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2005, 24 (03): 0-0 doi:

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2005-03期目录

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GENERALIZED 3D LIMIT-EQUILIBRIUM METHOD FOR SLOPE STABILITY ANALYSIS AND ITS APPLICATION

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2005, 24 (03): 365-365 doi:

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A new three-dimensional slope stability analysis method is developed based on 2D Janbu¢s generalized procedure of slices，in which all forces acting on the discretized columns are considered and static equilibrium in three directions is satisfied. In this method，the potential sliding mass is divided into rigid columns. Each column is separately analyzed by using two types of relations，geometric relations and force and moment equilibrium formulations. By introducing force boundary conditions，the stability problem is determined statically. This method may be applied to various types of potential sliding surfaces with complicated geological boundaries and stratifications，water pressure and earthquake loading. Also the method extends traditional limit-equilibrium method that only gives one value of the safety factor for an integrated slope，and the safety factor and sliding direction for each column are analyzed according to the characteristics of its sliding surface. With this method，the potential sliding direction of each column can be obtained. As an extension of 2D Janbu¢s method，this method also has the advantages and disadvantages of 2D Janbu¢s method. Moreover，The results calculated by the method for a slope in Yunyang，Chongqing，China，are given in detail，such as the safety factors and sliding directions of columns. The results obtained by 2D Janbu¢s method for a longitudinal section of the slope are presented also for comparison.

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FUZZY C-MEANS CLUSTER ANALYSIS BASED ON GENETIC ALGORITHM FOR AUTOMATIC IDENTIFICATION OF JOINT SETS

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2005, 24 (03): 371-371 doi:

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Identification of discontinuity parameters of rock mass through field investigation of joint sets or subgroups is fundamental to rock engineering design. A fuzzy C-means cluster analysis method based on genetic algorithm for automatic identification of joint sets is introduced. This method eliminates the local optimality disadvantages of fuzzy C-means cluster algorithm and the subjectivity of traditional methods such as pole and contour plots in determination of clustering demarcation. Based on field measured data of joint sets，analysis steps，parameter selection，cluster validity，and determination of dominant direction for identification of the joint sets by the method，are discussed.

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NON-PROBABILISTIC RELIABILITY CONVEX MODEL METHOD FOR STABILITY ANALYSIS OF SURROUNDING ROCK MASS OF UNDERGROUND STRUCTURE

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2005, 24 (03): 377-377 doi:

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In reliability analysis of stability of surrounding rock mass for underground engineering，due to the particular characteristics of physical and mechanical parameters of rock mass，the variation interval of these parameters can only be obtained based on rock mass classification，while it is very difficult to obtain probability density function and subjection function of these parameters for rock mass. Therefore，the stability and reliability of surrounding rock mass，calculated by traditional probabilistic statistics model and fuzzy probability model，only has theoretical significance. Based on the characteristics of surrounding rock mass of underground engineering，the convex model is adopted to simulate uncertainties of rock mass parameters and to change state equation into affine function. For the underground structure with specified design safety margin，the response output interval of structure can be calculated through affine function whose independent variable is defined in convex set. The stability and reliability of the surrounding rock mass of underground structure can be determined by comparing design safety interval with response output interval. For the underground structure without design safety margin，non-probabilistic stability reliability index is defined through the analysis of ratio of average value in limit state equation to its deviation on convex set. Probability density function and subjection function need not be fitted in non-probability convex model methods. Therefore，non-probability convex model methods need less information than traditional stability reliability analysis method. The analysis results of non-probability methods are more accurate than that of traditional method. The results of engineering analysis show the convex model method of non-probabilistic reliability is feasible.

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TESTING STUDY ON DEFORMATION BEHAVIOR OF ROCK IN LONGTAN HYDROPOWER PROJECT UNDER TENSILE CONDITION

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2005, 24 (03): 384-384 doi:

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Because of the difficulties of experimental equipments and techniques，the experiment of rock under tension is more complex than that under compression. In some conditions，rock failure in situ begins with tension. In order to test the limit tensile strain of rock，the relationship between stress and strain，and the mechanical characteristics of rock，the methods for determining the stress-strain curves of rock specimens under tension are introduced，and the tensile stress-strain curves are analyzed. Meanwhile，the mechanical properties by direct tensile test are also compared with those by split method.

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RESEARCH ON SWELLING AND STRAIN SOFTENING MODEL OF SWELLING ROCK IN HONGSHANYAO

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2005, 24 (03): 389-389 doi:

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A series of experiments were performed in rock mechanics rigidity servo-testing system (MTS815.02) and rock odometer to determine the swelling behavior of red sandstone taken from a foundation pit of Hongshanyao project (HSYP) in Nanjing. The experimental data show that the curve of swelling strain-water content is logarithmic. Because of variation of hydroscopicity ratio，the mechanical properties of swelling rock，such as the elastic module，Poisson’s ratio，and yield limit and etc. will change. As a result of hydroscopicity ratio effect，the swelling stress，plastic flow，and yielding criteria which varies with the hydroscopicity ratio，are coupled together. Based on the experimental results，the elasto-plastic constitutive model with swelling and strain softening for swelling rock is proposed .

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RESEARCH ON SOFTENING MICRO-MECHANISM OF SPECIAL SOFT ROCKS

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2005, 24 (03): 394-394 doi:

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Softening mechanism of soft rocks is the basis of the mechanical characteristics of soft rocks and engineering design. Combined with the Dongjiang to Shenzhen Water Supply Reconstruction Project in Guangdong Province，a series of experiments on saturated soft rocks including red sandstones and mudstones，which are widely distributed in South China，are designed and conducted. By some testing methods，such as scanning electron microscope，polarizing microscope，energy spectrum analysis，X-ray diffraction，physicomechanical experiments of soft rocks，as well as chemical analysis of water sample，the research obtains a series of data，such as microstructures，mineral composition，physicomechanical properties of soft rocks，and chemical composition of water solution. Then，more attention is paid to the softening mechanism of the soft rocks. The research results show that the softening mechanisms of soft rocks include water-absorbing expansion of clay mineral，disintegrating mechanism，ionic exchanging and absorbing action，mineral dissolution and creation of fusible mineral，micro-mechanical mechanism of the interaction between soft rocks and water，and the nonlinear chemical dynamics mechanism. The main causes of softening of soft rocks are water-absorbing expansion of clay mineral，ionic exchanging，and absorbing action and micro-mechanical mechanism under the interaction between soft rocks and water. Mechanism of nonlinear dynamics can explain the dynamic chemical process，and it is one of the important directions of quantitative research on softening of soft rocks in the future.

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THREE-DIMENSIONAL DISCONTINUOUS DEFORMATION ANALYSIS ON SURFACES OF ROCK BLOCKS WITH GENERAL MODEL OF WATER PRESSURE DISTRIBUTION

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2005, 24 (03): 401-401 doi:

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The discontinuous deformation analysis(DDA) is a powerful numerical method for the analysis of discontinuous rock mass behaviours. And the three-dimensional discontinuous deformation analysis(3D DDA) is extended to allow the consideration of groundwater pressure. In geological modelling，various geo-information can be expressed as functions of spatial variables. On the basis of groundwater observation data，a three-dimensional piezometric surface using a relevant fitting function is constructed. And a general model of water pressure distribution on the surfaces of rock blocks is established. The water pressure submatrices are then derived by minimizing the total potential energy and are added to the global matrices. The extension to 3D DDA has been incorporated into a 3D DDA computer program，and numerical results from two test cases show the reasonability of the method.

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SENSITIVITY ANALYSIS OF MECHANICAL PARAMETERS TO DEFORMATION OF SURROUNDING ROCKS FOR A TUNNEL IN JINCHUAN DEPOSIT Ⅱ

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2005, 24 (03): 406-406 doi:

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In order to provide bases for parameters selection of stability analysis in Jinchuan nickel mine，which is one of the largest bases of metal resources，nonlinear elastoplastic finite element method is used for the sensitivity analysis of four mechanical parameters to the deformation of surrounding rocks of a tunnel in Jinchuan deposit Ⅱ. The analytical results show that the sensitivities of these parameters to deformation are different and the sequences of sensitivity，in a decreasing order，are the deformation modulus，the friction angle，the Poisson’s ratio，and the cohesion force. Especially，the sensitivities of deformation modulus and friction angle are comparatively higher than those of the two other parameters. Based on this result，more attentions should be paid to the deformation modulus and the friction angle in similar studies and analysis in Jinchuan deposit Ⅱ.

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COMPREHENSIVE FORECASTING METHOD FOR ESTIMATING ROCK BURST

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2005, 24 (03): 411-411 doi:

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By analyzing and classifying the developing conditions of rock burst，a new integrated rock burst forecasting method，i. e.，analytic hierarchy process (AHP)-fuzzy programming (FUZZY)，is developed. Many kinds of factors are considered in the method，such as stress state of rock mass，rock property，adjoining rock conditions and so on. The weight of every factor is given for the AHP method and the importance of every factor is evaluated to avoid the limitation of single criterion in the forecasting and evaluation of rock burst. The method can be applied widely to projects or rock burst forecasting and evaluation.

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CENTRIFUGAL MODELLING OF HIGH DOUBLE-FACE REINFORCED EARTH RETAINING WALL

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2005, 24 (03): 417-417 doi:

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Double-face reinforced earth retaining walls of 30.0～62.5 m high are modelled in centrifuge. The number of models is 34. In the tests，the maximum height of the retaining wall，the variation of lateral earth pressure，the vertical earth pressure and the shape of failure plane are determined. The experiments show that when the compacting factor is 0.90，the maximum height of the retaining wall with or without steps is 62.5 m，and when the compacting factor is 0.80，the height of the retaining wall with steps is 33.0 m and that without steps is 30.0 m. Failure surface begins at the foot of the earth retaining wall. When it arrives at the top of the backfill，the distance from the failure surface to the facing wall is 0.169 times the wall height. The failure width is (0.08～0.35)times the wall height on the top. The failure envelope is a log-spiral. When the construction is completed，the lateral displacements of the walls are almost finished with small values. The lateral earth pressure changes along the retaining wall. In the region 4 cm far from the top of backfill，the lateral earth pressure is near active earth pressure，while under the region，it is smaller than the active earth pressure and only a few points are between earth pressure at rest and active earth pressure. The vertical earth pressure has the similar distribution as that of lateral earth pressure. The obtained results can offer references to engineering design.

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THERMO-EFFECT ON HIGH-SPEED LANDSLIDE

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2005, 24 (03): 424-424 doi:

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The effects of the thermal and the pore pressure generated by high-speed landslide are discussed. First，the controlling equations that govern the thermo-pore-mechanical phenomenon in high-speed landslide are given. Second，the initiation conditions of slide-band(shear band) and the evolution of the band are discussed. At last，the generation and diffusion of the thermal and pore pressure which may cause the obvious decrease of friction coefficient in slide-band are analyzed by numerical simulation. The results show that the instabilization，which is the precursor of the forming of slide-band，initiates once the thermo-softening effect overcomes the strain-hardening effect. After instabilization the localized shear strain becomes severe. Generally，the bandwidth develops with time，which can cause severe changes of the strain and the strain ratio in the band. The drastic changes of strain and strain ratio can cause distinct increase of pore pressure and temperature in the band. The accelerated motion is caused by material strain softening，which further promotes the material strain-rate softening inside the shear band. Owing to the speed of initiating process，heat is trapped inside the shear band，which leads rapidly to the increase of pore pressure，total loss of strength，and uninhibited sliding motion on a small-friction or frictionless base.

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TESTING STUDY ON CHARACTERISTICS OF STRENGTH AND DEFORMATION FOR COARSE MATERIALS

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2005, 24 (03): 430-430 doi:

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Based on the stress path of dam，the triaxial tests of coarse materials are carried out with constant ratios of the principal stresses and the stress increments to obtain the corresponding stress-strain relationship of course materials. According to the strength characteristics of coarse materials，a function is determined to describe the yield criterion of coarse materials. Based on this yield criterion and elasto-plastic theory，an elasto-plastic constitutive model for coarse materials is established. It can be expressed in invariants with clear concept，no odd dots and less parameters. In order to apply it to finite element method，the elasto-plastic matrix is deduced. It is shown that the stress-strain relations hip of coarse materials is in good agreement with experimental data.

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LIMITATIONS OF BIOTECHNICAL SLOPE PROTECTION AND CONTRIBUTION OF VEGETATION TO DEEP SEATED LANDSLIDE PREPARATION

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2005, 24 (03): 438-438 doi:

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The mechanical reinforcement provided by roots is remarkable. However，because the root zones of most plants distribute generally within 1.5 m underground，failure planes of deep seated landslides typically pass well below the rooting zone. As an important discharge way，the transpiration can lower groundwater table of slope aquifer. Because transpiration takes place mainly in intermittent periods of rain events or in dry season，it can not substantially reduce peak groundwater levels in precipitation. Vegetation cover has minimal effect in deep landslide mitigation. Dry crack，animal passage way，expanding fractures，and structural pores related to vegetation cover，constitute a relatively stable macrospore system in upper slope mass，which improve markedly the recharge environment of groundwater and make slopes absorb all precipitation except interception by vegetation. The compound circulation model of ‘Infiltration-groundwater runoff-transpiration’ in vegetated slopes lead to the continued increase of groundwater runoff rate and the gradually dropoff of rock-mass composite quality. Biogeochemical processes，such as root breathing and litter degrading，release acidic substances like CO2 and organic acids and raise the acidity of soilmass and the erosiveness of the infiltrating rain. At the same time，the pre-event water giving place to the event water in vegetated slopes makes saturation index of water-rock exchange phases keep a low level and chemical water-rock interaction can continue. Therefore，the contribution of vegetation to the deep seated landslide preparation is notable.

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TESTING STUDY ON COMPACTION BREAKAGE OF LOOSE ROCK BLOCKS

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2005, 24 (03): 451-451 doi:

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Through experimental results on the compaction breakage of loose rock blocks，some breaking laws are obtained. The results show that the majority of blocks are broken before the relative load reaches 0.5 or 0.6 compared to unixial compressive strength. When the stress exceeds such level，the broken rate of blocks is very small. Therefore，the grading of granular tends to keep constant even if the exerted load is increased. For soft rock，e.g.，coal，the ultimate fine particles have a greater percentage. However，for hard rock，e.g.，sand stone，the difference of ingredient of each class of particle is not apparent. For rock blocks with different strengths，the curves of grading of granular have strong similarity and relativity and can be described by polynomial.

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STUDY ON MECHANICAL PROPERTIES OF MARBLE UNDER LOADING AND UNLOADING CONDITIONS

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2005, 24 (03): 456-456 doi:

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It is shown by tests that there are some differences between mechanical properties of rock masses under loading and unloading conditions. A series of tri-axial tests under loading and unloading conditions are done on the marble samples from the slopes of the Jinping Primary Hydropower Project to study the mechanical properties of marble. Then the mechanical parameters are calculated and interpreted，and the complete stress-strain curves are studied and compared. The results of these tests show that there are obvious differences between mechanical properties of marble under loading and unloading conditions. Under the unloading condition，the deformation modulus and the compressive strength decline，and for the shear strength，c declines a great deal，but j increases a little. In the failure process，the lateral strain under unloading condition increases much more than that under loading condition with the same confining pressure，the plasticity declines and the brittleness increases. The results show the concrete difference of mechanical properties of marble under loading and unloading conditions and offer important references to engineering problem.

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FRACTAL GEOMETRY STUDY ON STRUCTURE OF JOINTED ROCK MASS

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2005, 24 (03): 461-461 doi:

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On the basis of statistical homogeneity of structure，the rock mass structure is studied by applying fractal geometry. Firstly，the 3D network modeling technique is used to establish the probability model for the randomly distributed discontinuities in the statistical homogeneity of structure. With the aid of computer，the structure of rock mass is regenerated on the screen. Secondly，2D and 3D specimens are extracted from the 3D network model of discontinuities，and finally the fractal dimensions of the specimens are computed. The results indicate that the 3D fractal dimension is equal to the 2D fractal dimension added by one. This means that，from 3D point of view，the structure of jointed rock mass has the property of self-similarity.

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CORRELATION ANALYSES OF BLASTABILITY INDEXES FOR ROCK MASS

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2005, 24 (03): 468-468 doi:

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Selection of specific rock property parameters is the basis for quantitatively determining blastability of rock mass. Based upon comprehensive analyses of the parameters that may affect blastability，linear correlation analyses are made based on the data obtained from tests of static and dynamic properties，specific gravity，and integrity coefficients of 14 types of rock，and the results are discussed. It is found that static tensile strength and specific gravity of rock，together with the integrity coefficient of rock mass，are lightly，or not，correlated. It is proposed that these three parameters can be used to serve as the basic indexes for quantitative description of blastability of rock mass.

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FINITE ELEMENT ANALYSIS ON ELASTO-PLASTIC CONSOLIDATION OF HIGH EMBANKMENT IN MOUNTAINOUS AREA UNDER COMPLEX CONDITIONS

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2005, 24 (03): 474-474 doi:

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Based on the main features of high embankment in mountainous area，finite element analysis is made on the elasto-plastic consolidation under complex conditions with the consideration of different land forms，different contact conditions，different outlet locations and drainage conditions of groundwater，and different filling speeds. The relations between failure and deformation of high embankment are therefore obtained. The results are helpful to understand the failure and deformation of high embankment，and can provide reference to construction.

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IN-SITU TESTING STUDY ON LINING SYSTEM OF DOUBLE-ARCHED TUNNEL

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2005, 24 (03): 480-480 doi:

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The variation of stress and deformation in tunnel lining system is the direct indication of its safety. Systematic in-situ testing scheme is established for Jinzhuling double-arched tunnel. The testing results of stress in the lining system and displacement in the vault are analyzed in detail，and some suggestions are given for the design and construction of double-arched tunnel.

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DISTRIBUTION LAWS OF STRATUM STRESS WITH WORKING FACE EXCAVATION IN SUBWAY TUNNELS

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2005, 24 (03): 485-485 doi:

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Based on field test of subway tunneling in Shenzhen，the stress distribution characteristics in working face are studied systematically and the distribution laws are explained. The sectional character of stress distribution in surrounding rock mass of shallow tunnel is proposed. The research can be concluded as follows：(1) For shallow tunnel，the earth pressure at arch points is not equal to overlying strata load；and (2) the pressure at arch foots is higher than their strength. The pore water pressure at arch is minus，which means soil is loose. Tensile stress is found in the pre-reinforced structure and self-support structures can exist in the overlying strata.

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VERIFICATION OF REINFORCED EFFECT ON GEOGRID CUSHION FOR FOUNDATION STRENGTHENING

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2005, 24 (03): 490-490 doi:

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In Quanzhou city，there are two ancient city-gate buildings which need to be reconstructed，i. e.，the Chaotianmen and Linzhangmen city gate buildings. The foundations of the two structures are very sensitive to settlement and have to be strengthened. The original design scheme was pile foundation plus concrete slab with steel bar reinforcement. Since it is expansive and hard to construct，an alternative method is taken into account. The geogrid reinforcement cushion is used underneath the footing. However，due to lack of experience of local soil，21 field loading tests were carried out to verify the effect of geogrid cushion. The results show that the bearing capacity of the foundation reinforced with geogrid cushion is increased almost twice as the natural foundation. Meanwhile，the deformation behavior of the reinforced foundation is also improved. The differential settlement is harmonious and the total settlement can also be reduced. The in-situ monitoring shows that the maximum settlement for Chaotianmen city gate building is less than 1.0 cm，while for Linzhangmen city gate building almost no settlement is observed. It means that the new design can completely meet the requirement of those structures. Moreover，the cost of reconstruction work was reduced more than 3 million RMB and the construction was also simplified.

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GENERALIZED LIMIT EQUILIBRIUM METHOD FOR SLOPE STABILITY ANALYSIS

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2005, 24 (03): 496-496 doi:

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The basic equations of generalized limit equilibrium method (GLE) are introduced，in which the difference from the classical methods is that the value and direction of interslice force are regarded as unknowns. The Rapid Solver is adopted to solve equations. Through defined function of interslice force angles，GLE can emulate rigorous methods such as Spencer and Morgenstern-Price methods，as well as other simplified methods satisfying force equilibrium，such as the unbalance thrust force method，Corps of Engineers，and Lowe-Karafiath method and etc.. The results show that GLE is a practical method with high precision and has the advantages of simple formulation to program easily.

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COMPARATIVE STUDY ON BELLED AND EQUAL-DIAMETER PILES

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2005, 24 (03): 502-502 doi:

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Four groups of vertical loading tests were performed on belled piles and equal-diameter piles at four sites to make comparative study. The results are shown as follows. At site 1，the shaft diameter and length of the two piles are the same. With a 30 mm settlement，the peak load of the belled pile is 5.5 times that of the equal-diameter pile. When the peak load is 2 700 kN，the settlement of the belled pile is only 1/22 of that of the equal-diameter pile. When the concrete quantity of the belled pile is increased by 1 m3，the peak load of the equal-diameter pile can be increased by 1 746 kN. At site 2，the length of the shorter equal-diameter pile is almost the same as that of the belled pile，and the longer equal-diameter pile is 1.65 m longer than the belled pile. With a 10 mm settlement，the peak load of the belled pile is 3.58 and 1.70 times as that of the shorter and longer equal-diameter piles，respectively. This indicates that the effect of belled pile in shallow and weak soil layer is better than that of the equal-diameter pile in deeper and stronger soil layer. At site 3，the lengths of all piles are almost the same，and the shaft diameter of the equal-diameter pile is 1.0 m larger than that of others. The volume of equal-diameter pile is 2.09 times as that of the belled pile，and the bearing capacity of the equal-diameter pile is larger than that of the belled pile when the settlement is less or equal to 5 mm. However，the ultimate bearing capacity of the belled pile is larger than that of the equal-diameter pile. At site 4，the shaft diameters and lengths of two piles are the same，respectively，and there is 0.2 m thick residue at the bottom of the belled pile. The load-settlement curves of two piles are very close，which indicates that the bearing capacity of two piles are almost equal. This demonstrates that the residue at the bottom of the belled pile should be removed in order to fully mobilize large bearing capacity of the belled pile.

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TESTING STUDY ON DIVING DRY-VIBRATED COMPACTED AND ANTI-PULL STONE COLUMN

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2005, 24 (03): 507-507 doi:

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Based on the in-situ tests，the behaviors of single diving dry-vibrated compacted and anti-pull stone column with steel bars are studied during the compression-uplift cyclic loading. The study shows that the stresses are concentrated in the reinforcing steel bar and increase with the number of cycle. The bolted body of bottom mainly provides anti-pull bearing capacity. Compression-uplift cyclic loading has little effect on the settlement and stress of anti-pull stone column. Residual strain always exists after unloading no matter the pullout force is large or small，and increases slowly with the number of cycle. Uplift cyclic loading has little effect on the settlement of anti-pull stone column. Anti-pull bearing capacity and settlement of anti-pull stone column have visible linear relations before reaching the failure load. The failure characteristics of anti-pull stone column are very clear and the failure load of the anti-pull stone column can be obtained easily.

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TESTING STUDY ON DEFORMATION CHARACTERISTICS OF SATURATED SAND UNDER REPEATED SPHERICAL STRESS

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2005, 24 (03): 513-513 doi:

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Cyclic triaxial tests are conducted on saturated sand under drained conditions with cyclic loading and unloading of spherical stress，and constant deviator stress. The systematic test results are analyzed for the deformation variation with cyclic number and the influence of dry density and consolidated stress condition. It is shown as follows：(1) cyclic spherical stress mainly causes volumetric strain，apparent residual，and cyclic volumetric strain，and the later presents compressive(loading) and swelling (unloading) physical states. At the same time，the deviator strain is very small and can be omitted；(2) the relationship between volumetric strain and the logarithm of spherical stress ratio is linear both in compressive and swelling physical states. The linear parameters have relationship with cyclic number，dry density as well as consolidated stress condition；(3) the linear relation in compressive physical state has some ‘memory’ of consolidated stress，which makes the linear relation a turn at a point of spherical stress under isotropic consolidation，and under anisotropic consolidation it disappears；(4) secondary cyclic loading mainly increases the intercept of the linear relation，and its slope scarcely changes in two physical states；(5) using the revealed law and related parameters，the volumetric strain can be calculated by following spherical stress change and the calculation results are preferably consistent with those by experiment.

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EFFECT OF KEEPING CORE SOIL ON STABILITY OF TUNNEL WORKING FACE

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2005, 24 (03): 521-521 doi:

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Based on the fact that the vertical displacements of ground surface are much greater than the permissible value in the period of the 1st Shenzhen urban tunneling operation and by means of the three-dimensional finite element method，the effect of the length of bench and core soil on the squeezing of tunnel working face，the displacement ahead of the face and stress distribution on the face are analyzed. Some valuable conclusions for the shallow tunnel construction are proposed.

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STUDY ON EXCAVATION METHOD UNDER SHALLOW OVERBURDEN OF SOFT-FLOW GROUND

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2005, 24 (03): 526-526 doi:

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Considering the characteristics of tunnel section of Nanjing metro between Gulou station and Xuanwumen station，the deformation of the tunnel，resulting from the excavation in the soft-flow ground with or without relatively hard crust layer，is simulated by centrifuge model tests. It is found that if the ground surface has hard crust layer，the main deformation of the tunnel is crushed deformation on two sides，otherwise，the main deformation is compressive one in vertical direction. Meanwhile，according to the support system and stress distribution of the tube shed and steel arch，the calculation formulas of the crushed soil deformation are established，and the tiny arch effects between pipes are presented. It is shown that the soil strength and the deformation modulus can be strengthened by grouting method，so that the tiny arch is reinforced and the crushed soil deformation is considerably reduced. Based on the in-situ deformation of the Nanjing metro，the ground deformation resulting from the construction of the tunnel in soft-flow ground is analyzed，and the correspondent construction measures are presented.

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APPLICATION STUDY ON STABILITY ANALYSIS AND TREATMENT WITH BLAST-UNLOADING FOR LANDSLIDE

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2005, 24 (03): 532-532 doi:

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The directional blasting is implemented for unstable landslide to toss soil from the top to the toe to lower the gravity center of the landslide. The Sweden circle method is adopted for the stability analysis of landslide，and the chamber charge，blasting acting index and the minimum holdout line are designed and calculated. The equilibrium method of physical volume is used to estimate the heap outline after blasting，and the stability of the landslide is analyzed again. Special measures are taken to weaken blasting vibration and the blasting control purpose is achieved.

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PRESSURE-BEARING CAPACITY OF SPREAD FOUNDATION WITH REINFORCED AEOLIAN SAND

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2005, 24 (03): 537-537 doi:

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Behavior of spread foundation on aeolian sand with geo-grids subjected to pressure force is studied with model tests. The properties of direct shear friction and pull-out friction actions are studied. Fourteen types of geo-grid reinforced aeolian sand are selected in the model tests to show that the pressure-bearing capacity of geo-grid reinforced aeolian sand is 11.0%～453.0% higher than that of the unreinforced. The pressure-bearing capacities of rectangle box geo-grid and two layers of geo-grid are higher than those with other types of geo-grids for the same embedment，and the anti-displacement property is improved. It is shown that the mechanism of pressure-bearing capacity is due to the compression of sand，shearing resistance of sand，the mutual frictional action，and restrain action between geo-grids and soils. The formula for calculating pressure-bearing capacity of spread foundations with reinforced aeolian sand is derived and the calculated results agree well with those measured. The rectangle box geo-grid and two layers of geo-grid are shown to be effective to reinforce the aeolian foundation.

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PRACTICE ON ROADWAY LAYOUT OF COMBINED MINING IN STEEP INCLINED THIN SEAM GROUP AT ZHAOJIABA COAL MINE

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2005, 24 (03): 542-542 doi:

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Zhaojiaba coal mine is located in Wangchang county，Sichuan province. It is a small-size coal mine with production capacity of 300 kt/a. After comparing mining options in steep inclined thin seam group at Zhaojiaba coal mine，the roadway layout of combined mining is selected. The mining procedure，mining methods，and reasonable malposition under different seams and different mining sections are studied by theoretical analysis，in-situ measurement and numerical calculation. The practices show that the roadway layout of combined mining is safe and economical benefit can be improved. The results of the practice are referable to the design of roadway layout and mining method with similar conditions.