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2008, 27 (02): -216 doi:
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DISCRETE-CONTACT-FRACTURE ANALYSIS OF ROCK AND CONCRETE

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2008, 27 (02): -217 doi:
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Mechanical characteristics of rock，concrete materials and structures are described. State-of-the-art numerical modeling and methods for analysis of rock and concrete structures are summarized. The scientific and technological frontier issues are reviewed；and case studies of employing discrete-contact-fracture analysis models for safety evaluation of high dams and foundations are accomplished. Finally，it is pointed out that the prospect of development for rock and concrete is to construct a unified numerical model of combining continua and discrete media. Thus，analysis of rock and concrete starting from damage initiation in meso-scale(even micro-scale) to complete process of rupture in macro-scale can be performed.

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EXPERIMENTAL STUDY ON PERMEABILITY IN LOW PERMEABILITY MEDIA

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2008, 27 (02): -236 doi:
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It is a hot issue to study the transport properties of rocks with low permeability(≤10－16 m2) in geological disposal of radioactive waste，underground gas and oil storage tanks and construction of deep cavern groups. Based on the developed low permeability test equipment，gas transport properties of typical Jinping marbles are studied under steady flow of nitrogen. Also numerical simulation of gas flow through marble is performed. Comparisons are made between pseudo pressure method and an exact method by considering Klinkenberg effect in gas transportation equation. Fitting results using the exact method show better agreement with laboratory testing results and the transport parameters gained are more convincible. Numerical study and test results both show that：(1) low permeability test equipment can be used to study transport properties of dense rocks under different temperatures and stress conditions；(2) it is necessary to consider Klinkenberg effect in the study of gas transport properties in dense rocks，and the results from numerical study considering Klinkenberg effects agree very well with laboratory test results；and (3) intrinsic permeability of Jinping marble is about 10－20 m2.

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DYNAMIC CAUSTICS EXPERIMENT ON CRACK PROPAGATION OF JOINTED MEDIUM FRACTURE WITH CONTROLLED BLASTING

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2008, 27 (02): -244 doi:
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The crack propagation mechanism and influence of closed and open jointed medium were studied on crack propagation law of cutting seam cartridge fracture with controlled blasting. Dynamic caustics experiment of blasting loading was carried out in PMMA material by forming initial cracks through cutting seam cartridge directional fracture. The experimental results show that those two kinds of jointed medium have great influence on crack propagation；and the initial cracks do not traverse joints；and wing-cracks are generated at both ends of joints and basically go on extending along original explosion crack. In open joint experiment，a caustics speckle appears in two wing-cracks about 25 μs after cutting seam cartridge blasting；and the largest width of wing-crack is 2.5 cm. While in closed joint experiment，a caustic appears 1 μs after cutting seam cartridge blasting，which is 24 μs ahead of open joint and the largest width of wing-crack is 5.6 cm. The dynamic stress intensity factor(SIF) of wing-crack changes from small to large firstly，and then falls from large to small. During the initial stage，dynamic stress intensity factor is smaller than that of . The peak value of closed joint is larger than that of open joint；the former is 1.72 MN/m3/2，and the latter is 1.28 MN/m3/2. The research results can provide theoretical basis for directional fracture with controlled blasting of jointed rock mass.

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DISCUSSION ON MATHEMATICAL FITNESS AND MECHANICAL
MODEL OF EXPERIMENTAL RESULTS

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2008, 27 (02): -251 doi:
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Many hypotheses or mechanical models are used to describe the mechanical properties of rock，in which some parameters are determined by experimental results. The mechanical model should have feasible and wider applications other than the experiment itself. Mathematical equations are used to fit the experimental data if the mechanical models have not been clearly invented. It is better to optimize fitness equations based on the mechanical and dimensional analyses，and to show the rock mechanical properties with the parameters in the equations. The relations between axial bearing capacity and confining pressure of cylindrical specimens with various sizes are introduced；and the differences between mechanical models and fitness equations are analyzed. Some fitness equations in literatures are discussed. The fitness equations should be shown with such a physical fact that the experimental results are not merely determined by the experimental parameters，also influenced by some factors which can not be controlled. The fitting precision can be improved better when more parameters are used in the equation，but excess of fitting precision may make the equation untrue totally.

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STUDY ON RELATIONSHIP BETWEEN CONVERGENCE LOSS AND LONGITUDINAL DEFORMATION CURVE IN TUNNEL EXCAVATION BY USING THREE-DIMENSIONAL FINITE ELEMENT ANALYSIS

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2008, 27 (02): -258 doi:
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The objective of this study is that the application of convergence-confinement method and the 3D numerical analysis by using the finite element programming developed in laboratory are employed to analyze the interaction behaviors between rock mass and support system in tunnel excavation. The parametric studies of elastic rock mass，initial stress and tunnel radial displacement are taken account of the relationship between the convergence loss and the longitudinal deformation curve(LDC) with conditions of supported or unsupported tunnels. The analytical solutions of equations are compared with the results obtained by 3D numerical analysis to find out the influences of convergence loss. According to the obtained results，the comparison between numerical calculation and theoretical analysis shows that：(1) the convergence loss is particularly function of the LDC；(2) the influence of parameters considered can be eliminated by the process of normalization for the LDC；(3) the estimated preconvergence normalized by the maximum convergence value approximately equal from 25% to 36% at the advancing excavation face in elastic condition；and (4) the convergence loss from the proposed equations of LDC in two-dimensional condition can be probably used to not only describe the three-dimensional advancing effects，but also estimate the variation of stress-displacement of rock mass and support system in tunnel excavation.

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RESEARCH ON HOMOGENIZATION-BASED MESOMECHANICAL DAMAGE MODEL AND ITS APPLICATION

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2008, 27 (02): -266 doi:
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The present study aims to establish a homogenization-based constitutive thermodynamic framework for the description of anisotropic damage by mesocracking. With the help of the basic solution to Eshelby¢s matrix- inclusion problem，a new micromechanics-based damage-friction coupled model is developed for rock materials，which are considered here as heterogeneous solids composed of elastic solid matrix and imbedded penny-shaped microcracks. From mesomechanical analysis，the general form of the macroscopic free energy is obtained，from which the conjugated thermodynamic forces are derived within the standard thermodynamic framework. Further，similar to classic plasticity theory，a Coulomb-typed interfacially frictional sliding criterion at mesoscopic scale is used as loading function and as commonly；a non-associated flow rule is adopted in determination of the evolution rate of friction-induced inelastic deformation. The proposed model has the ability of taking into account the main phenomena due to microcracking such as nonlinear stress-strain relations，damage induced anisotropic behaviours，coupling between damage and friction on cracks surfaces，sensitivity of mechanical responses to confining pressures，volumetric dilation as well as unilateral effects due to total or partial closure of microcracks，etc.. In order to illustrate the predictive ability of the proposed model，comparisons are performed between the model predictions with experimental data from conventional triaxial compression tests on a marble. The results show a generally good agreement；and the validation of the proposed mesomechanics-based damage model is checked.

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ANALYSIS OF PLASTIC DEFORMATION AND ENERGY PROPERTY OF MARBLE UNDER PSEUDO-TRIAXIAL COMPRESSION

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2008, 27 (02): -273 doi:
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Triaxial compression experiments are carried out for marble specimens by servo-controlled testing machine. After the specimens failed，they were then completely unloaded；and then uniaxial compression tests were carried out for the damaged rock specimens. Based on the experimental results，the plastic deformation and energy properties of marble specimens are analyzed under different confining pressures. At the same time，the uniaxial strength，elastic modulus and energy property of damaged specimens after unloading are investigated. The results show that marbles process the clear BDT(brittle-ductile transformation) property. The stress-strain curve shows the yield platform under higher confining pressure，i.e. the plastic deformation of rock specimen continues to increase with the axial deformation，but the supporting capacity by friction keeps basically a constant. The dissipated energies of rock specimens before yielding are comparatively less in the process of triaxial compression，but more energies in the process of plastic deformation. Moreover，the plastic deformation of rock specimen has a good linear relationship with the dissipated energy. Under high confining pressure，rock specimen will dissipate more energy in order to make the specimen fail completely. The strength and elastic modulus of the damaged specimens decrease linearly with the increase of plastic deformation. The produced plastic deformation under lower confining pressure has distinct effect on the strength and elastic modulus. However，in the yielding and softening phases after peak strength，the decrease of the supporting capacity of rock specimen is linearly accorded with the increase of plastic deformation. The softening modulus and elastic modulus of damaged specimens have no clear relationship with the peak strength，showing the localized behaviors of failure.

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CALCULATION AND DISCUSSION ON CRITICAL COLLAPSE DISTANCE OF TUNNEL UNDER PENETRATION WEAPON EXPLOSION

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2008, 27 (02): -281 doi:
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Based on the existing empirical collapse distance formula，the influence coefficients of the ratio of the collapse distance and the tunnel span are considered；and a formula that is suitable for engineering calculation is then put forward. The numerical calculation results show that the critical collapse distance of peeling-off increases as the tunnel span extends，but there exists a limit value，which is related to rock quality and charge quantity. The limit value decreases with the increase of the rock quality；while on the other hand，the limit value increases with the decreasing of the charge quantity. If the tunnel span is given，the critical collapse distance increases with the augmentation of charge quantity. At the beginning of the increment，the increasing rate of the critical collapse distance is much higher than that of any later time. The distance is linear with the oblique angle and increases as the angle becomes larger. When the charge is placed in a vertical position to the target，the value of collapse distance is maximum based on the calculation result of the formula.

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CENTRIFUGAL TEST ON REINFORCED EMBANKMENT WITH LIME-STABILIZED SOIL AS BACKFILL ON SOFT CLAY

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2008, 27 (02): -287 doi:
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Two centrifugal tests of reinforced and unreinforced embankments with lime-stabilized soil as backfill on soft clay with vertical drains were performed to investigate the reinforcement mechanisms and effects. The instruments used to measure displacement，pore water pressures and earth pressures were installed；and the strain gauges were glued with epoxy resin on the surface of the model with geogrid. The following test results are achieved. (1) Compared with the unreinforced embankment，the settlement of reinforced embankment is reduced approximately by 8%；and the heave of the reinforced embankment foundation is observed，whereas unreinforced embankment dominantly shows settlement. (2) Pore water pressures in the foundations of reinforced and unreinforced embankments are basically similar；and during each loading break，pore water pressures are obviously dissipated. (3) Earth pressures under embankment base are distributed uniformly due to geogrid reinforcement. Earth pressures under central part of the reinforced embankment are 6%–10% less than those of unreinforced embankment，whereas earth pressures under the slope toes of the former are approximately 40% greater than those of the latter. (4) Tensile forces in the model geogrid have a good changing law with the acceleration increasing. During loading break，tensile forces increase，which is consistent with the settlement changing law. The distribution of the tensile forces shows uniform until the reinforced embankment is loaded up to 2 m in height. Afterwards，the tensile forces at the central part obviously increase more than those at two sides. (5) An idea to add geosynthetics to the embankment¢s lime-stabilized soil is proposed so as to improve its tensile strength，which also makes the embankment more stable.

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ANALYSIS OF MESOMECHANICAL TEST OF ROCK SALT CONSIDERING COUPLED STRESS-DISSOLVING EFFECTS UNDER UNIAXIAL COMPRESSION

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2008, 27 (02): -294 doi:
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Through a large number of mesomechanical tests of rock salts under uniaxial compression considering coupled stress-dissolving effect，the differences of dissolving action on rock salts with/without considering stress are found；and the variation of dissolving action on rock salts considering stress can be described quantitatively with the relationship of dissolved masses. It can also be expressed with macro-dissolving velocity，axial plastic strain，and dissolving time with analyzing the data of the tests. Through analyzing the difference of crack shapes under different crack expansion phases after dissolution，the mechanism of variation of macro-dissolving velocity under different axial plastic strains is studied. Difference of mechanical properties of rock salts with/without considering the dissolving effect has also been achieved. With the gained relationship between stress and dissolving time upon the dissolution stage，the mechanism of variation of mechanical properties of rock salt considering dissolving effect，which is shown as critical stress intensity factor(SIF) of crack that is decreased because of dissolving，has been concluded. The achieved results can provide a foundation for the further analysis of coupled stress-dissolving mechanism of rock salt.

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DISCUSSION ON MACAO PILE FOUNDATION CODE

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2008, 27 (02): -303 doi:
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There are some differences between the design of pile foundation of Macao and the technical code for building pile foundations in Mainland of China. Taking a car park for heavy vehicles in Macao for example，four bored piles were tested with self-balanced load method. The similarities and differences of the two codes in tip resistance of bored piles，side friction resistance of bored piles，design safety factor and upside load effect coefficient were discussed. According to the results of the four-pile tests with self-balanced load method，the axial compression and anti-pulling behaviors of the bored piles were analyzed with the two codes，respectively. Furthermore，the results indicate that the value of the bored pile tip resistance is the same as the precast pile¢s value with the Macao code. However，the value is three or four times higher than the actual one. Thus，the rationality of the test program and the test results were doubted. In order to overcome the disadvantages of Macao code in bored pile tip resistance，the designers，owners and contractors of the project from different countries or regions consulted for several times. Finally，the test results were modified to be rational. These experiences may provide the lessons and references to the similar international cooperating projects.

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ANALYSIS OF TREATMENT SCHEME FOR SOFT FOUNDATION IN EXPRESSWAY WIDENING PROJECT AND ITS VERIFICATION

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2008, 27 (02): -309 doi:
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Due to the rapid increase of traffics，more and more early-built expressways will be reconstructed；and the control of differential settlements between old and new roadbeds on soft foundation is one of the key technical issues. Focusing on a typical soft foundation segment treated with dry jet mixing(DJM) piles in the Shanghai— Nanjing expressway widening project，the influences of pile length，pile distance，pile lateral friction force，geogrid and construction rate to the coordinated deformation between old and new roadbeds are analyzed with FLAC3D programme. The procedure is firstly analyzed for the influence of different pile lengths and distances on the deformations of soft foundation. Then，based on the proposed pile length and distance，the influences of pile lateral friction force with/without laying geogrid and construction rate are considered. The results indicate that pile length and distance are the most significant influential factors while the others are relatively minor ones. It is also shown that the excess pile length has little effect on settlement reduction；and excess pile distance can not meet the settlement control standard. It is suggested that the rational pile length is to ensure piles embedded in supporting soil layer about 2.5 m，and the rational pile distance is about 1.1 m. If actual pile lateral friction force is not 50% lower than the designed value，the influence is comparatively small on post-construction and differential settlements. Considering laying geogrid over the soft foundation treated with piles and pile caps has not distinct improvement on differential settlements；and the construction rate has potential influence on settlement rate but little influence on accumulated settlements with a loading rate of 10 kPa/d. According to the above results，an optimized treatment scheme for widening soft foundation is advanced and adopted. The settlement monitoring results show that the numerical calculation results agree well with the actual settlements；and the settlements indexes can meet the requests of engineering design.

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STUDY ON DISCRIMINANT CLASSIFICATION METHOD FOR GROUND FORMATION IN IDENTIFICATION OF GEOTECHNICAL ENGINEERING INTERFACES

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2008, 27 (02): -316 doi:
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Classification of rock drillability in real time using the curves of drilling process parameters is a bottleneck of the development and application of the instrumented drilling system. According to analysis of statistical mode recognition and characteristics of drilling parameter data，a discriminant classification method and validity test method have been established respectively for known categories and categorical numbers as well as for unknown categories and categorical numbers by minimum-distance clustering criterion. The methods have been used to classify the weathered granite formation by diamond penetrating specific energy curve. The results show that the clustering approach possesses excellent performance in classification，high precision and low misjudgment ratio and well agrees with the geological logs of rock core in general weathered granite formations，which can provide a quantitative discriminant approach for automatic classification of geotechnical engineering.

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UNDERGROUND GOAF RISK EVALUATION BASED ON UNCERTAINTY MEASUREMENT THEORY

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2008, 27 (02): -323 doi:
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Based on the uncertainty measurement theory，a risk-evaluating and order-arranging model of mining underground goaf was established. Considering the geologic condition and engineering status of underground goaf，14 factors that influence the stability of underground goaf were taken into account；and uncertainty measurement function was obtained based on the in-situ data. The uncertainty problems in risk evaluation were solved by qualitative analysis and quantitative analysis respectively. Entropy theory was used to calculate the index weight of factors；and credible degree recognition criteria were established according to the theory uncertainty measurement. The results of risk evaluation can be obtained with the credible degree criteria. This method can also arrange the order of risk degree. Furthermore，this model was employed to evaluate 15 risk underground goafs in Dabaoshan mine. Compared with the results of fuzzy synthetic evaluation method，the results show that uncertainty measurement method is reasonable and can be applied to the actual engineering.

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STUDY ON ACCUMULATIVE PLASTIC STRAIN MODEL OF SOFT CLAY UNDER CYCLIC LOADING

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2008, 27 (02): -331 doi:
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The effects of accumulative plastic strain on degradation characteristics of Hangzhou saturated soft clay subjected to undrained cyclic triaxial loading are investigated at different cyclic stress ratios，overconsolidation ratios(OCRs)，frequencies of cyclic loading and consolidation ratios. It is observed that the degradation index is reduced with increase of accumulative plastic strain. The degradation index decreases slightly at the beginning of cyclic loading；and then the degradation index increases greatly as the strain increases. However，when the strain increases further，the degradation index changes a little. The plastic strain accumulates significantly and the relationship curves of the accumulative plastic strain and degradation index move right as the cyclic ratio increases. At a lower frequency，the curves move left with the increase of frequency. However，at a higher frequency，the effects of frequency on the relationship curves are less distinct. The curves move left as the OCR increases. The curves move upright with the increase of consolidation ratio. Based on the test results，an empirical accumulative plastic strain model is proposed by introducing a comprehensive impact parameter. The model is further introduced into modified Iwan model to describe the stress-strain relationship of soft clay. The comparison of simulation results with test data shows the proposed model is reasonable.

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EXPERIMENTAL STUDY ON PRECURSORY INFORMATION OF DEFORMATIONS OF COAL-ROCK COMPOSITE SAMPLES BEFORE FAILURE

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2008, 27 (02): -339 doi:
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The failure features of the composite samples under uniaxial loading are discussed. The characteristics of energy dissipation and translation in the process of coal-rock sample failure are analyzed；and an experimental system for analyzing the mechanism and precursory information of the failure of coal-rock composite samples is developed. The system is composed of the thermal infrared(TIR) observation system，the stress and strain measurement system，and the acoustic emission monitoring system. In order to investigate the TIR and acoustic responses of different kinds of coal-rock composite samples，two types of composites are tested，which are composed of three bars of sandstone-coal-mudstone and two bars of sandstone-coal，respectively. The uniaxial compressive load tests are carried out to observe the features of TIR，acoustic emission and strain precursory information in the process of sample failure. The detailed investigations on the precursor information of stress points are conducted based on the TIR images，infrared radiation temperature，infrared radiation images，acoustic emission，and strain date. The analytical results show that the coal-rock composite specimens are under stress accelerated accumulation state before failure. Moreover，it is more difficult to forecast the failure of coal-rock composite samples compared with the failure prediction of normal coal samples.

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HISTORICAL EARTHEN KILN REINFORCEMENT WITH MICRO-SOIL NAILING AND MINI-CHEMICAL GROUTING TECHNIQUES

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2008, 27 (02): -347 doi:
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Preservation of historical earthen ruins against damage is one of the difficult problems. The main geological issues of such earthen ruins are weathering，cracking and falling of the surface soil. Conventionally used soil nailing and chemical grouting techniques have the following limitations when applied to strengthen these ruins. One is that the large diameter of drill hole will disturb the soil ruins and leave evident spots of appearance. The second one is that chemical grouts flow towards ground surface and will also spoil the appearance of the soil ruins. And also the high injection pressure may lead to micro-cracks inside the earthen ruins. Further spraying chemical grouts on the surface is frequently used in practice，but the permeation quantity and solidification effect are difficult to evaluate. From the objectives of strengthening and preserving Dougaeri historical earthen kiln No.2，the micro-soil nailing and mini-chemical grouting techniques have been developed to overcome the above limitations. The two techniques can be used together or individually according to the specific requirements. The important micro-equipments developed are mortar injector and balloon cover injection tip，which are suitable for nailing and chemical grouting in micro drill holes(f 5–7 mm). The feasibility and adaptability of the techniques have been evaluated in a field model kiln test. A fast Lagrangian analysis of continua(FLAC) code has been employed to perform stability analysis. The reinforcement design with the micro-techniques has been presented considering the different stabilities and possible failure modes at different locations of the kiln. The recommended design has been successfully applied to the practical works. It is envisaged that the micro techniques will have broad applications to strengthening and preserving historical earthen ruins due to its portability，little disturbance and well-field adaptability.

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IN-SITU TEST ON STRESS CHARACTERISTICS OF COMPOSITE FOUNDATION WITH SPARSE T-SHAPED RIGID PILES UNDER WIDENING EMBANKMENT

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2008, 27 (02): -354 doi:
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In-situ full-scale tests on stress characteristics of composite foundation with sparse T-shaped rigid piles were carried out under the condition of experimental section of Shanghai—Nanjing Expressway widening project. Based on the test data，the level and distribution of pile-soil stress were analyzed；and the pile-soil stress ratios calculated with different methods were studied. The results indicate that pile-stress concentration effects are related to the embankment height and the sites of piles. Pile-stress concentration effects can be found if the height of embankment constructed with soil mixed with fly ash and lime is larger than 120 cm；and they will not be encountered under the embankment slope near slope-foot. The pile-stress concentration effects of the piles in the middle of composite foundation are greater than those of the piles at the range of composite foundation. The bearing capacity of soils under the pile-cap works only when pile-stress concentration effects are great；and the difference between the stresses on the caps and those under the caps all indicate that the soils under the caps are nearly separated from the caps. Pile-soil stress will be adjusted continuously during embankment construction；and the observed pile-soil stress ratios range from 1 to 12. The observed pile-soil stress ratios can not correctly reflect the stress characteristics of composite foundation with sparse T-shaped rigid piles under widening embankment；and it is suggested that pile-stress concentration effects should be evaluated with pile-site stress ratio.

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EQUIVALENT VERTICAL DYNAMIC STIFFNESS FOR EMBEDDED RIGID CYLINDRICAL FOUNDATION IN SATURATED SOIL

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2008, 27 (02): -361 doi:
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Considering the interaction between the soil and the side of the foundation，the dynamic response of a rigid cylindrical massive foundation embedded in saturated soil under vertical time-harmonic excitations is investigated based on Biot¢s dynamic equations. The soil below the foundation base is represented by a saturated half space while the soil over the foundation base is represented by an independent saturated soil composed of a series of infinitesimally thin independent saturated layers. It is deemed that the interaction between the base of the foundation and saturated soil is independent of embedment depth. The foundation is perfectly bonded to the surrounding soil；and the contact surface between the saturated soil and the foundation base is fully permeable. Combining the mixed boundary conditions at the interface between the foundation and the saturated soil，the vertical dual integral equations are established. Solutions for the equivalent vertical dynamic stiffness of rigid cylindrical embedded foundation in saturated soil are obtained by solving the integral equations using Hankel integral transforms. The accuracy of the presented solution is verified by degenerating the saturated soil to an elastic soil and by comparing it with the existing solutions for ideal elastic soil. Numerical results indicate that both real and imaginary parts of the equivalent vertical dynamic stiffness of rigid cylindrical foundation embedded in saturated soil depend significantly on the dimensionless frequency of excitation；and there is a linear increase in the real and the imaginary parts of the equivalent vertical dynamic stiffness as the depth ratio increases. Furthermore，the permeability coefficient has significant effect on the equivalent vertical dynamic stiffness；and the effects become more obvious as the dimensionless frequency of excitation increases

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CENTRIFUGAL MODEL TEST ON DYNAMICAL CHARACTERISTICS OF LANDSLIPS OF LOOSE SLOPE UNDER SEISMIC LOADING

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2008, 27 (02): -368 doi:
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Based on the principle of pseudo static loading and centrifugal model tests，the dynamical characteristics of landslips of loose slope under seismic loading are analyzed by means of the landslips of sand-pile models with one slope，which are used as simplification pattern of loose slopes. Firstly，three centrifugal model tests of uniform sand with size distribution of 0.5–1 mm and 8–10 mm and non-uniform sand with a heterogeneous coefficient f = 3.10，are designed. In these centrifugal model tests，the dynamical characteristics of landslips of loose slopes are simulated under seismic loadings with three magnitudes，i.e. V，VI and VII. The test results show：(1) landslips of uniform sand with size 0.5–1 mm obey quasi-cyclical distribution under seismic loadings with magnitudes V，VI and VII；(2) landslips of uniform sand with size 8–10 mm and nonuniform sand with f = 3.10 obey negative power distribution law under seismic loading with magnitude V，displaying self-organized criticality(SOC)；and (3) landslips of uniform sand with size 8–10 mm and nonuniform sand with f = 3.10 show normal distribution under seismic loading with magnitudes VI and VII. As for the three dynamical characteristics，it is indicated that the landslips of uniform sand with size 0.5–1 mm under seismic loading with magnitudes V，VI and VII are predicted；but the landslips of uniform sand with size 8–10 mm and nonuniform sand with f = 3.10 under the three earthquake magnitudes can not be accurately forecasted. The research conclusions can offer some favorable references to aseismic design of loose slopes.

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NUMERICAL ANALYSIS OF SOIL SLOPE STABILITY CONSIDERING TENSION AND SHEAR FAILURES

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2008, 27 (02): -375 doi:
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The authors consider that unstable slopes are caused by composite failure of tension and Mohr-Coulomb shear of sliding soil mass，but not caused by single shear failure. The composite failure criterion，which is applicable to rock and soil，is discussed. When the prevailing large-scale finite element programs that only the single shear model is included in their material models are used to analyze soil slope stability，there are two ways to consider shear failure of soil mass. The one is to redevelop subroutine of user-defined mechanical model，which can express the composite failure criterion of soils. The other is that the just connection between the shear failure zone and tension failure zone should be regarded as the criterion of sliding failure of soil slopes. Numerical modeling analysis is performed with seven kinds of soil slopes by using the finite element method and the fast Lagrangian finite difference method. The comparisons show that the results from the two methods considering the composite failure of tension and shear of soil mass coincide very well. Since the tension strengths of soils are lower than those of shear strengths，if the tension failure of soil mass is not taken into account，the factors of safety of slope stability are possibly 1% to10% higher than those of theoretical ones. Therefore，it is necessary to consider the tension failure of soil mass in soil slope stability analysis. Meanwhile，some laws about the shapes of composite sliding surface of the seven sorts of soil slopes are obtained；and they can be used to judge whether critical sliding surface searched by other analytical methods of slope stability is reasonable or not.

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TRIAXIAL SHEAR PROPERTIES OF UNDISTURBED LOESS Q2

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2008, 27 (02): -383 doi:
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A series of triaxial shear tests with controlled suction and net constant confining pressure and the tests with controlled water content and constant confining pressure were conducted to study the effects of deformation，strength and yield properties of unsaturated undisturbed loess Q2 with suctions or initial water contents. The test results show that the failure model of unsaturated undisturbed loess Q2 with controlled suctions equaling 100，300 and 450 kPa is shown with plastic failure；but the failure model of unsaturated undisturbed loess Q2 with controlled initial water contents equaling 4.78% and 7.64%，respectively，is displayed with brittle failure. The stress-strain curves of undisturbed loess Q2 will change from strain softening to strain hardening with the decrease of suction(or the increase of water content) and the increase of consolidation cell pressure. The cohesion of unsaturated undisturbed loess Q2 has a linear increase with the increase of suction within research suction range(100–450 kPa)，but the friction angle is found to have little change with the change of suction. A new method to identify the field stress of undisturbed loess Q2 under triaxial shear condition is suggested. The net mean yield stress and deviatoric yield stress both increase with suction，where the deviatoric yield stress has a linear increase with net mean yield stress under the same suction or water content.

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EXPERIMENTAL STUDY ON MIXTURE RATIOS OF GROUTING MATERIAL FOR IMPROVEMENT OF PULL-OUT BEHAVIORS OF ROCK CABLES

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2008, 27 (02): -390 doi:
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The influence of mixture ratio of grouting material on the pull-out behaviors of rock cable is obvious，which is one of key parameters for the optimal design of prestressed anchorage systems. Unfortunately，few studies are found about the influence of mixture ratio of grouting material on the pull-out behaviors of rock cable；and there are not sufficient or professional standards established for the special grouting material in prestressed anchorage specifications. Based on many investigations of in-situ projects，eleven cement-based grouting materials with different mixture ratios and related physico-mechanical characteristics are respectively tested；and the laboratory pull-out test has also been carried out to study the influence of mixture ratio of grouting material on the limit bearing capacity and load-displacement behaviors of rock cable. The results of pull-out tests show that mixing appropriate amount of sand into cement-based grouting material could increase the fracture energy，thus enhance the roughness of cementation interface between cable and grouting material，and increase the restraint of cable untwisting expansion. The limit bearing capacity of rock cable，consequently，is remarkably improved. However，it has less effect through decreasing the water-cement ratio to elevate the limit bearing capacity of rock cable. Debonding along the cable-grouting material interface is the dominant failure model of conventional prestressed cable bolt，so great importance should be attached to the failure model in the design of anchorage engineering and revision of technical specification for prestressed anchors in the future.

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ANALYSIS OF DYNAMIC ABRASION OF SHIELD CUTTERS IN SANDY COBBLE STRATUM

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2008, 27 (02): -397 doi:
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The main types of shield machines used recently in tunnel construction are earth pressure balance(EPB) shield tunneling and slurry shield tunneling. In order to reduce shield cutters wear，the parameter in shield construction advancing should be rational. This is fundamentally critical to ensure the shield to advance distantly in sandy cobble stratum. Sandy cobble is a typically unstable stratum and its mechanical properties are unfavorable for force transitivity and spread. Sandy cobble is also of unfavorable plasticity and fluidity，which will bring serious abrasion to shield cutters. By employing the latest dynamic supervisory gear，the abrasion of shield cutters used in shield tunnel section of Jiaomen Northern Load station to Beijing Southern station of Beijing metro line 4 was monitored；and the monitoring data were analyzed with the least square method. With abrasion coefficient as dependent variable，and advancement rate，total thrust，cutter-head rotation speed and cutter torque as independent variables，four regression expressions were established and eight regression graphs were drawn. Based on the regression expressions and graphs，the rational range of advancing parameters was proposed；and the fitting expression of abrasion of shield cutters to advancing distance was established，which may provide theoretical basis for reducing cutter abrasion in practical engineering，and for estimating the longest advancement distance in similar stratum. Based on the fitting expression of abrasion of shield cutters to tunnel advancing，the longest advancement distance is found to be 1.84 km in this stratum. The research conclusion is helpful for shield selection and engineering construction with similar geotechnical conditions.

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COUPLING ANALYSIS METHOD FOR ELASTOPLASTIC CONSOLIDATION OF CLAY CONSIDERING STRESS PATHS

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2008, 27 (02): -403 doi:
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A simplified coupling analysis method for elastoplastic consolidation problem of clay under different stress paths is presented. An elastoplastic constitutive model of clay is constructed on different initial conditions based on numerical modeling method and it can be adopted with Biot consolidation theory. Then the incremental governing partial differential equations are established for plane strain consolidation problem. Based on the constitutive models，a Poisson equation for pore water pressure is derived and the basic solution is obtained. Because the volumetric strain can be acquired as the right term of the equation by the constitutive model straightly；the deformation field of soil skeleton and pore water pressure field are coupled directly. Thus the Poisson equation is more accurate than the classic diffusion equation and it is easier for solving than the Biot functions. Moreover，the interaction between the volumetric strain and shear strain is considered. A semi-analytical and semi-numerical method for the nonlinear consolidation equations with the coupling fluid-solid issue is presented and its finite element program is given. Moreover，a systematic numerical approach from numerical modeling through simulation for soil consolidation is established. The computational results of some examples under different stress paths show that this approach is simple and able to reflect the influences of some facts，such as stress paths and load scope，on displacement，settlement and pore water pressure of foundation. Especially，stress path affects the solid deformation field evidently.

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ANALYSIS OF STRESS AND DEFORMATION OF PRESTRESSED ANCHOR CABLE COMPOSITE SOIL NAILING

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2008, 27 (02): -410 doi:
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[PDF 439 KB] (1365)

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As an efficient supporting method，prestressed anchor cable composite soil nailing is widely adopted in geotechnical engineering. But the analysis of prestressed anchor mechanism is not sufficient. And the research on in-situ test of prestressed anchor cable composite soil nailing is seldom seen. Firstly，a brief introduction to the mechanism of prestressed anchor cable composite soil is given. Then，the horizontal and vertical displacements of foundation pit supported by prestressed anchor cable composite soil nailing are presented. The stresses of soil nailing and anchor head of prestressed anchor cable under excavation are also attained. Finally，the characteristics of stress and deformation of the prestressed anchor cable composite soil nailing with ANSYS10.0 are analyzed. Conclusions can be drawn as follows：(1) the results from in-situ test are in accordance with those from FEM simulation；(2) cohesion and elastic models of the soil in foundation pit，which is supported by prestressed anchor cable composite soil nailing，will be improved；(3) more earth pressure is shared by the anchor cable，and earth pressure shared by soil nailing is reduced for prestressed anchor cable composite soil nailing supporting；(4) earth pressure on the side of foundation pit is smaller when prestressed anchor cable composite soil nailing supporting is introduced；(5) the stress and deformation of soil nailing and prestressed anchor cable both have the excavation effect，time effect and space effect；(6) the horizontal deformation of the side of foundation pit is drum-shaped，and the vertical deformation of the side of foundation pit agrees well conventional rule；(7) the deformations of foundation pit，including the horizontal displacement and the vertical displacement，are better controlled when using prestressed anchor cable composite soil nailing supporting；and (8) prestressed anchor cable composite soil nailing supporting technique can gradually improve the supporting capacity during excavation，which satisfies the requirements of variations of the stress and deformation induced by the construction process and some uncertain factors. The achieved results can provide some references to the design and construction of similar projects.

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STUDY ON EFFECTIVE STRESS AND DYNAMIC CONSTITUTIVE MODEL OF PHYSICAL STATE AND APPLICATION TO SATURATED SANDY SOILS

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2008, 27 (02): -418 doi:
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[PDF 569 KB] (1150)

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Firstly，on the basis of discussion on current analysis methods in soil dynamic responses，the dynamic stress-strain characteristics of sandy soil is revealed by systematical dynamic triaxial tests under fully drained condition with constant spherical stress but cyclic deviator stress，constant deviator stress but cyclic spherical stress as well as cyclic spherical and deviator stresses. These constitutive relationships are further combined with the framework of transient dynamic theory with a total(static and dynamic) effective stress space divided into different zones by critical state line，phase transformation line，and stress space divided into different zones by critical static state，phase transformation line and stress historical line. The constitutive model can be used to consider the sandy soil properties of nonlinearity，hardening，shear dilatation-contraction，compression-swelling，and stress path dependence and coupling of spherical stress with deviator stress. The study is performed upon the relationships of spherical stress-volumetric strain，spherical stress-deviatoric strain，and deviatoric stress-deviatoric strain. In additional，the fundamental of a 3D dynamic consolidation with governing equations based on the basis of transient dynamic theory is introduced with effective stress and dynamic constitutive relationships of physical states. Also，it is established with the coupling of dynamic response with dynamic consolidation，the coupling of static stress and dynamic stress，the coupling of pore water pressure generation，pore water pressure diffusion，and dissipation to simulate true process of stress-strain response of sandy soils and form a complete theoretical framework system of seismic response analysis approach based on effective stress and physical states of sandy soils.

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COMPARISON OF ENERGY DISSIPATION ANALYTICAL METHODS FOR CAVITY EXPANSION CONSIDERING LARGE DEFORMATION AND VOLUMETRIC CHANGE IN SAND SOIL UNDER HIGH STRESSES

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2008, 27 (02): -426 doi:
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[PDF 308 KB] (1125)

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According to Mohr-Coulomb failure criterion，the stress-strain-volume change relationships，the volume balance and energy conservation equations，and the rules of large deformation and non-associated flow under high stresses， the limit bearing capacities of cavity expansion are given considering the large deformation and dilation with volumetric change and large deformation，respectively. The developed theory considering the large deformation agrees with the results of in-situ test，which can give reasonable results than those of theory considering the volumetric change. Furthermore，as for the influence of the dilation，the limit expansion pressure has nonlinear relationship with the dilation and the shear modulus in sand soil.

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本刊2007年第11，12期被EI收录论文(53篇，收录率为100%)题录

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2008, 27 (02): -428 doi:
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学会决定联合创办《学报》英文版及招聘高级英文编辑

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2008, 27 (02): -430 doi:
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[PDF 101 KB] (1018)

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