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2007, 26 (06): -0 doi:
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2007-06目录

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ROCK RHEOLOGICAL MECHANICS AND ITS ADVANCE IN ENGINEERING APPLICATIONS

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2007, 26 (06): -1106 doi:
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The recent development in some aspects on the research of rock rheology and its engineering applications are discussed；the main contents are listed as follows：a comprehensive introduction of the rock engineering rheology problems，laboratory as well as in-situ study on the soft rock and rock mass of rich growth with joints and fissures，identification of rheological models and their parameters estimation，applications of rheological mechanics to the convergence-confinement method and its applications to the design optimization of tunnel structures，nonlinear rheological behavior of tunnel surrounding rocks in high earth stress region and its mechanical effect of tunnel lining-support，study on rock rheological damage and fracture mechanics. Besides，this paper gives a brief discussion on the rheology problem in soil mechanics and soil engineering. Finally，several understandings on the research work are presented in prospect of the rheological mechanics in geotechnical engineering in the future.

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FORMATION MECHANISM AND TREND ANALYSIS OF LIFTING OF VALLEY AND DAM IN JIANGYA HYDRAULIC PROJECT

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2007, 26 (06): -1107 doi:
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Jiangya Hydraulic Project is situated in the basin of the Loushui River in Hunan Province，China. After the reservoir is impounded，significant lifting deformation of the dam along with its surrounding valley is observed. The theory of the formation mechanism and the future forecasting are discussed. The 131 m high dam of Jiangya Hydraulic Project is located on the northwest limb of regional syncline(Jiangya syncline)，there exist a series of aquifers and impermeable layers. A hot water artesian aquifer is found right under the dam foundation. The reservoir impounding began in Aug. of 1998，and to Feb. 2001，the biggest lifting of both banks of the valley was measured 21.8 mm，generally 15–10 mm；the lifting of the grouting gallery in the dam was measured 34.5 mm with a mean value of 31 mm. Based on both the site investigation and data analysis，the hypothesis of dilatancy mechanical model，that the lifting deformation is caused by the pressure change resulting from moving interstitial water in rock mass is proposed. In order to verify the model，a rock mechanical simulation test has been carried out using the MTS stiff testing machine. The test result strongly supports the model. According to the results combined with in-situ geological analysis，the“syncline flexural slip”mechanism is believed to be responsible for the lifting of Jiangya dam and its surrounding banks. The authors also forecast that this lifting and subsiding phenomenon will reduce progressively，and eventually diminish. The latest data have confirmed the forecast made five years ago.

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COMPOSITE ELEMENT METHOD AND APPLICATION OF TRACE SIMULATION FOR STRAIN LOCALIZATION BANDS

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2007, 26 (06): -1116 doi:
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The composite element method(CEM) is used to simulate the effects of strain localization bands，based on which a new trace algorithm of the propagation of strain localization bands is proposed. The softening effects within the strain localization bands are illustrated as the decrease of the material parameters，the locations and directions of all the potential strain localization bands are logged and simulated. With the rock fracture statistics technology，the failure passage can be fitted；the messages of this failure passage together with the messages of the initial grid are then used to generate the topology messages of composite elements，based on which the calculation is repeated to check the trace procedure of the strain localization propagation. The trace algorithm proposed does not request the continuity of strain localization propagation paths，and the interaction among localization band segments can be taken into account. The feasibility and reliability of the algorithm are verified by a slope example. The expectation of the algorithm in engineering practices is shown by the comparative study of the Baozhusi gravity dam project.

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STUDY ON BEARING CAPACITY AND SETTLEMENT OF SHALLOW
FOUNDATION WITH VOID

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2007, 26 (06): -1123 doi:
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Several factors，such as the void location and the void shape，affect the bearing capacity behavior of shallow foundation. The cavity effect on the bearing capacity of strip foundation above a void is investigated analytically by using the elastoplastic 2D FEM. The relation between load and settlement of shallow foundation is analyzed for different conditions of the void；and the failure mechanism of ground is also examined. The analytical results indicate that there is a critical effect region for the void under the shallow foundation. Only when the void is located within this region，the bearing capacity and settlement of strip foundation vary considerably with the void location. In addition，based on the above finite element results，a simple calculation method is proposed for the cavity effect on the bearing capacity of strip foundation.

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DETERMINATION OF FLUID INCLUSION LINES USING
EDGE-DETECTION TECHNIQUE

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2007, 26 (06): -1132 doi:
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Fluid inclusions(FI) are widely spread in microcracks and composed of fluid inclusion planes(FIP) and fluid inclusion lines(FIL)—the intersections of FIP with some observed planes. These microscopic compositions(FI) or structures(FIP and FIL) with different geometrical and configuration parameters may record the history of deformations and/or fractures in rocks. The original images are obtained from a camera on a heating-freezing stage. These images are first transformed into gray images and broken into blocks by image segmentations. For each block，the inflection point，derivative and color-based methods are all used to detect the edges for each fluid inclusion. The Roberts，Prewitt and Sobel algorithms are used in the inflection point. The LOG and Canny algorithms are used in the derivative method. In order to get better boundaries，the mathematical morphological analyses are used to extend edges，connect discontinuous points，fill pores in outlines，eliminate irrelative parts，smoothen projecting parts and aggregate the smaller inclusions into big ones. The inflation，erosion，seed-filling，boundary connection，smoothening methods are used in the mathematical morphological analysis. After re-orientation for each block，edge points and lines are ascertained in the global coordinate system. According to the geometrical properties of inclusions from edge detection，especially from the mathematical morphological analysis，FILs and their configuration parameters are finally obtained with the least square method. The geometrical properties include positions，areas and long-axis directions. The configuration parameters include length，and width. All of these procedures are coded into a program. Due to the reflection of FIL on the characteristics of microcracks and the formation relationships between the micro- and macro-structures，the analysis presented here may theoretically provide a good foundation to reveal the micromechanics of the change process for different geological phenomena in rock area.

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CALCULATION OF ULTIMATE BEARING CAPACITY OF PRESTRESSED CABLE BASED ON UNIFIED STRENGTH CRITERION

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2007, 26 (06): -1138 doi:
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Based on the unified strength theory，the limit equilibrium principle and the shape of rapture of surface，a formula，which takes into account the shape of rapture surface，dip angle of cable，grouting pressure，varieties of rocks，are deduced. In order to validate the practicability of the calculation formula，by taking different influential factors into account，a comparison between the theoretical and actual data is made in soft rock and hard rock. The results reveal that，with the increase of the coefficient of weight b，the ultimate bearing capacity of cable increases too，yet the shape of fracture plane doesn¢t change；the ultimate bearing capacity of cable depends much more on the boundary strength between grouting and rock，or grouting and cable than that of the fracture plane of cone. In soft rock，the ultimate bearing capacity of prestressed cable，less influenced by the grouting pressure，depends mainly on the boundary strength between rocks and grouting. In hard rock，the grouting pressure plays an important role on the ultimate bearing capacity and the height of rock cone. When the grouting pressure increases，the ultimate bearing capacity and the height of rock cone increase too. In technical application，by utilizing the intensity parameter formula of unified strength theory，the intensity parameters of soil and rocks corresponding to the coefficient of weight b which contains the contribution of the second principal stress，can be calculated.

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DETERMINATION OF IN-SITU STRESS BY HYDRAULIC FRACTURING TESTS ON PREEXISTING FRACTURES CONSIDERING STRESS GRADIENT AND ITS ENGINEERING APPLICATION

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2007, 26 (06): -1145 doi:
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Abstract：The theory of in-situ stress determination based on hydraulic fracturing tests on preexisting fractures(HTPF) is presented. The similarities and differences between the HTPF and the classical hydraulic fracturing(HF) technique are discussed. The inversion method for 3D in-situ stress field considering stress gradient along the vertical borehole axis is also introduced. In the course of searching for the principal stresses of stress field in a liquefied petroleum gas underground storage project，the regional stress field is supposed to be continuous only in a small section near the cavity area and the referential point is also chosen to be located in this area. Compared with previous studies that the regional stress field is assumed to be continuous in the whole depth of the borehole and the referential point is chosen to be at ground surface，the result by the proposed method is more reasonable. The complete stress tensor of regional stress field is obtained based on the genetic algorithm；and the result is satisfactory.

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COMPLETE COUPLING ANALYSIS OF TRANSIENT FLUID FLOW AND ELASTIC STRESS IN FRACTURED ROCK MASSES

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2007, 26 (06): -1150 doi:
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In order to reflect the actual behavior of the seepage field and deformation field during the environment change and construction processes，the basic equations and finite element expressions for complete coupling analysis of transient fluid flow and elastic stress are developed according to the assumption of small deformation and incompressible fluid flow in complicated fractured rock masses. A unified hybrid media model is used to simulate the seepage field；and both the equivalent continuum media model and the discrete media model are adopted to simulate the elastic deformation field. The coupled equations are solved directly by use of the four-freedom complete coupled method with FEM. And the modified initial flow method is adopted to deal with the free surface of unconfined seepage. Finally，the above method is applied to the fractured rock bank slope of a reservoir. Both the static and dynamic coupled processes of seepage field and stress fields are simulated during the rising of water level in reservoir；and the variations of both the displacement field and the seepage field are studied. The result shows that the dynamic action of water flow for quick rising can lead to a great difference in the settlement of the reservoir bank slope and reduce the bank slope stability；but slowly rising process can be solved as the static problem.

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TEST STUDY ON ANCHORAGE FORCE OF PRESTRESSED ANCHOR CABLES FOR FOUNDATION PIT

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2007, 26 (06): -1158 doi:
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There are many influence factors on anchorage force of prestressed anchor cables for foundation pit. The main influence factors are physico-mechanical properties of rocks and soils in anchorage area，the construction technological process of anchor cables，and loss of prestress in locking anchors，etc.. Based on engineering tests，it is analyzed that the tension force of each anchor cable is distributed unevenly. There are two causes for this phenomenon：(1) acted by the gravity，the jack axis deviates from the axis of prestressed anchors；(2) because of the error between construction angle and design angle of drilling hole，the prestressed anchor cables is not vertical to the anchorage block. The loss of prestress is discussed in single tension locking and cycle tension locking，and continuous monitoring of anchorage force is described in deep excavation. The acceptance test criteria for pulling resistance are discussed，the simplified calculation method of elastic deformation of prestressed anchor cable is presented；and a revised proposal is put forward. Three indices such as total displacement，increment displacement by each grade load and percentage of rebound should be considered in the acceptance test for pulling resistance of anchor cables.

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INTELLIGENCE IDENTIFICATION OF THREE-DIMENSIONAL ELASTOPLASTIC MODEL PARAMETERS IN TUNNEL ENGINEERING BASED ON IMPROVED GA-SVR ALGORITHM

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2007, 26 (06): -1164 doi:
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The support vector regression(SVR) algorithm has been introduced into parameters identification of numerical model in geotechnical engineering to take advantage of its merits such as small sample，good generalization and global optimization. But，the standard SVR algorithm can only solve one-dimensional output variable regression problem，thus restrict its application in back analysis field. In this paper，an improved SVR algorithm is introduced by decomposing multi-dimension output variables to many one-dimensional output variables，and then the multi-dimensional output variable regression is translated into a multi-layer standard SVR problem. In order to find the optimal parameters of this improved SVR model during sample training course，the genetic algorithm(GA) is combined with it to form the improved GA-SVR algorithm. After the optimal nonlinear mapping between the numerical model parameters and displacement is constructed，GA is used to identify the numerical model parameters within their search interval. In virtue of MATLAB toolbox，GA also is integrated into BP neural network to form the GA-BP algorithm. By comparing the identification results of three-dimensional elastoplastic model parameters in tunnel engineering by the two different algorithms，it can be concluded that the improved GA-SVR algorithm can obtain a higher identification precision and calculation efficiency than the GA-BP algorithm and can be applied to similar calculation parameters identification in geotechnical engineering.

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EXPERIMENTAL AND ANALYTICAL STUDY ON HYDRAULIC FRACTURING OF CYLINDER SAMPLE

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2007, 26 (06): -1173 doi:
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Nine groups of hydraulic fracturing tests of thirty thick-wall cylinder samples are performed；and the experimental results are analyzed. The analytical methods reported in some studies based on Lame¢s formula of the thick-wall cylinder are incorrect. Infiltration theory of hydraulic fracturing is presented. Based on elasticity mechanics and mathematics，an analytic distribution result of thick-wall cylinder under stable infiltration is put forward and it is verified by commercial software. A rigorous theory foundation is established for the research of hydraulic fracturing of rock masses. Failure condition of thick-wall cylinder on hydraulic fracturing is discussed. And a semi-empirical formulation on critical stress of hydraulic fracturing is presented.

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CENTRIFUGE MODELLING TEST ON COVERED SHEET-PILED STRUCTURE OF WHARF

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2007, 26 (06): -1182 doi:
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A covered-type of sheet-piled structure has recently been proposed to overcome the problem that the conventional sheet-piled structure is only applicable in medium and small wharfs，which has long been the difficult problem of port engineering. Incorporating with the construction need of a deep water berth of 100 000 DWT，a study for the proposed covered sheet-piled structure is conducted by means of centrifuge model test to investigate the distribution of bending moment of the front sheet-piled wall，covered sheet-piled and anchor wall，and the horizontal displacement on the top of the wall and the tension force of connecting rod. To illustrate the contribution of barrier piles to the wharf performance，the conventional structure without barrier piles under no surface work load as well as the proposed new structures are modeled，in which the surface load，ratio of embedment of front wall，and distance between front wall and barrier pile are considered as influential factors. Test results show that the maximum bending moment of the front sheet-piled wall is obviously decreased，with smaller magnitude of seawall horizontal displacement and tensile force of connecting rod. Thus the problem perplexing engineers is promisingly overcome by application of this new structure of sheet-piled wall. Three modes of connection are conducted in the model test to find out the best connection mode between the front sheet-piled wall and the barrier piles，such as rigid connection through breast wall，rigid breast wall connect with vertical freedom，and hinge jointing connection through short connecting rod，respectively. It is found that the third one，i. e. the hinge jointing connection through short connecting rod，is preferable to the others in decreasing bending moment of these structure elements. Based on the analysis of the test results，an optimum scheme is recommended for the project to be built.

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STUDY ON REASONABLE COVER THICKNESS FOR SUBMARINE TUNNEL OF CHAOTIANMEN IN CHONGQING BY SHIELD CONSTRUCTION

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2007, 26 (06): -1188 doi:
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The determination of the cover thickness of the submarine tunnel is very important，because it will be very dangerous if the cover thickness is too small，whereas the length，slope gradient and cost will be increased after a larger cover thickness is chosen. At first，the reasonable cover thickness for submarine tunnel of Chaotianmen in Chongqing is proposed by comparing this tunnel with some domestic and foreign well-known submarine tunnels. According to the Technical Specification for Construction of Highway Tunnel，a new concept of standard tunnel is put forward. Based on the actual situation of Chongqing Chaotianmen tunnel，by comparing the crown displacement and the principal tensile stress of standard tunnel and this tunnel in different cover thicknesses，the reasonable cover thickness is finally put forward.

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INVESTIGATION ON COMPRESSION-SHEAR FRACTURE CRITERION OF ROCK BASED ON FAILURE CRITERIA

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2007, 26 (06): -1194 doi:
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Based on the analysis of the tip stress field of the compression-shear mixed-mode crack，the initial angle of compression-shear mixed-mode crack is deduced according to the minimum J2 criterion. By considering the rock compression-shear mixed-mode fracture and the rock yield criterion together，two fracture criteria of the rock compression-shear mixed-mode crack are obtained by use of Mohr-Coulumb and Drucker-Prager yield criteria which are adopted widely used in geotechnical materials. The calculation results show that the fracture criteria of the rock compression-shear mixed-mode crack based on the strength criteria are rational；and that the ratio between the fracture toughness of pure type II crack and pure type I crack is related with the Poisson¢s ratio and the inner friction angle of the rock when the initial angle of the pure type II crack is a fixed value，instead of other rock mechanical parameters.

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FRAGMENTATION DISTRIBUTION PREDICTION OF ROCK BASED ON DAMAGE ENERGY DISSIPATION

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2007, 26 (06): -1202 doi:
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A set of prediction method of rock fragmentation is presented. Generally，there are three kinds of methods to predict fragmentation. The first is to predict the fractal number of fragmentation by relating it with fractal dimension number of crack in the rock. The second belongs to geometric method that directly computes the size of fragmentation by searching the possible crossed cracks. The third is by using energy dissipation during rock fracturing，upon which this paper is focused. In fact，fragmentation is a brittle fracture event which can be studied within the frame of damage mechanics. With the increment of compression，fractal distributed cracks cut the intact rock into fragmented bodies and eventually results in a fractal distributed fragmentation system. According to the principle of conversation of energy，a theoretical formula is established，which represents the relationship among fragmentation size，fractal dimension number of fragmentation system，and damage variable. In order to use the formula in engineering，it is simplified to take a form of relating fragmentation size only with damage variable，provided that the fractal dimension number of fragmentation system is given. Because of the characteristics of self-similarity of fragmentation system，the formula of size-damage can be generalized to fragmentation prediction of jointed rock. When predicting fragmentation of jointed rock，the first is to calculate damage variable by joint data measured from rock mass，and the second is to calculate the minimal size of the fragmentation system according to the size-damage formula. Finally，an example of fragmentation prediction of jointed rock in Jinchuan Corp. is given. In addition，a method of setting up damage model suitable for engineering is also presented. The research has significance in predicting the fragmentation in block caving.

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STUDY ON CONSOLIDATION SETTLEMENT OF DREDGER FILL UNDER DEADWEIGHT USING LARGE STRAIN THEORY AND CENTRIFUGE MODEL TEST

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2007, 26 (06): -1212 doi:
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The consolidation settlement of the dredger fill under deadweight in Lingangxincheng area of Shanghai is studied using large strain theory and a centrifuge model test. The settlement and final time of consolidation under deadweight are achieved from large strain agrees with centrifuge model test. For the same degree of consolidation，the time of consolidation got from large strain theory is more than that got from centrifuge model test before consolidation of dredger fill is completed. The consolidation settlement under deadweight includes two stages：quick and slow consolidations. The quick consolidation takes about 1 year. At the initial stage of the quick consolidation，soil settles fast. Fifty percent of the settlement is completed after half a year. Eighty percent of the total settlement takes place during the quick consolidation. The remaining 20% of the settlement occurs during the slow settlement. An empirical formulation is determined through curve fitting to describe the relationship between settlement and time. The formulation can be used to predict the consolidation settlement of dredger fill.

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INNER-FORCE AND DISPLACEMENT ANALYSES OF LOAD-BEARING AND ANTI-SLIDE PILES BY p-y CURVE METHOD

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2007, 26 (06): -1220 doi:
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Load-bearing and anti-slide piles have a popular application in the construction of freeway in mountainous area with double functions：not only bearing the load from the superstructure but also counteracting landslide-thrust from the side of pile foundation；and the mechanical behaviors of piles are much more complex than anti-slide piles or simplex inclined-loading piles. Moreover，the interaction between pile and surrounding rock or soil is highly nonlinear，which makes it complicated for traditional finite element method to build analytical model；and the computing result is hard to converge. Based on the deep research of load transfer mechanism and stress characteristic for this kind of piles，the action of rock or soil around piles is regarded as external load，and the p-y curve is adopted to describe the nonlinear behavior of contact between piles and surrounding rock or soil. Therefore，a differential equation considering some influencing factors is set up with the corresponding finite difference solution being obtained as well. Application to an engineering case shows that the method is forthright，accurate and feasible to engineering application.

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DISCUSSION ON PARAMETERS DETERMINATION OF VISCOELASTIC MODEL IN CREEP TEST

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2007, 26 (06): -1226 doi:
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The viscoelastic model，which consists of spring and dashpot，has been widely used in geotechnical engineering as it has explicit physical and mechanical meaning. Generally，the model and its parameters obtained from creep test in one-dimension，are applied to the model in three-dimensional geotechnical engineering based on a few hypotheses，such as constant Poisson¢s ratio，constant volumetric modulus and so on. While parameters of the viscoelastic model are differently used in creep test and in geotechnical engineering，and their conversion relations are not definitely presented in the predecessor¢s studies. Especially，the fact that viscous parameters should be changed accordingly is often ignored. In this paper，the creep equations in one-dimension with the above hypotheses are indirectly obtained from the equations in three-dimensions. The conclusion that the creep equations are different with different hypotheses in one-dimension is drawn. Then，the method to determinate parameters of the viscoelastic model is suggested. As an example，the generalized Kelvin creep equations with the hypotheses are solved with the proposed methods and contrasted with the common creep equation without hypothesis. The conversion relations of model parameters under different hypotheses are presented and validated by a geotechnical engineering instance.

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RESEARCH ON FUZZY ANALYTIC APPROACH FOR STABILITY ANALYSIS OF JOINTED ROCK SLOPE

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2007, 26 (06): -1232 doi:
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The stability of jointed rock slope is controlled by the shear strength of joints and rock block simultaneously. Based on the research of failure mode of jointed rock slope with two sets of joints，the fuzzy characteristics of mechanical parameters in jointed rock slope are taken into account during stability analysis by fuzzy method. Formulae are proposed for the calculation of fuzzy safety factors of jointed rock slope. A program that can automatically search the potential sliding surface of jointed rock slope is also presented. The case study results indicate that the fuzzy analytic approach for stability analysis of jointed rock slope can offer more objective knowledge for slope stability and reference to bolt design when the jointed rock slope is unstable；therefore the failure situation because of the uncertainty of parameters can be avoided effectively.

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DIGITAL STRATA MODELING AND ITS APPLICATION TO XIANG¢AN SUBSEA TUNNEL IN XIAMEN

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2007, 26 (06): -1237 doi:
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Combining with the project of Xiang¢an subsea tunnel in Xiamen，an elaborate summary of the current 3D strata modeling theory is firstly presented；and then a triangular prism strata modeling is put forward. In the process of modeling，geological exploration holes are abstracted as scattered points；and these points are built into 2D meshes by the Delaunay algorithm. The 3D strata is built by triangular prisms which are formed based on the connection relationship of drill holes determined by the planar position of mesh nodes. This model has the merit of easy to storage，space analysis，visualization，etc.. Thirdly，the tunnel and auxiliary facilities models are built in 3D graphics platform. Finally，the spatial analysis including information query，strata cutting and strata excavation are realized based on the strata and tunnel models.

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GIS AND PROBABILITY INTEGRAL BASED APPROACH FOR SUBSIDENCE PREDICTION AND APPLICATION TO BEIMINGHE IRON MINE

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2007, 26 (06): -1243 doi:
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The mining subsidence mechanism of metal mine with fractured blocky rock mass is different from that of coal mine with layered rock mass. In order to guide the safety production and prevent the ground subsidence，the Beiminghe iron mine is taken as the research background. Based on GIS(geographic information system) and probability integral approach，a research is done for predicting the subsidence of Beiminghe iron mine. A three-dimensional calculating model related to geographic，geologic and inherent information is established；and then the system MSDAS-GIS，which is developed by the probability integral and component techniques，is used to predict the mining subsidence. By using the effective spatial analytical function and the drawing tool of GIS，the analytic results intuitively show the degree and scope of mining subsidence. By comparison with the observation data of the ground surface and actual situation，the proposed approach is verified and a three-dimensional visual platform is offered for safety control of the metal mine.

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WAVELET NEURAL NETWORK BASED ON ADAPTIVE PARTICLE SWARM OPTIMIZATION AND ITS APPLICATION TO DISPLACEMENT BACK ANALYSIS

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2007, 26 (06): -1251 doi:
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The model of wavelet neural network(WNN) is optimized by using adaptive particle swarm optimization (APSO)，which is named as wavelet neural network based on adaptive particle swarm optimization(APSO-WNN). The optimized model combines good time domain，frequency domain，and good resolving power of the wavelet transform，self-study of traditional neural network，and quick convergence to the optimum solution of the adaptive particle swarm optimization. Therefore，it has the advantages of great efficiency and good fault-tolerance and robustness，which makes it easy to solve the geotechnical engineering problem with characteristic of fuzziness and nonlinearity. For comparison，the models of APSO-WNN and GA-ANN(artificial neural network optimized by genetic algorithm) are used to calculate the elastic modulus of the high slope of the Three Gorges Project on the basis of the measured displacements. The result shows that the former model takes smaller time compared with GA-ANN in a same precision level. Those show that APSO-WNN model is an excellent model. At last，the calculated elastic modulus is used to forecast the displacements of the monitoring points of high slope of the Three Gorges Project. Forecasting values are in good agreement with the measured values，which indicate that the APSO-WNN model can be well applied to the displacement back analysis in geotechnical engineering.

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DEFORMATION MONITORING AND MECHANICAL BEHAVIORS OF PIPE-ROOF IN SHALLOW TUNNELS

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2007, 26 (06): -1258 doi:
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The longitudinal deformations of the pipe-roofs in the entrance of Tujiangchong tunnel are monitored by installation of a series of strain gauges to investigate the mechanical behaviors of the pipe-roofs during the tunnel excavation；and the working mechanism of pipe-roofs in shallow tunnels is discussed. The rigid joint Winkler elastic foundation beam model is revised；and a new double-parameter elastic foundation beam model for pipe-roof in shallow tunnels is put forward. The corresponding deformation equations，stress and strain formula are deduced；and the solutions of this model are given. The proposed elastic joint double-parameter elastic foundation beam model has been used successfully in the evaluation of mechanical behaviors of the pipe-roofs in Tujiangchong tunnel. It shows that the calculation results agree well with the measured values；and the elastic joint double-parameter elastic foundation beam model is reasonable in the analysis of the mechanical behaviors of pipe-roofs in shallow tunnels.

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ANALYSIS OF DISTRIBUTION RULE OF GEOSTRESS IN CHINA

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2007, 26 (06): -1265 doi:
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The initial geostress measurement results up to now in China are reviewed. Three typical results from the southern mountainous area in Fujian Province，Baka oilfield in Xinjiang autonomous region and No.2 mining area of Jinchuan nickel mine in Gansu Province are listed. The ratios of the average horizontal geostresses and the vertical geostresses(RAHVG) varying with depth are plotted in a dispersed point chart following the Hoek- Brown¢s method. The regression curve and the maximum envelope curve as well as the minimum envelope curve for RAHVG are fitted in the dispersed point chart. Compared with the Hoek-Brown¢ curve，when the depth is more than 1 200 m，the RAHVG are greater than that of Hoek and Brown. The maximum envelope curve for China is almost consistent with that of Hoek and Brown，but the minimum envelope curve for China shows smaller than Hoek-Brown¢s minimum envelope curve. Furthermore，the dispersed point charts are plotted and the same type of the RAHVG curves is fitted for the rock types of the magmatic rock，sedimentary rock and metamorphic rock based on the initial geostress measurement results. The regression results of the three different rocks show the different properties in RAHVG curves. When the depth is more than 500 m，the RAHVG curve for the sedimentary rock is approaching to 1.0. For the magmatic rock in China，the values in the RAHVG curve are bigger than those of the other two types when the depth is less than 500 m，but smaller when the depth is more than 500 m. The measurement geostresses for the metamorphic rock are more dispersed than those for the other two types of rocks. The fitted regression curves are of importance for the numerical analysis of underground engineering.

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TEST STUDY ON HIGH TEMPERATURE ACCELERATED CURING OF LIME-FLYASH STABILIZED SAND GRAVEL

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2007, 26 (06): -1272 doi:
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Lime-flyash stabilized sand gravel is a kind of inorganic binder stabilized material，and usually is used for making base course and subbase course. According to application specifications，some important pavement structure design parameters，such as splitting strength and compressive modulus of resilience，need a long-term curing period，and the lime-flyash stabilized sand gravel curing time is 180 d. Because design period is very short at present，parameters cannot be tested during the design cycle in time，which influences the prompt demonstration of the design plan. Now，the high temperature accelerated curing research method of inorganic binder stabilized material is used to establish the formulas between temperature and time，so as to determine the material strength within shorter time through improving curing temperature. However，because the strength of material is confirmed by empirical formulas，in which there are some shortcomings such as the applicable scope of results being small，so the practicability needs further study. The strength development rules of lime-flyash stabilized sand gravel curing in high temperature are found by test(the suitable curve)；and based on the rules，the strength of accelerated curing short-term is 7 days，which is proximate to the strength of standard curing long-term 180 days. This method is to test the strength after the curing condition is changed，but not to calculate the long-term strength by short-term test results；so the test results are similar to those on standard curing condition. With the technology of SEM，the microstructures of lime-flyash stabilized sand gravel curing in high temperature for 7 days and the standard temperature for 180 days are respectively analyzed. The test results show that their microstructures are similar，showing the feasibility of the method of high-temperature accelerated curing to shorten the curing period of lime-flyash stabilized sand gravel.

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AN IMPROVED SOLUTION OF HEWLETT¢S METHOD FOR SOIL ARCHING EFFECT ON PILED EMBANKMENTS

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2007, 26 (06): -1278 doi:
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The bearing mechanism of piled embankments，i. e. stress transfer and distribution in the embankments under the interior and exterior loads，can be represented by soil arching effect. Based on Hewlett¢s soil arching analysis，a more rational boundary condition is assumed when the plastic point begins at the top of the pile cap；an improved analysis method of three-dimensional soil arching effect in piled embankments is proposed；and an analytical solution for pile efficacy is obtained. General expressions are developed giving the load，distribution ratio of pile cap to soil between piles in terms of pile cap size and centerline space，height of the embankment，the friction angle of the granular fill which forms the embankment，and so on. The results of load distribution ratio of piles obtained from Hewlett¢s solution and the improved method are compared in detail. Finally，a practical case is analyzed to verify the feasibility of the improved method.

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TEST OF COMPOSITE PILES UNDER LATERAL LOADING
IN SOFT GROUND

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2007, 26 (06): -1284 doi:
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[PDF 251 KB] (1203)

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A new-style composite pile is obtained by inserting a prestressed concrete pile into a cement-mixing pile. To study the bearing capacity and failure mode of the composite pile under lateral loading，the lateral loading tests of two composite piles with/without pile cap are carried out and the failure modes and property of interaction of pile and soil are obtained. As a new-style pile，its key characters are analyzed，such as critical load，limit load，lateral deformation，failure modes of two composite piles with/without pile cap，influence of lateral resisting-force coefficient of soil and pile cap on lateral bearing capacity and failure mode. To reasonably evaluate the test results，the limit load and deformation are also analyzed. Test and analysis results show that the pile cap plays an important role in resisting lateral load and the property of resisting lateral force of the composite pile with pile cap is higher than that of the composite pile without pile cap. Composite piles with pile cap have better lateral bearing capacity. Pile cap changes the failure mode between prestressed concrete pile and cement soil into the failure mode between cement soil and soil. To calculate the lateral bearing capacity of composite piles，the calculation formulae of lateral bearing capacity based on critical method and turning point method are studied and the turning point method shows more reasonable and operational than the critical method in application.

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STRENGTH REDUCTION FEM IN STABILITY ANALYSIS OF SOIL SLOPES SUBJECTED TO TRANSIENT UNSATURATED SEEPAGE

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2007, 26 (06): -1290 doi:
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[PDF 389 KB] (1519)

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The basic equation for unsaturated transient seepage is discussed from consideration of mass conservation of solid and liquid phases，the stability of soil slope due to drawdown of water level is analyzed by the strength reduction FEM combined with transient unsaturated seepage calculation；the results are compared with the results of limit equilibrium approach. The comparison shows the validity of the strength reduction FEM to evaluate the stability of slopes subjected to transient unsaturated seepage；the conclusions provide references to the engineering practice. Topics for the further research in this area are also suggested.

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第十次全国岩石力学与工程学术大会等

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2007, 26 (06): -1297 doi:
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[PDF 195 KB] (1072)

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第十次全国岩石力学与工程学术大会等