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2007, 26 (04): -0 doi:
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DISCUSSION ON YIELD AND FAILURE OF GEOMATERIALS AND STABILITY ANALYSIS METHODS OF SLOPE/LANDSLIDE—COMMUNION AND DISCUSSION SUMMARY OF SPECIAL TOPIC FORUM ON GEOLOGIC DISASTERS IN THE THREE GORGES PROJECT REGION

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2007, 26 (04): -649 doi:
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[PDF 306 KB] (1126)

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LINEAR AND NONLINEAR UNIFIED STRENGTH THEORY

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2007, 26 (04): -662 doi:
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[PDF 515 KB] (1808)

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Unification of a priori unrelated concepts，methods，theories or phenomena is an important characteristic of the beauty of a scientific theory. Strength theory deals with the yield and failure of materials under the complex stress state. It includes the yield criteria(for those materials which have the same strength both in tension and compression) and failure criteria(for SD materials，i.e. strength difference of materials in tension and in compression). It is an important foundation for research on the strength of materials and structures. Strength theory is widely used in physics，mechanics and engineering. It is of great significance in theoretical research and engineering application，and is also very important for the effective utilization of materials. It is an interdisciplinary field where the physicist，civil and mechanical engineers interact in a closed loop. The unified strength theory gives a series of new failure criteria，establishes a relation among various failure criteria，and encompasses previous yield criteria and failure models as special cases. The single-shear strength theory including the famous Tresca yield criterion and the Mohr-Coulomb strength theory，the twin-shear strength theory including the twin-shear yield criterion and the twin-shear failure criterion are all special criteria of the unified strength theory. The unified strength theory has been applied to many fields. The unified strength theory is not a single criterion；it is a series of failure criteria，a system of strength theory. A series of new failure criteria and yield criteria between the single-shear theory and twin-shear theory can be introduced from the unified strength theory. The unified strength theory，however，is a combination of the linear criteria. It cannot unify the nonlinear criteria. It can only approximate nonlinear criteria. A new mechanical model and a new general unified strength theory of materials under complex stress state are proposed. It establishes a relation among various failure criteria including the linear and nonlinear criteria. The new theory encompasses the most familiar failure criteria as special cases；and a series of new criteria can be introduced. The single-shear strength theory，the twin-shear strength theory and the octahedral-shear strength theory are all special cases of the new general unified strength theory. This new unified strength theory including the linear and nonlinear criteria can be adopted for more materials.

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STUDY ON PHYSICAL MODEL OF COMPLETE FAILURE PROCESS OF QUASI-BRITTLE MATERIALS IN TENSION

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2007, 26 (04): -670 doi:
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[PDF 314 KB] (1421)

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A physical model composed by mesoscopic physical elements system is attempted to be established. By tracking its movement process，the complete damage and failure process of heterogeneous materials under quasi-statically uniaxial tension can be simulated. Based on the macroscopic response of quasi-brittle materials，the improved parallel bar system(IPBS) model which considers the equivalent relationship between effective stress and nominal stress of damage materials has been established. Further，considering the size effect in local softening phase，based on the hypothesis of tensile failure within the rupture process zone of limited length，the non-local damage physical model—double constitutive physical model(DCPM) is presented. The constitutive relation during the whole loading process is deduced；and the failure mechanism of the heterogeneous material is discussed from a novel viewpoint. The two characteristic states of damage material appearing during the loading process，when reaching the peak nominal stress and the macro-crack，respectively，can be distinguished. Regarding the later as the critical state，the whole loading process can be divided into the even damage phase and the local breakage phase. It is illustrated by examples that the model can simulate perfectly the macroscopic properties behaved by the quasi-brittle specimen under uniaxial tension. A novel material fracture theory，i. e. internal mechanical capability of material exerting mechanism theory，is proposed. It is considered that the whole damage process is controlled by this internal rule.

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SIMULATION OF ROCK CRACK PROPAGATION USING DISCONTINUOUS DEFORMATION ANALYSIS METHOD

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2007, 26 (04): -682 doi:
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An approach for modeling rock crack propagation using discontinuous deformation analysis(DDA) method is presented. In the proposed approach，the triangular block system is automatically generated in the area of interest by adopting the advanced front method. During this process，numerous artificial joint interfaces，compared to real joint interfaces，come into being. These artificial joint interfaces provide the paths along where cracks generate and propagate. The strength of the artificial joint takes the same value as that of the intact rock；and the failure of the artificial joint is controlled by the maximum tensile-stress criterion and Mohr-Coulomb criterion. In this way，the proposed method can easily simulate the generation，propagation and coalescence of rock crack；the whole process of rock fragmentation is thereafter reproduced. Moreover，with the introduction of the artificial joint concept into the discontinuum-based model，the proposed approach can be used to simulate the cases of continuum，semicontiuum as well as discontinuum without any mathematic difficulty. Based on the proposed algorithm，the corresponding VC++ program module is developed. For verification，several numerical examples are computed to study the propagation and coalescence of the closed joints in rock mass under uniaxial compression. The simulated results are compared with the existing physical and numerical test ones. They show a favorable agreement，and the laws of the crack propagation are in accordance with the phenomena observed in the tests. These indicate that the proposed method for crack propagation analysis is correct and effective.

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DEVELOPMENT OF HYPERBOLIC MODEL FOR FULLY GROUTING ROCK BOLT AND PARAMETERS ANALYSIS FOR ANCHORING EFFECT

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2007, 26 (04): -692 doi:
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[PDF 185 KB] (1707)

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According to local deformation theory，taking the action of rock mass against grouting rock bolt as a serious of spring，the shear resistance increases linearly with shear displacement between grouting mass and surrounding rock，and the hyperbolic model for grouting rock bolt has been developed on the base of rock bolt¢s force equilibrium. The distribution of shear resistance，axial force and shear stress density along the grouting rock bolt is obtained. From the shear stress and axial force of grouting rock bolt，the parameters affecting the anchoring effect have been analyzed. It is concluded that the larger the radial of rock bolt is，the greater the anchoring effect is；the greater the elastic modulus of rock bolt is，the better the anchoring effect is；and as the comprehensive parameter of grouting mass and surrounding rock increasing，the anchoring effect becomes better.

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EFFECT OF LOAD TRANSFER OF UNCONSOLIDATED CONFINED AQUIFER ON COMPOUND BREAKAGE OF KEY STRATA

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2007, 26 (04): -699 doi:
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With a specially designed experimental instrument，the mechanism of load transfer within an unconsolidated confined aquifer and its effect on compound breakage of key strata have been studied. The results show that (1) the unconsolidated confined aquifer plays a crucial role in load transfer because of its fluidity and replenishment in time，making the loads of overburden soil evenly transfer into the bedrock through the unconsolidated confined aquifer and the load keep constant during the excavation process； (2) under the condition without unconsolidated confined aquifer，the load on the bedrock will be reduced sharply during the excavation. Therefore，in the process of load transfer within the unconsolidated confined aquifer，the key strata of overburden rock are prone to have a compound breakage when the load on the upper interface of bedrock is great and the bedrock is very thin. Based on the mechanism of the effect of unconsolidated confined aquifer on the compound breakage of key strata，the fully mechanized support crushing accidents taking place during coal mining under the unconsolidated confined aquifer and thin bedrock in some collieries of East China have been well explained.

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PARALLEL NUMERICAL ANALYSIS OF COUPLED FLUID FLOW AND STRESS BASED ON DUAL POROSITY MEDIA MODEL

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2007, 26 (04): -705 doi:
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[PDF 293 KB] (1479)

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To simulate the permeability and coupling characteristics of pores and fractures in intack rock，an iterative computation model for the analysis of coupled fluid flow and stress is established based on the dual porosity media model. The permeability coefficient and porosity of rock are updated by volumetric strain. The coupling model of fracture system is established by cubic element model；and the permeability coefficient and porosity are renewed as effective stress changes. Considering enormous time steps and huge workload in the coupling analysis，the element-by-element(EBE) finite element parallel computation method is adopted for numerical simulation. Corresponding parallel program for coupling analysis，GoupledGF，is developed and then implemented on cluster of workstation. Coupling analysis of fluid flow and stress is conducted for an enclosed area including a production well and an injection well. The total amount of time steps is about 22 000. Computational results show that the parallel coupling analysis model is very effective for the coupling analysis.

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STUDY ON DEFORMATION LAW AND FAILURE MECHANISM OF ANCHORAGE-SURROUNDING ROCK SYSTEM UNDER TENSILE-SHEAR COMPLEX STRESSES—TAKING SUPER-LARGE SUSPENSION BRIDGE ON BALING RIVER FOR EXAMPLE

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2007, 26 (04): -712 doi:
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[PDF 674 KB] (1209)

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Anchor basement is the key bearing component of suspension bridge；and its deformation and failure mechanism is the foundation of strength and stability evaluation. Several facts are found through the in-situ pull model test. The total displacement and the rate of residual displacement on the back anchor face show saddle and V-shaped distribution，respectively. The displacement of the surrounding rock on the flank appears plug-style distribution，and the rate of the permanent deformation is high. According to the numerical model test to be by fast Lagrangian analysis of continuum in 3D(FLAC3D)，some conclusions are also drawn：(1) the stress field shows subsection character，and the stress transfer route between fore part and back part of the anchor body is different；(2) the plastic zones which appear plug-style are mainly found beside the anchor and in the upper rock mass；(3) tensile-shear complex failure maybe happen in the rock-anchor system. The plastic zones and the prominent deformation zones in the rock mass should be paid more attention during design and construction.

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COMPARISON TEST STUDY ON MECHANICAL PERFORMANCE OF LOADED BOLT AND UNLOADED BOLT AGAINST CORROSION

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2007, 26 (04): -720 doi:
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By the simulation corrosion test of loaded and unloaded bolts in moist air and Na2SO4 solution，the relation curves of the mechanical performance with the corrosive conditions and the corrosion time are given. The mechanical performance is compared between these two types of bolts. At the same time，the influential trend of the load on the mechanical performance of the corroded bolt is analyzed. The test results show that：(1) after being corroded in the moist air，there is no prominent difference in mechanical performance between loaded bolt and unloaded bolt；but after being corroded in Na2SO4 solution，both the ultimate bearing capacity and the maximal tensility of loaded bolt decrease far more than those of unloaded bolt，and the endurance and service life of loaded bolt will also be shortened much more severely.

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NUMERICAL SIMULATION MODEL OF HYDRAULIC FRACTURING
OF ROCK WITH A SINGLE FRACTURE UNDER NATURAL
HYDRAULIC POWER

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2007, 26 (04): -727 doi:
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[PDF 253 KB] (1114)

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The hydraulic fracturing in fields of water conservancy，hydropower and mining engineering is produced by natural hydraulic power. Its boundary conditions are different from those in artificial hydraulic fracturing applied in fields of petroleum and natural gas engineering. Considering hydraulic fracturing characteristics of natural hydraulic power in the fields of water conservancy and hydropower engineering，a numerical simulation model of hydraulic fracturing of rock with a single fracture initially filled by saturation water is built. It is assumed that the flow in the fracture is the Newtonian fluid without compressibility. It is in accordance with lubrication theory. The flow pattern is one-dimensional laminar flow. The fracture flow is meshed as one-dimensional element. The differential equation of water pressure gradient of fracture inner surface and opening width is induced using semi-analytical and semi-numerical methods. This method simplifies coupling analysis iteration and improves analysis precision. The fracture propagation model employs Hillerborg cohesive zone one model COD criterion modified by damage factor. The interface elements with zero thickness are arranged in possible fracturing zone. Through adding or deducing the number of interface element，the dynamic motions of fracture and procedure iteration process are carried out. Finally，the hydraulic fracturing process of rock sample with a single fracture is simulated. The simulation results are compared with other experimental ones. The inner water pressure distribution law is consistent with experimental one. The rationality of the model and reliability of the calculation results are confirmed.

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BACK ANALYSIS OF RESERVOIR STRESS FIELD WITH LOGGING DATA OF CASING DEFORMATION

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2007, 26 (04): -734 doi:
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[PDF 259 KB] (1098)

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A new method is proposed which is used to approximately calculate the in-situ stresses with the logging data of casing deformation and to inverse the stress field of reservoir. Firstly，the uniform or average in-situ stresses may be determined on the bases of the damage pressure which can be determined by API. The relation among flexibility ratio, displacement ratio and stress ratio may be determined by analyzing of the elastic system with the casing and formation. The flexibility ratio depends on the elasticity and the geometry structure of the system. The displacement ratio is calculated by the logging data of the casing deformation. The stress ratio can be obtained by the flexibility ratio and the displacement ratio. Therefore，the nonuniform in-situ stresses can be obtained by the stress ratio and the average stresses. Secondly，taking the in-situ stresses as the foundational data，the finite element and inverse method are utilized to calculate the stress field of the reservoir. Finally，the method is applied to Daqing Oilfield preliminarily. The method makes it possible to inverse stress field in the formation where the data of in-situ stress measured are scarce.

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PRELIMINARY STUDY ON PERMEABILITY TENSOR CALCULATION OF FRACTURED ROCK MASS AND ITS REPRESENTATIVE
ELEMENTARY VOLUME

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2007, 26 (04): -740 doi:
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[PDF 410 KB] (1970)

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Based on the technology of three-dimensional joint network simulation and superposition principle of seepage energy，the calculation method is presented to determine the three-dimensional permeability tensor and the representative elementary volume(REV) size of fractured rock masses. The method is feasible and reasonable to calculate permeability tensor of fractured rock masses considering the distribution and connection of joint network and the influence of aperture changes(decided by stress fields) on permeability tensor according to cubic law. The factors influencing the permeability characteristic and REV size of rock masses such as trace length，space，aperture，inclination and the number of joint sets are discussed. As an example，the permeability tensor and REV size of fractured rock masses on the right bank of Laxiwa Hydropower Station are studied. At the same time，the stress-dependent permeability issue is investigated. The results is worth using in engineering design.

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LOWER BOUND LIMIT STUDY ON PLASTIC LIMIT ANALYSIS OF ROCK SLOPE USING FINITE ELEMENTS BASED ON NONLINEAR PROGRAMMING

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2007, 26 (04): -747 doi:
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[PDF 374 KB] (1219)

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Based on the theory of lower bound limit，finite element discreteness technique and nonlinear mathematical programming，the finite element plastic limit analysis method is used to evaluate the stability of rock slope. By using nonlinear Mohr-Coulomb yield condition，equilibrium condition，stress boundary condition and stress discontinuity equilibrium condition，the finite element modes of joint elements with zero thickness and equal thickness are proposed in the plastic limit analysis；and the nonlinear mathematical programming models of finite element plastic limit analysis，which contains joint elements，are established. Then，the optimization strategy of nonlinear mathematical programming problem is provided. At last，the stabilities of three 2D slopes are analyzed with the presented method. The results are compared with those obtained by other approaches. The feasibility of the method is verified.

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PARAMETER IDENTIFICATION OF ROCK RHEOLOGICAL MODEL BASED ON EXTENDED KALMAN FILTER

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2007, 26 (04): -754 doi:
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[PDF 385 KB] (1445)

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The extended Kalman filter method is presented for parameters identification of rock rheological model considering the uncertainty of data due to the complexity of rock material and different observation conditions of laboratory or in-situ experiments. In this method the rheological mechanical parameters are improved iteratively as the state vector of a random process. The Kalman filter function is formulated to perform parameter identification. The method is applied to a kind of clayey soft rock from Goupitan Hydropower Station. Parameters of the generalized Kelvin model are estimated based on the results obtained from uniaxial compression creep tests. The estimated results show the good precision of the extended Kalman filter method. The influence of measuring errors is also discussed. Numerical experiments are carried out to verify the greatly antinoise capability of the current method. It provides an efficient theoretical tool for solving the uncertainty effects in the identification of rock mechanical parameters.

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COMPARISON OF DYNAMIC CAPABILITIES OF GRANITE AND CONCRETE UNDER UNIAXIAL IMPACT COMPRESSIVE LOADING

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2007, 26 (04): -762 doi:
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Experiments with strain rate varying from 101 s－1 to103 s－1 on granite and concrete under uniaxial compressive loading are conducted with the modified split Hopkinson pressure bar(SHPB). It can ensure the symmetrical stress in the specimens before fracture and avoid the fluctuation of test data due to input shaky stress pulse by adding the copper wafer as the pulse shaper. The experimental results show that the compressive strength and the fragment numbers of rock-like materials increase with the strain rate. The fragment size decreases with the strain rate. The initial elastic modulus，the failure strain and the ratio of the energy absorption of granite and concrete can be seen no relations with strain rate under condition that strain rate ranges from 101 s－1 to 103 s－1. The stress-strain curves，the energy absorbency-time curves and the ratio of the energy absorption-time curves of granite and concrete are compared. It is illustrated that the microstructure characteristic，impedance，compression deformation capability of rock-like materials are crucial factors influencing the characteristics of dynamic fracture. The research method and conclusions can be used to analyze the dynamic behavior of the other brittle materials.

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EXPERIMENTAL STUDY ON SAND CONSOLIDATED ANCHORAGE PRESTRESSED BOLT AND ITS APPLICATIONS

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2007, 26 (04): -769 doi:
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[PDF 333 KB] (1147)

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Sand consolidated anchorage prestressed bolt is composed of bolt，sand cylinder，steel circular plate，wooden sealed，trap，etc.. In order to apply sand consolidated anchorage prestressed bolt to anchorage engineering，experimental study is conducted in the Three Gorges Project on Yangtze River and underground caverns in Fengtan Hydropower Station. 12 bolts with high-strength materials and diameter of 32 mm are arranged in a granite slope in the Three Gorges Project. The experiments show that the tension of the bolt is over 300 kN；and the ultimate strength is about 540 kN. Design methods and construction techniques for sand consolidated anchorage prestressed bolt are provided according to the experimental study；and the prestress monitoring is carried out to test the bolt¢s long-term stability. Ten bolts with common materials are arranged in quartz sandstone slope in underground caverns in Fengtan Hydropower Station. The holes are drilled by different types of construction machinery. According to the experimental study in Fengtan Hydropower Station，new technologies such as a new type sand consolidated anchorage prestressed bolt with rigid seal to block sand are innovated，which has been authorized invention patents by Chinese Patent Office.

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STUDY ON DISTRIBUTION CHARACTERISTICS OF 3D STRESS AND THICKNESS EFFECTS OF COAL-SEAM IN UNSYMMETRICAL DISPOSAL AND FULLY-MECHANIZED TOP-COAL CAVING

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2007, 26 (04): -775 doi:
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[PDF 474 KB] (1098)

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In order to explore the influence of mining heights on the three-dimensional stress distribution of coal-seam in unsymmetrical disposal and fully-mechanized top-coal caving，based on unsymmetrical disposal characteristics，the analyses of numerical simulation and in-situ observation are synthetically applied according to the geological and technical conditions of the working face 1151(3) in Xieqiao Mine. The characteristics of 3D stress distribution of coal-seam and its thickness effects are obtained. The results show that the seam stress on working face represents unsymmetrical distribution in unsymmetrical disposal；and the abutment pressure peak value and its distance to face and stress-relaxed area are maximum at the side of coal pillar. The coal-seam thickness effects behave that the stress peak value and 3D stress distribution of coal-seam are changed with mining height changing. The seam-stress peak value decreases with the increasing of mining height，but the distance between peak value location and coal-seam wall augments and the abutment pressure shift to further coal-seam wit the increasing of the mining height. The study will provide lots of theoretic references to reasonable preservation of coal pillar，layout of gateway，stability control of surrounding rock，increment of the recovery ratio and efficiency of caving，etc..

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STUDY ON CALCULATION AND DISTRIBUTION CHARACTERISTIC OF VERTICAL PERMEABILITY COEFFICIENT WITHIN CONDUCTION-CONVECTION TEMPERATURE FIRLD IN FISSURED ROCK ZONE

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2007, 26 (04): -780 doi:
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[PDF 291 KB] (1151)

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The advantages with the use of the temperature field method to study the parameters of groundwater seepage field and the temperature characteristic of conduction-convection temperature field affected by vertical seepage are described briefly. According to the temperature characteristic curve of conduction-convection temperature field in aquifer and seepage filtration equations，the function relationship between temperature and depth is formed，considering the characteristic of temperature field affected by vertical seepage；and the vertical permeability coefficient is calculated via iterative equation and program. Based on the statistical characteristics of above results，a few samples following the normal distribution，the log-normal distribution and the uniform distribution are created respectively. Then，the model of evanescent expander-curve is presented；and the statistical characteristics of the vertical permeability coefficient and the three kinds of distributions are studied and contrasted. The results show that the probability distribution characteristic of the vertical permeability coefficient in fissured rock zone is much close to the log-normal distribution. Several complicated factors including subjective and objective ones can be avoided；and the process and analysis results are clear using the method of temperature field and statistics to study the parameters of groundwater seepage field such as the vertical permeability coefficient in fissured rock zone.

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EVALUATION OF GLOBAL SAFETY DEGREE OF
JINPING HIGH ARCH DAM

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2007, 26 (04): -787 doi:
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Jinping High Arch Dam is the highest double-curvature thin arch dam in the world at present. The water pressure is huge，and the design is beyond the present criterion. The asymmetric characteristics of Jinping High Arch Dam include the landform of two banks，the geological conditions of two banks and the sunlight time of dam surface. For the asymmetries and high water pressure，the safety of Jinping High Arch Dam is one of key issues in the design and construction of Jinping High Arch Dam. With 3D nonlinear finite element method，the stress field and displacement field of Jinping High Arch Dam under some working conditions are studied；and the effects of the geologic formation of two banks on working behavior of arch dam are investigated. The stresses and displacements of dam body are apparently asymmetric for the left and the right banks. The reasons of the asymmetry are not only the asymmetric stiffness of two banks of foundation，but also the asymmetry of dam shape. So the shape of arch dam should be further optimized. The global safety degree(GSD) of Jinping High Arch Dam for natural foundation is studied under different failure modes：GSD that caused by upstream overloading water pressure is about 5.0；GSD that caused by shear strength reduction of rock in dam foundation is about 3.0；GSD that caused by earthquake is about 6.0. According to the distribution of failure zone，the important parts of reinforcing treatment are proposed，i.e. the part above elevation 1 800 m of downstream side of the left arch and that between the elevation 1 630 m and elevation 1 800 m of upstream side of the right arch end.

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STUDY ON ROCK-BREAKING MECHANISM OF HIGH-PRESSURE PDC BIT WITH DUAL-FLOW CHANNEL

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2007, 26 (04): -795 doi:
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The three-dimensional dynamic numerical model of PDC bit to break rock has been set up，in which the finite element models of rock，jet and mechanical tooth are created respectively based on elastoplastic mechanics，hydrodynamics and kinematics of rigid body. The interaction between jet or mechanical tooth and rock is simulated by dynamic contact method. The dynamic boundary is controlled by Hoffman failure rule. The single-step Houbolt algorithm is adopted to solve the dynamic equation. The rock-breaking mechanism has been analyzed comprehensively by various ways such as the interior stress distribution of rock，the weight on bit and torque of bit impacting rock，the volume of rock breaking，the energy of rock breaking，etc.. The influences of the number of blade and the position of high-pressure nozzle on bit breaking rock have been studied；and the structure of the dual-flow channel PDC bit has been optimized.

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STUDY ON POROMECHANIC BEHAVIOURS OF SATURATED POROUS CHALK

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2007, 26 (04): -804 doi:
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The experimental results suggest that the mechanical behaviours of chalk can be modeled in terms of elastoplastic model with two plastic deformation mechanisms：plastic compaction(pore collapse) and plastic shear. From this observation，a constitutive model based on Gurson criterion and Pietruszczak criterion is proposed to study the mechanicals behaviour of chalk. The model contains two yield functions and corresponding plastic flow rules. The performance of the model has been verified for the chalk in drained hydrostatic and triaxial tests；and a good agreement has been obtained. It is well known that minerals，structure and saturation conditions have important influences on the mechanical behaviours of chalk. Moreover，the influence of pore pressure is also very important. Consequently，pore pressure should be taken into account in the modelling of mechanical behaviour of saturated porous chalk. Coussy¢s poroplastic theory is used for the extension of this model to describe poromechanical coupling of chalk. According to the general framework of poro-elasto-plastic modelling，the concepts of the effective stress tensors，especially the concept of plastic effective stress tensor，are discussed. In order to study the poromechanical behaviour of chalk in consideration of pore pressure variation，two yield functions and plastic potentials are expressed as the function of the plastic effective stress tensor. Then the plastic behaviour of saturated porous chalk can be studied in undrained conditions，especially in undrained triaxial compression condition. In general，the model¢s predictions are in satisfactory agreement with the experimental results. It is shown that the proposed model is able to describe the poromechanical behaviour of saturated porous chalk by using the concept of effective stress.

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STUDY ON MODIFICATION OF GEOSTRESS AND FORECAST OF ROCKBURST BASED ON DESTRUCTIVE SIZE OF ROCKBURST

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2007, 26 (04): -811 doi:
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[PDF 366 KB] (1249)

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Combining the actual rockburst status after excavation，based on the previous research data in the earlier stage，the character of the tectonic stress in Cangling Tunnel is studied. Finite element method is adopted to simulate the site excavation steps. At the same time，the tectonic stress is changed on the boundary of the model to simulate the actual rockburst areas；and the most proximal area¢s value is adopted to decide the section tectonic stress. Then，other sections¢ values are revised. After comparing the theoretical values with the site measured values，it is concluded that the revised tectonic stress is coincident with the basic rule. It is also presented that the calculating status is parallel with rockburst areas in undisturbed area. It comes to an end that the method to forecast rockburst is feasible and reasonable.

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STUDY ON RULE OF GEOSTATIC ACTIVITY BASED ON MICROSEISMIC MONITORING TECHNIQUE IN DEEP MINING

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2007, 26 (04): -818 doi:
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By introducing the basic principle of the microseismic monitoring technique and the components and structure of the ISS microseismic monitoring system used in Dongguashan Mine，the relative concentrating area of the geostatic activities is compartmentalized in the first mining area of Dongguashan ore deposit within different periods. The system and the principle of the seismology are adopted to study the intensity distribution of the stress and displacement to discover the temporal and spatial change rules of the geostatic activity produced by the mining and to evaluate the geostatic activity situation and the stability of the insulating pillar and main mining area. The study indicates that the change of the concentrating area of geostatic activity is dependent on the underground mining activities. Every concentrating area is corresponding to the position of each mining project. The geostatic activity changes in time and space with the change of mining project position accordingly. The geostatic activity within the mining area of stope is relatively stable. The distribution of geostatic activity in excavating area is separate and reduces quickly or even disappears with the completion of excavation. The rock mass within the first mining area of Dongguashan ore deposit is stable now. The practice proves that the microseismic monitoring technique is an effective method to study the rule of geostatic activity in deep mining. The result settles an important base for Dongguashan Mine to produce safely.

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NUMERICAL MODEL AND NUMERICAL ALGORITHM OF GENERALIZED GRADIENT-DEPENDENT PLASTICY MODEL

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2007, 26 (04): -825 doi:
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Considering the Laplace operator of plastic strains in the double yield functions，the control equations of the generalized gradient-dependent plasticity model are established to describe both the strain localization characteristics and the basic mechanical characteristics of geomaterials. In order to get the numerical solution of the control equations，the displacement and the plastic multiplier are discretized by virtual work equation and the consistency condition of yield functions separately. A set of nonlinear equations taking the displacements and the plastic factors of nodes as the unknown variables are obtained；and the boundary conditions and the increment algorithm of the equations are given. The numerical examples indicate that：(1) when strain localization appears，the plastic shear strain and the plastic bulk strain mainly concentrate in localization band；(2) the mesh-dependency does not appear any more when the size of mesh changes；(3) when the parameters reflecting localization increase，the width of the strain localization band will be widened obviously.

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MONITORING AND CONTROL OF CONSTRUCTION DEFORMATION OF URBAN SHALLOW-BURIED LARGE-SPAN DOUBLE-ARCH TUNNEL
UNDER COMPLEX CONDITION

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2007, 26 (04): -833 doi:
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The shallow-embedded depth and dense surrounding buildings are two main characteristics of urban road tunnel. Taking the construction of Jiuhuashan Tunnel in Nanjing for example，the contents，technique and method of deformation monitoring of urban shallow-buried large-span double-arch tunnel under complex geologic condition are described in detail. The deformation of tunnel during different construction stages is monitored and analyzed；and the engineering measures to control deformation are put forward. The result shows that (1) the deformation and stability time of tunnel are closely related with the geologic conditions，and increase with the surrounding rock becoming worse. (2) the deformation of the soft ground has lagging effect；and the time effect of the deformation is more prominent than the spatial effect of the deformation. (3) the enclosure of the lining is an effective method to improve the performance of lining and to restrain the deformation of tunnel；and it¢s important to construct the inverted arch and to close the lining. The experience and conclusions presented can provide reference to design，construction and research of similar tunnel.

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PROBABILITY METHOD TO DETERMINE SHEAR STRENGTH
OF SLIDE ZONE CLAY FOR NEOGENIC LANDSLIDE IN THREE GORGES RESERVOIR AREA

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2007, 26 (04): -840 doi:
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[PDF 251 KB] (1265)

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Rock and soil are existing in the nature with strong spatial variation and regionality. The regional property of slide zone clay is one of important reasons that some characters of landslide failure are similar in the Three Gorges reservoir area. According to characteristics of slide zone clay，the Three Gorges reservoir area is divided into three parts：from dam site to Miaohe，from Miaohe to Fengjie except Zigui basin，from Fengjie to Chongqing and Zigui basin，where 391 groups of shear strength data of slide zone clay have been collected. Probability distribution of shear strength parameters of each part is determined by statistics；and these distributions are the prior ones. Based on these distributions，the shear strength parameters of slide zone clay of neogenic landslide can be presumed by Bayes estimation. For landslide with a few test values，the shear strength parameters can be optimized by Bayes estimation；and for neogenic landslide without test values，the shear strength parameters of slide zone clay can be obtained with some data of neighbouring and similar landslides by Bayes estimation. The method has been proved by Qianjiangping landslide(2.4×107 m3)，a typical neogenic landslide in the Three Gorges reservoir area. The method that shear strength parameters of slide zone clay are gained by Bayes estimation is important to prevent and control neogenic landslide in the Three Gorges reservoir area.

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STUDY ON CONSOLIDATION AND PERMEABILITY PROPERTIES OF LIANYUNGANG MARINE CLAY BASED ON PIEZOCONE
PENETRATION TEST

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2007, 26 (04): -846 doi:
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[PDF 297 KB] (1590)

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The coefficient of consolidation and coefficient of permeability of the Lianyungang marine clay are studied by laboratory and piezocone penetration test(CPTU) in order to evaluate the consolidation and permeability characteristics. The horizontal coefficient of consolidation ch of the clay is also back analyzed according to field data of monitored settlement. Comparisons of the results obtained by different methods indicate that the values of horizontal consolidation coefficients determined by CPTU are in the range of (3.0–6.5)×10－3 cm2/s，typically 2–4 times higher than those of vertical consolidation coefficients. The value of horizontal consolidation coefficient with back analysis is slightly lower than that deduced from CPTU based on Teh and Houlsby¢s method. It could be possible due to the smear effect incurred during the installation of the vertical drains. For Lianyungang marine clay，it is recommended that Teh and Houlsby¢s method，which takes the rigidity index into consideration，should be used. The coefficient of permeability of Lianyungang marine clay is in the order of 10－6–10－8 cm/s. The value of horizontal permeability coefficient measured by falling-head permeability tests agrees well with that determined by CPTU. It can be indicated when the vertical drains are used in Lianyungang marine clay，the smear effect on consolidation properties of soil has to be taken into consideration in the soil improvement design. For soil improvement schemes of the Lianyungang marine clay，the coefficient of consolidation determined by CPTU dissipation tests is recommended in practice.

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THEORETICAL STUDY ON PILE-SOIL HOMOGENEOUS TRANSVERSELY ISOTROPIC MODEL

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2007, 26 (04): -853 doi:
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[PDF 345 KB] (1108)

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Based on the assumption of strain compatibility，pile-soil ground is homogenized. Combined with transversely isotropic constitutive equations，the elastic modulus and Poisson¢s ratio of composite ground are gained. Compared with the results of finite element method，the results of this method are validated. In the end，the influences of piles on rebound and deformation of a large deep foundation pit are analyzed. According to the comparisons of measured results and calculated ones，the applicability and predominance of the method are validated；and the workload and calculation time will be simplified and saved.

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DISCUSSION ON “MASS TRANSFER MODELING METHOD FOR EVOLUTION EVALUATION OF SLOPES”

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2007, 26 (04): -860 doi:
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[PDF 123 KB] (892)

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REPLY TO“DISCUSSION ON‘MASS TRANSFER MODELING METHOD FOR EVOLUTION EVALUATION OF SLOPES’”

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2007, 26 (04): -861 doi:
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[PDF 795 KB] (987)