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2004, 23 (20): -0 doi:
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THREE DIMENSIONAL ELASTO-VISCOPLASTIC COMPOSITE ELEMENT MODEL FOR DISCONTINUOUS ROCK MASSES

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2004, 23 (20): -3390 doi:
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[PDF 517 KB] (929)

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The principle of composite element method is illustrated，and an algorithm for jointed rock masses is implemented on the basis of the principle. The most remarkable feature of the algorithm is that each composite element may contain several discontinuity segments，such as faults and joints. The main advantages of the composite element method is that it can be incorporated into conventional finite element analysis procedure，and the mesh generation of the large-scale rock structures with considerable number of discontinuities，which require discrete treatment in the calculation，is not restricted by the number，position and orientation of the discontinuities. Comparision study between composite element method and conventional finite element method is carried out to show the validity and robustness of the new method.

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2004, 23 (20): -3397 doi:
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2004, 23 (20): -3405 doi:
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[PDF 267 KB] (736)

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2004, 23 (20): -3413 doi:
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[PDF 153 KB] (1231)

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DIP EFFECT OF STRUCTURAL PLANE ON SHEARING STRENGTH PARAMETERS OF ROCK MASS

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2004, 23 (20): -3418 doi:
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Through researching the dip effect of layer plane on the shearing strength parameters of argillaceous siltstone and limestone and the dip effect of structural plane on the mechanical property of gypsum samples，the dip influence of structural plane on the parameters of shearing strength of stratiform and stratified structures is analyzed in detail，and the mechanism of anisotropy of mechanical property of stratiform and stratified structure is discussed. The principle of determining shearing strength parameters of stratiform and stratified structur is put forward. The correlation formulas between the dip of structural plane and parameters of stearing strength are established for different kinds of stratiform and stratified rock masses，respectively. The triaxial tests of gypsum samples of stratiform and stratified structures show that the proposed formulas are useful for determination of shearing strength of the similar rock structures.

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TESTING STUDY ON FRACTAL CORRELATION LAW OF CRACKS
IN MINED ROCK MASSES

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2004, 23 (20): -3426 doi:
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By using simulant testing of similar material，the forming process and the distribution status of the cracks in mined rock masses are simulated. The fractal correlation of cracks in caving zone，fractured zone and bend zone in goaf is studied. The testing results indicate that the fractal dimension of the cracks in mined rock masses is enlarged with increment of mining width，and the expansion factor of rock masses and subsidence coefficient of overlying strata become big with increment of fractal dimension of the cracks in mined rock masses.

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BIFURCATION ANALYSIS ON DEFORMATION LOCALIZATION
OF GEOMATERIAL

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2004, 23 (20): -3430 doi:
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[PDF 293 KB] (1116)

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The bifurcation phenomena，such as shear bands in geological structures，branching behaviors in rock tests and instability in geotechnical engineering，are described and some corresponding mechanisms are discussed. The theories widely applied in bifurcation analysis of localization in mathematics，structural mechanics analysis and geomaterial deformation are presented in detail. The processes for shear bands in loaded geomaterial to deform from toughness to brittleness，and then to lead to fracture of specimens，can not be well imitated by existing analysis methods. The plastic dilatable constitutive relationship together with symmetric group theories and asymmetric bifurcation analysis method are involved in the preliminary analysis. However，their effects are limited. The disturbed state concept proposed by Desai is introduced as a valuable way for the bifurcation analysis of material at the post-peak，with loading rate dependency，and under dynamic loading.

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2004, 23 (20): -3439 doi:
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NUMERICAL METHODS AND APPLICATION FOR JOINTED ROCK MASS，PART 1：APPROACHES AND DISCUSSIONS

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2004, 23 (20): -3444 doi:
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[PDF 297 KB] (2065)

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This paper narrates the typical modes of rock mass failures in engineering activities，the conditions under which such failures occur，and the approaches to predict these failures. A brief description is presented of the evolution，the current state，and the feature of numerical modelling methods for jointed rock mass. Attention is paid to the technique of generating 3-dimensional joint net in rock mass and randomly simulating the properties of each individual joint on the basis of accessible functions in a 3DEC numerical model. Such technique enables 3DEC to build up a model that contains various joints corresponding to the realistic distributions of joints in rock mass and，furthermore，achieve a determinative description of joint distributions by transplanting joint mapping data into a 3DEC model. This，in some degree，fulfills the numerical modelling of geomechanical behaviours of jointed rock mass combined with the computerized simulations of its geometry. The essential principles are discussed of applying numerical modelling techniques for discontinuum into engineering projects.

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HEURISTIC ANT COLONY ALGORITHM INVOLVING CHAOS
OPERATOR AND ITS APPLICATION TO SEARCH FOR CRITICAL
SLIP SURFACE OF SLOPE

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2004, 23 (20): -3450 doi:
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The chaos operator is introduced into the basic ant colony algorithm for enhancing the variety of solutions and the ability to find global optimization solution，and the heuristic search pattern is established to increase the computing efficiency of local optimization solution. Thus，the phenomena of stagnation existing in basic ant colony algorithm is avoided and the search performance is considerably improved. The application of heuristic ant colony algorithm involving chaos operator to the analysis of slope stability is discussed based on Spencer¢s slice method and Janbu¢s slice method. A case study is given to verify the proposed method. The results show that the proposed algorithm is practical and reliable.

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FINITE ELEMENT ANALYSIS ON TEMPERATURE FIELD OF QING-TIBET RAILWAY EMBANKMENT ON PERMAFROST

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2004, 23 (20): -3454 doi:
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Qing-Tibet railway in building traverses 550 km-long continuous permafrost region. Railway embankment construction on permafrost will substantially disturb the balance of heat and mass transfer between the ground surface and atmosphere and cause the redistribution of underneath temperature field. The trend of permafrost evolution can be deduced and stability of railway embankment can be evaluated according to the distribution of underneath temperature field. Temperature was monitored after the Qing-Tibet railway embankment was formed. In this paper，finite element method is used to simulate the temperature field of railway embankment. Firstly，temperature data monitored in a whole freeze-thaw cycle is used as the original temperature field. Then，the new variable of enthalpy is introduced to solve the phase-change problem. Finally，ANSYS is used to simulate temperature field under embankment from the year 2003 to 2030. The computation results indicate that permafrost can be protected with enough height of embankment and insulation protection，whereas the natural permafrost table in undisturbed ground declines year by year with annual average increment rate of 0.02 ℃，and at the same time，the difference of temperature field distribution between the sun-slope and the shade-slope will cause non-uniform deformation of roadbed and cracking on the surface.

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STUDY ON MONITORING AND BACK ANALYSIS FOR ROAD TUNNEL WITH COMPLEX GEOLOGY

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2004, 23 (20): -3460 doi:
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The items and methods of monitoring for expressway tunnel constructed by NATM with complex geology are discussed. Back analysis is made by using monitored data with extended Kalman filter-FEM and the time-varying estimation of the distribution of internal shear strain and plastic zone are obtained. Result shows that the distribution of plastic zone for rock mass is asymmetrical and it is in agreement with the monitored data. The internal development state of surrounding rocks is revealed and valuable guidance is provided for optimizing construction method.

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2004, 23 (20): -3465 doi:
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APPLICATION OF GENETIC ALGORITHM TO EVALUATE 3D PERSISTENCE OF JOINTED ROCK MASS

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2004, 23 (20): -3470 doi:
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3D persistence of rock mass is a very important factor that influences the mechanical behaviors of jointed rock mass. Based on the 3D probability distribution model of the discontinuities established through the 3D numerical modeling technique of network，a new conception and solution of 3D persistence of rock mass are put forward on the basis of the potential failure path of jointed rock mass. With the solution of persistence，the most possible failure path in rock mass can be found out. In the process，the theory of genetic algorithm with the characteristics of biological background is adopted to determine the optimized 3D persistence in complicated jointed rock mass. This new method has been used in a practical hydroelectric project，and the result shows that the new method is available for engineering design.

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2004, 23 (20): -3475 doi:
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[PDF 182 KB] (1229)

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WEIGHT-VARIABLE IDENTIFICATION MODEL OF COMPREHENSIVE EVALUATION ON BURST LIABILITY OF COAL

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2004, 23 (20): -3480 doi:
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First，the influence factors on burst of coal are studied. On the basis of the theory of identifying attribute，the weight-variable identification model is built up to comprehensively evaluate the burst liability of coal and rock. Coefficient of variable weight is decided by the parameter value of each evaluation units. The burst liability is comprehensively evaluated according to credit level and identification attribute classification is made. Forecast of burst liability can be made before production，so that there is enough time to adopt the measure of relieving danger and to achieve safe production. What is more，the same attribute can be classified into sub-classification by sort in the light of comprehensive score. The example shows that results of this paper are the same with these by elasticity energy index. Furthermore，the proposed method can release the integral danger of evaluation units and describe the dangerous relationship between collectivity and part media.

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CORRELATION BETWEEN CRACK WIDTH AND VARIETY OF
CT VALUES IN SANDSTONE SAMPLE

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2004, 23 (20): -3484 doi:
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[PDF 159 KB] (874)

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By using the newly made multi-functional CT experiment equipment with mid-low pressure，real-time observation by CT scan is made for the dry sandstone samples and the sandstone samples with seepage under triaxial stress conditions. Through the meso-scale CT testing，the correlation between crack width and CT value in the sandstone sample is discussed and the calculation formulas of crack width are put forward based on the testing results.

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2004, 23 (20): -3489 doi:
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[PDF 519 KB] (1177)

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TESTING STUDY ON MINING OF WATERPROOF COAL PILLARS IN THICK LOOSE BED AND THICK COAL SEAM UNDER ULTRATHIN
OVERLYING STRATA

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2004, 23 (20): -3494 doi:
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Based on the analysis of petrofabric property of engineering in thick loose bed，water-bearing strata and water-resisting layer in ultrathin overlying strata，as well as weathered zone in basement rock，the maximum height of caving zone of overlying strata and the effective height of water flowing-fracture zone in the condition of different caving ratios are studied by using the model test of simulated material and numerical simulation. The results show that the content of clay minerals in weathered zone of basement is relatively high，which results in weak permeability and strong regenerated water tightness，which is of double functions of water tight and restrain of continuous development of the height of water flowing-fracture zone under mining conditions. The overlying strata bend wholly and sink slackly，and the effective height of water flowing-fractured zone is in accordance with the caving zone height of overlying strata. The study results are applied to the caving area 810# of Luling mine. The top-coal caving mining is done in waterproof coal pillars，in which experimental exploitation is successful in two working faces. The sum of 4×105 t coal is produced safely，and the recovery ratio is up to 86.7%，so that significant economical benefits are obtained.

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CUSHION INFLUENCE ON BEARING CAPACITY OF COMPOSITE
FOUNDATION WITH CEMENT-FLYASH-GRAVEL PILES

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2004, 23 (20): -3498 doi:
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[PDF 183 KB] (1950)

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In order to exactly determine the bearing capacity of composite foundation with cement-flyash-gravel (CFG)piles by in-situ static loading test and study the influence of cushion thickness and material on the bearing capacity，six vertical loading plate tests of composite foundation with single CFG pile were carried out in field with various cushion thicknesses. Six earth pressure gauges were embeded in the cushion for each loading test to measure the soil resistance. Based on the test results，the stress ratio，n，of pile to soil，bearing load ratio，k，of pile to soil，and the development of stress ratio with time are analyzed. It is shown that the thickness and material of cushion have great influence on the bearing capacity of composite foundation with CFG pile in loading test，and there is a match problem between them. The suitable cushion thickness is 50～150 mm for a mixture of coarse sand and detritus，and the developing coefficient of bearing capacity of the soil between piles is 0.75～1.0.

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APPLICATION OF FRACTURE FAILURE STRENGTH MODEL TO SUPPORT FOR LARGE SCALE OIL-DEPOT ROCK SLOPE

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2004, 23 (20): -3504 doi:
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There are lots of pore spaces，joint planes and cracks，and they are a kind of initial damage in rock mass. It is the initial damage，damage evolution and propagation fracture that result in various failure of jointed rock mass. The influence of crack propagation process and interaction of cracks on rock mass strength is systematically studied according to propagating-fracture mechanism of jointed cracks. A fracture failure strength model for jointed rock mass is established，and applied to guide reinforcement design for a high rock mass slope at Dawan oil depot in Guangdong Province. Some satisfactory computational results are obtained and remarkable economic benefits are achieved from the model.

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2004, 23 (20): -3509 doi:
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COMPOSITE EXAMINATION AND NEW CONSOLIDATION METHOD FOR DEFECT OF IN-SITU BORED PILE OF BRIDGE

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2004, 23 (20): -3518 doi:
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[PDF 157 KB] (1468)

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A practical bridge engineering with in-situ bored pile foundation is introduced. After 32 in-situ bored piles are constructed，the dynamic low strain test is applied to the whole piles. The defects of 2 piles are revealed，then 3 piles，2 defect piles and 1 random pile，are examined with static loading test and pile sample digging test. The results of composite examinations show the insufficiency of vertical bearing capacity of pile and defect of pile shaft. According to the test results，geological condition and construction diary，the defect causes of piles are comprehensively analyzed，and remedial measures，such as high pressure jet method and pile tip cleaning out method，are taken. After the defect piles are consolidated，the dynamic low strain test and static loading test are applied to the consolidated piles again，and the results of examination show that the treatments meet the demand of design.

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2004, 23 (20): -3523 doi:
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[PDF 224 KB] (1033)

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2004, 23 (20): -3529 doi:
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[PDF 221 KB] (834)

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EFFECT ANALYSIS OF TRAIN-INDUCED DYNAMIC LOAD ON OVERHEAD CROSSING STRUCTURE UNDER RAILWAY

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2004, 23 (20): -3536 doi:
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[PDF 285 KB] (1038)

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The dynamic response of the system composed of rail wheel，rail and tunnel under railway is analyzed with elastoplastic finite element method. The influence of the structure under rail with bigger stiffness on variation regularity of vertical dynamic stress in roadbed is studied. The additional dynamic stresses of tunnels with different depths are also discussed. The ideal touch model between tie and bed and the ideal elastoplastic dynamic model of soil are adopted for analysis. The analysis results indicate that the attenuation of additional dynamic stress along depth is reduced with existence of the structure under rail. The deeper the tunnel is，the lower the whole level of dynamic stresses in roadbed is and the smaller the influence on tunnel is. In addition，the fatigue failure of concrete due to long-term train-induced dynamic load should be considered in design.

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2004, 23 (20): -3541 doi:
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[PDF 381 KB] (1274)

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2004, 23 (20): -3547 doi:
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[PDF 213 KB] (1112)

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CALCULATION OF INNER FORCE OF SUPPORT STRUCTURE FOR LANDSLIDE/SLOPE BY USING STRENGTH REDUCTION FEM

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2004, 23 (20): -3552 doi:
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[PDF 659 KB] (1257)

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The failure of landslide/slope belongs to the category of failure mechanics. When the stress and strain of failure surfaces reach the limited state and the shear strengths are fully utilized，the slope failure occurs at the same time，which is the failure criterion of slope failure mechanics. Usually，the soil does not reach the limited state completely when there is interaction between soil and support structure，instead，some soil is in the elastic state and some soil is in plastic limited state. This stress state is not the design state. The design method of limited state is adopted in geotechnical engineering for many years，which utilizes the soil shear strength fully and assume the soil to reach the plastic limited state completely，so that a safe and economic structure is made. This principle should be followed when the internal forces of support structure is calculated by FEM，and the lateral earth pressure computed by FEM should be equal to the earth pressure by traditional limited equilibrium method. Under this condition，the interaction between the soil and support structure is considered. According to this principle，the shear strength reduction FEM is adopted to analyze the interaction between soil and support pile with prestressed cable. The thrust distribution in landslide and internal forces of support pile are obtained with the c-tanj reduction. Through a series of case studies，the applicability of proposed method is clearly exhibited.

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2004, 23 (20): -3559 doi:
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[PDF 127 KB] (1040)

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2004, 23 (20): -3563 doi:
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[PDF 69 KB] (988)

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