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2009, 28 (12): -0 doi:
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DEVELOPMENT OF THERMO-GASEOUS-MECHANICAL COUPLING TRIAXIAL TESTING SYSTEM OF LOW PERMEABILITY MEDIUM AND ITS APPLICATION

YANG Jianping，CHEN Weizhong，TIAN Hongming，WU Guojun

2009, 28 (12): -2382 doi:
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[PDF 303 KB] (1603)

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A new thermo-gaseous-mechanical coupling laboratory apparatus measuring rock properties is developed and used to measure gas flow rate for two different specimen sizes of 50 mm and 100 mm in diameter. Either axial or radial permeability way can investigate gas transport properties in rocks. The maximum test temperature is 90 ℃，the maximum axial force of triaxial piston can be 1 000 kN and the maximum confining pressure is 40 MPa. Difficult techniques for permeability test of low permeability medium such as long testing time(lasting one week)，sample sealing performance under high temperature(less than 90 ℃)，accuracy of micro-flow measuring，uniformity and constancy of testing temperature during test are solved. Tests are carried out on dense marble samples taken from Jinping II hydropower station. Test results show that the apparatus can satisfy the requirement for thermo-gaseous-mechanical coupling test for low permeability medium. Using this equipment，transport parameters of surrounding rock are available for environment evaluation and steady analysis in important projects such as oil/gas storage in depth，oil/gas exploitation in low permeability oil/gas field，gas drainage in gas mine and geological disposal of high radioactive waste.

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STUDY OF COMPLEMENTARY SUPPORTING TECHNOLOGY OF EXTREMELY SOFT ROCK MINING ROADWAY

JIANG Yaodong1，2，WANG Hongwei2，ZHAO Yixin1，2，LIU Changhai3，ZHU Xidong3

2009, 28 (12): -2390 doi:
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By using the method of strengthening broken rock and increasing supporting resistance，the mechanical properties，deformation and failure characteristics of surrounding rocks in Xiaokang coal mine are analyzed. Meanwhile，the instability mechanism of soft rock mining roadway is obtained and it is pointed out that the main reasons of supporting failure are inconsistent deformation，low supporting resistance and failure to utilize the supporting capability of the surrounding rocks. Taking the S2N8 haulage roadway of Xiaokang coal mine for example，the complementarity of the high strength bolt，high pretension cable，metal mesh and U-shaped contractible frame in the process of reinforcing surrounding rock is studied. Based on these studies，the complementary supporting technology of high strength and pretension bolt-mesh-cable supporting together with U-shaped contractible frame is introduced. In addition，in-situ industrial test has also been implemented；and the results show that the complementary supporting system can successfully avoid the multi-rebuilding in extremely soft rock mining roadway and the supporting once for all in Xiaokang coal mine can be adopted.

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UNIAXIAL COMPRESSION EXPERIMENTAL RESEARCH ON DEFORMATION AND FAILURE PROPERTIES OF BRITTLE MARBLE SPECIMEN WITH PRE-EXISTING FISSURES

YANG Shengqi1，DAI Yonghao2，HAN Lijun1，HE Yongnian1，LI Yushou1

2009, 28 (12): -2404 doi:
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[PDF 475 KB] (1392)

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Uniaxial compression experiments were carried out for brittle marble with pre-existing fissures by the rock mechanics servo-controlled testing system. Based on the experimental results of complete deformation curves，the effect of the geometric distribution of fissure parameters(bridge angle，fissure distance，fissure length，fissure number and fissure angle) on the deformation and failure properties of brittle marble were analyzed. Compared with the intact marble，the marble with pre-existing fissure takes on the localization deformation and asymptotic failure. The peak strength，elastic modulus and peak axial strain of marble with pre-existing fissure are all lower than that of intact marble，and the reduction extent is closely related to the distribution forms of pre-existing fissure. Expect for the marble sample with fissure distance equals 48 mm(the reduction amplitude of deformation modulus is 24.8%)，the marble specimen with bridge angle equals 120°(23.7%) and the marble sample with fissure angle equals 60°(43.8%)，the reduction amplitude of deformation modulus is in the range of －3.8% to 7.8% for other marble samples with two pre-existing fissures，in which the difference is smaller. The longer the fissure length is，the more the fissure number is and the larger the fissure angle is；the lower the peak strength，the elastic modulus and peak axial strain are；however there are no distinct laws between the bridge angle，fissure distance and mechanical parameters of marble sample. The failure mode of marble specimen takes mainly on the four modes：tensile mode，compression mode，shear mode and mixed mode，which are closely related to the geometric distributions of pre-existing fissure. The intact marble sample takes on the typically axial splitting tensile mode. The rock samples with the shorter fissure length(16 mm) and the smaller fissure angle(30°) take on the tensile mode，however the rock samples with the longer fissure length(24 mm) and the larger fissure angle(60°) take on mixed mode(shear and tensile). The smaller the fissure distance is，and the more the fissure number is，the more complexed the coalescence mode of rock samples is，which takes on mixed mode(shear，tensile and compression).

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STUDY OF CONNECTIVITY OF DISCONTINUITIES OF BOREHOLE BASED ON DIGITAL BOREHOLE IMAGES

WANG Chuanying1，ZHONG Sheng2，SUN Weichun3

2009, 28 (12): -2410 doi:
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[PDF 266 KB] (1023)

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The extension of a discontinuity and the connectivity of discontinuities in adjacent boreholes were discussed. The conditional restriction of connectivity of discontinuities in adjacent boreholes was further studied according to their depths，rock characters and filling conditions of the discontinuities in adjacent boreholes. Finally，a case study of the discontinuities of adjacent boreholes in certain mining area was given；and it is proved to be available for determining the connectivity of discontinuities in adjacent boreholes by the method of digital borehole images.

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ACOUSTIC EMISSION EVOLUTION IN INDENTATION FRACTURE OF ROCKS UNDER DIFFERENT LATERAL STRESS-FREE BOUNDARIES

CHEN Lihsien1，HUANG Kuochung2，CHEN Yaochung2

2009, 28 (12): -2420 doi:
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[PDF 574 KB] (1132)

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Automatic efficiency and engineering safety are both enhanced by using mechanical excavation in tunnel construction；nevertheless，the mechanism for excavation by mechanical cutter is still uncertain. The interaction between the cutter and the position of weak plane during cutting is important for studying the behavior of rock fragmentation，so quasi-brittle materials were used to investigate the fracture mechanism of wedge indentation in order to provide references for the construction in practice. Equipment of a normal wedge indentation was established；and non-destructive acoustic emission(AE) technique was applied for the tests. It simulates discontinuous weak plane of the open joint under the lateral stress-free boundary for indentation at various positions by a wedge with a sharp-shaped tip at angle of 90°. In order to obtain a complete loading history，crack mouth opening displacement(CMOD) control was adopted to avoid unstable fracture after the peak level. From the experimental results，features of geometrical similarity were observed for the crack paths at different indentation positions. When positions approach to the lateral stress-free boundary，the maximum indentation force and the maximum indentation depth both decrease；however，the impact for nominal indentation pressure is not significant. Moreover，it is figured out that microseismic events received by the AE technique can stand for the initiation of the microcracks. Outcomes of AE locations are verified to be very precise by comparing the microseismic events with the macroscopic initial fracture and its development. Localization takes place earlier as indentation approaches to the lateral stress-free boundary；and the radius of elastoplastic interface becomes smaller.

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ROADWAY SUPPORT DIFFICULTY CLASSIFICATION AND CONTROLLING TECHNIQUES FOR HUAINAN DEEP COAL MINING

ZHANG Nong，WANG Cheng，GAO Mingshi，ZHAO Yiming

2009, 28 (12): -2428 doi:
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[PDF 280 KB] (1184)

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系统分析淮南矿区深部煤巷围岩赋存的地质特征、控制难度和应力状态等因素，确定影响煤巷稳定及锚杆支护选型的最主要和敏感因素为巷道顶板应力强度指数、帮部煤体松散范围系数、顶板软弱岩层不安全因子3个综合指标，通过大量测试矿区深部巷道围岩地应力和煤岩试块物理力学性能，对这3个综合指标体系进行科学合理分类，在此基础上划分深部煤层巷道围岩稳定性控制难度级别，针对各难度级别，提出以新型“三高”(高强度、高预拉力、高刚度)锚杆控制技术为基础的深部煤巷围岩控制对策。应用该方法对矿区几个典型矿井的深部煤层巷道围岩稳定程度进行难度分级，采取针对性技术措施和支护参数，维护巷道稳定。研究成果在淮南矿区获得全面应用，对我国煤矿深部煤层巷道支护技术具有一定的理论意义和实用价值。

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COMPREHENSIVE ANALYSIS METHOD FOR ADVANCED FORECAST OF GEOLOGY IN TUNNELS

LI Tianbin1，MENG Lubo1，ZHU Jin1，2，LI Yonglin2，MOU Li2

2009, 28 (12): -2436 doi:
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[PDF 222 KB] (1873)

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By the analysis of physical difference of tunnel media and comparative evaluation of suitability of common advanced prediction of geology，a principle of comprehensive prediction that takes the geological analysis as the target，combining geological analysis and geophysical exploration，considering the condition inside and outside of the tunnel，employing long-term and short-term prediction methods，and adopting mutual geophysical parameters，is proposed. The system and organization of comprehensive geological prediction in tunnels are established. Then，the comprehensive prediction workflows of common unfavorable geological conditions such as fault，breaking of rock mass，enriched groundwater，karst，soft rock mass in tunnels are presented. Parameters of relevant geological and geophysical prospecting characteristics are given；and comprehensive classification system is built. Finally，a comprehensive prediction model for solving geological problems has been constructed with fuzzy neural network(FNN). The comprehensive prediction system is used in Tongluoshan karst tunnel and the accuracy of the prediction is 80%.

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IMPROVEMENT OF WETTING DEFORMATION ANALYSIS METHOD OF COARSE-GRAINED MATERIALS

SHEN Guangjun，YIN Zongze

2009, 28 (12): -2444 doi:
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[PDF 282 KB] (952)

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The advantages and disadvantages of single-line method and double-line method for determining wetting deformation of coarse-grained materials are analyzed. The idea of combining single-line method test with double-line method to solve wetting deformation problem is presented. The wetting deformation tests of coarse- grained materials are carried out on the single-line method and double-line method by use of large triaxial test apparatus. Some laws of the test results between the single-line method and the double-line method are found by studying the wetting deformation characteristics. The test results by other scholars also verify these laws. The mechanism of these laws is discussed. Based on these laws，an improvement analysis method for determining wetting deformation is presented. Finally using improvement method and double-line method to predict the result of the experiment；the predicative results show that the improvement method is much better than the double-line method. The calculated results of the improvement method are quite agree with the test results.

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LOADING CONDITION FOR SPECIMEN DEFORMATION AT CONSTANT STRAIN RATE IN SHPB TEST OF ROCKS

ZHOU Zilong1，2，LI Xibing1，YAN Xiaoming1

2009, 28 (12): -2452 doi:
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[PDF 350 KB] (1399)

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The relationships among specimen stress，incident stress，reflected stress and transmitted stress were analyzed；and the loading condition for specimen deformation at constant strain rate was found out，i. e.，only when the loading stress and deformation stress in specimen have the same changing pattern，the specimen deforms at a constant strain rate. The tests show that constant strain rate of specimen can be achieved by pulse shaper method and special shape striker method. Double specimen method is actually a special case of pulse shaper method. Pulse shaper method is favorable for tests of perfect elastic brittle material. And special shape striker method is useful for the split Hopkinson pressure bar(SHPB) tests of materials with power function constitutive relation or materials with no foregone constitutive information. Special shape striker method has more repeatability than pulse shaper method. Special shape striker method with half-sine incident wave can reduce the influences caused by wave dispersion.

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INFLUENCE OF COUPLE STRESSES ON CRACK GROWTH AND ITS SCALE EFFECT

ZHANG Dunfu1，LI Shucai1，2，NIU Haiyan1，LI Xiaoqin1

2009, 28 (12): -2458 doi:
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[PDF 270 KB] (999)

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Compared with the classical elasticity theory，couple stresses theory considering the rotation of the micro structure of the gradient(i. e.，bending curvature)，can show effects of bending deformation. The meshless method and the couple stress theory were combined together. Discrete model of element-free Galerkin method based on couple stresses theory was provided. The maximum circumferential tensile stress crack propagation criterion was adopted. The crack-I plane problem in tension was studied to determine the basic parameters of the method and to solve the key technology of the algorithm application. The initial rupture of crack in rock mass under compression was studied with different micro scales. And then crack growth trace in rock mass loaded compressive stress was numerically simulated with a given micro scale. The results indicate that the couple stresses have no effect on crack-I and a significant influence on complex crack bending propagation. For complex crack，crack propagation angle，crack propagation steps and crack propagation load show remarkable scale effects.

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COMPRESSION BEHAVIORS OF CRUSHED COx ARGILLITE USED AS BACKFILLING MATERIAL IN HLW REPOSITORY

TANG Chaosheng1，CUI Yujun2，TANG Anh-Minh2，SHI Bin1

2009, 28 (12): -2465 doi:
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[PDF 250 KB] (850)

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In high-level radioactive waste(HLW) repository，backfilling material should be pre-compacted. The compression characteristics are very important for the design and security of HLW repository. The Callovo- Oxfodian(COx) argillite(France) is now proposed，after being crushed and compacted，as an alternative backfilling material in the geological HLW repository. In this investigation，the compression behavior of COx argillite with two different grain size distributions(GSDs)，which were obtained by two different crush procedures，was studied by running 1D compression tests with several loading-unloading cycles. It is found that the compression curves are significantly influenced by the GSD of the soils. To obtain the same degree of compaction，the axial stress applied to finer soil is much higher than that of coarser soil. In addition，the compression index at initial water content of the finer soil is bigger than that of coarser soil. During the compression，both the compression curves of the finer and coarser soils tend to be close to each other with increasing dry density. It is shown that the effect of GSD on the compression behavior is weakened after the soil is highly compacted. The swelling index at initial water content increases with the dry density and seems to be independent of the GSD. During saturation，the highly compacted coarser soil sample(rd = 2.0 g/cm3) shows evident collapse behavior under 7 MPa axial stress. The compression index decreases and the swelling index increases after the saturation.

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WATER INRUSH COEFFICIENT-UNIT INFLOW METHOD FOR WATER INRUSH EVALUATION OF COAL MINE FLOOR

QIAO Wei，LI Wenping，ZHAO Chengxi

2009, 28 (12): -2474 doi:
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[PDF 386 KB] (1314)

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Based on the water inrush coefficient Ts，the unit inflow q，an index reflecting water bearing of the aquifer，is introduced. Based on statistical analysis of a large number of examples of water inrush，the relationships between water inrush potential，water inrush coefficient，and the water-enriched properties of aquifer are further researched. The achieved laws of water inrush are discussed. And a new method for evaluating risk of floor water inrush is put forward. The method of water inrush coefficient-unit inflow method can be a supplement for evaluating water inrush coefficients. The achieved results can be provided for evaluating water inrush risk of floor in deep mining of some mining areas，in which the water-enriched properties of aquifer are not obvious but water inrush coefficient is larger.

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TEST STUDY OF 3D DEFORMATION FEATURE OF SPECIAL MOVEMENT JOINT OF SECTIONAL HORSESHOE-SHAPED TUNNEL CROSSING GROUND FISSURE

HU Zhiping1，WANG Qiyao1，HUANG Qiangbing2，ZHU Qidong1，LI Anxing1

2009, 28 (12): -2481 doi:
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[PDF 474 KB] (1051)

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In order to study the three-dimensional(3D) deformation feature of special movement joint and the deformation failure model of sectional horseshoe-shaped tunnel lining structure crossing the ground fissure with 40°，the sectional horseshoe-shaped tunnel lining structure modelling experiment crossing the ground fissure with 40° is designed，which is based on the Xi¢an metro tunnel engineering and the geological environment of Xi¢an ground fissure and similarity theory. The soil settlements on the top of model，the bottom soil pressure and the 3D deformation character of the movement joint show that the deformation and damage mode of lining structure of sectional horseshoe-shaped tunnel crossing the ground fissure with 40° are shearing failure alone the movement joint in global. The deformations of movement joint include vertical dislocation，axial tension and horizontal offset，but the lining structure concrete is not damaged. The 3D deformation component of movement joint on lining structure crown is larger than that on lining structure soffit，and the distribution rule of deformations both on crown and soffit is the same. The vertical dislocation of hanging side is larger than that of lying side，but the difference of axial tension between hanging side and lying side is small；and the horizontal offset occurs on the ground fissure mainly. According to the similarity theory，when the settlement of hanging side of ground fissure is up to 90 cm，the total vertical dislocation of five movement joints will be up to 72 cm；and the total axial tension will be up to 34.5 cm；the maximum horizontal offset will be up to 32 cm.

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ROCK MASS STRUCTURE DIGITAL RECOGNITION AND HYDRO-MECHANICAL PARAMETERS CHARACTERIZATION OF SANDSTONE IN FANGEZHUANG COAL MINE

YANG Tianhong，YU Qinglei，CHEN Shikuo，LIU Honglei，YU Tianliang，YANG Liming

2009, 28 (12): -2489 doi:
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[PDF 662 KB] (1257)

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A 3D contact-free measuring system(3GSM) is employed to acquire the geometrical information of rock mass structures of sandstone in the 12th coal seam floor of Fangezhuang coal mine. A series of digital images of rock mass surface are captured by the system. And then the spatial distributed information of the geometric configuration of joints is extracted from the images to rebuild the 3D digitized fracture network of rock mass；and the connectivity of the fracture network is identified. On the basis，the characterization method of hydraulic parameters of rock mass is established based on the discrete medium mechanical model and in-situ data. By using this method，hydraulic parameters of sandstone in the 12th coal seam floor are determined；and the size effect of the parameters is also studied. The works can realize the optimum connection between the digital information of rock mass structures and the quantitative determination of hydraulic parameters，so as to provide more reliable basic data for the stability analysis of rock engineering and risk evaluation of water inrush of the 12th seam floor in Fangezhuang coal mine.

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EXPERIMENTAL STUDY OF FAILURE CHARACTERISTICS OF ROCK CONTAINING FLAW UNDER CYCLIC LOADING

HU Shengbin1，2，DENG Jian2，MA Chunde2，WANG Weihua2

2009, 28 (12): -2495 doi:
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[PDF 319 KB] (1205)

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Experimental study of failure characteristics of rock containing flaw under cyclic loading is carried out by using similarity materials. The similarity materials are elaborately designed by cement mortar and filling materials to simulate rocks with hole，flexible filling，or rigid filling. The characteristics of rocks containing flaw for the low-cycle fatigue damage are observed；and the three stages of the irreversible uniaxial deformation process are presented. Different defects in rock-like materials have great influence on their fatigue life and initiation and propagation of fatigue cracks. Experimental results show that the uniaxial deformation can be divided into three stages：initial deformation stage，constant-speed deformation stage，and acceleration deformation stage. Fatigue cracks are prone to initiate and propagate on the interface of defective and basis materials，where stress is concentrated. Conclusion can be made that with the same load conditions and the same sizes of flaw，the greater diameter of the hole is，the shorter fatigue life of hole-defect specimen is. It is also found that the fatigue lives of rigid-filling specimens are the shortest；the hole specimens take the second place；flexible-filling specimens have the longest life.

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EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF LAYERED MARBLE UNDER UNLOADING CONDITION

PEI Jianliang，LIU Jianfeng，XU Jin

2009, 28 (12): -2502 doi:
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[PDF 287 KB] (1143)

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The layered marble samples are collected from the underground powerhouse of Jinping I hydropower station which is a large-scale national key project. To simulate the excavation unloading effect，a series of triaxial unloading tests are carried out on MTS815 Flex Test GT rock mechanics test system，and a series of triaxial loading tests for comparison are also performed. The results show that there are obvious differences among mechanical properties of layered marble with different axial compression directions. When the axial compression parallels bedding plane，the shear strength parameters c and φ decline but residual strength parameter φr increases under unloading condition. When the axial compression is perpendicular to bedding plane，the shear strength parameters c and φ increase but residual strength parameter φr declines compared with the results of axial compression paralleling bedding plane under the same unloading condition. The prompt lateral expansion causes the failures of these rock samples and confining pressure unloading after peak strength significantly weakens their bearing capacities. The elastic modulus increases approximately with initial confining pressure increasing in loading and unloading cases，but the rule of deformation modulus at peak strength is reverse. For a single sample under unloading condition，whether axial compression is perpendicular to or parallels the bedding plane，the deformation modulus always decreases with confining pressure declining；and the value of the former is 20%–51% higher than that of the latter；but the lateral expansion ratio(m) of the former is 3%–12% lower than that of the latter；and the rule is reverse. Under the same unloading condition，axial compression paralleling bedding plane is more easily to cause the failure of rock samples than axial compression perpendicular to bedding plane；but the latter samples are of more obvious brittleness. These conclusions reveal the unloading properties of layered marble and offer important reference to solve practical engineering problems.

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APPLICATION OF EXTENICS METHOD TO COMPREHENSIVE SAFETY EVALUATION OF ROCK SLOPE

TAN Xiaolong1，2，XU Weiya1，2，LIANG Guilan3

2009, 28 (12): -2509 doi:
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[PDF 189 KB] (1157)

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A multi-hierarchy and multi-index comprehensive evaluation system of rock slope is established；and the safety grade standard and the corresponding range of index are suggested as well. Based on matter element theory and the dependent function of extenics set，the extenics evaluation model for rock slope is proposed. Meanwhile，the detailed implementing approach is presented and the relevant numerical computation code is programmed. The method is applied to evaluating the comprehensive safety of the high rock slope on the left spandrel groove of Jinping I hydropower project. It is obtained that the grade eigenvalue is 4.001 and safety grade is IV which means that the comprehensive safety grade of the high rock slope is between hyper-stability and stability. This case has shown that the extenics evaluation model for rock safety is feasible to evaluate the safety of rock slope comprehensively. This method can be applied to evaluating rock slope during construction period of the project and operation period as well.

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DEFORMATION MONITORING AND CONTROL OF SUPER LARGE SECTION HIGHWAY TUNNEL WITH DIFFERENT SURROUNDING ROCKS

ZHOU Dingheng1，CAO Liqiao2，QU Haifeng3，YI Li4，FANG Shitao5

2009, 28 (12): -2519 doi:
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[PDF 514 KB] (1180)

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Based on Longtoushan tunnel which is the largest in China at present in Guangzhou，the contents，technique and method of deformation monitoring of super large section tunnel are descried. The deformation law of the slope，surrounding rock and support system with different surrounding rocks are analyzed；and the engineering measures to control the deformation are put forward. The result shows that：(1) the construction of the up-stage in the right hole，the down-stage in the left hole and the up-stage of the core soil，which cause large rock deformation，are the main points for controlling the rock deformation；(2) the deformation has a exponential relationship with the radius of tunnel；and (3) the enclose of lining and using of cross anchor is effective method to improve the performance of lining and to restrain the deformation of the tunnel；and it is important to construct the inverted arch and close the lining. The study results can be for reference in the design，construction and research of similar tunnels.

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EXPERIMENTAL STUDY OF DYNAMIC CHARACTERISTICS OF GRANITE UNDER CYCLIC LOADING

ZHU Mingli1，2，ZHU Zhende1，2，LI Gang1，2，QIU Yuhua1，2，CHEN Zhe3，LI Jinwang3

2009, 28 (12): -2526 doi:
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[PDF 292 KB] (1366)

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The uniaxial compression-deformation test，cyclic loading and unloading tests on slightly weathered and middle differentiation biotite granite comes from the Changjiang of Hainan nuclear power first-stage construction conventional island are performed on the RMT–150B multi-function automatic rigid rock servo controlled testing machine. The granite hysteretic characteristics of dynamic stress-dynamic strain curves and the law between elastic modulus and dynamic elastic modulus，damping ratio are researched. And the viscoelastic generalized Kelvin rheological model is used to describe granite hysteresis curve and energy loss. The results show that the curves of strain and stress for loading and unloading are hysteresis loops. With the increase of cyclic number，hysteresis loops move to the direction of axial strain increasing，more and more dense. The areas of hysteresis loop and the maximum elastic strain energy decrease with increase of elastic modulus；however the dynamic elastic modulus is opposite. First，damping ratio increases with increase of elastic modulus；but after reaching its peak value，damping ratio decreases with increase of elastic modulus. The biotite granite hysteretic loop and energy loss can describe well by generalized Kelvin rheological model. The results offer great reference to seismic response analysis and site safety evaluation of the Changjiang nuclear power plant.

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INVESTIGATION ON LAW OF METHANE GAS FLOW IN COAL WITH COAL-GAS OUTBURST HAZARD AND LOW PERMEABILITY

HU Guozhong1，WANG Hongtu2，FAN Xiaogang2，YUAN Zhigang2

2009, 28 (12): -2534 doi:
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[PDF 313 KB] (1390)

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For knowing the law of methane gas flow in coal with coal-gas outburst hazard and low permeability (CCOHLP)，an experimental study of methane gas flow in coal samples，produced by raw CCOHLP from a coal mine at Nantong coalfield，is performed with self-developed triaxial load system and by way of steady-state flow under different confining pressures. It presents the comparison of test data on methane gas flow in CCOHLP processed by the traditional method of computing permeability and the method of fitting permeability with Klinkenberg effect. It is proved by experiments and numerical simulation that：(1) the Klinkenberg effect of methane gas flow in low permeability coal is especially prominent；(2) for the low permeability coal，the Klinkenberg coefficient b and the absolute permeability is related to a power function；meanwhile，the absolute permeability and bulk stress is related to a quadratic polynomial function；(3) the Klinkenberg coefficient b increases gradually with the decreasing absolute permeability；meanwhile，the absolute permeability decreases gradually with the increasing bulk stress；(4) the processing results of test data are with reason by the method of fitting permeability considering Klinkenberg effect；and (5) the algebraic expression on effective permeability of low permeability coal obtained by this experiment reflects the combined impact of gas pressure and stress on methane gas flow and it is able to simulate the methane gas flow in CCOHLP.

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A STUDY OF CONSTITUTIVE MODEL COUPLING DILATANCY AND
DEGRADATION FOR JOINTED ROCK

XIAO Weiguo1，DUI Guansuo1，CHEN Tielin1，REN Qingwen2

2009, 28 (12): -2543 doi:
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[PDF 312 KB] (1154)

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Based on the failure mechanism of jointed rock mass under shear loading，a new constitutive model is presented；the essence of which is dilatancy softening phenomenon and strengthening phenomenon that should be considered separately when asperity surface will undergo the wearing，grinding and crushing. From many direct shear tests，it is concluded that the jointed rock mass will generate dilatancy and wear as the behavior of overriding and shearing for asperity surface under normal and shear loadings. When damage is accumulated to a certain extent，it will result in softening. A new concept of initial shear stress is introduced to reflect the above characteristics. On the other hand，as the motion of broken granules，the mechanical behavior of shear which is controlled by asperities will gradually transform to compact controlled layer；and it makes shear strength increase. This microscopic change effects are described by considering elastoplastic kinematic hardening model. The constitutive equations are derived with combining kinematic hardening model and initial shear stress. The validity of proposed constitutive model is verified through applications to several existing laboratory test results on intact and artificial jointed rocks.

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RESPONSE ANALYSIS OF SHIELD TUNNELLING-INDUCED LAYERED SOIL DEFORMATION BASED ON DEFORMATION CONTROLLED BOUNDARY ELEMENT METHOD

HUANG Maosong1，2，ZHANG Zhiguo1，2，WANG Weidong3

2009, 28 (12): -2553 doi:
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[PDF 437 KB] (1156)

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The boundary element method with displacement controlled pattern is presented to analyze the response of shield tunnelling-induced undrained layered soil deformation. The elastic layered half space soil model is combined with the method to consider the soil nonhomogeneous characters，whereas solutions only existed in homogeneous soils by the simplified method before. The oval-shaped ground deformation pattern is imposed to the tunnel opening boundary；and the boundary integral equations are established for the opening boundary value problems of multilayered soils. Then the low-order constant elements in the boundary discrete equations are replaced by the high-order isoparametric elements；and the fundamental solutions for multilayered soils are coupled with the boundary element method，whereas Kelvin and Mindlin solutions based on homogeneous materials are chosen previously. Finally the undrained soil displacements on the condition of given opening boundary displacements are obtained. It is shown that the method can solve the problems subjected to homogeneous soils as well as nonhomogeneous soils. The results indicate that as for the layered soils where the differences of elastic parameters among successive layers are large；the error is not negligible，which is obtained employing average elastic modulus and average Poisson¢s ratio based on homogeneous soils converted from layered soils. It may provide certain basis to draw up correctly protective measurements of environmental effects influenced by adjacent shield tunnelling.

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SIMULATION ANALYSIS AND EXPERIMENTAL TEST ON FROST DEFORMATION OF FREEZING WATERPROOF CURTAIN IN DEEP FOUNDATION PIT

HUANG Jianhua1，2

2009, 28 (12): -2560 doi:
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[PDF 487 KB] (944)

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From the process of frost heaving behaviors of deep foundation pit，the studies including nonlinear finite element simulation analysis，model experiment and in-situ test while considering the balance of initial ground stress and its thermo-mechanical coupling analysis are given. The frozen mechanics and deformation of waterproof curtain including frozen heaving features and its relationships with freezing soil properties and constraint conditions are presented. Also，the unloading mechanism and deformation-reducing effects of stress relief slot in deep foundation pit of soft soil are proposed. Research achievements from calculation analysis of practical projects may provide theoretical basis for reasonable design and safe construction of similar projects in the future dense popularization regions.

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THEORETICAL ANALYSIS OF PARTIALLY PENETRATED SAND DRAINS FOUNDATION IN CONSIDERATION OF SMEAR EFFECT

GUO Biao1，GONG Xiaonan1，LU Mengmeng2，LI Ying1

2009, 28 (12): -2568 doi:
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Under equal strain assumption and instantaneous loading condition，the consolidation of soft soil with partially penetrated vertical drains under single-drainage condition and double-drainage condition is studied. Vertical and radial seepages of soils under sand drains are considered through setting suppositional sand drains. Meanwhile，in order to consider the fact that the larger the distance from sand drain is，the lighter the disturbance of construction is，the horizontal permeability of soils is expressed in unified way through introducing a function. Three types of variation patterns of the horizontal permeability of soil in the disturbed soil zone are considered，including the constant distribution pattern，the linear distribution pattern and the parabolic distribution pattern，and an analytical solution is obtained. Corresponding computer program is developed and several problems that should pay attention to during the process of programming are expounded；then the consolidation behavior of partially penetrated sand drains foundation is investigated. The results show that the consolidation is the fastest if the parabolic distribution pattern is considered；the consolidation is slower if the linear distribution pattern is considered；the consolidation is slowest if the constant distribution is considered；and that the larger the disturbance zone is；the slower the consolidation is；the greater the disturbance is，the slower the consolidation is；the deeper the sand drains is，the faster the consolidation is；the larger the permeability coefficient of sand drains is，the faster the consolidation is.

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ON APPLICATION OF SOIL-WATER CHARACTERISTIC CURVES TO LANDSLIDE FORECAST

LIN Hungchou1，2，YU Yuzhen3，LI Guangxin3，PENG Jianbing1

2009, 28 (12): -2576 doi:
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The determination and application of soil-water characteristic curves(SWCCs) are key issures for unsaturated soil mechanics in geotechnical engineering practice. Unfortunately，it is hard to use in practice owing to the complexity of SWCCs. Hence，the landslide model tests for soil slope under artificial rainfall and numerical analyses are used to study the practicability of main drying and wetting curves in SWCCs. In the numerical analyses，the pore water pressure in slopes is calculated by the finite element analysis of water flow through unsaturated-saturated soils；and the slope stability is evaluated by finite element method in consideration of shear strength reduction technique. The results show that the actual occurrence time of landslide is between the evaluated time of main drying curve and main wetting curve in general condition；and the occurrence time of landslide which is evaluated by main drying curve is shorter than main wetting curve. It is implied that the main drying curve and main wetting curve can be used to build rainfall warning criteria for rainfall-induced landslide hazards. Consequently，the main drying and wetting curves of SWCCs are the most significant simplified hysteresis model for unsaturated soil slope seepage numerical analysis. Because the main drying and wetting curves represent the two boundaries of soil state path；it is appropriate for using these two boundary curves to build up rainfall warning criteria of landslide hazards for specific mitigation purpose such as emergency response.

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APPLICABILITY OF FINE SAND CUSHIONS FOR EMBANKMENTS
ON SOFT FOUNDATION

LI Lingling1，CHEN Zhenhua2，WANG Lizhong1

2009, 28 (12): -2584 doi:
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[PDF 486 KB] (902)

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Sand cushion and geotextile reinforcement are often used to treat soft clay foundation. Emphasis is placed on the case，a typical engineering in Baishawan—Shuikou surrounding beach in Pinghu，Zhejiang Province. Based on the nonlinear finite element analysis，requirements of permeability of sand cushion and effects on deformation and stability of embankment are studied. The effect of geotextile reinforcement and the feasibility of the low-cost blowing sand diking technology on soft soil ground are discussed. Results of FEM computation about consolidation，settlements and stability are analyzed. Associated with the in-situ data，it is suggested that the permeability parameter k of sand mat is large than 5×10－3 cm/s. Furthermore，when the permeability of sand cushion does not meet the request，the whole stability of embankment can be increased significantly by using geotextiles；and this increase depends on the style of the geotextile. It is shown that if the grain composition and permeability of sand and the style of geotextile reinforcement are selected appropriately，the blowing sand dike technology on soft soil ground is available. The conclusion can be useful in practice.

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COMPACTION PROPERTIES OF BENTONITE-SAND MIXTURE AS BUFFER MATERIAL FOR HLW DISPOSAL

ZHANG Huyuan，LIANG Jian，LIU Jisheng，CUI Suli

2009, 28 (12): -2592 doi:
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It is proposed that a mixture of bentonite and quartz sand might be a suitable backfill/buffer material for HLW disposal in China after reviewing the foreign research results，because bentonite can be optimized by addition of certain content of quartz sand to improve the heat conductivity and mechanical strength without an obvious increase in permeability. The compaction properties of GMZ001 bentonite-sand mixtures with a series of sand additions ranging from 0% to 50% are studied by standard and modified proctor compaction tests，and the static compaction tests under 20 MPa and 50 MPa pressures are designed. Test results show that the relationship between maximum dry density and optimum water content follows the same power function for all of the mixture specimens prepared in different compaction methods with different compaction efforts，while linear correlations exist for mixture specimens prepared in different compaction methods and compaction efforts. These correlation functions provide useful tools for convenient selection of compaction methods in practice. It is concluded that addition of 10%–30% quartz sand to GMZ001 bentonite can improve the compaction quality without altering the estimated impermeability of the backfill/buffer material.

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STUDY OF ELECTRICAL CONDUCTION CHARACTERISTICS OF ROCK-SOIL MASSES IN MINES AND ITS APPLICATION TO ENGINEERING

WANG Hua

2009, 28 (12): -2593 doi:
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[PDF 102 KB] (1021)

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2009, 28 (12): -2594 doi:
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[PDF 100 KB] (1615)

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2009, 28 (12): -2595 doi:
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[PDF 337 KB] (781)

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