，plastic deformation occurs at the same time. (3) The nature of the gradual failure under condition of rheological unloading is the damage accumulation with time，and accompanied by crack extension，which is called time-dependent damage and fracture. (4) As the confining pressure unloading step by step，the deviator stress，unloading steps in history and the experienced creep time increase，which results in the irrecoverable strain and damage of the rock sample increasing，the accumulated time-dependent damage and fracture are more intense，the rheological rate and creep deformation of the sample is bigger under which the axial load is smaller under this stress level，and the unloading effect and the rheological characteristics is more apparent，accompanied by significant lateral expansion at the same time，leading to remarkable creep dilatancy. (5) Unloading creep damage and plastic deformation has significant influence to subsequent mechanical behavior.

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Experimental study of pre-peak and post-peak stress relaxation behavior of silty mudstone

YU Huaichang，DONG Jinyu，LIU Handong，HUANG Zhiquan，SHI Guangcheng

2016, 35 (S1): 2663-2672 doi: 10.13722/j.cnki.jrme.2014.1538

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The pre-peak and post-peak stress relaxation tests under triaxial compression were conducted on silty mudstone samples from Badong Formation strata in the Three Gorges Reservoir area. The pre-peak stress relaxation of rocks was divided into elastic and yield stages，and the post-peak stress relaxation of rocks was separated into strain softening and residual strength stages according to the test results. The variations of relaxation magnitude，degree，time and rate of rocks with time in four stages were analyzed，and the differences between pre-peak and post-peak stress relaxation characteristics of rocks were investigated in detail. A damage variable was proposed considering the deterioration of relaxation moduli of rocks with time. A new nonlinear damage model was established by introducing the damage variable into three-parameter generalized Kelvin model. The Levenberg-Marquardt algorithm was used to identify the pre-peak and post-peak model parameters of rocks. The variations of model parameters in four stages were analyzed，and the differences between pre-peak and post-peak model parameters were investigated according to the identification results. Finally，the mechanisms of pre-peak and post-peak stress relaxation behavior of rocks were discussed. The results show that：(1) through comparing four values of relaxation magnitude，degree，time and rate of rocks among different stages，it is found that four values of paramters in the strain softening stage are larger than those in three other stages，which should be paid more attention in rock engineering. (2) The post-peak values of G1，G2 and H1 in 5–9 strain levels are 1–53 percent of corresponding pre-peak values in first strain level. (3) The influence of post-peak rapture on the viscoelasticity of rocks is the largest，followed by the viscosity，and that on the instantaneous elasticity of rocks is the smallest. (4) The values of G1 and H1 decrease sharply in the strain softening stage，and the value of G2 drops dramatically in the yield stage. (5) The pre-peak and post-peak stress relaxation behavior of silty mudstone is mainly derived from the initiation and growth of microfissures and the initiation，growth and coalescence of macrocracks in rocks，respectively. Therefore，the mechanisms of pre-peak and post-peak stress relaxation behavior of rocks are different.

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Research on rapid and long-runout mechanisms of rockslide debris using ring shear tests

ZHANG Ming1，2，WANG Zhengbo1，2，SUN Lin3

2016, 35 (S1): 2673-2681 doi: 10.13722/j.cnki.jrme.2014.1609

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Catastrophic event induced by rapid long runout rockslide debris occurs frequently in West mountainous areas of China. There is an urgent need to study transport mechanisms of this kind of geohazard. Taking the Wenjiagou rockslide debris triggered by 2008 Wenchuan earthquake for example，the paper studies the internal structure of its deposit through the gully exposed in the deposit. The result indicates that “inverse grading” structure is obvious in the deposit，and the mean size of grains gradually increases from the base to the surface. The ring shear test is used to model the long-shear course of grains at different depths during transport course. The results suggest that grain crushing is one of the main reasons leading to inverse grading structure of the deposits. During transport，the normal stress is largest at the base and progressively decreases from the bottom up to the surface. The grains at the base experiences maximum normal and shear stresses and are crushed to finest material. Accordingly，the frictional resistance of the grains at the base decreases，reducing the frictional resistance between debris and the ground. We term this process the “finer-base effect” and suggest that it may be one of the mechanisms leading to high speed and long runout of rockslide debris. The conclusions of this paper could be a scientific basis for hazardous forecasting of rapid and long-runout rockslide debris in mountainous areas in West China.

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Study on strength parameters of in-situ rock mass considering intermidiate principal stress

FAN Lei，HUANG Zhengjia，ZHOU Huoming，ZHANG Yihu，LI Weishu

2016, 35 (S1): 2682-2686 doi: 10.13722/j.cnki.jrme.2014.1628

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In order to research the strength characteristics of the surrounding rocks in deep tunnels and underground powerhouses，two series of in-situ true triaxial tests for basalt and schist rock masses were carried out. Then，based on Mohr-Coulomb and Mogi criteria，evaluation of strengthen parameters considering the intermediate principal stress was discussed. The research indicated that，according to the strength values of basalt and schist rock masses obtained by in-situ true triaxial tests，the Mohr-Coulomb criterion regression equations passed the F-test at a significance level of 0.05，however，the Mogi criterion regression equations passed the F-test at a higher significance level of 0.01. Therefore，using Mogi criterion may be better to analyze the in-situ true triaxial tests data. The values of strength parameter calculated by Mogi criterion considering the intermediate principal stress were higher 6% than the values calculated by Mohr-Coulomb criterion ignoring the effect of the intermediate principal stress. But，the values of strength parameter c calculated by Mogi criterion were lower 60% than the values calculated by Mohr-Coulomb criterion.

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FANG Xinyu1，XU Jinyu1，2，LIU Shi1，WANG Peng1

2016, 35 (S1): 2687-2694 doi: 10.13722/j.cnki.jrme.2014.1631

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Electrohydraulic servo test system was adopted to conduct the Brazilian disk splitting tests of granite specimens after heated. The failure modes，load-displacement curves and tensile strengths of granite heated to different temperatures (25 ℃–1 000 ℃) were compared and analyzed. The two parameters，radial modulus and thermal damage variable，were defined in order to study the thermal damage properties of granite under the condition of tensile failure. The results show that with the increase of heating temperature，a brittle-plastic transition occurs inside the granite specimens，of which the load-displacement curves vary from concave-shape to convex-shape. The tensile strength and radial modulus both show a downward trend and obvious staged characteristics，wherein the radial modulus grows up rather than decreases at 100 ℃. Similarly，the thermal damage variable increases with the growth of temperature on the whole，but shows negative at 100 ℃. At last，the thermal damage evolution equation and temperature-mechanics constitutive model suitable for the condition herein are deduced and discussed while the model curves basically match the experimental curves.

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Research on particle breakage of rockfill material based on modified Duncan-Chang model

LI Xuemei1，2，LI Hongwen1，3，ZHENG Minsheng1，2，ZHANG Xiaohua1，2

2016, 35 (S1): 2695-2701 doi: 10.13722/j.cnki.jrme.2014.1716

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Rockfill material shows obvious strength softening and dilantancy during shearing process，which can not be described effectively by the classic Duncan-Chang model. The better fitting results can be achieved by introducing modified Duncan-Chang model. The equation b－c = 0.25 is given as judgment criterion of whether the material has softened or not. Particle breakage level is connected with material strength and deformation by introducing Hardin breakage index. The results show that with the breakage level increasing，the strength decreases obviously，while deformation mostly depends on confining pressure. Based on improved Duncan-Chang model，the relationship between dilatancy d and stress ratio is given. Compared with existing theories，it shows more reasonable and convenient.

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Acoustic emission study on frozen sandy mudstone in Brazilian splitting test

LIU Bo1，2，ZHANG Gong1，LI Shouding3，LI Xiao3，XU Wei1，YANG Weihong1

2016, 35 (S1): 2702-2709 doi: 10.13722/j.cnki.jrme.2014.1747

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The physical-mechanical properties and the damage mechanism of frozen sandy mudstone in the low temperature are significant to the deep shaft construction in water-rich western China. Based on Meilin Temple mining projects in Ordos of Inner Mongolia，sandy mudstone in depth of more than 690 meters is selected to study Brazilian splitting tests under three different temperatures. Furthermore，acoustic emission apparatus is utilized to monitor the changes of AE energy，acoustic emission(AE) amplitude and peak frequency during the tests with the increase of load. The results show that temperature is critical to the degradation effect of sandy mudstone，and the splitting tensile strength of －20 ℃ sandy mudstone reduces by 37.47% and 29.2%，compared with samples at room temperature and －10 ℃，respectively. The phenomenon of crack compaction is found in early loading period at room temperature，and the changes of three different kinds of AE parameters verifies each other during the tests and the whole damage process of sandy mudstone can be described. The damage evolution based on cumulative AE energy reflects the process of internal fracture generation-propagation-transfixion -failure，which is used to evaluate the damage degree of frozen sandy mudstone and to afford a new thought for the real problems of seepage and mine flooding in actual artificial freezing engineering.

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Hydraulic fracture prediction theory based on the maximum tangential strain criterion

TANG Shibin，ZHANG Heng

2016, 35 (S1): 2710-2719 doi: 10.13722/j.cnki.jrme.2015.0029

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A maximum tensile strain criterion is proposed to study the crack growth of hydraulic fracturing，which incorporates the effect of T-stress on crack growth. The critical water pressure and crack initiation angle at the onset of crack growth are studied. Furthermore，the effects of crack inclination angle，confining pressure，fracture process zone，T-stress and Poisson's ratio on the critical water pressure and crack initiation angle are also analyzed. The results show that the critical water pressure increases while crack initiation angle decreases with the increase of confining pressure，the radius of fracture process zone and Poisson's ratio. T-stress has little effect on propagation of fracture driven by water pressure. However，it is significantly effect on the propagation of crack driven by external loading. The theoretical results well agree with experimental data，which indicates the importance of considering the T-stress in the crack initiation criterion.

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Experimental study on hydraulic fracture geometry of tight sandstone from Xujiahe group

WEI Yuanlong1，YANG Chunhe1，2，GUO Yintong2，LIU Wei1，WANG Lei2，HOU Zhenkun1，XU Feng2

2016, 35 (S1): 2720-2731 doi: 10.13722/j.cnki.jrme.2015.0114

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To investigate the propagation characteristics and spatial distributions of hydraulic fractures of tight sandstone，the large real traixial physical model experiment system has been selected to conduct hydraulic fracture tests on the outcrop tight sandstone samples drilled from Xujiahe Group，Jiannan Area. Based on the tests results，the mechanism of crack extension and initiation is exposed and bedding plane with the fracture morphologies has been analyzed. Also，the effects of types and delivery capacity of fracture fluid and differential parameters of in-situ stress on the fracture morphology have been discussed. The results indicate that hydraulic fractures of tight sandstone are easy to extend along one direction and present single-wing style，so they are less likely to form crossover crack network. As to tight sandstone，the rock properties play important roles in controlling initiation and extension mode of fractures. In summary，there are four kinds of hydraulic fracture initiation modes and six kinds of extension mode. And，pumping pressure-time curves can be divided into four types：the 1th curve type is correspinding to single-wing，planar crack；the others are belonged to network crack. The fracture pressure has a linear relation with delivery capacity，and it is irrelevant to differential parameters of in-situ stress. Its worth mentioning that leak-off effect should not be considered unless distilled water is employed as fracture fluid.

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Modification of Hoek-Brown criterion and its application

LI Shuobiao1，2，XUE Yadong1，2

2016, 35 (S1): 2732-2738 doi: 10.13722/j.cnki.jrme.2015.0210

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Hoek-Brown failure criterion has prominent advantages. However，when using the criterion，it is difficult to accurately obtain disturbed factor D and geological strength index GSI-value，that are the two main parameters in the criterion. According to this，This paper puts forward a convenient and accurate method to determine the two parameters，after summary analyzing scholars improvements of the traditional Hoek-Brown criterion. To get the disturbed factor D，this paper uses the square of ration between P-wave velocity of rock mass and rock. Then to obtain the GSI-value，this paper uses the relationship between the P-wave and rock mass rating RMR-value. Further，This paper puts the formulas of D and GSI into Hoek-Brown criterion to obtain a new modified criterion. In order to verify the modified criterion is reasonable，rock mass physical-mechanical parameters are respectively calculated by modified criterion and Hoek-Brown criterion for comparison，basing on the Yellow River Maerdang hydropower station dam foundation rock mass engineering case. The results of the two criterions show the same trend and the numeral difference is very small. Therefore，the modified criterion can satisfy the engineering application. Especially，it can be used to quickly and accurately calculate the two main parameters in Hoek-Brown criterion，and then calculate the mechanical parameters of rock mass.

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Experimental study on deformation and strength properties of hollow cylindrical specimens of limestone under compression

SU Chengdong1，2，LI Bingyang1，WU Qiuhong3

2016, 35 (S1): 2739-2748 doi: 10.13722/j.cnki.jrme.2015.0308

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A series of uniaxial and pseudo-triaxial compression tests on hollow cylinder specimens with 50 mm in outer diameter and 6–25 mm in inner diameter were carried out to study the effects of nonuniform stresses on the deformation，strength and failure characteristics. The test results show that：(1) There is no significant difference among peak strength，elastic modulus and hole diameter under uniaxial compression，failure patterns of specimens are tensile-shear failure，the hole remain hasn’t occur to collapse；(2) The effect of inner diameter on deformation characteristic isnt obvious before yield stage under the triaxial compression，but it has significant effect on the deformation characteristics of post-peak strength. There is no obvious difference between elastic modulus，inner diameter and and confining pressure；(3) The material strength of modified Coulomb prediction is more about 11% than uniaxial compression peak strength，which equals to regression results of intact specimen and has no direct connection to inner diameter and confining pressure. The effect of inner diameter and confining pressure is complex，when material strengths are predicted by modified twin-shear strength criterion. The predictive value of material strength is no significant difference between hole diameter and confining pressure when the inner diameter is less than 11 mm，it decreases as the inner diameter or confining pressure increase when hole diameter is more than 16 mm；(4) The failure characteristic of hollow specimens are affected by hole diameter and confining pressure under triaxial compression，the bearing capacity will decrease when the inner diameter is bigger.

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Non-equilibrium effect of rock under quasi-static loading condition

WANG Xinyu1，SHAO Zhushan1，SONG Lin1，2

2016, 35 (S1): 2749-2757 doi: 10.13722/j.cnki.jrme.2015.0652

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Rocks possess viscosity property，which cannot be ignored. Deformation behaviors of rock-like materials display the characteristics of the rate-dependence，which manifest macroscopically non-equilibrium nonlinear effect of elastic aftereffect，creep，and relaxation. Based on the classic Preisach-Mayergoyz space theoretical model，anelastic mesoscopic unit(AMU) possessing time-dependent peculiarity is introduced to obtain the modified PM theoretical model. By adopting the modified PM space model，characteristic of stress-strain curves with different loading rates and the non-equilibrium effect are studied in detail. Finally，experimental approach to obtain the deformation-time curve of the AMU and reconfiguration of the modified PM space is proposed. Results obtained in this paper indicate that，the area of stress-strain hysteresis loop increases with increment of loading rate. The larger the loading rate，the longer the time is taken for the sample to reach equilibrium state.

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Distribution and control technology of rock damage induced by air-deck charge presplitting blasting

ZHU Qiang1，2，CHEN Ming1，2，ZHENG Bingxu3，YAN Peng1，2

2016, 35 (S1): 2758-2765 doi: 10.13722/j.cnki.jrme.2014.1465

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Presplitting blasting with air-deck charge has been applied as a new contour blasting technique，but the rock damage characteristics of which has severely limited its application prospect. The air-deck charge presplitting blasting experiment has been conducted in Jingshansi iron mine. And the rock damage characteristics was studied by using a method of combining acoustic detection with numerical simulation. It is reported that there were significant differences between air-deck charge presplitting blasting and traditional presplitting blasting in the distribution of rock damage. The damage zone size of the rock near the charging section was much larger than that near air section，which was also larger than the rock damage zone size in traditional presplitting blasting. There was smash district in remaining rock near the charging section. While in some intact rock mass，the damage zone of the rock near air section was not obvious. Taking advantage of indirect initiation and casing charge structure could be benefit to decreasing the rock damage effects of presplitting blasting with air-deck charge.

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Research advances of tunnel boring machine performance prediction models for hard rock

LIU Quansheng1，2，LIU Jianping1，PAN Yucong1，KONG Xiaoxuan2，

2016, 35 (S1): 2766-2786 doi: 10.13722/j.cnki.jrme.2014.1601

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With significant sensibility to the varying geological conditions and enormous financial investment in the earlier phase of tunneling project，predicting of TBM performance accurately with special geological conditions has a crucial importance for selecting tunnel construction method，arranging construction schedule and assessing excavation cost. In this study，the hot topic on research advances of TBM performance prediction models both at home and abroad are systematically reviewed firstly，and the widely adopted ones are introduced detailedly. The results based on the statistical counting of the occurrence frequency of rock mass properties and machine parameters used in 17 models including theoretical models and complex empirical models show that the dominating rock mass properties affecting TBM performance include discontinuity spacing，intact rock uniaxial compressive strength， angle between the discontinuity and tunnel axial，tunnel diameter and rock brittleness，etc. And the main machine parameters contributed in the performance predictions are mostly thrust per cutter，rotating speed of cutterhead，cutter diameter，cutter spacing，cutter tip width and angle of contact area between rock and disc cutter，etc. The influence of each controlling parameters on TBM performance prediction is discussed based on the statistical results. Finally，according to the developing history of the foreign prediction models，some useful suggestions are put forward for the development of TBM performance prediction models in China.

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Stress from crystllization in ideal pores

JU Xiaodong1，FENG Wenjuan1，ZHANG Yujun2，ZHAO Hongbo1

2016, 35 (S1): 2787-2794 doi: 10.13722/j.cnki.jrme.2015.0723

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For those rock-like brittle porous media，the water or salts crystallization states in pores are depend on factors as crystal type and pore shape，especially for the latter one，which control the whole crystal growth process and the magnitude and distribution of crystallization pressure between pore wall and crystal. Four kinds of ideal pore shapes were generalized from actual pores based on former researches as cylinder，sphere，elliptic cylider and ellipsoid. Cuvatures and key curvatures of these ideal shaps were calculated with the principles of differential geometry，and then formulas for the calculation of crystallization pressure magnitude and distribution within crystallization process were proposed. At last，took the crystallization of NaCl in elliptic cylindrical and ellipsoidal pores of different specifications for examples，calculated the distribution and variation of crystallization pressure within the growth of NaCl crystal，then compared and analysed the effects of specification on crystallization pressure.

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Experiment study of synergistic anchorage efficiency in anchorage body with preload bolt

LONG Jingkui1，2，LIU Yutian3

2016, 35 (S1): 2795-2802 doi: 10.13722/j.cnki.jrme.2015.0864

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In order to study the synergistic anchorage efficiency in the anchorage body with preload bolt，a set of specimens are made under laboratory conditions. By applying various preload to the bolt，the experiment analyzes the stress value at different measuring points within the anchorage body and the features of stress distribution. It proves the objective existence of the synergistic anchorage efficiency in the anchorage body，puts forward the concept of synergistic index，and develops its calculation formula. In this way，the evaluation method of the synergistic efficiency is established. The study shows that the scope of synergistic anchorage efficiency within the anchorage body takes the shape of an ellipse，and increases when the preload rises. It is inferred that the bolt preload plays an important role in enhancing the synergistic anchorage effect in the anchorage body，expanding the scope of synergistic anchorage efficiency，and improving its strength and stiffness.

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Algorithm and simulation methods for the soft longitudinal joint of the concrete faces in high concrete-faced rockfill dams

ZHOU Mozhen，ZHANG Bingyin，WANG Wei

2016, 35 (S1): 2803-2810 doi: 10.13722/j.cnki.jrme.2015.0943

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In high concrete-faced rockfill dams(CFRDs)，soft longitudinal joint is an engineering measure widely applied to avoid extrusion damage of the concrete faces. Based on analyzing the compressive features of the soft filler in normal direction，a bilinear compression model was proposed. During the simulation，the soft longitudinal joints are treated as soft contact interfaces，where the penetration represents compressive displacement. Applying the computational contact mechanics，the perturbed Lagrange formulation was proposed to develop a soft joint contact algorithm. The effectiveness of this algorithm was verified by a three-dimensional contact patch test，and then it was applied to Tianshengqiao–I CFRD in China. The numerical results show that soft longitudinal joints can significantly reduce the axial extrusion stress of the concrete faces.

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Test investigation of triaxial compressive strength of coarse sandstone after high temperature

XU Chongbang1，ZHOU Hesheng2

2016, 35 (S1): 2811-2818 doi: 10.13722/j.cnki.jrme.2015.1328

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The mechanical property，specimen quality and wave velocity of coarse sandstone after different high temperature be test studied by the servo-controlled testing machine RMT–150B and ultrasonic nondestructive testing instrument TUA2000A. The test results show that：(1) The wave velocity of rock is nonlinearity deducing with temperature increase，ranges of reduction of stage from 400 ℃ to 800 ℃ is the maximum. (2) Quality of specimens is deducing with temperature increase，the quality loss maximum is smaller，therefore，the effect of temperature on quality of specimens could be ignored. (3) It is still a strong liner relationship between the triaxial compressive strength and the confining pressure to coarse sandstone after high temperature，its confining coefficient is a constant，and the theoretical value of uniaxial compressive strength is expressed by the quadratic polynomial on temperature and confining pressure. (4) Its internal friction is a constant without change to high temperature，and the cohesive strength be controlled by high temperature. (5) The theoretical formula about triaxial compressive strength be established with the valve value of temperature and confining pressure，and it accurately reflects the relationship between the strength and temperature，confining pressure

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Research on influence of initial horizontal principal stress on stress shadow

XIA Lei，ZENG Yawu，JIN Lei，YE Yang

2016, 35 (S1): 2819-2825 doi: 10.13722/j.cnki.jrme.2015.1555

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The concept and theory of stress shadow were introduced. The particle discrete element model was constructed with the fluid-solid coupling calculation. The distribution of the induced stress due to the stress shadow around a single hydraulic fracture was simulated and analyzed. The analysis shows that the mainly effect of stress shadow is the increasing of the minimum horizontal stress，and the effect has dual character. The effect of initial horizontal stress on hydraulic fracture was analyzed using the established model. The result shows that the induced stress due to the stress shadow was increasing with the increasing of the ratio of the initial horizontal principal stress，and it was more disadvantageous to the dehiscence and development of the new fractures. When the hydraulic pressure in the initial fracture was closed to or greater than the maximum initial horizontal stress，the propagation direction of the hydraulic fracture caused by the infusion holes would be changed，and it was conductive to the formation of a complex fracture network.

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Experimental research on size effect of acoustic emission location accuracy

XU Jiang1，2，LI Yi1，2，TIAN Aoxue1，2，QU Jiamei1，2

2016, 35 (S1): 2826-2835 doi: 10.13722/j.cnki.jrme.2015.0921

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Using PCI–2 type acoustic emission(AE) testing system to experiment the pencil lead break test under different sizes specimens in order to study on the size effect of acoustic emission location accuracy. The results suggested that：When using absolute value analysis method for analyzing processing data，as for the same plane， the bigger size，the greater average position deviation but the less location accuracy. When using the data normalization analysis method，as for the same plane，the relative error of 100 mm specimens is minimal. At the same time，combining with the relative error and the better points analysis results，it showed that it is better to use 100 mm specimen when someone need to carry out the rock acoustic emission location experiment. While it also showed that different point location also can make great influences on emission location accuracy. The closer distance to the boundary，the greater average position deviation is. After projected the coordinates of each point into three-dimension and analyzed，it can be seen that the value of perpendicular direction vector is variable， but the direction is fixed which means all of them point to the specimen internal. As for the parallel vectors，the value and the directions are variable. When compared the value of perpendicular direction vectors with parallel vectors，perpendicular direction vectors must be larger than parallel vectors.

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Study of borehole geometric shape features under plane stress state

WANG Chuanying，HAN Zengqiang，WANG Jinchao，WANG Yiteng

2016, 35 (S1): 2836-2842 doi: 10.13722/j.cnki.jrme.2015.1045

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Stress relief method is a widely applied method in the measurements of deep crustal stress. In this method，the crustal stress is usually calculated by using the quantitative relationship between borehole deformation and crustal stress. The study object of this research is geometric shape features under plane stress state. In order to solve the geometric shape issues of elastic objects structure which is not considered in theory of elasticity，strict mathematical derivation and transform is determined based on high geometry theory and elasticity theory. The conclusion is proved that geometric shape of borehole after deformation is ellipse and the standard elliptic equation is derived. Through the research on ellipse geometric shape features，a method how to get ellipse geometric parameters is put forward and a crustal stress calculation formula is transformed based on ellipse geometric parameters. In the last，a simulation example is used to analyze this method，the result show that the method is feasible and the stress calculation formula is correct. Through the research of relationship between borehole geometric shape and stress，a new stress measurement theory based on borehole geometric shape is constructed. The research is of great important to measurements of deep crustal stress.

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Testing study of rheological characteristic of marble being in residual strength stage

LIU Zhiyong1，2，ZHUO Li1，2，XIAO Mingli1，2，XIE Hongqiang1，2，HE Jiangda1，2

2016, 35 (S1): 2843-2852 doi: 10.13722/j.cnki.jrme.2015.1150

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The diversion tunnel of Jinping II hydropower station contains marble and has large burial depth and high geostress，which give rise to the marble has prominent rheological phenomenon. Part of the engineering rock mass is in residual strength stage，so it is significant to understand the rheological characteristic of marble being in residual strength stage. Triaxial creep tests were carried out for the marble samples which had experienced triaxial compressive full tests. Based on the tests，the creep characteristic and long-term strength of the marble being in residual strength stage were systematically discussed. The study showed that the marble has transient deformation，decelerating creep stag and steady-state creep stage with different confining pressure. Attribute to a plenty of fractures，for the marble being in residual strength stage，the capacity of transient deformation and creep deformation is heavy stronger than that of the intact marble. The whole creep deformation and the steady creep speed increase with deviatoric stress. Furthermore，long-term strength of marble，less than instantaneous strength，improve when confining pressure increasing. Due to the weakening in the creep process，the samples mostly do not have cohesion and the frictional angle enhance，compared with the samples which had gone through triaxial compressive full tests but not creep tests. Therefore，it is reasonable to disregard the cohesion in significant engineering. Eventually，based on the creep characteristics of the marble，the Burgers model was treated as theoretical model to fit the processed creep curves，the parameters were obtained by Levenberg-Marquardt algorithm. At the same time，the evolution of the parameters of the Burgers model also were discussed. The research showed that the Burgers model has a perfect agreement with experiment data，which fully reflects the rheological characteristic of the marble being in residual strength stage. Moreover，for the marble being in residual strength stage，the parameters of the Burgers model exhibit the characters of nonlinear. With the deviatoric stress increasing，elastic modulusand viscous coefficientdecrease and viscoelastic shear modulusand viscoelastic coefficientincrease at first and then decrease.

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Development and application of fracturing and seepage experimental system for multi-physical field and multiphase coupling of porous media

YIN Guangzhi1，2，3，LI Wenpu1，2，3，XU Jiang1，2，3，LI Minghui1，2，3，WANG Weizhong1，2，3，LI Xing1，2，3，JIANG Changbao1，2，3，DENG Bozhi1，2，3

2016, 35 (S1): 2853-2861 doi: 10.13722/j.cnki.jrme.2014.1490

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Fracturing and seepage experimental system for multi-physical field and multiphase coupling of porous media was self-developed. The system consisted of host，electrohydraulic servo pumping station，gas pressure and water pressure supply system，measurement and control system. The maximum axial stress is 1 000 kN and the maximum confining pressure is 60 MPa，and two kinds of specimen size are 50 mm×100 mm and 100 mm×200 mm. Characteristics of the system are illustrated as follows. (1) The experimental research of multi-physical coupling of porous media can be performed under different in-situ stress and mining stress and temperature and fluid pressure conditions. (2) The hydraulic fracturing test could be conducted and the change of permeability before and after fracturing can be measured accurately. (3) The seepage test of porous media of hydrosphere multiphase fluid can be performed under different in-situ stress and mining stress conditions. (4) Vacuum system is designed to precisely control the test conditions，it can control vacuum of system internal. (5) The system main component confining pressure chamber is designed of lifting on the hoisting mechanism to limit the displacement，it realizes system security of test operator and test system and test environment. Based on this experimental system，conventional triaxial loading and hydraulic fracturing test was performed on the raw coal and sandstone specimen and its reliability was verified. The experimental system can be used to provide theoretical basis for the seepage and enhanced permeability mechanism of reservoir under multi-physical field coupling conditions. The research has an important guiding significance on controlling of deep coal and rock dynamic disasters and enhancing recovery of unconventional gas.

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Laboratory test research on borehole strain and electrical resistivity response characteristic of coal samples in hydraulic fracture process

MA Yankun，LIU Zegong，CHENG Yunhai，ZHOU Jian，WU Hao，SUN Jian

2016, 35 (S1): 2862-2868 doi: 10.13722/j.cnki.jrme.2015.0157

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In order to analyze damage evolution state of coal sample in hydraulic fracture process，a joint test method combining borehole strain and electrical resistivity has been proposed. The borehole strain and electrical resistivity response characteristic of coal samples in hydraulic fracture process have been studied with self-developed hydraulic fracture experimental system. The curves of borehole strain，electrical resistivity and water pressure have been obtained while the response mechanism is analyzed. The results show that there is strong regularity in borehole strain and electrical resistivity curves. The borehole strain curves show “V” shape while the electrical resistivity curves show “” shape. When water takes up the space of borehole，the electrical resistivity of coal samples reaches the minimum value. When the borehole fractured，borehole strain and electrical resistivity increase to the maximum value gradually. Borehole strain reflects the deformation characteristic of borehole during hydraulic fracture process while the electrical resistivity reflects the initiation and development of fissure inner coal samples. Volume fracturing of coal samples causes the dilatation of fissure，resulting in sudden change of electrical resistivity. The curves of borehole strain，electrical resistivity and water pressure have rich information for fracturing of coal sample in hydraulic fracture process. And it provides a new method to analyze initiation behavior of coal sample in hydraulic fracture process.

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The evolution of sandstone energy dissipation under cyclic loading and unloading

DENG Huafeng1，2，HU Yu1，2，LI Jianlin1，2，WANG Zhe1，2，ZHANG Xiaojing1，2，HU Anlong1，2

2016, 35 (S1): 2869-2875 doi: 10.13722/j.cnki.jrme.2015.0278

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To analyze the evolution law of rock energy dissipation，a series of uniaxial cyclic loading and unloading tests for sandstone have been designed and conducted. The typical cyclic loading and unloading hysteresis loop characteristic curve has been analyzed in detail，the variation and relationship of the total power，the elastic deformation energy，dissipated energy，energy dissipation rate，residual strain，damage variable and some other parameters during loading and unloading process have been discussed. The results showed that：(1) during cyclic loading and unloading process，the stress-strain hysteresis is obvious，and there is significant residual strain，whose effects should be considered in the calculation of the energy parameters. (2) Considering the impact of residual deformation and hysteresis effects，modified calculation methods of energy parameters during cyclic loading and unloading process have been proposed. (3) When rock samples is close to failure during the cyclic loading and unloading process，there is a significant increase for the energy parameters and residual strain，and the energy parameters and residual strain can effectively predict the destruction of rock samples. (4) The correlation of energy dissipation rate and residual strain shows from another perspective that the residual strain cannot be ignored in the calculation of energy parameters. The research results have a good reference value for the analysis of rock damage evolution law during cyclic loading and unloading process.

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Experimental study on physico-mechanical properties of grouted completely weathered granite

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

2016, 35 (S1): 2876-2882 doi: 10.13722/j.cnki.jrme.2015.0378

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In order to study the physico-mechanical properties and slake durability of grouted completely weathered granite，triaxial shear test，permeability test and slake durability test were carried out with different grout filling ratios. The test results show that stress-strain curves transform from strain-hardening to strain-softening when the grout filling ratio increasing. With the increase of grout filling ratio，the cohesion and deformation modulus increase exponentially，and internal friction angle varies in parabolic form，while permeability coefficient decreases in the form of negative exponential. Based on these test results，regression equations of cohesion，internal friction angle，deformation modulus and permeability coefficient to grout filling ratio are established respectively. And the mechanism of grouting for reinforcement and water sealing has been discussed briefly. The research results have a guiding significance for the evaluation of grouting effect and determination on the grouting scheme and quantity.

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Study on deformation mechanism and energy dissipation of rock creep under step loading

XIN Yajun1，2，LI Mengyuan1

2016, 35 (S1): 2883-2897 doi: 10.13722/j.cnki.jrme.2015.0724

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Based on analysis of deformation mechanism and energy conversion in rock loading-creep-unloading，the creep tests of step uniaxial loading on two groups samples were operated by RLW–2000 rock triaxial rheometer. The rock energy dissipation was analyzed in different strain differences，the relationship of different loading level(or cycle number) and deformation modulus were determined，and curve paths of loading creep and unloading stress were studied. The results showed that energy conversion had two parts of loading strain and creep one in step-loading rock creep. With strain difference of every loading increasing，rock plastic strain and dissipation energy increased nonlinearly，and the opens，strain differences and loss rock energy of plastic strain and dissipation energy curves increased. In same loading，rock plastic strain energy was larger than dissipation one，and the relationships of strain difference and plastic strain energy，dissipation one，can be described by quadratic polynomial and power function respectively. Rock deformation modulus increased from abruptly to slowly，and then relative gently with loading level(or cycle number) increasing，and deformation modulus of the higher-strength rock was larger than the lower one in same loading level(or cycle number). Rock loading creep strain and unload stress relaxation increased with loading level increasing，the creep strain in higher-strength rock was less than the lower and stress relaxation went by contrary in same loading level. Loading curve of the higher-strength rock was cross the stress relaxation zone of last step unloading，and the lower one cross the creep strain zone.

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Experimental research on mechanical properties of western Hubei-Eastern Chongqing carbonaceous shale cap rock under unloading stress path

HUO Liang1，YANG Chunhe1，2，MAO Haijun2，LIU Junxin3，YUAN Yusong4

2016, 35 (S1): 2898-2906 doi: 10.13722/j.cnki.jrme.2015.0148

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Western Hubei-Eastern Chongqing region is a major exploration block of oil and gas. The area has been suffered long term uplift and erosion，which may resulted in cap rock failure. To investigate the sealing effectiveness of cap rock during geological evolution，a series of triaxial unloading tests of shale samples have been conducted under initial confining pressures of 10，20，30，40，50 MPa. The results show that under different confining pressures，the unloading properties of carbonaceous shale are as follows. During unloading process，lateral strains are greater than axial strains under lower confining pressure，with the increase of confining pressure，lateral strains are less than axial strains；Strength values and strength parameters of unloading tests are both higher than those obtained from conventional triaxial compression tests；The fracture modes are obviously affected by the initial confining pressure：under low initial confining pressure，samples split into several large pieces；with the increasing of confining pressure，the fracture modes gradually transfer to main shear failure；under the confining pressure of 40 MPa，the fracture mode is characterized by occurrence of cracks-net；Also，rupture coefficient of lateral pressure is proposed to evaluate sealing effectiveness of cap rock. Based on the results of tests and erosion thickness of Western Hubei Eastern Chongqing area，we could conjecture that north of Shizhu composite anticline and west of Fangdou Mountain composites syncline are favorable place for exploration.

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Experimental study of different shape bedrock surfaces about deformation and failure of soil and rock mixture

SUN Yongshuai1，2，HU Ruilin1

2016, 35 (S1): 2907-2914 doi: 10.13722/j.cnki.jrme.2015.0184

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Soil-rock mixture landslide is one of the most common disasters types in the mountain. The deformation and failure of landslide are usually affected by the relatively stable bedrock interface，which is called as the bedrock surface. Based on it，the test is carried out through an in-house developed large shear test for studying the influence of the different shape bedrock surface on the stability of slope. The results show that the change value of the pore water pressure and earth pressure increase firstly and then decrease. Because of the internal soil-rock structure changes and fissure changes of soil & rock mixture，the curve of the pore water pressure change value and earth pressure change value will fluctuate for some times after the maximum value. When the shape of bedrock surface is straight，the intersection angle between bedrock surface and sliding surface is smallest，the maximum shear stress is largest，it needs to take the longest time when pore water pressure change value and earth pressure change value reach the corresponding maximum value. When the shape of bedrock surface is stepped，the intersection angle between bedrock surface and sliding surface is largest，the maximum shear stress is smallest，it needs to take the shortest time when pore water pressure change value and earth pressure change value reach the corresponding maximum value.

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Model test and analysis about loose failure of tunnel surrounding rock mass containing weak interlayer

HUANG Feng1，2，ZHU Hehua3，XU Qianwei4

2016, 35 (S1): 2915-2924 doi: 10.13722/j.cnki.jrme.2015.0200

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Since weak interlayer often has a deterministic effect on the stability of tunnel surrounding rock mass. Its formation mechanism and area of loosening and failure zoon are the important basis for deciding reasonable support method. By taking a high way tunnel engineering through faults，lab similar model test was chosen to study the progressive process of surrounding rock mass loosening and failure zoon with weak interlayer in the case of no support system. An elasto-plastic damage constitutive model is introduced to numerically simulate the case of model test by FEM，which will be compared with model test. The study shows that：(1) the loosening zone and failure one of tunnel surrounding rock mass have similar formation mechanism with each other，which are initialize at lower part and expanded to upper one with arch shape because of the impact of interlayer. (2) The surrounding rock mass stress variations of upper part are obviously bigger than those of lower one after tunnel excavation. Based on the value of tangential stress increment，the area of loosening zone can be determinate. (3) Discriminating by damage variable in numerical analysis，the failure zoon of surrounding rock mass has a good agreement with that of model test，which is proved theoretically feasible.

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Centrifugal model test on seismic response of colluvial landslide reinforced by cantilever anti-slide pile

TU Jiewen1，LIU Hongshuai2，TANG Aiping1，ZHENG Tong3

2016, 35 (S1): 2925-2934 doi: 10.13722/j.cnki.jrme.2015.0306

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Centrifuge shaking table model test of colluvial landslide reinforced by cantilever anti-slide pile was designed and carried out on a centrifuge shaking table at 50 gravitational accelerations in order to research its seismic response，the distribution regularity of dynamic soil pressure after pile and dynamic bending moment of the anti-slide pile. During the processing of the model test，bedrock wave(Qingxi wave) was inputted from the bottom of the model by scaling the amplitude of the input seismic wave. The seismic performance of colluvial landslide reinforced by cantilever anti-slide pile under earthquakes of different intensities is studied by monitoring the acceleration response of landslide at different positions，the dynamic soil pressure after pile and the strain of the anti-slide pile. Results show that the acceleration response of landslide increases with the increasing height of landslide. The landslide shows an obvious elevation amplification effect，i.e.，the increasing rate of the peak ground acceleration(PGA) amplification coefficients becomes notably larger approaching the slope crest，and the acceleration response characteristic of the landslide surface shows the surface effect under earthquake. The dynamic response of the soil is restricted by anti-slide pile to a certain degree. The dynamic soil pressures after pile rapidly increase to peak value and then keep roughly stable along with the excitation of earthquake motion. And they will form dynamic soil pressures to act on the anti-slide pile. The maximum dynamic bending moment of the pile appears near the bedrock surface，which the distribution rule reflects the convex form. Both the dynamic soil pressure after pile and dynamic bending moment of the pile will increase with the increasing the strength of seismic wave. The results provide a good foundation for seismic design of the cantilever anti-slide pile.

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Simplified calculation method and affecting factors analysis of h-type anti-slide pile

ZHANG Yongjie1，2，ZHOU Huan2，FENG Xiating1，WANG Guiyao2，LI Shaojun1

2016, 35 (S1): 2935-2943 doi: 10.13722/j.cnki.jrme.2015.0701

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The h-type anti-slide pile used in large landslides treatment is divided into two sections according to its bearing and deformation characteristics，which are the anti-slide section and anchorage section. Their bearing and deformation analysis models with the action of the landslide thrust were proposed based on the effecting characteristic of rock-soil mass to the front or back row piles. And their simplified calculation methods of internal force and deformation were also established based on the structure mechanics and pile foundation analysis theory. Then，the simplified calculation method of h-type anti-slide pile was presented. Finally，the influence rules of different loading conditions，pile section size，pile spacing，anchorage depth and other factors to the h-type anti-slide pile internal force and deformation were analyzed by the typical engineering example. The results show that the calculation results with these two methods are more in line with the actual engineering situation and close，which one is calculated by considering the rock-soil mass action force between the front and back row piles and another by distributing the landslide thrust with the proportional coefficient. The affection of cantilever length and landslide thrust to pile internal force and deformation are the greatest. The affection of pile section size to the pile top deformation is more than to the internal force. The cantilever length and landslide thrust should be determined reasonably during optimal design. The anchorage section length can be determined between 1/3 and 1/2 times of pile length. The transverse beam rigidity can be selected between 1.0 and 2.0 times of pile rigidity. And the piles space can be designed between 2.0 and 4.0 times of pile diameter in order to make the rock-soil mass between piles produce pressure and resistance or transfer landslide thrust.

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Research on the behavior and mechanism of the slate from the slope at the gully of debris flow respond to climate environment

CUI Kai1，2，WU Guopeng1，WANG Xiuli1，CHEN Wenwu2，LU Haimin2

2016, 35 (S1): 2944-2952 doi: 10.13722/j.cnki.jrme.2014.1712

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For knowing the degradation processes of slate on suffer layer of mudflow channel in Zhouqu and Wudu located at the middle and lower reaches of the Bailong valley，we studied the physical degradation of slate using field photograph，varying quality variations，elastic velocity，stress-strain curves，and uniaxial compressive strength. These tests were carried out following varying numbers of cycles of thaw-freeze，wet-dry weathering. By applying correlation regression and fitting analyses，we real the degradation rules regarding the correlative index of slate by contrasting analyses following thaw-freeze，wet-dry weathering processes. The degradation of response of the functions to the degradation of slate is used to elucidate the degradation behavior and mechanisms of slate in the different functions and manifest that the major influent factor is the function of wet-dry. Our results provide a reference for evaluating slope stability，and predicting the potential for debris flow disasters in the study region.

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Study on calculation model of flexural behavior of shield segment joint

CHEN Biguang1，2，CHEN Weizhong2，GUO Xiaohong1

2016, 35 (S1): 2953-2959 doi: 10.13722/j.cnki.jrme.2015.0332

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A stress related stiffness reduction factor is firstly proposed to describe flexural behaviour of shield segment joint without packing material. An empirical formula of the factor is suggested based on the results of flexural tests. Explicit analytical solutions of moment-rotation relation for shield segment joint is derived，which can be directly used in structure analysis of shield segments. The suggested analytical solutions can reflect the influence of axial force on the flexural behaviour. The entire process that the flexural stiffness of segment joint decreases with increasing rotation angle until the destruction can be described well by the suggested analytical solutions. The comparison with full scale tests shows that the analytical solutions have good agreement with test results. Therefore，the analytical solutions suggested here may have great value in engineering.

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Test and theoretical analysis of change laws of earth chamber pressure

JIN Dalong，YUAN Dajun，LI Xinggao

2016, 35 (S1): 2960-2967 doi: 10.13722/j.cnki.jrme.2014.1440

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The simulating driving test of shield machines is carried out by using a model shield of earth pressure balanced type with cutterheads of different open area ratios. Through measuring the earth pressure inside and outside the chamber，the relationship between earth pressure and open area ratios of cutterheads is gotten. Based on the theory of fluid mechanics，a calculation formula of the pressure change is deduced and the quantitative analysis of the influence of aperture ratio，tunnel diameter，soil parameters，additional stress on changes of the earth chamber pressure can be performed by means of the deduced formula. According to the formula，when the angle of internal friction and cohesive increase，the difference of chamber pressure and earth pressure outside become greater. Besides，when the rate of opening on cutterdisc and diameter of shield tunnel increate，the difference of chamber pressure and earth pressure outside become smaller. Comparisons between results of theoretical calculations and the other means，such as field monitoring and discrete element simulation analysis are done，which confirms the rationality of the gotten formula.

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Full-scale model test on behaviors of urban underground water delivery pipeline crossing active ground fissure zone

HUANG Qiangbing1，2，LIANG Ao1，MEN Yuming1，2，LIU Hongjia1，MA Yujie1

2016, 35 (S1): 2968-2977 doi: 10.13722/j.cnki.jrme.2015.1289

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Ground fissure is the most typical geological disaster which has endangered the safe use of underground pipes in Xi 'an city. Based on the analysis of the harm on underground pipes induced by ground fissure，full-scale model test was carried out to study the force condition，deformation and failure modes of underground pipeline crossing the active ground fissure. The model test results show that whichever layout mode of underground pipeline is (riding or joint riding across ground fissure)，the stress on the pipeline is sophisticated and pipeline is in tension and compression simultaneously. The deformation and failure modes of pipeline can be divided into two kinds that one is reverse bending-elastic foundation beam failure mode，the other is terminal warping-cantilever beam failure mode. The critical value of ground fissure dislocation leading to crack failure of underground pipeline is 6cm. For pipeline riding across ground fissure，cracks mainly appear in the range of 0.5 m from the position of ground fissure at foot wall. As to pipeline with joints riding across ground fissure，cracks mainly appear at the spot with a distance of 1.2 m from ground fissure at the hanging wall. So keeping a certain distance from the ground fissures and reasonable planning should be adopted for the underground pipeline construction in ground fissure developed areas. As for underground pipelines crossing the ground fissures，the necessary countermeasures such as shallow buried pipe ditch，overhead setup，flexible pipes，joint reinforcement，underground corridor and monitoring and early warning etc. should be taken to avoid and prevent the crack failure of pipelines induced by active ground fissure. The conclusions can be presented as the reference to plan of new pipeline network and old network reconstruction in Xian city and also to pipeline engineering construction of other developed areas of ground fissures.

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Experimental study of nonlinear evolution mechanism of coal strength under multi-loading rates and its application

LI Haitao1，2，SONG Li3，ZHOU Hongwei1，SONG Feng4

2016, 35 (S1): 2978-2989 doi: 10.13722/j.cnki.jrme.2015.0226

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The mechanical behavior of coal and rock is complex due to the highly complex natural structure. Mechanical tests for multi-loading rates of coal from the same source were carried out，a non-linear evolution law that the compressive strength first increased and then decreased with the increase of the loading rate was observed. According to the repeatability principle，the existence of the non-linear law was confirmed. Details of mechanical behavior of coal in test show that，the microscopic bearing structure would store more deformation energy while the development of crack was inhibited at high loading rate，for coal with low strength，the microscopic bearing structure would break off easily in large scale. Namely，whether the development of crack is fully or not will both reduce the strength. Therefore，the existence of “critical loading rate” between highest and lowest loading rate corresponding to highest strength is proved to be inevitable，and the local fracture plane formed by the break off of microscopic structure is the key factor causing low compressive strength at high loading rate. The characteristic that the lower strength at high loading rate corresponding to lower bursting possibility was taken as the starting point of field application of the non-linear evolution law，the “loading rate sensitivity” and scale conversion method of loading rate based on filed monitoring were proposed to realize the application to specific field，which showed a good applicability.

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Applicability of the NGA model in Lushan earthquake region

JI Kun，WEN Ruizhi，REN Yefei，WANG Hongwei，HUANG Xutao

2016, 35 (S1): 2990-2999 doi: 10.13722/j.cnki.jrme.2014.1374

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The Mw6.7 Lushan earthquake on April 20，2013 provided the opportunity to validate the applicability of American Next Generation Attenuation Relationship(NGA-West 1 and NGA-West 2 model). A total of 42 free-field strong-motion recordings within the rupture distance of 200 km were used in this study. Firstly we established an empirical attenuation relationship for the peak ground acceleration and spectral acceleration. The residuals analysis shows that the model can properly reflect the attenuation tendency of the parameters. It was found that the NGA models underestimate the parameters slightly in short period less than 0.2 s，overestimate significantly in long period over 1 s. Compared with the NGA-West 1 model，the NGA-West 2 model not only performs better for the discreteness of short period spectral acceleration，but also reduces the residuals in long period

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Prevention and control of coal burst on gob-side entry in deep coal seam with fully mechanized sublevel caving mining

CHENG Yunhai1，2，JIANG Fuxing3，HU Zhaofeng4，LIN Jikai1

2016, 35 (S1): 3000-3007 doi: 10.13722/j.cnki.jrme.2014.1417

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Coal burst is hard to control and induced easily in gob-side entry. In order to eliminate coal burst risk for fully-mechanized face，lacking protection seam to release rock pressure，with strong coal burst proneness located in over 1 000 m depth in Huafeng coal mine，the return air way of next working face was settled just below transportation lane floor of the mined working face，and no section coal pillar mining was realized. Support strength was calculated with strata structure model，and lateral pressure of gob-side which was obtained by generalized coulomb theory have been taken into consideration for support design. Regional early warning was realized by microseismic monitoring(MS) and AE(sound monitoring)，while temporary warning was realized by on-line stress monitoring and drilling cuttings prediction. It shows that no coal burst risk existed in gob-side entry，So the previous blasting and large diameter pressure relief process could be eliminated. The research is of reference value for coal burst of gob-side entry prevention and control in deep coal mine.

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Shallow-hole blasting mechanism and its application for gob-side entry retaining with thick and hard roof

ZHANG Zizheng1，2，BAI Jianbiao1，2，CHEN Yong2，HAO Shengpeng1，2

2016, 35 (S1): 3008-3017 doi: 10.13722/j.cnki.jrme.2014.1442

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In order to avoid large area roof weighting and other dynamic disasters for gob-side entry retaining with thick and hard roof，combined with geological conditions and engineering practice of gob-side entry retaining with hard roof in Xinchao Colliery，this paper uses theoretical analysis to expound the zone characteristics of shallow-hole blasting and gives out calculation formula of zones respectively. Also the numerical calculation software of LS-DYNA3D is used to establish a model for shallow-hole blasting，analyze the evolution law of the effective stress and confirm relevant parameters of shallow-hole blasting with theoretical calculation results. Based on these research results，control countermeasures have been proposed，which include shallow-hole blasting technology for immediate roof caving，roadside backfill body construction technology with high water material for main roof caving，and road-in support technology of combination bolt support with hydraulic prop support. The field practice and observations show that the application of shallow-hole blasting technology has achieved an expected effects for ground rock control

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Failure characteristics of floor under predssure inclined and extra thick coal seam in full-mechanized top coal caving faces

CHEN Jigang1，2，XIONG Zuqiang3，4，LI Hui4，YU Yang5，NIE Baisheng1，WANG Shidong4，WANG Xiaolei4

2016, 35 (S1): 3018-3023 doi: 10.13722/j.cnki.jrme.2014.1450

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Characteristics of floor failure is very significance for mining under pressure. Taking Wenming coal as the experimental mine，by using the equipment which is sealed two ends by capsules in borehole，affused measurable water between the two capsules and borehole televiewer system and ground penetrating radar，height of floor under large mining depth inclined and extra thick coal seam in fully-mechanized top coal caving face is monitored and analyzed through the digital relationship of fractures around mining such as numbers and depth，numbers and width. At the same time，numerical model experiment of stress change and characteristic of plastic zone are carried out. The results show that：(1) Height of floor under large mining depth inclined and extra thick coal seam in fully-mechanized top coal caving face is 30.1 m；(2) The fracture width is mainly with less than 5 mm before mining and the fracture width is mainly 16–20 mm after mining；(3) The number of fractures is small before mining，with the mining of working face，the number of fractures is on a rising-down-invariant trend；(4) The abutment pressure concentrated coefficient of working face inferior is greater than the above；(5) Floor vertical stress curve on the tilt direction distribution is“spoon”shapes，with the depth of floor increased the pressure release level is decreased and to form the large plastic failure zone.

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Study on the formation mechanism of Jiweishan landslide in Wulong，Chongqing，China-based on centrifugal model test

DENG Maolin1，2，3，XU Qiang1，ZHENG Guang1，DONG Xiujun1

2016, 35 (S1): 3024-3035 doi: 10.13722/j.cnki.jrme.2014.1582

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The formation and evolution process of Jiweishan landslide in Wulong as for typical apparent dip slid landslide was studied by using the centrifuge modeling test. The test model with the relevant instruments and equipment which includes the base，karst zone and the sliding body of the geomechanical model were made by barite powder，quartz sand，gypsum，glycerin，cement and water in certain proportion，and then the centrifugal test was operated according to the relevant rules. The test results show that the front karst zone“easy compression”provide the“quasi free surface”effect for the slope creep，and lead to the“soft base effects”failure mode. The premise of the landslide instability is forming the second fracture face，which reproduce“creep-crack-compressive (crushing)-shear”the disaster-causing mechanism of Jiweishan landslide. It turned out that the karst zone“easy compression”is one of the key conditions for the evolution of the slope，and also the centrifuge modeling test is an effective method to study rock landslide.

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Reconstruction of three-dimensional gas pressure field of mining coal seam based on Matlab and measured data

MA Haifeng1，2，3

2016, 35 (S1): 3036-3041 doi: 10.13722/j.cnki.jrme.2014.1368

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In order to master the three-dimensional distribution of gas pressure of coal seam and the location of gas pressure concentrated area，the paper studied the distribution of gas pressure and the variation disturbed under mining by using the method of field test and theoretical analysis. The results show there is a single hump-shaped peak zone of gas pressure along strike，however，no peak zone along the tendency. The greater the mining disturbance，the greater the gas pressure peak，and the peak position closer to the working face. And the paper reconstructed static gas pressure field of far-field seam and dynamic gas pressure field of near-field seam by using three interpolation methods of linear interpolation，spline interpolation and cubic interpolation based on Matlab programming. It can be obtained through comparison of interpolation results that the proposed interpolation method based on least squares fitting cubic polynomial reflects the three-dimensional distribution of gas pressure better，the smoothness and continuity is better than that of linear interpolation and spline interpolation，and there is no unreasonable mutation，the interpolation method reconstructs the three-dimensional gas pressure field more authentically. It provides a basis for the prediction of the gas pressure concentrated zone.

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Slip mechanism of wedge and barrel anchorages under dynamic disturbance

MA Zhenqian1，JIANG Yaodong2，3，YANG Yingming1，ZHANG Kexue1

2016, 35 (S1): 3042-3050 doi: 10.13722/j.cnki.jrme.2014.1690

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Coal mining could cause rock collapses and surface subsidence，other underground engineering，such as hydropower chambers and subway tunnels，are noncomparable with the intense disturbance induced by coal mining. In order to study the slip mechanism of wedge and barrel anchorages under dynamic disturbance，this paper takes II82 mining area in Luling coal mine as engineering background. II82 pedestrian rise was subjected to severe disturbance of upper working faces，so the slip mechanism of wedge and barrel anchorages was analyzed from the aspect of dynamic disturbance by using finite difference method software FLAC2D. The results show that in early dynamic disturbance the displacement differences of shallow and deep medium in surrounding rock lead to the anchor cable load reduce，and then it was in tension in the process of reinforcement. The dramatic changes in anchor cable load could not make the anchor cable pre-tightening like constant loading，on the contrary，the anchorage was broken by instant slip. The problem of anchorage slip under dynamic disturbance could be effectively solved by combining extrusion anchorage and screw anchorage，and it was successfully applied in Luling coal mine

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Research on seemingly unrelated regressions model of landslide displacement prediction of multiple monitoring points

LUO Wenqiang，JI Yanan，WANG Chunyue，SONG Zijian

2016, 35 (S1): 3051-3056 doi: 10.13722/j.cnki.jrme.2015.1038

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In the process of landslide deformation monitoring，multiple monitoring points were arranged on the same landslide usually. These data of monitoring points reflected the trend of the landslide deformation and destruction from different sides，so there was a certain correlation among data of monitoring points. However，this correlation has not been considered into research on the same landslide deformation prediction of multiple monitoring points. Seemingly unrelated regressions(sur) model established in this paper could effectively deal with the correlation among data of multiple monitoring points，and could process the cumulative displacement data of multiple monitoring points in one model，and then more accurate results of deformation prediction of landslide were obtained. As an example，two regression equations were established based on the cumulative displacement data of monitoring points ZG93 and ZG118 of baishuihe landslide，then according to two-step feasible generalized least squares(FGLS)，covariance matrix of error of two regression equations was obtained. The regression equations were actually related due to the covariance matrix of error was non-diagonal，which met the conditions of SUR model，so SUR model of the two monitoring points could be created to complete the deformation prediction of two monitoring points ZG93 and ZG118 synchronously. Finally compared with the results of ordinary least squares(OLS)，parameter estimation of SUR model was closer to the true value and the average relative error of SUR model was less than OLS model，so the prediction accuracy of SUR model is higher than OLS model.

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Stress and deformation analysis of shield incline shafts segment due to dewater settlement of aquifer

SHI Xiaomeng1，LIU Baoguo1，LI Tao1，DU Xin2

2016, 35 (S1): 3057-3063 doi: 10.13722/j.cnki.jrme.2014.1717

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This paper pointed out the influence of dewatering settlement on the structure of shield inclined shafts in the aquifer. The dewater settlement laws of aquifer were analyzed，and the compression ratio of aquifer was selected as the parameter to represent the dewater settlement performance. The load and deformation which the shield segment suffered during aquifer dewatering were studied，and the cantilever beam model under even load was built. The elastic-plastic analytical solutions of the stress and deformation of the shield incline shafts were given through the equivalent continuum model. At last，the mechanical model proposed in this paper was applied to the shield inclined shaft in Shenhua Xinjie coal mine，and the stress and deformation of the incline shafts due to dewater settlement of aquifer were worked out.

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The failure modes，failure mechanisms and countermeasures of columnar jointed basalt rock mass

NI Shaohu1，2，HE Shihai1，CHEN Yimin1，2，PAN Yibing1，2，LU Kang1，YANG Fei1，ZHENG Haisheng1

2016, 35 (S1): 3064-3076 doi: 10.13722/j.cnki.jrme.2015.0006

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Columnar jointed rock mass is a geological endemism in volcanic rock area with special geological genesis. Its engineering characteristics and excavation responses are obviously different from that of common intact rock mass. In this work，according to the excavation responses and revealed phenomenon of columnar jointed basalt rock mass in tunnel，the typical failure modes and their failure mechanisms of columnar jointed basalt rock mass are studied and summarized，with rock mechanics theoretic analysis and numerical analysis. In addition，based on the unloading and relaxation characteristics of columnar jointed basalt rock mass and in-situ monitoring and test data，the reasonable and feasible support methods and construction methods are discussed and proposed，such as support measurements，support opportunity，excavation scheme， demolish control and so on. These proposed methods are good for controlling columnar jointed rock mass relaxation，deformation and relaxation spreading，so as to enhance the stability under complex geological conditions of underground space such as chamber，house，tunnel and shaft and etc.. The effectiveness and reliability of above-mentioned research results are tested and verified during follow-up tunnel excavation.

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A data driven self-adaptive update landslide susceptibility assessment system

WANG Lili1，SU Cheng1，FENG Cunjun2，ZUO Shilei2，HUANG Zhicai1，ZHANG Xiaocan1

2016, 35 (S1): 3076-3083 doi: 10.13722/j.cnki.jrme.2015.0070

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To maintain the susceptibility assessment model up-to-date and to improve the accuracy of assessment result，a data driven self-adaptive update mechanism in landslide susceptibility assessment system is proposed to accommodate changes of conditioning factors and increasing number of landslide inventories. Based on the theory of conditioning factor processing and selecting method，support vector machine and three evaluation indices (accuracy，kappa coefficient and AUC)，a landslide susceptibility assessment system has been designed and implemented. The system includes 4 modules：data preprocessing，landslide assessment model construction，model performance evaluation and landslides prediction. The self-adaptive update mechanism will be triggered by data changes. To fit the landslide assessment model for the latest regional environment and characteristics of landslides，the system will rebuild the training set and reconstruct the landslide assessment model once the conditioning factors and landslide inventories change or the assessment result cannot satisfy requirements. The experimental results in Wencheng County，Zhejiang Province，China show that the system can be updated automatically with changes of data to accommodate the latest environment and can improve the landslide susceptibility assessment result effectively as the abundance of conditioning factors and landslide inventories.

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Application of the PPP-BOTDA distributed optical fiber sensor technology in the monitoring of the Baishuihe landslide

YI Xianlong，TANG Huiming，WU Yiping，GE Yunfeng，FAN Xiaoguang，ZHANG Shen

2016, 35 (S1): 3084-3091 doi: 10.13722/j.cnki.jrme.2015.0074

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The object of monitoring lies in the anterior part of Baishuihe landslide. In the deformation monitoring，the PPP-BOTDA distributed optical fiber sensor technology is adopted. The information captured by the device is the strain caused by sliding mass. Two optical fibers，the temperature fiber optic sensor and the strain optical fiber sensor，are buried under the surface of the landslide. For the oscillation of the three groups of monitoring data，the Butterworth low-pass filter is particularly designed to minimize the influence of the noise signals；and the comparison among the four groups of different sampling frequencies were conducted to reveal the most suitable value of the n and the Wn. Then the area difference between the curve and the horizontal axis along the optical fiber line is utilized to make quantitative evaluation of the strain. The findings show that the method of the Butterworth low-pass filter and the area difference value is helpful to indicate the difference of the strain. It is proved to be effective according to the in-site observation. The results present that it is of reference value for the fiber optic sensing technology applying in the landslide monitoring.

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Two-dimensional evaluation model of rock mass based on combination weighting and cloud model

WEI Bowen1，HUANG Haipeng1，2，XU Zhenkai1

2016, 35 (S1): 3092-3099 doi: 10.13722/j.cnki.jrme.2015.0076

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Dam foundation rock mass quality evaluation is a multi-factor system process of synergy effect，in view of the problems existing in the evaluation process，the introduction of Cloud model，projection pursuit method and analytic hierarchy process(AHP) and fuzzy entropy theory，is put forward based on the improved Cloud-PP-AHP rock mass quality evaluation model for the two-dimensional. The model on the basis of rock mass quality evaluation index system and classification standard and evaluation index is calculated which belong to different quality levels of cloud model parameters；Based on hierarchy analysis and projection pursuit method to solve the combination weights of the indexes；Plug in the measured data of rock mass，for evaluation of rock mass is affiliated with various quality grades of integrated uncertainty；Assisted by fuzzy entropy E as the contestant，jointly build the rock mass quality grade evaluation of two dimensional evaluation model. Finally the model is applied to a hydropower station dam foundation rock mass quality evaluation，the evaluation results with other evaluation methods were analyzed，the results show that the model is applied to rock mass quality evaluation of effective and feasible，and the evaluation results intuitive，for rock mass quality evaluation provides a new way.

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Probabilistic seismic landslide hazard zonation method and its application

LIU Jiamei1，GAO Mengtan1，WU Shuren2

2016, 35 (S1): 3100-3110 doi: 10.13722/j.cnki.jrme.2015.0118

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Earthquake is a random process. Recent landslide hazard analyses were carried out based on ground motions with given probability of exceedance，ignoring the impact of some potential earthquakes，representing a conditional probability of earthquake induced landslides. This paper presents a new method for potential seismic landslide hazard zonation at regional scale in terms of landslide probability. It is based on the probabilistic seismic hazard analysis and Newmark’s displacement model，incorporating the effects of focal mechanism，site condition and topography. We applied this method to Tianshui study area and generated a regional seismic landslide probability hazard map in 50 years，combining the potential seismic source zones which were used for the new generation seismic zonation map of China，empirical engineering geology lithology formations，and topographic slop data. The results show that the high hazard zones mainly concentrated at the loess or mudstone areas with slope greater than 30 degree，especially on the banks of Wei River，Xi River and Niutou Revier，posing a threat to Longhai Railway line and the surrounding of Tianshui city.

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Study on the evaluation method of slope disaster status based on the reliability of fracture degree

GUO Rukun，FENG Chun，ZHOU Dong，LI Shihai

2016, 35 (S1): 3111-3118 doi: 10.13722/j.cnki.jrme.2015.0216

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Because of the heterogeneity of rock and soil medium，a slope disaster status evaluation method based on the fracture degree and its reliability is presented. The mean，variance and the distribution form of the rock and soil mechanical parameters based on experiments are used to generate sample. A random sample of geotechnical parameters accord with the certain probability distribution is obtained by the Latin hypercube sampling(LHS) method. Then a large number of numerical cases with different parameters are executed by continuous- discontinuous element method(CDEM)，and fracture degree of each case is obtained. Based on the law of large number，the probability of the status which reaches and exceeds the catastrophic status can be obtained. Based on the geometric model of Liangshuijing landslide，the relationship between fracture degree and the probability distribution of cohesion and inner friction angle is discussed，and the probability of integral sliding with given parameters is 60.7%.

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New-type piezomagnetic overcoring measurement system and its test analysis

WU Manlu，ZHANG Chongyuan

2016, 35 (S1): 3119-3126 doi: 10.13722/j.cnki.jrme.2015.0280

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Aiming at the shallow measuring depth and low work efficiency of traditional piezomagnetic overcoring system，a new-type one is developed. The borehole data acquisition unit is firstly developed. This unit and piezomagnetic stress measuring elements are integrated in the measuring. The original mechanical stressing manner is changed to an electric control way. The electronic compass is adopted to further improve the directional accuracy. The new-type piezomagnetic overcoring measurement system mainly consists of the new-type piezomagnetic measuring probe，electric stressing device，and electronic compass directional device. Installation of probe and pre-stressing and orientation of measuring element are controlled by computer software. The measuring data is collected and stored by borehole data acquisition unit automatically. Hence，the measuring depth and efficiency are greatly improved. In addition，magnetic property and structure of the piezomagnetic measuring element and measuring method are improved，as well. Adopting high frequency-light excitation，comparison measurement，and intelligent signal processing technology，both the sensitivity and accuracy of piezomagnetic measuring element have a greater improvement. An experimental test for new-type piezomagnetic overcoring system is conducted and compared with hydraulic fracturing measurement results in a borehole at Wenquan Town，Beijing. The test results are quite good and indicate that the new system can meet the need of deep-hole in situ stress measurement completely.

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The quantitative analysis of the face stability on soil tunnel

HUANG Jun1，2，DANG Faning3，ZHOU Lei3，DANG Kangning2，GUO Chanjuan4，QIN Yuan1

2016, 35 (S1): 3127-3137 doi: 10.13722/j.cnki.jrme.2015.0294

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The quantitative relationship between the face stability and construction conditions on soil tunnel is introduced. First，an implicit function to strength parameters and construction parameters is proposed by analyzing the safety factor of face stability. The implicit function is transformed to the polynomial expression on construction parameters via multi-function Taylor formula. A technical method of getting the approximate expressions of safety factor of face stability under a single construction parameter is introduced. Mainly，the response surface methodology is used to determine the Taylor expansions of under multiple variables of construction parameters. It illustrated the applications of the proposed methods in ideal tunneling model. Finally，in the Shizilong tunnel project，the results showed that a first-order Fs model of in the initial region of U1 was appropriate，and then gradient ascent method is used to optimized the regional U2. By the central composite design，a validity second-order Fs model is calculated，and the effectiveness was verified by ANOVA.

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Stability evaluation of hillside under the transmission tower based on improved attribute recognition model

WU Yijiang1，CHEN Bo2，RUAN Hang2，WANG Ganjun1，NIE Wenxiang1

2016, 35 (S1): 3138-3146 doi: 10.13722/j.cnki.jrme.2015.0322

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The hillsides under the transmission towers have the characteristics including little investigation information and no supporting measures. Stability of the hillsides under transmission towers is one of the important factors for the normal operation of transmission lines. The stability evaluation of hillsides is realized based on an improved attribute recognition model. Firstly，according to influence factors of hillsides instability in a certain area，hillside angle，landform，vegetation development characteristics，rock mass and soil characteristics，incident angle of rainfall，weathering and degree of human activity are selected as the stability evaluation indicators of hillsides. The comprehensive empowering method is used to determine the weight of the evaluation indicators. Then the single index attribute measurement functions of the highest level and second highest level in the grading criteria are analyzed and presented in detail to be more formal so that all attribute measurement functions are rigorously constructed to compute attribute measurement of single index. Finally，the stability identification and classification of hillsides under the transmission towers are recognized by Grey Relational Analysis. This method is applied to the hillsides under the transmission towers in Zhongshan，and the assessment results do agree well with the results of the practical condition，so as to provide an effective method for the stability evaluation of hillside under the transmission tower.

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Research on calculating gas pressure with gas flow in crossing borehole

ZHOU Rui1，2，YAN Binyi2

2016, 35 (S1): 3147-3152 doi: 10.13722/j.cnki.jrme.2015.0327

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To improve the efficiency of testing gas pressure，the partial differential equation of gas radial flow in crossing borehole was established by using Law of conservation of mass and Darcys Law，then the gas pressure function was solved with Laplace Transform，thus the effectived emission radius and drainage radius were found；Considering the seepage flow manner of gas，the attenuation function and curve of gas flow in crossing borehole were obtained，so the method of calculating gas pressure and which represented the difficulty of gas emission in crossing borehole were proposed. Maximum error of gas pressure was 9% except gas pressure was under 0.28 MPa was showed by testing results in Gaoyuan coal mine. So without the need for accurately measuring gas pressure，calculation with gas flow could meet the needs of the coal mine with a factor of safety.

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Reliability analysis on stability of gravity dam foundation over multiple sliding planes based on GA

WANG Gang，QIN Jingjing，GUAN Lili

2016, 35 (S1): 3153-3161 doi: 10.13722/j.cnki.jrme.2015.0468

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It is a primary issue for the design of concrete gravity dam to analyze dam foundation instability. Always the performance function of reliability analysis is nonlinear and implicit on the case of multiple sliding planes in the dam rock base. it is so complicated that there are little literatures on extensively researching about this case. According to the geometric interpretation of the realiability index，the reliability calculation can be treated as mathematical optimization. So a reliability calculating method on the basis of genetic algorithm(GA) is suggested to evaluate the stabiliy reliability index of concrete gravity dam foundation over multiple sliding planes. The method can avoid many restrictions of the first order second moment(FOSM) method associated with the explicit performance function. By camparison with the calculated results by different methods for two testing examples and an actural gravity dam，the method is verified to be accurate，efficient and rational. It has much merit and can be utilized to the practical complex engineering，for which the performance function for reliablity analysis is nonlinear and explicit or implicit. The method will benefit the further research and provide good technical support on the stabiliy safety assessment and structrual design of gravity dam.

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An asymmetric support technique for fully-mechanized coal roadway nearby narrow pillar based on the fracture position analysis in basic roof

YIN Shuaifeng1，CHENG Genyin1，HE Fulian2，XIE Fuxing2，SHAN Yao1

2016, 35 (S1): 3162-3174 doi: 10.13722/j.cnki.jrme.2015.0479

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The support for the fully-mechanized coal roadway nearby narrow pillar in the mining face 20103 of the Wangjialing coal mine suffered large asymmetric deformation. In order to solve this problem，a technique was proposed. In the first step，the fracture position of the basic roof and two-way movement behavior was investigated using the method of borehole observation，then combing the CT scan technology for the asymmetric evolution process of coal roof microcracks，an asymmetric support technology using both parallel-arranged composed of channel steel truss cable and single cable was designed. Its composition structure and controlling mechanism were then researched in detail. The following results were obtained：(1) Away from the tunneling face 20103 100–300 m，fracture took place at the top of the narrow pillar，apart from the central plane of the roadway 2.918 m；(2) Roof delamination and horizontal dislocation have occurred twice in coal roof caused by the rotation and descending of basic roof: the first delamination led to a regional scale faults in the roof near the pillar side and parallel to the entry direction；the second delamination led to some site scale roof falls near the pillar side；(3) Microcracks development on either side of the entry roof were asymmetric: the amount，developing speed and faults formation interval were discrepant between the horizontal dislocation zone and the stable zone；(4) The feature of the asymmetric support method using parallel-arranged composed of channel steel truss cable and single cable include: weak sites extra-strengthened，tuned by weaker support at relative strong sites，line shape supports accompanied by point supports，and the load on every supports were balanced. This method has been successfully implemented in the working face 20103，deformation on the roof at pillar side and coal rib side were adjusted to synchronous，the host rock was very effectively controlled. The result and experience are very useful to similar engineering conditions theoretically and practically.

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Microseismicity and stability evaluation of the underground powerhouse at Houziyan hydropower station subjected to excavation

XU Nuwen1，2，DAI Feng2，LI Biao2，ZHU Yongguo3，CHENG Lijuan4，WANG Qi1

2016, 35 (S1): 3175-3187 doi: 10.13722/j.cnki.jrme.2015.0516

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In order to real time monitor and evaluate the surrounding rock mass stability and identify the potential hazardous regions of the underground caverns at the Houziyan hydropower station subject to excavation，the comprehensive method incorporating numerical simulation，microseismic(MS) monitoring，traditional monitoring and field observation was adopted. Some results are obtained as follows：(1) MS monitoring can realize the real-time monitoring，analysis and evaluation of surrounding rock mass stability of the underground caverns due to excavation-induced unloading. (2) micro-fractures concentration areas of surrounding rock mass and potential hazardous regions in the underground caverns were delineated by the temo-spatial evolution of microseismicity. (3) the initiation，propagation and coalescence of micro-fractures due to excavation can be reflected by MS monitoring. With regard to the field construction and reinforcement of the underground caverns，the obvious and intense concentrations of MS events have already been regarded as the early warning of reducing the construction schedule. (4) the conventional monitoring methods such as multi-point extensometers，convergence gauges and anchor stress gauges，etc.，were used to verify the truthfulness and effectiveness of the results of MS monitoring. The presented results demonstrate that the combination of MS monitoring，numerical modeling，traditional surveying and in situ observation approaches lead to a better understanding of excavation behavior of underground caverns and a more satisfactory control of the working in terms of safety in the complex geological and excavation-induced unloading conditions. Furthermore，the results can provide some guidelines for later excavations and supports of the underground powerhouse.

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Study on calculation method of anchored stabilizing piles based on displacement of soil around piles

YE Xiaoming，WANG Zhen，GAN Fei

2016, 35 (S1): 3187-3194 doi: 10.13722/j.cnki.jrme.2015.0615

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Traditional anchored piles calculation model cant scientifically consider the effects of anchor to pile-soil interaction，often leads to unreasonable anchor tension and pile body internal force. This paper saw whole pile as a beam on elastic foundation，a two-stage pile-soil interaction mechanics control equations based on displacement method was established. The mathematics analytic solution of control equations were obtained by initial parameter method. Matlab computing program was compiled for the calculation of internal forces and displacements. The comparison with a set of model test data showed that：the displacement method calculation model and its analytic solution in this paper is feasible. The model was applied to a project case showing that：the displacement method calculation model can consider the role of soil around piles in tensioning stage，and can consider the interaction of pile-soil-anchor.

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Empirical methods to determine the rock masses parameters

ZHANG Zhanrong1，YANG Yanshuang2，ZHAO Xinyi1，SHENG Qian3，ZHU Zeqi3

2016, 35 (S1): 3195-3202 doi: 10.13722/j.cnki.jrme.2015.0758

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The deformation modulus of rock mass is a very important input parameter in any analysis of rock mass behaviors which include deformation calculation or stability analysis. In-situ tests，which can determine this parameter directly and is the most reliable methods，are time consuming and expensive. When in-situ tests cant be made enslaved to something，empirical method，which estimates the value of rock mass deformation modulus on the basis of rock mass classification schemes，would be a good choice. A lot of foreign scholars had established empirical relationships between rock mass deformation modulus and classification system，but the domestic researchers pay little attention in this field. Standard for Classification of Engineering Rock Masses，which was issued in 1994，is the national standard of Chinese. It has been widely used in geotechnical engineering，but the research achievement which related to the rock mass parameters are so little that it is very necessary to study in this area. Using the data by a large number of in-situ tests from large-scale water conservancy and hydropower projects in China，a new relationship between the deformation modulus of rock mass and BQ index is proposed，based upon the principle of statistics and correlation analysis. In order to improve the precision of the empirical formula，a new relationship is proposed between the deformation modulus of rock mass and BQ index，the properties of the intact rock，and it is validated by data from the Three Gorges Project. It would be a useful reference for parameter determination of rock mass in our country.

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Water-richness evaluation of ordovician limestone based on grey correlation analysis，FDAHP and geophysical exploration

QIU Mei1，2，SHI Longqing1，2，TENG Chao1，2，HAN Jin3

2016, 35 (S1): 3203-3213 doi: 10.13722/j.cnki.jrme.2015.0916

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Exploitation of the deep coal is seriously threatened by water inrush from Ordovician limestone in North China type coalfield，so the coal mine safety production is directly related to the water-richness evaluation of Ordovician limestone aquifer. The water-richness of aquifer is evaluated by the units-inflow，which is the criteria according to regulations for mine water prevention and control. While the data are sparse in field exploration，the water-richness can not be evaluated comprehensively and objectively. In view of the above issue，the water-richness evaluation method based on grey correlation analysis，Fuzzy Delphi Analytic Hierarchy Process and geophysical exploration is proposed. Based on the background of Liangzhuang coal mine， the work of water-richness evaluation was carried out. Four major controlling factors were selected，including water inflow of drilling，the thickness of upper Majiagou Formation of Ordovician limestone aquifer，fault influencing factor and drilling flush fluid consumption. The total weights of all factors were obtained by the use of expert scoring method and grey correlation method. Following the above outlines，the mathematical model of water-richness index was established based on the method of grey correlation analysis and FDAHP. The data of geophysical exploration were collected to test the accuracy of the model and determine the partition thresholds. In addition，the results of water-richness index and geophysical exploration were used to evaluate the water-richness of Ordovician limestone. Furthermore，the validity and reliability of evaluate results were verified by engineering practices，including the data of water leakage of Ordovician limestone drills，Water inrush points，pumping tests and water source wells. In the absence of actual data of units-inflow，this study provides a way to evaluate the water-richness of Ordovician limestone aquifer.

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Analysis of microseismic activity parameters pre- and post roof caving and early warning

ZHANG Chuxuan1，2，LI Xibing1，DONG Longjun1，MA Ju1，HUANG Linqi1

2016, 35 (S1): 3214-3221 doi: 10.13722/j.cnki.jrme.2015.0928

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The studying on parameters of microseismic activity play an important role in rock mass stability prediction. The change pre- and post Roof Caving of microseismic activity parameters including b value，Energy Index，Schmidt number and cumulative apparent volume were discussed in this article. The author puts forward the concept of“the ratio of energy index and cumulative apparent volume(EEI)”and “the ratio of Schmidt number and cumulative apparent volume(EScs)”. The EEI and EScs could be used as the parameters of rock mass stability prediction. Based on the research of b value and number of events，the general pattern of microseismic monitor forecasting were built. The pattern were used in rock mass stability prediction in Yongshaba mine，and the results showed that：the b value had the function of risk warning because it first increase then decrease pre- and post roof caving. The decrease of energy index and Schmidt number with the increase of cumulative apparent volume meant sudden release of accumulated strain energy in rock mass. The phenomenon indicated deterioration of rock stability. The early warning period that comprehensive determined by this microseismic monitoring forecasting method was more suitable for mine，and reserved response time for workers to avoid risk.

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Analysis of precursor of rock burst based on the fractal characteristics of the mine borehole strain observation data

ZHANG Yuezheng1，JI Hongguang1，XIANG Peng1，PENG Hua2，SONG Zhaoyang1

2016, 35 (S1): 3222-3231 doi: 10.13722/j.cnki.jrme.2015.0958

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There is a close relationship between the movement of rock burst and the regional stress field. In order to explore the evolutionary mechanism of the stress field of rock body in the related area and the precursory information of the disasters. The borehole strain observation technology was firstly applied in the monitoring of dynamic disasters in mines. The changing characteristic of borehole strain data and its correlation to rock burst are also analyzed quantitatively by using fractal box dimension. The results show that borehole strain observation technology is applied in the monitoring of dynamic disasters in mines，which can directly and accurately record the dynamic changes of rock mass in the region. It is simple and effective to deal with the borehole strain data in the background of the trend of solid tide by using fractal method. Fractal box dimension can be quantified to evaluate the complicated changes of the strain data and the extent of distortion of solid tide. The nonlinear space-time evolution process of rock burst is quantitatively characterized by the change of fractal box dimension of borehole strain. The up to down of box dimension can be regard as a precursory characteristics of rock burst.

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Research on correlations between slope stability and rainfall of high steep slope on Nanfen open-pit iron ore

YANG Xiaojie1，2，HOU Dinggui1，2，HAO Zhenli1，2，TAO Zhigang1，2，SHI Haiyang1，2，JIN Kun1，2

2016, 35 (S1): 3232-3241 doi: 10.13722/j.cnki.jrme.2015.0959

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The stability of high steep slope has become a major safety concern in the process of open pit mining in NanFen open-air iron ore. According to the results of engineering geological investigation and the analysis of geologic characteristics and hydrogeology conditions，It found that rainfall in rainy season is an important cause of landslide，the monitoring data of slope stability and rainfall at the same period are analyzed，It is concluded that when the rainfall is more than 100 mm，the slope failure is closely related to the rainfall. Finite element simulation software SEEP/W is used to simulate all the stages of rainfall infiltration of high steep slope，the slope safety factor at the different seepage moment is calculated，this results not only prove the accuracy of statistical analysis but also reveal the mechanical mechanism of slope instability，meanwhile it found the landslide has a lag of about 24 hours in heavy rain，the effective treatment method for high steep slope hydrology disaster of NanFen open-air iron ore is put forward. The results of this study may be useful for the protection of the same projects.

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Constitutive model of structured loess incorporating the breakage law obtained by discrete element method

HU Haijun1，2，JIANG Mingjing2

2016, 35 (S1): 3241-3248 doi: 10.13722/j.cnki.jrme.2014.1372

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The strength and deformation character of structured loess are closely related to the breakage of internal microstructure and the breakage law of microstructure has not been measured by experiment due to the limitation of microstructure test technology. Hence the evolution law of the breakage parameter for ideal structured loess under loading and wetting，which is obtained by discrete element method(DEM)，is incorporated in the binary medium model with the form of strain sharing and the mechanical responses of the model are obtained to verify the reasonability of the breakage evolution law. Firstly，the constitutive equations are given，in which the model of bonding element adopts elastic model，frictional element adopts modified cam clay model and the formula form of breakage parameter are obtained from the numerical test on the ideal structured loess under loading and wetting. Secondly，the numerical program is compiled to verify the behavior of the model in one dimensional compression test，one dimensional wetting test，conventional triaxial compression test and the triaxial wetting test. The results indicate the model can reflect the deformation behavior of loess in one dimensional compression test and the relation between collapsibility coefficient and vertical pressure in one dimensional wetting test. It can simulate the variation of volumetric strain during shearing under different consolidation pressure，the variation of initial elastic modulus with confining pressure in conventional triaxial compression test and the wetting induced deformation law in triaxial wetting test. The effect of bonding element parameter on mechanical character is apparent. The breakage law obtained by DEM experiments is more reasonable than the existing law for triaxial compression test with strain-hardening behavior.

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Study of the macro-meso correlation of geogrid-soil interface and assessment method of reinforced performance

MIAO Chenxi1，ZHENG Junjie1，CUI Lan1，CUI Mingjuan1，ZHAO Jianbin2

2016, 35 (S1): 3249-3258 doi: 10.13722/j.cnki.jrme.2014.1433

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The interface characteristic of geogrid and compacted materials plays an important role in the design of reinforced soil structures. The pull-out test of triaxial geogrid was conducted by 3-D discrete element method to investigate the correlation between macro and meso mechanical responses. Simultaneously，the influence of particle size on reinforcement effect was discussed. The mechanical behavior of reinforced soil and geogrid under pull-out loading was systematically analyzed. The evolution law of the pull-out force and mesoscopic fabric anisotropy indices was shown. Based on the pull-out test results，an assessment method was established to estimate the reinforcement effect of geogrid. Numerical results reveal that the velocity vector of particles in the interfaces can reflect the interaction between geogrid and soil instantaneously. The fabric anisotropy coefficient is suitable to describe the development of macroscopic strength. In a certain particle size scope，the reinforcement effect would be primarily controlled by the specific surface area of grain system and the critical edge load of reinforced soil would decrease with the increase of particle size.

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Experimental study of the change law of consolidation coefficient of the plateau lacustrine peaty soil

GUI Yue1，YU Zhihua1，LIU Haiming1，CAO Jing1，WANG Zhaochang2

2016, 35 (S1): 3259-3267 doi: 10.13722/j.cnki.jrme.2014.1445

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Based on a series of test results，the one-dimensional consolidation coefficient and consolidation mechanism of plateau lacustrine peaty soil from Kunming and Dali city were studied，and some factors，such as the depth of sampling，consolidation pressure(p)，loading method， loading ratio(R) and preloading were discussed. Test results showed that the consolidation coefficients(Cv) of peaty soil decreased with increasing of consolidation pressure firstly，then reduced slowly and stably. The relationship between the consolidation pressure and the consolidation coefficients of peaty soil was a power regression. Under preloading，the consolidation coefficients of peaty soil were pretty much exactly the same as the nature sample when preloading was lower than 100 kPa. It was lower than the nature sample once the preloading was larger than 200 kPa. When consolidation pressure was larger than 200 kPa，consolidation coefficients of peaty soil changed little with consolidation pressure increased. The mechanisms of consolidation were analyzed，which caused the peculiar consolidation properties was rarely structural strength of natural peaty soil. With consolidation pressure increasing，peaty soil changed from porous to relatively dense state.

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Relationship study of thermal conductivity and strength for PS reinforced earthen sites

OUYANG Xiangeng1，ZHANG Dexuan2，WANG Xudong3，GUO Qinglin3

2016, 35 (S1): 3268-3273 doi: 10.13722/j.cnki.jrme.2014.1504

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In order to explore the evaluating method of infrared imaging detection technique(differences in thermal conductivity) for potassium silicate(PS) reinforced earthen ruins soil，adopting the disturbed soil collected from Jiaohe ruins to make soil models，which are reinforced by different concentration of PS，the mechanical strength and thermal conductivity of soil models were determined. It is shown that mechanical strength increase and thermal conductivity reduce for PS reinforced soil. Under the condition of the same dosage of PS，the larger the concentration of PS is，the higher the mechanical strength of soil is，but the smaller the thermal conductivity of soil is. Through analyzing the experiment data regression，thermal conductivity and strength has a good linear negative relationship. Finally，explore the alterative mechanism of thermal conductivity of soil in the effect of PS，describe the relationship between thermal conductivity and strength in the from microstructure of soil. The relationship above shows that thermal conductivity can be used to evaluate the reinforcing effects of earthen sites，which provides a possible method to carry out the non-destructive inspection of the effect for PS reinforced earthen ruins soil.

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Application of cone penetration test for the analysis of pile-run of long and large diameter piles in offshore geotechnical engineering

JIA Zhaolin1，YAN Shuwang1，YAN Aiwu2，ZHANG Xiaowei3

2016, 35 (S1): 3274-3282 doi: 10.13722/j.cnki.jrme.2014.1612

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Cone penetration tests are more and more widely used in ocean engineering. Super long and large diameter piles are commonly adopted for constructing ocean platform foundations. The pile-run phenomenon frequently takes place because of the great weight of both the pile and the hammer. The American Petroleum Institute(API) recommendations are commonly used to assess the static pile bearing capacity，which is the sum of the pile end resistance and the shaft friction. The calculation method for estimating the soil resistance during pile-run is different from the static bearing capacity calculation and should be associated with practical engineering observation. Based on the cone penetration test(CPT) data，a procedure for calculating the soil resistance is put forward，in which the shaft friction is computed by using existed method and the tip bearing capacity computed by the improved Laboratoire Central des Ponts et Chaussées(LCPC) method. By comparing the soil resistance and the weight of the pile plus the hammer，the equilibrium conditions of pile-run can be established. The suggested method has been used to predict pile-up in a project in the South China Sea，and the calculated results agree well with the observed data，indicating that the proposed method may be helpful to the pile foundation designers in ocean engineering.

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Mechanism of permeability and control of compaction for red clay under the influence of acid rain

XIAO Guiyuan1，2，CHEN Xuejun2，WEI Changfu2，3，HUANG Xiang2，CHEN Long2

2016, 35 (S1): 3283-3290 doi: 10.13722/j.cnki.jrme.2015.0040

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Acid rain will dissolve some of the material of red clay，which is the important factor of red clay roadbed diseases. The research on the penetration mechanism of red clay in acid environment and recommendation of subgrade compaction standards to red clay roadbed has a strong practical significance. Use simulated acid rain of different pH value the solution leaching undisturbed of red clay by designing new leaching equipment to conducting penetration test，phase analysis test and SEM experiments，to deeply analyze the impact of acid rain on the factors and mechanisms of Guilin red clay permeability. Further research on the relationship between changes in permeability and the degree of compaction of reshape red clay by the experimental study. The results show that：Red clay permeability decreases with increasing dry density. Chemical compounds of four metal elements(Fe，Si，Al，K)，which are the main compositions in laterite soil，all can be dissolved by acidic substances，and due to the dissolution caused by acid rain. The lower the pH value of acid rain，the greater the degree of dissolution of these substances，the greater the influence on permeability of laterite soil. When using red clay as roadbed filler in acid rain areas of pH value not less than 3，the degree of compaction not less than 95% could be controlled to prevent the adversely affect of acid rain on the laterite soil subgrade effectively.

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Experimental study of anisotropy and non-coaxiality behavior of natural clay by using drained shear test

CHEN Jinmei1，GUO Lin2，CAI Yuanqiang1，2，CHEN Jingyu1

2016, 35 (S1): 3291-3298 doi: 10.13722/j.cnki.jrme.2015.0090

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Recent studies on anisotropy of soft clay are mostly carried out under undrained condition. There is a lack of anisotropy study of soft clay under drained condition. By using hollow cylinder apparatus(HCA)，a series of drained shear tests were carried out，under different direction of principal stress and different intermediate principal stress coefficient. The results show that the isotropic consolidated soft clay has different stress-strain behaviors with different directions of principal stress. Compared to undrained condition，strain development is more gentle under drained condition and the inflection point of rapid strain development is not that obvious. Intermediate principal stress coefficient has a significant effect on strain development，especially when it lies in the range of [0.5，1.0]. The non-coaxiality of soft clay turns out to highly depend on the direction of principal stress. The non-coaxiality is not remarkable when the direction of principal stress is around 0°or 90°，and 45°is a inflection point for the non-coaxiality of soft clay. The conclusions made by this paper can help us have a better understanding of the anisotropy of soft clay under drained condition，also provide a foundation for establishing constitutive relations and guiding engineering design.

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Study of calculation methods of composite geomembrane concentration in high earthrock cofferdam

WANG Yongming1，DENG Yuan1，REN Jinming1，ZHU Sheng2，CAI Jianguo1，LIANG Xianpei1

2016, 35 (S1): 3299-3307 doi: 10.13722/j.cnki.jrme.2015.0121

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Composite geomembrane is a type of geosynthetics with the main components of geomembrane at one side or both sides stuck with geotextile. Composite geomembrane has been widely applied in the field of water conservancy，transportation and disposal of nuclear waste landfill for its low permeability，strong deformation adaptability，convenient erection and dismantling. Aiming at the problem of centralized damage and leakage induced by tensile failure or tear of composite geomembrane in the extensive use of rapid construction of high water head rockfill cofferdam，some analysis were conducted and revealed that structural damages were induced by strain concentration which exceed the limit elongation of composite geomembrane located in these junctional zone between hard foundation and soft composite material. Based on the theoretical analysis of composite geomembrane material mechanical properties as well as microscopic mechanism interaction between the geomembrane and joint，the description method of geometry and physics of composite geomembrane strain concentration were suggested. The corresponding peripheral membrane element FEM prediction mode was also put forward based on the treatment method of Concrete Face Rockfill Dam peripheral joint. The constitutive relation and displacement model were planted in the 3D FEM program. The strain concentration behavior of geomembrane in Baihetan hydropower 85 m height earth-rock cofferdam was obtained. Valuable data and conclusions were obtained to guide the safe utilization and generalization of composite geomembrane in high water head condition and complex stress state.

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Permeability reduction model of particles deposit in porous medium considering changeable porosity

LIU Quansheng，CUI Xianze，ZHANG Chengyuan

2016, 35 (S1): 3308-3314 doi: 10.13722/j.cnki.jrme.2015.0424

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It is of significance to research the permeability reduction process due to particles deposit in porous media，especially in the recharge of groundwater，oil exploration and pollutant transportation engineering. A permeability reduction model of particles deposit in porous medium considering changeable porosity was proposed based on the results of theoretical analysis and sand box tests. Firstly，the change of porosity due to particles deposition was obtained，relationship between porosity and permeability was built using Kozeny-Carman equation，and distribution law of particles was obtained with convection-dispersion equation under continuous injection way. Then，various tests were conducted by the self-developed sand transportation-deposition equipment，and comparisons were made between the calculated and measured results. Finally，the error between predicted and the measured permeability reduction were analyzed. The results revealed that influence on pore structure and permeability due to particles deposition was reflected by the model effectively. The predicted results were close to the measured ones，which show the rationality of the model. Errors between predicted and measured were observed，which were mainly caused by inaccuracy of the proposed model and inherent defect of test methods.

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Research of finite difference method on retaining structures with internal braces in deep excavation engineering

CHEN Linjing1，SUN Yongjia1，2，WANG Zhigang1

2016, 35 (S1): 3315-3322 doi: 10.13722/j.cnki.jrme.2015.0714

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To overcome the defects of the single parameter m method which the current specification recommended，put the composite stiffness principle and bi-parameter method that applied to piles subjected to laterally concentrated loads extended to calculate the deformation and internal force on internal braces retaining structure in deep excavation. Based on the principle and the method，the modified finite difference solution of beam on elastic foundation was presented. In addition，the incremental method was introduced to consider the dynamic construction process. The composite stiffness EI and bi-parameters m and n were obtained through the back analyses from the field measurement. The result showed that both the calculated horizontal displacement and bending moment by the method proposed in this paper were in good agreement with the measured data. In contrast，the result by the current single-parameter method was unsatisfactory. The parameters obtained through the back analyses can be applied to the uniform structures in the same foundation pit or similar retaining structures and engineering geological conditions in the same areas. Undoubtedly it can obtain more accurate results than the current single parameter method.

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Study of bearing capacity of a single pile in sand considering the mud cycle time

ZHAO Chunfeng1，2，LIU Fengming1，2，YANG Yanzong3，ZHAO Cheng1，2

2016, 35 (S1): 3323-3330 doi: 10.13722/j.cnki.jrme.2015.0721

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For the bored pile with slurry wall protection，it is necessary to take use of mud protection in the forming process of cast-in-situ bored piles，which makes mud cakes around piles too thick，resulting in decreasing of the bearing capability of single pile and failure to meet design requirements. Indoor model tests on the behaviours of four bored piles with slurry wall protection under compression were presented. The four piles have different mud cycle times and instrumented with strain gauges along the pile shafts. The results show that along with the mud cycle time of single pile increase，the pile top settlement increases，when other conditions keep the same. It was shown that the top settlement of test piles of S2，S3 and S4，respectively increases 14.0%，26.2%，and 53.8% comparing with the test pile of S1. The distribution of axial force of piles was related to the mud cycle time of single pile in the tests，with the increase of the mud cycle time of single pile，the decreasing extent of axial force of piles reduces，the pile side resistance decrease，the resistance of pile tip develops gradually. However，the change of the pile side resistance is different in different depths. The pile side friction resistance increases with the depth under the same displacement between pile and soil，and the threshold displacement for developing side resistance increases with the mud cycle time of single pile increase.

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Effects of contact angle on suction measurement with tensiometers and axis-translation technique in unsaturated soils

YANG Song1，WU Junhua2，HUANG Jianfeng1，DONG Hongyan1

2016, 35 (S1): 3331-3336 doi: 10.13722/j.cnki.jrme.2015.0844

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Contact angle change is going to affect the properties of water-vapour interface in unsaturated soil. In order to study the change of contact angle in suction measurement with tensiometers and axis-translation technique，and the effects of this change on the measurement，based on the principles of surface chemistry，drying process is divided into two parts，one is external forces pattern，another is evaporation pattern. Wetting process is also divided into two parts，external forces pattern and condensation pattern. According to this，in drying process，contact angle characteristics of suction measurement with tensiometer and axis-translation were analyzed. It can be concluded that，in drying process，matric suction measured by axis-translation is higher than tensiometers with the same water content. In wetting process，matric suction measured by axis-translation is smaller than tensiometers with the same water content. The conclusion is proved by contact angle measurement tests and matric suction tests. Different type of suction measurement method should be matched with different situations. The axis-translation should be used in some unsaturated soil problems such as rain infiltration，groundwater level decline. The tensiometers could be applied to drying shrinkage in unsaturated soil.

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Theoretical study of reinforced depth of plastic vertical drain considering the water flux

GAO Huiqiang1，2，MO Haihong1

2016, 35 (S1): 3337-3342 doi: 10.13722/j.cnki.jrme.2015.0967

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Its soil strength increases only a little and its effective depth is very small in the newly hydraulic reclamation silt foundation treatment. A new idea about analysis of reinforcement depth was proposed. The consolidation degree of soil at any point was calculated by iterative method base on the conventional consolidation equation for sand-drained ground under negative pressure，and the reinforced depth was deduced through the consolidation degree. The variation of reinforced depth was analyzed. The results show that：fill in the vacuum preloading of the newly hydraulic reclamation silt foundation，the water flux of plastic vertical drain(PVD) have a significant influence on the effective reinforced depth. Within a certain period of consolidation(90 days)，the hard soil layer between the PVDs will form 5–10 m. The thickness of hard soil will increase by extending consolidation time. When the water flux dropped 60%，the reinforced depth will little change with increasing consolidation time. Therefore，influence of PVDs water flux is considered in design and construction.

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Characteristics of macropores in soil of slope under different vegetation measures

ZENG Qiang1，XU Zemin1，GUAN Qi2，CHEN Jipu1

2016, 35 (S1): 3343-3352 doi: 10.13722/j.cnki.jrme.2015.0293

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We had collected the soils of high-cover basalt slope grown with Pinus yunnanensis and Cynodon dactylon，and investigated the properties of macropores which have a significant effect on the formation and occurrence of landslide based on the water breakthrough method and variance，regression analysis. It was demonstrated that the vegetation type can not control the general evolution law of the water movement in macropores，but it does influence the amplitude and stability time of the water breakthrough curve. The two soils showed the characteristic that large diameter(＞2.4 mm) macropores accounts less amount，and the small macropores accounts more. Different vegetation soils have the different macropore quantity in different depth，but it has no influence on the spatial distribution of large macropore quantity. The diameter of macropores in the two soils mainly concentrate in 2.6–0.6 mm，while the range of average diameter is 1.86–1.0mm. Macropore size range is much more controlled by the type of vegetation than its size distribution. The water flow rate in different vegetation soils are influenced in different level by the macropore character. On the whole，with the depth increases，the two soils macropore quantity，average-maximum-minimum diameter，macroporosity and the stable infiltration coefficient will decrease. Roots and organic matter have different influence on macropores properties in different vegetation soils. For soils grown with Pinus yunnanensis and Cynodon dactylon，particle distribution has no obvious contribution to the the macropores properties in different depths. The results have shown that the macropores lower limit scale value is 600 μm.

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Effect analysis of excess pore water pressure on face stability caused by thrust undulation

SONG Jinhu1，CHEN Kunfu2，MA Yuan3，AN Libin1

2016, 35 (S1): 3353-3364 doi: 10.13722/j.cnki.jrme.2014.0883

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In shield tunnlling there are many factors can affect the stability of the thrust force such as the changes of geology conditions，soil cutting by the cutter head，and the regular stop of the shield for segment assembly. The excess pore water pressure caused by the fluctuations force can be accumulated so large that the stability of the tunnel face could be affected. The layered soil analysis model was established at first and the calculation method of the excess pore water pressure near tunnel face was obtained by combining the Terzaghis one-dimensional consolidation theory. Then the calculation method of the effect of the excess pore water pressure on the tunnel face stability was given out using the wedge analysis model. From the calculation result it can be concluded that the safety factor of tunnel face can be reduced by the excess pore water pressure. So the effect of the fluctuations thrust force should be considered in the calculation of the minimum support face pressure. At last the excess pore water pressure and the decreasing coefficient of safety factor with different construction conditions were given out through parameter analysis.

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Experimental study of head fixity conditions of pile group in sheet-pile bulkhead

(1. State Key Laboratory of Hydrology-water Resources and Hydraulic Engineering，Nanjing Hydraulic Research Institute，Nanjing，Jiangsu 210029，China；2. HydroChina Guiyang Engineering Corporation Limited，

2016, 35 (S1): 3365-3371 doi: 10.13722/j.cnki.jrme.2015.0957

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Laterally loaded vertical piles with load-relief platform has successfully been introduced to deep-water sheet-pile bulkhead so that a part of massive lateral load due to horizontal soil movement can be transferred through pile group on to deeper and larger soil layers to keep the bulkhead stable within allowable displacement limits. Two types of head fixity conditions，capped head and pinned head，are often used in pile group. Obviously，head fixity conditions have great effects on force bearing status and displacement characteristics of cast-in-place piles，load-relief platform and other structural elements in the sheet-pile bulkhead. Two series of centrifuge model tests are carried out to simulate the sheet-pile bulkheads with pile group with two different head fixity conditions. The bending moments of piles and front wall，earth pressures on retaining side of front wall are measured together with tension forces of tie-rod and horizontal displacements of structural elements. It is found that the lateral pile group with capped head is more powerful than the pile group with pinned head in carrying earth pressure load，reducing tension forces of tie-rods and limiting horizontal displacements of structural elements. However，it is also found that the maximum bending moments of piles with capped head occur close to the pile cap level，and the estimated values are equal to the value of pile's maximum allowable bending moment. Therefore，it is appropriate to the lateral pile group with pinned head which can eliminate the above problem while tension force of tie-rod and inclination of front wall due to horizontal displacement can also be controlled within their allowable limits.

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Three-dimensional DEM simulation of cone penetration test by using circumferential periodic boundary

YANG Yancheng1，DENG Yibing1，SHI Danda1，XUE Jianfeng2

2016, 35 (S1): 3372-3384 doi: 10.13722/j.cnki.jrme.2015.1124

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In order to explore the micro-mechanism of CPT，a new circumferential periodic boundary was developed to consider the three-dimensional axisymmetric problem with 1/4 of the cylinder. To validate the method，a drained triaxial test was modeled with the proposed method and the traditional full model. The results are comparable and the proposed method is very effective. The method was further used to simulate a cone penetration test in dry Fontainebleau sand. It was found that，the variation of cone radial stress and tip resistance during penetration from the model are in good agreement with the reported test results. The micromechanical responses，such as the distributions of particle displacement，internal stress and local porosity to cone penetration are extensively studied. The evolutions of fabric anisotropy during penetration are also discussed. The relationship between stress and fabric is quantitatively described using fabric tensor，which reveals the mechanism of cone penetration capacity microscopically. The results of the work not only improve the efficiency of three-dimensional discrete element method(DEM) simulation，but also promote better understanding of CPT mechanism.

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Quantitative research on grouting reinforcement of soft fluid-plastic stratum

SUN Zizheng1，LI Shucai1，LIU Rentai1，GAO Bo2，ZHANG Qingsong1，ZHANG Lewen1

2016, 35 (S1): 3385-3393 doi: 10.13722/j.cnki.jrme.2015.1152

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Characteristics of soft fluid-plastic stratum include low load-carrying capacity，poor cementing power and rich water，which makes it much difficult to control. In order to study the relation between grouting parameters and physico-mechanical parameters of soft fluid-plastic stratum，field tests of the grouting reinforcement were carried out using cement-silicate grout with different proportions. Based on the formation macro mechanics performance，the quantitative relation of grouting influencing factor and improvement of physical and mechanical properties of the soft fluid-plastic stratum is established via analyzing the change law of elastic modulus，cohesion，internal friction angle and permeability coefficient. Moreover，the criterion on excavation of soft ground has been demonstrated based on grouting reinforcement mechanisms. The results would have certain value for developing the grouting reinforcement mechanism of soft fluid-plastic stratum.

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Unloading model test and numerical simulation analysis on high fill loess open cut tunnel with EPS

LI Sheng1，LI Shanzhen1，WANG Qicai1，MA Li2，WANG Qingshi1，XU Wenqi1

2016, 35 (S1): 3394-3401 doi: 10.13722/j.cnki.jrme.2015.1401

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In order to study the unloading effect and mechanism of EPS，through the indoor model test，the change rule of vertical earth pressure and soil displacement were studied on trench high fill loess open cut tunnel of load reduction with different densities and thickness EPS. The results show that laying EPS at a certain height of open cut tunnel can change the direction of relative settlement，cause the soil stress redistribution，promote the formation of the soil arch effect and reduce the vertical earth pressure on the top of the open cut tunnel. The smaller EPS density，the bigger the thickness，the vertical earth pressure unloading on the top of open cut tunnel is obvious. At the same time，the vertical earth pressure distribution is decrease→increase→decrease with the increase of distance from the axis as laying EPS，it appears turning point in 0.7 and 1.3 times width. Finally，through the comparison of the numerical simulation and model test，the accuracy of model test and the rationality of selected parameters of numerical simulation are tested. The soil arch effect showing the stress concentration are vividly described by using numerical simulation method，the unloading mechanism of EPS is reveals. The research results can provide reference basis for design and construction of the EPS unloading measures for trench high fill loess open cut tunnel.

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A dynamic behavior test new technology with electromagnetic excitation and its application for soil residual force testing

LI Zhangming1，GUO Lingfeng1，LI Zhengdong1，LAI Jiankun1，ZHAO Zhilin1，WANG Qian1，YANG Wenlong2

2016, 35 (S1): 3402-3407 doi: 10.13722/j.cnki.jrme.2015.1542

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In order to supplement the existing geotechnical engineering testing technology，for indoor geotechnical engineering impact test and in-situ dynamic plate load testing，a test device and a test method for high-energy electromagnetic force impact of intelligent control were developed，and applied to residual force study in soft ground treatment with static-dynamic drainage consolidation(SDDC). Under the complex stress conditions with SDDC，the residual force test results showed that：(1) The high-energy impact test was carried out very well with the multi-level electromagnetic impact instrument，and the impact force on the impacted object is the object quality 2 000 times more. (2) Under a certain impact load and soil storage conditions，the phenomenon of residual force in soil does exist. (3) The residual stress in soil is mainly related to soil structure and structural changes，and has a certain relationship with the consolidation process in SDDC.

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Calculation method of additional load of adjacent metro tunnels due to foundation pit excavation

WEI Gang，ZHAO Chengli

2016, 35 (S1): 3408-3417 doi: 10.13722/j.cnki.jrme.2015.1551

[PDF] 2885 KB (141)

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To consider the influence of the soil unloading stress of the bottom and the surrounding walls by the foundation pit excavation and retaining structure，the mechanics model of foundation pit excavation was established. Based on Mindlin formula，the calculation formula of metro tunnels additional load caused by adjacent foundation pit excavation was derived. And the influence factors were analyzed，such as the foundation pit excavation size and tunnel position and the reinforcement control measures. The calculation results show that：(1) Soil unloading stress of the surrounding walls has a large effect on tunnel when the foundation pit beside tunnels，conversely the influence of soil unloading stress of the bottom is small. However，the influence of soil unloading stress of the bottom will increase when the depth of excavation is shallow. (2) In the horizontal direction to the foundation pit，the pull power on the tunnel is large. But In the vertical direction，the pressure power up or down on the tunnel is small. (3) The change of s，B，d and β will play a largest important role in the stress of tunnels in the horizontal direction. The influence of the change of L is second. And the influence of h is the smallest. (4) The change of d will play the most obviously important role in the stress of tunnels in the vertical direction，then is the change of s，B. The influences of other factors are not obvious.

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A testing method for shear-wave velocity and relative density of cohesionless soil using bending-element technique

WANG Yunlong，CAO Zhenzhong，YUAN Xiaoming，CHEN Longwei

2016, 35 (S1): 3418-3423 doi: 10.13722/j.cnki.jrme.2015.1382

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Shear-wave velocity and relative density are important parameters to assess the properties of cohesionless soil. To measure the shear wave velocity of gravelly soil，a combined test system of shear-wave velocity and relative density was developed. The system was established on a specific steel bearing cylinder combining bending-element technique，and then applied on soil samples with different relative densities prepared by a vertically vibrating table. The first-arrival time of shear-wave in bending-element technique is corrected. The system is designed to test shear-wave velocity of gravel with maximum particle diameter less than 50 mm，and then to build relationships of shear-wave velocity with respect to relative density of cohessionless soil. Four types of samples，i.e.，standard sand samples，granite samples，60% gravel content samples constituting of standard sand and granite，and samples prepared according to the mean grading of gravelly soil that liquefied in Wenchuan earthquake，are tested and the results indicate that shear-wave velocity of gravelly soil is large than sand under same relative density. Shear-wave velocity of gravelly soil increases exponentially with respect to increasing relative density. Comparing to GDS apparatus，the testing shear-wave velocity of gravelly soil are similar yet the design system is more applicable and more convenient.

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Experimental study of the thermal effect of pile bottom water on the rheological property of model pile-frozen soil

WU Yaping1，LIU Zhen1，WANG Ning1，LIU Yazun1，LU Xiaoqiang1，NIU Fujun2

2016, 35 (S1): 3424-3431 doi: 10.13722/j.cnki.jrme.2015.1088

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In order to investigate the influence of pile bottom water on the stability of pile foundation in frozen soil，the concrete model piles and pile bottom water thermal device were made. The contrast experiment method was adopted by loading step by step to study the effect of pile bottom water heat on the rheological properties of frozen soil pile-soil，in which transfer curves of tangential freezing stress on pile body and pile tip resistance were obtained. Under the different load level，the influences of pile bottom water on the relative displacement between pile and soil，pile tip resistance，rheological characteristics of pile-soil，load transfer characteristics，and bearing characteristics of pile foundation were analyzed. The results show that the pile bottom water weaken the freezing strength of frozen soil in pile side and soil resistance at pile bottom，which increase relative displacement between pile and soil and pile-soil rheological effect. The pile bottom water can impact the load proportion of the freezing force and end resistance of a pile foundation，in which the pile foundation is excessively dependent on the tangential freezing stress on pile body to bear the load. Above effects increased with the load level result in a serious decline of bearing capacity of pile foundation.

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Indoor experiment on vacuum preloading of wheat straw roller

LIANG Tonghao1，YAN Zhengchun1，LIU Chao2，YU Xiaojuan3

2016, 35 (S1): 3432-3440 doi: 10.13722/j.cnki.jrme.2015.1118

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As coastal development proceeds，the disposal of silt with high water content raises challenges to engineering construction in coastal soft soil areas. Because conventional approaches such as excavation，replacement，drying or modification with ash are either costly or restricted by site，weather or other factors，and straw combustion causes air pollution，wheat straw rolls was proposed to be used as new vertical drains in place of sand drain or plastic drainage board used in traditional vacuum drainage consolidation for treating silt with high water content. For discussing the feasibility and applicability of treating silt with high water content by straw drains on vacuum preloading，a series of indoor experiments have been performed. For providing theoretical basis for optimization design of straw drain，the sensitivity analysis on factors influencing drainage result and theoretical research on the optimal level combination design have been made. Indoor experiments show that treating silt with high water content by straw drains on vacuum preloading is feasible and effective. The larger is the diameter of straw roll，the better is the drainage effect，and the larger is the consolidation settlement. Indoor experiment and grey correlation analysis reveal that the diameter is more sensitive than the initial density. Indoor experiments and variance analysis reveal that the diameter of straw roll is the primary factor while the initial intensity is the secondary factor and the optimal combination of the factors is 20 cm diameter and 0.121 g/cm3 density.

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The quantitative relationship of soil resistivity and saturation degree

NIE Yanxia1，2，HU Liming1，2，WEN Qingbo1，2

2016, 35 (S1): 3441-3448 doi: 10.13722/j.cnki.jrme.2015.1190

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At present，high-density electrical resistivity tomography(HERT) has been widely used in environmental geotechnical engineering，especially seepage and solute transport. High-density electrical resistivity tomography provides a new method to satisfy the necessities of three-dimensional，non-destructive，and real-time measurement. In order to carry out soil seepage migration process of observation and quantitative analysis，a quantitative relationship model of soil resistivity and saturation needs to be established. The calibration tests are carried out to determine the quantitative relationship between the soil resistivity and saturation of the soil combined Archie model，and the 1 g model tests are used to verify the quantitative formulas validity and applicability. The results show that the real-time saturation data obtained by the quantitative formula of soil resistivity and saturation correspond well with the measured data. The accuracy of the quantitative formula of soil resistivity and saturation meets the requirement. Based on the quantitative formula of soil resistivity and saturation，high-density electrical resistivity tomography can be applied to achieve real-time measurement and quantitative analysis of seepage mechanism in soil.