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2010, 29 (04): -0 doi:
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CASE STUDIES OF ROCK BOLTING IN COAL MINE ROADWAYS

KANG Hongpu，WANG Jinhua，LIN Jian

2010, 29 (04): -664 doi:
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[PDF 555 KB] (2688)

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Based on analyzing bolting mechanism，the theories of high prestress and intensive bolting are put forward，which emphasize the decisive part of the bolt prestress and its diffusion. It is pointed out that the primary supporting should be able to control the displacement and damage of the surrounding rock as soon as possible under complicated conditions. The complete bolting techniques for coal mine roadways are introduced，including geomechanics testing，the dynamic information method for bolting design，the materials of high strength bolts and cables，the construction quality detecting and monitoring techniques，and the combination techniques of bolting and grouting. Typical cases are described on the basis of roadway types，including the roadway with buried depth more than 1 000 m，the entry in soft rock，the entry strongly affected by active mining activity，the large section open-off cut，the entry driven along next goaf with a thin pillar，the entries retained for next sublevel and in the goaf，and the damaged chamber with soft and broken surrounding rocks. On the basis of the features of the roadways and field testing results，the reinforcement designs are carried out；and the rationality of the designs and the stability of surrounding rock are evaluated through the analysis and feedback to field monitoring data. These practices point out that the high prestress and intensive bolting system，combined with grouting if necessary，can effectively control the violent displacements of the surrounding rock and good reinforcement effects can be achieved.

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EXPERIMENTAL STUDY OF COALBEDS METHANE REPLACEMENT
BY CARBON DIOXIDE

LIANG Weiguo，WU Di，ZHAO Yangsheng

2010, 29 (04): -673 doi:
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Carbon dioxide is one of the main greenhouse gases. Geological disposal of carbon dioxide in coalbeds is regarded as an economical approach because of the mutual benefit of greenhouse gas sequestration and recovery of coalbed methane by replacement. In the past，most of works were focused on either theoretical analyses and numerical simulations，or experiments of adsorption and desorption of different gases on coal grains in size of millimeters or the less. In this paper，the experimental study results of carbon dioxide storage and methane replacement in coal specimens of large size(100 mm×100 mm×200 mm) are presented，which realistically simulates the process of the greenhouse gas sequestration and methane replacement in coalbed. In the experiment，the permeability of coal specimen is measured firstly with methane and carbon dioxide respectively；and it is found that the permeability of coal is different for the two gases. The permeability for carbon dioxide is larger than that for methane two magnitudes at least under the testing condition. There exists a negative exponent relationship between the permeability and applied body stress on the specimen. Under the simulated stress condition in the experiment，17.47 to 28.00 units of carbon dioxide can be stored in per unit of coal；and the replacement ratio of carbon dioxide to methane is as large as 7.03 to 13.91. The processes of injection，adsorption and desorption，replacement，and output of gases can proceed smoothly under the given pressures；the percentage of methane in the production gas can be amounted to 20% to 50% at the early stage and still can be maintained at the level of 10% to 16% even at the last stage during the experiment process. It is concluded that the effects of carbon dioxide storage and methane replacement are determined by several factors including injection replacement pressure，injection amount and velocity，methane content in the coalbed，and the development of pores and fissures in the coalbed，etc.. During the process of carbon dioxide injection and gas replacement，coal body swelling can be found with comprehensive effects of gas adsorption and desorption，and the deformation of coal framework. The research is expected to provide certain illuminations for practice of carbon dioxide disposal in coalbed or methane replacement recovery by carbon dioxide in the future.

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MINING TECHNIQUE WITH PRESET PACKING BODY IN ROADWAY FOR THICK COAL SEAM WITHOUT COAL PILLARS

MA Liqiang1，2，ZHANG Dongsheng1，2，WANG Hongsheng1，2，LI Yongsheng3

2010, 29 (04): -680 doi:
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To decrease the loss of coal pillar for thick coal seam，a new technique with preset packing body for thick coal seam without coal pillars is put forward based on the analysis of reasonable model of surrounding rock structure. The actual steps for mining are：(1) the entry-in packing should be preset ahead of the coalface，which is nearby the coal wall of the next coalface；and (2) the gob-side entry of the next coalface is driven along the packing body without coal pillars. If the new technique is applied for an old entry，which is excavated with normal cross-sections，the coal wall of the next coalface should be enlarged and supported also by cablet ahead of the coalface. The key technique is the materials chosen and their mixture ratios of the packing body to guarantee the stability of packing body，and also the entry surrounding rock under the premise of minimizing the width of packing body. The selected filling material is mainly supported by a small amount of waste rock slag cement，sand cement mixture of water body，cement，sand，slag waste rock according to the weight in proportion to the ratio 1∶1∶4.7. The results of industrial test and field measurement show that the technique is successful；and it can be applied to thick coal seam with similar conditions. Meantime，it can enhance the recovery rate of coal resources and the economic efficiency.

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MEASUREMENT ANALYSES OF ROCK MASS MOVEMENT AND DEFORMATION DUE TO UNDERGROUND MINING OF DEEP FRACTURED OREBODY IN GUANZHUANG IRON MINE

LI Wenxiu1，WANG Shanshan1，LIU Lin1，MENG Qingli1，LIU Xiaomin1，MEI Songhua2

2010, 29 (04): -688 doi:
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It is the purpose of this paper to discuss the problem of rock mass displacement and deformation due to deep underground mining of fractured thick iron orebody. The laws of ground surface subsidence and rock mass movement and deformation in north area of Guanzhuang iron mine due to deep underground mining are studied. The ground surface subsides continuously；and rock mass fails slowly in the mine. Based on the ground surface subsidence and surrounding rock deformation monitoring and numerical simulation methods，a comprehensive method is put forward to analyze the displacement and deformation mechanism of rock mass due to underground mining. Several measurement and analytical methods have been given for predictions and analyses of rockmass dispacements and deformations due to deep mining of fractured thick iron orebody. They are classified as meaurement methods(creep analyses，ground movements analyses，surrounding rock deformations analyses and in-situ stress measurements) and numerical methods(ANSYS and FLAC). New monitoring data have been analyzed to study the rock mass deformations due to deep mining of fractured thick iron orebody in Guanzhuang iron mine. It has also been compared to the results obtained by numerical analyses. By mechanical analysis as well as case study，rock mass deformation and ground subsidence caused by the deep iron ore mining are studied. The results show that the displacements of overburden layer are characterized by uniform and entire compression，displacements and deformations. The laws of surface subsidences are that the surface deformations are continual and slow with a long last period of movement. A case study shows that this method is an available approach to investigate the mechanism of rock mass deformation and ground surface subsidence.

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EXPERIMENTAL STUDY OF PERMEABILITY OF ANTHRACITE AND GAS COAL MASSES UNDER HIGH TEMPERATURE AND TRIAXIAL STRESS

FENG Zijun1，WAN Zhijun2，ZHAO Yangsheng1，LI Genwei2，ZHANG Yuan2，
WANG Chong2，ZHU Nanjing3

2010, 29 (04): -696 doi:
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[PDF 322 KB] (1368)

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Utilizing the 600 ℃ 20 MN servo-controlled rock triaxial testing machine with high temperature and high pressure developed by the authors，the research of permeability of anthracite from Jincheng and gas coal from Xinglongzhuang coal mine with 400 mm long and 200 mm in diameter is carried out under in-situ stress with depth of 500 m and different temperatures，considering coefficient of horizontal pressure 1.2. The research results indicate that：(1) A critical temperature is found when the permeability of samples experienced changes with temperature from room temperature(RT) to 300 ℃，evidencing that the permeability of coal samples reaches the minimum value at this temperature stage. (2) A peak temperature is also found from 300 ℃ to 600 ℃，and the permeability at this temperature point reaches the maximum value at temperature over 300 ℃. (3) The process of coal samples¢ permeability changing can be divided into three stages by the critical temperature and peak temperature from RT to 600 ℃. The permeability decreased from RT to the critical temperature；it increases between the critical temperature and the peak temperature；above the peak temperature，it decreases as well. (4) The critical temperature and the peak temperature of permeability are related with coal rank. The critical temperature of anthracite is from 150 ℃ to 200 ℃ and the peak temperature is between 450 ℃ and 500 ℃；the range from 200 ℃ to 250 ℃ is the critical temperature of gas coal and the peak temperature does not emerge with the experimental temperature changing from RT to 400 ℃.

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STUDY OF DEFORMATION PROPERTIES OF JOINTED SPECIMENS UNDER UNLOADING CONDITIONS

XIA Caichu1，2，LI Hongzhe1，2，3，LIU Sheng1，2

2010, 29 (04): -704 doi:
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A series of triaxial tests on intact and jointed granite specimens under loading and unloading conditions are conducted，and the results reveal that：(1) in the axial loading and unloading tests，unloading stress-strain curves of intact specimen are almost the same as loading curves，while curves of jointed specimens show distinct difference；(2) deformation properties of jointed specimens show sharp difference under two unloading paths. To reveal the test results and deformation behavior of jointed specimen in theory，numerical model for jointed specimens under different stress paths is formed and methods to determine joint deformation parameters are proposed. Taking account of the difference in constitutive model of jointed rock specimens under loading and unloading conditions respectively，numerical analysis agrees with the test results，which shows that the model can be applied to the description of the deformation behaviors of jointed specimens under unloading conditions. The result can also be used to reveal unloading deformation characteristics of rock mass containing a set of joints.

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RESEARCH ON CHARACTERISTIC PARAMETERS OF SANDSTONE THREE-POINT BENDING FAILURE UNDER DIFFERENT TEMPERATURES

ZUO Jianping1，2，ZHOU Hongwei1，2，LIU Yujie2

2010, 29 (04): -712 doi:
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Based on three-point bending tests，the characteristic parameters of Pingdingshan sandstone under different temperatures have been investigated. The variation of three characteristic parameters with thermal effects is focused on，namely，elastic modulus，damage parameter and ductility ratio. Based on numerical statistical method，a new parameter has been put forward to characterize rock material property，namely，numerical elastic modulus. The method is convenient for experimental methods to determinate elastic modulus for brittle materials. Thermal damage has been defined according to the variation of elastic modulus at different temperatures with Lemaitre¢s damage theory. A piecewise four-order polynomial has been used to fit the nonlinear relationship between the thermal damage and temperatures. And the fitting results agree well with experimental results. The thermal damage under different temperatures can be divided into four stages，namely，instable stage of thermal damage，initial thermal damage stage，stable thermal damage stage and fast thermal damage stage. At last，based on concrete structure theory，ductility ratio to characterize the ductility property of sandstone at different temperatures is employed；and the ductility ratio value of two may be approximately as the point of brittle-ductile transition.

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EXPERIMENTAL STUDY OF SHEAR DEFORMATION CHARACTERISTICS OF ROCK MASS DISCONTINUITIES

SHEN Mingrong1，2，ZHANG Qingzhao2

2010, 29 (04): -719 doi:
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[PDF 252 KB] (1457)

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A series of shear tests under different normal stresses are carried out on regular dentate rock mass discontinuities. The mechanical properties of regular dentate rock mass discontinuity under shearing and the main law of its strength and deformation are discussed. Through analyzing the test data，it carries on further investigation on shear deformation curves of the discontinuities under shear stress and shear deformation characteristics of the discontinuities with different roughnesses. Then the constitutive relation of shear deformation characteristics is put forward. Meanwhile，the changes of integrated shear strength parameters of the discontinuities under the shearing condition are researched；and an empirical formula for evaluating the shear strength is set up. The dilatancy characteristics of the discontinuities under shearing are analyzed；and an interpretation of the phenomenon is provided.

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THREE-DIMENSIONAL ARBITRARY FRACTURE NETWORK SEEPAGE MODEL AND ITS SOLUTION

ZHANG Qihua，WU Aiqing

2010, 29 (04): -730 doi:
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[PDF 588 KB] (1165)

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For the three-dimensional arbitrary fracture network seepage model，it is necessary to solve two key problems，i.e. how to get the seepage paths cutting by 3D arbitrary fracture networks，and how to analyze the seepage of two-dimensional arbitrary-shaped zone. All enclosed blocks cutting by arbitrary fractures can be searched by spatial block identification(3D block cutting) method. The boundaries of all blocks form the seepage paths. So the relationships of calculating nodes of seepage FEM can be determined by the connection relationships of the blocks¢ boundaries. On the other hand，block boundaries formed by fractures or openings are composed of closed loops with all kinds of shapes. The seepage occurring in the loops can be treated as 2D continuum seepage in the fracture¢s local coordinate system，and it can be solved by simplex integration even though the shapes of loops may be arbitrary. Then，according to the relationships of calculating nodes，the total seepage matrix and functions can be obtained；and the seepage calculation can be completed. At last，some cases are analyzed to check the theoretical schemes and calculating programs. The results of 3D fracture network seepage are applied to the block system for progressive failure analysis.

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MANIFOLD CUT AND GENERATION OF THREE-DIMENSIONAL MANIFOLD ELEMENT UNDER FE MESH COVER

LI Haifeng1，ZHANG Guoxin1，SHI Genhua2，PENG Xiaochu1

2010, 29 (04): -742 doi:
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[PDF 895 KB] (1618)

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The generations of three-dimensional manifold element and contact detection algorithm are the bottleneck problems that restrict the development of three-dimensional numerical manifold method. The generation of three- dimensional manifold element is studied. Based on previous works，the authors build mathematical cover system by three-dimensional finite element mesh generation technology，and develop three-dimensional block-cut technology into manifold cut technology for the formation of three-dimensional manifold element. Through the improvement of block data structure and block recognition algorithm，the authors extend coding algorithm of physical cover system by Dr. SHI Genhua from two-dimensional to three-dimensional；and then the generation of three- dimensional manifold element is achieved. And on this basis，the authors develop a three-dimensional manifold cutting program 3D_MC.f90；it can generate an arbitrary three-dimensional manifold element under tetrahedral and hexahedral mesh covers. As can be seen through several examples，manifold block shape and coding algorithm of node and element by three-dimensional manifolds procedure can meet the definition requirements of three-dimensional manifold element. It is proven that this algorithm is correct from the view of manifold cut.

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STUDY OF LAYERED ROCK MASS COMPOSITE MODEL BASED ON CHARACTERISTICS OF STRUCTURAL PLANE AND ITS APPLICATION

HUANG Shuling1，XU Jinsong2，DING Xiuli1，WU Aiqing1

2010, 29 (04): -756 doi:
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The common character of layered rocks is transversely isotropic due to the existence of regular bedding planes，which means that the failure mechanism and deformation characteristics of such rocks have the obvious difference with common rocks. In view of this point，a strain hardening-softening composite model of layered rock mass is proposed according to the physico-mechanical characteristics of structural plane and rock matrix，and it can be used to describe the anisotropic characteristics of rock strength and deformation，as well as progressive failure or sliding characteristics. Then，the proposed model has been successfully established and embedded on the basis of the third developing platform of constitutive model in FLAC3D，realizating nonlinear numerical calculation. The results including the comparison with classical theoretical solutions and numerical solutions，simulation of uniaxial and triaxial compressions of layered rock mass and so on prove that the proposed model is suitable for the description of the above characteristics. At the same time，the mechanical response characteristics and progressive failure processes of test blocks with different confined pressures and different dip angles are analyzed；and the failure or sliding mechanism of such rocks is discussed so as to better understand the mechanical properties. Finally，the proposed model is used to simulate a typical slope project and a cavern project；and the simulation results can be used to better explain in-situ deformation and failure phenomenon，and they are in accordance with engineering practice. It is shown that the proposed model is correct and feasible for the engineering application.

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ANALYSIS OF EFFECT OF STRESS ON DISSOLUTION MECHANISM OF
SALT ROCK

QIAN Haitao1，2，TAN Zhaoshuang3，LI Shouding2，4，WANG Sijing2

2010, 29 (04): -764 doi:
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Based on the theories of geochemistry，mineralogy，petrology，geo-thermodynamics，plastoelasticity，a comprehensive analysis of the effects of stress on dissolution mechanism of salt rock is carried out. And it reveals that stress has its effect at multi stages by many manners，and so the dissolution mechanism under stress is different from that without stress：(1) stress shows its influence directly by inducing additional free energy in the halite solid，which can increase the activity or concentration at the solid/liquid interface；(2) stress shows its indirect influences by changing the depth h of the bund layer at the surface of salt rock solid，velocity u and pattern of fluid water，and effective interaction area of dissolution between solid and water. It is found that the dissolution mechanism of salt rock under stress is a positive feedback loop owing to the coupling of stress-dissolution，and the essential relations between stress and dissolution are that strain energy can increase the chemical potential energy difference between water and solid at the solid/liquid interface，which can accelerate the reaction of dissolution progress and so shows its effects on the dissolution mechanism of salt rock.

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PERFECT ELASTOPLASTIC SOLUTION OF AXISYMMETRIC CYLINDRICAL CAVITY BASED ON LEVY-MISES CONSTITUTIVE RELATION AND HOEK-BROWN FAILURE CRITERION

HOU Gongyu，NIU Xiaosong

2010, 29 (04): -777 doi:
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Theoretical solution of axisymmetric cylindrical cavity under perfect elastoplastic condition is addressed by adopting the Levy-Mises constitutive relation and Hoek-Brown failure criterion. The authors complete the calculation of routine engineering examples adopting the solution formula，solution formula of Kastner equation，solution formula based on Drucker-Prager yield criterion，and numerical simulation experiments(FLAC3D) respectively. Moreover，the authors analyze and study the similarities and differences of the results calculated by different solutions. In the end，semi-analytical and semi-numerical solutions under perfect elastoplastic condition are addressed by adopting the Levy-Mises constitutive relation and generalized Hoek-Brown failure criterion.

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GEOSTRESS MEASUREMENTS BY HYDRAULIC FRACTURING METHOD AT GREAT DEPTH OF BOREHOLES AND NUMERICAL MODELLING PREDICTIONS OF STRESS FIELD

ZHANG Yanxin1，SONG Changsheng2，CAI Meifeng3，PENG Hua4

2010, 29 (04): -786 doi:
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Hydraulic fracturing is an efficient method for determining the stress field and is suitable at the early stages of projects when no underground access exists. Wanfu coal mine is located in the southwest of Shandong Province，China，which is prepared to construct with great annual coal capacity. The overburden soil layer is the alluvium of the Yellow River with the thickness of over 700 m. The depth of coal deposit is about 1 004.12 m. Determination of both the orientation and magnitude of in-situ stresses at great depth is quite difficult，so some new stress measurement techniques are employed. In the exploration area，a total of 37 hydrofracturing tests in 7 vertical exploration boreholes drilled from the ground surface are carried out. The results suggest that the maximum horizontal stress is dominantly oriented NEE-SWW. This stress direction is also in agreement with the direction derived from the focal mechanism in the area. At the same time，the maximum horizontal stress orientations are closely consistent with those in the general contemporary stress field in southwest of Shandong Province. The ratio of maximum horizontal principal stress to vertical principal stress is 1.44–3.22 with the average of 1.97 in 37 measuring points. It is shown that the prevailing stress field in Wanfu coal mine is controlled by the tectonic horizontal stress. Based on the geological conditions and rock mass properties，a 3D mechanical model is established and a regressive method for obtaining regional stress from limited stress data by using a 3D finite element method is proposed. According to the spatial distribution of the stress filed，the curves of principal stress for coal roof are plotted；and some adverse geological phenomena are discussed.

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EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF
GRANITE UNDER LOW TEMPERATURE

TANG Mingming1，WANG Zhiyin1，SUN Yili1，2，BA Jinhong1，3

2010, 29 (04): -794 doi:
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[PDF 514 KB] (1374)

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The granite samples were drilled form a proposed underground gas storage site in Jinzhou，Liaoning Province. The mechanical tests(uniaxial and triaxial) were conducted under different freezing temperatures(－10 ℃–
－50 ℃) and different moisture conditions(fully saturated and dry). Then the law of rock deformation，compressive strength of samples，and the relation between the shear strength parameters and the freezing temperatures were analyzed. The test results show as follows：(1) Whether the granite samples are dry or fully saturated，the uniaxial and triaxial compressive strength increased nonlinearly with the decrease of temperature. There is a threshold temperature below which the strength of granite becomes to stabilize. The effect of the low temperature on the mechanical properties is more obvious for saturated samples. (2) The cohesion increased significantly with the decrease of low temperature. For dry samples，the internal friction angle remained at about 57°. The internal friction angle of fully saturated samples increased about 3.43% when the temperature dropped from －10 ℃ to －50 ℃. In the freezing conditions，the moisture condition has an important impact on the change of the shear strength parameters. The results provide helpful insights for the construction of liquefied natural gas (LNG) storage at low temperature.

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STUDY OF FEEDBACK ANALYSIS AND SAFETY CONTROL OF LARGE-SECTION TUNNEL EXCAVATION UNDER INTENSIVE BUILDINGS

YANG Ping1，2，QIN Weimin3，YANG Yu4，WANG Tao5

2010, 29 (04): -803 doi:
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[PDF 444 KB] (1423)

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Wucun tunnel underpasses intensive buildings with high-risk characteristics such as ultra-shallow，large-span，complex construction process，high-protection demand on buildings in Xiamen City，and dynamic feedback analysis method is carried out during tunnel construction process in complex geological and environmental conditions. The monitoring measures for the safe construction of the tunnel mainly include building settlement，surface subsidence，building inclination，the tunnel vault subsidence，tunnel adjacent formation restraining，the soil body depth portion displacement，the soil body lamination subsidence，blasting vibration，subsoil water level and so on，especially static level sensor is applied to the important buildings for automatic monitoring. In accordance with ISO9001 quality certification system，a sound and efficient operation system is established in the feedback analysis process. Based on construction experience of city tunnel and the results of preliminary researches in Wucun tunnel，monitoring is carried out on the surrounding environment as well as on tunnel structure itself. In addition to routine monitoring tools，advanced technology such as automatic monitoring on differential settlement of buildings，monitoring information management and prediction systems，monitoring information feedback by LAN and WAN，early-warning facilities by desktop alarm systems and electronic display boards，are applied to dynamic feedback analysis throughout tunnel construction；so that the feedback analysis work has distinctive informationizing characteristics in Wucun tunnel engineering.

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OPTIMIZATION OF LARGE-SPAN METRO STATION CONSTRUCTION IN SOFT ROCK STRATA AND CONTROL OF GROUND SURFACE SUBSIDENCE

QI Taiyue，LIU Qiang，JU Guoquan

2010, 29 (04): -813 doi:
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In view of the influence of ground surface subsidence due to the optimization of construction methods of large-span metro station in soft rock strata，numerical simulation is firstly used to optimize and compare five construction methods；and the eight-step method is selected tentatively as the optimized one. Then the similar material model test is conducted to verify it. The results turn out to be perfectly matched by comparison and analysis，and it is found that five construction methods are able to meet the needs of controlling ground surface subsidence and keeping structural stability，in which the eight-step method is more optimized in terms of the control effect of ground surface subsidence and the state of structural stress；and that the key is the working procedure No.14.

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MIXED SEARCH ALGORITHM OF CRITICAL SLIP SURFACE OF COMPLEX SLOPE

CAO Ping，ZHANG Ke，WANG Yixian，HU Hanhua

2010, 29 (04): -821 doi:
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[PDF 336 KB] (1342)

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In view of the characteristic of complex slope，an improved method of selecting search variable is presented. The positions of two exiting points and arc height of the slip surface are taken as search variables，and assumptions aren¢t required. Divided-interval search has been introduced so as to locate the most dangerous slip surfaces and the next critical slip surfaces，of which the obvious advantage is employed to divide the search region，increasing the possibility of finding the global optimum. Chaos optimization method and improved complex method are combined to search the minimum safety factor and critical slip surface. Mixed search algorithm combines the merits of two algorithms，which can effectively avoid local minimum，and overcome time-consuming disadvantage of chaos optimization method. Mixed search algorithm is applied to searching the minimum safety factor of a complex slope；and the result shows that the rate of successful computation of basic complex method with improved search variable is 40%–60% higher than that with the current search variable. The minimum safety factor obtained by mixed search algorithm is ranging from 1.70 to 1.72. So mixed search algorithm is much more likely to find the global optimum of complex slope. And analyses of multi-step slope engineering example show that there are four next critical slip surfaces with small differences in safety factor；the relative difference is 7.6% in maximum，and 3.6% in minimum，but large differences in the location of critical slip surface.

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STUDY OF TRANSFORM MECHANISM OF LANDSLIDE-DEBRIS FLOW
WITH RING SHEAR TEST

ZHANG Ming1，2，HU Ruilin2，YIN Yueping3，CUI Fangpeng4

2010, 29 (04): -832 doi:
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[PDF 504 KB] (1701)

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Taking the Qingning landslide in Sichuan Province for an example，its transform mechanism of landslide-debris flow has been studied. After mastering its transform course，longly sliding and shearing course of slide body after its instability are simulated with ring shear test；the physico-mechanical characters during shearing course are monitored. The result shows that the soft base effect is an important factor for transform of landslide- debris flow besides excess pore water pressure，which is the focus of reseach at present. Because of shearing shrinkage，grain crushing and layering，the sliding body volume of soil reduces in the course of shearing，which makes excess pore water pressure increase，and thus its shear strength decreases. Simultaneously，a thick liquefied layer has been formed at the bottom of sliding body，of which thickness increases with shearing displacement increasing. The liqueafied layer carries sliding body moving fast and reduces its stability greatly，which is called“soft base”effect in this paper.

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FIELD MEASUREMENT AND ANALYSIS OF INTERACTION BETWEEN PILE AND SOIL AT A MEDICAL TECHNOLOGY BUILDING OF ZHEJIANG FIRST HOSPITAL

ZHANG Zhongmiao1，2，ZHANG Qianqing1，2，LI Jianhua3

2010, 29 (04): -841 doi:
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[PDF 368 KB] (1073)

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A well-instrumented field test for the interaction between piles and soils was conducted at a medical technology building of Zhejiang First Hospital. The measured data indicate that the average peripheral and the internal earth pressure account for 83.3% and 62.7% of the characteristic value of soil bearing capacity respectively，when the decoration period is completed，suggesting that the bearing capacity of the soil beneath the foundation slab is utilized to a greater degree. During decoration period，the measured average reaction force at pile top is more than 50% of the ultimate bearing capacity of a single pile，differing from a single pile in the traditional design situation. Moreover，the percentage of the total load shared by the soils gradually decreases with increasing load and reaches about 20% at the completion of decoration period. In addition，the measured average compressive steel stresses of surface and bottom base plate are very small，about 9.84 MPa and 7.68 MPa at the completion of this building respectively. These measured data are far lower than the ultimate compressive stress of the steel bar. At the same load level at the pile head，the measured shaft resistance of a foundation pile is less than that of a single pile in static load test because of the weakening effect of the foundation slab on the shaft resistance. Finally，the measured results show that the settlement of this building is small and uniform，satisfying the operation requirements.

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DETERMINATION OF SOIL SHRINKAGE CHARACTERISTIC CURVE OF SURFACE SOIL ON ANCIENT EARTHEN ARCHITECTURES

LIU Ping，ZHANH Huyuan，YAN Gengsheng，ZHAO Tianyu，WANG Xiaodong

2010, 29 (04): -849 doi:
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[PDF 264 KB] (1050)

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The paraffin oil method was proposed and conducted to determine the soil shrinkage characteristic curves(SSCC) for understanding the desiccation behavior of the wet surface of ancient earthen architectures. Test data and the model fitting results show that paraffin oil method is more accurate than the traditional methods. This study indicated that the soil paste shrink vertically at the primary dryings stage by gravity and then came to three- dimensional shrinkage with the further evaporation of the soil water. It was found that the measured SSCC was slightly shifted upward from the theoretical 1∶1 saturated line，which can be attributed to the air contained in the isolated micropores. Results of test also indicated that the shrinkage limits of the three silt soils were 1.1%，1.4% and 1.8% lower than the corresponding plastic limit，which was determined mainly by the clay content and the type of clay minerals.

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FINITE ELEMENT SIMULATION OF STRAIN LOCALIZATION ON A SHEAR BAND OF SAND UNDER PLANE STRAIN CONDITION

LI Fulin1，2，PENG Fangle1，2，LEI Liang1，2，KONGKITKUL W3

2010, 29 (04): -857 doi:
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[PDF 1493 KB] (1211)

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On the basis of the local strain fields in the specimen obtained from the drained plane strain compression (PSC) test on saturated sand，the strain localization on a shear band induced by post-peak softening is investigated. Under plane strain condition，the strain localization starts around the peak stress state；and a V-shaped shear band is formed at the residual stress state. It can be seen that sand has progressive failure feature with shear banding. The strain localization on a shear band induced by post-peak softening is one of the most important deformations and strength characteristics of sand. On the basis of dynamic relaxation method，a nonlinear finite element analysis(FEA) technique incorporating the three-component elasto-viscoplastic constitutive model for sand is developed to simulate the strain localization on a shear band. A strain localization parameter，S，is introduced into the constitutive model to describe the post-peak softening and shear banding. No direction of shear banding is specified in the finite element simulation. The direction of shear banding is implicitly assumed to be consistent with the direction of maximum shear strain. It is shown that the presented FEA can well simulate the strain localization on a shear band；and the maximum shear strain around the shear band is very close between physical test and finite element simulation. Therefore，the whole process simulation from pre-peak hardening，peak，post-peak softening to the residual stress state is implemented in the FEA. And the quantitative analysis of strain localization on a shear band for sand could also be done by the presented FEA technique.

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常州地区大直径钻孔灌注桩承载性状
及尺寸效应试验研究

刘福天1，2，赵春风1，2，吴杰3，刘丹4

2010, 29 (04): -864 doi:
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[PDF 282 KB] (1351)

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基于常州高架一期工程2根大直径钻孔灌注桩静载荷试验及桩身力学测试结果，研究常州地区大直径钻孔灌注桩加载过程中侧摩阻力和端阻力的发挥特点及荷载传递规律，得到极限状态下桩侧摩阻力和桩端阻力尺寸效应系数，对成孔卸载造成桩承载力降低及其他影响桩承载力的因素进行分析。试验研究结果表明：试桩的荷载–沉降(Q-s)曲线为陡降型，极限承载状态下，2根大直径钻孔灌注桩(长径比为36～43)端阻力分担总荷载的比例较小，分别为11.4%和18.1%，属于摩擦型桩；极限荷载时浅层黏性土发生侧阻软化，桩–土位移为3～7 mm，砂土中为4～7 mm；桩侧摩阻力与端阻力尺寸效应明显，大直径钻孔灌注桩侧摩阻力及端阻力尺寸效应系数与土的种类有很大关系，较《建筑桩基技术规范》(JGJ 94–2008)计算值偏小，侧阻尺寸效应系数平均值大约为0.85(砂土)和0.88(黏性土)，且具有沿深度减小的趋势，砂土和黏性土中桩端阻力尺寸效应系数分别为0.74和0.75。

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2010, 29 (04): -865 doi:
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2010, 29 (04): -866 doi:
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