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2005, 24 (02): 0-0 doi:

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2005-02期目录

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MODIFICATIONS TO THREE WELL-KNOWN METHODS OF
SLOPE STABILITY ANALYSIS

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2005, 24 (02): 183-183 doi:

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Substantial modifications to three well-known methods of slope stabilility analysis，i.e.，the Morgenstern-Price method，the rigorous Janbu method，and the Sarma method，are presented. Based on the basic assumptions used by these methods，formulas for computation of factor of safety are re-derived which are more concise and applicable than their original versions. For the Morgenstern-Price method，according to the force and moment equilibrium conditions of the slice，the expressions in algebric form (instead of differential or integral form) for the factor of safety Fs and for the scaling factor l are derived respectively，and only a simple iterative scheme is involved for rapidly obtaining converged solutions. For the rigorous Janbu method，the cause of non-convergence inherently in the original solution process is discovered，which can be eliminated by using smooth interslice moment distribution prescribed at certain locations within the sliding body，leading to stable convergence. For the Sarma method，a more concise process is involved in deriving the implicit expression for the factor of safety and the explicit expressions for critical seismic coefficient and critical reinforcing load factor. On modification，the computation processes associated with the three methods are largely simplified and converged solutions are always obtained. The modified versions of the three methods of slope stability analysis can be used by geotechnical engineers in the design of slopes and treatment of landslides.

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CRACKING IN TWIN-ARC HIGHWAY TUNNELS AND ITS
PREVENTION MEASURES

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2005, 24 (02): 195-195 doi:

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The complex construction procedure of twin-arc highway tunnels often leads to repeated rock disturbances. Unfavorable geological conditions and improper working procedures may also cause cracking in tunnel linings，thus create difficulties for groundwater inflow prevention and stability. The Sangongqing tunnel on the Yuanjiang—Mohe highway in Yunnan province is taken as a typical example and analyzed for the main factors of cracking of tunnel lining based on the observed monitoring data. It is found that the concrete temperature，non-uniform settlement of the tunnel floor，uneven pressure，and improper construction sequence，are the main causes for the cracks of twin-arc tunnel. Among them，the non-uniform subsidence of the tunnel floor，the uneven pressure，and the improper construction sequence，are the main factors influencing the stability of the twin-arc tunnels. For treatment of cracks of the twin-arc tunnels，according to their different causes，different measures can be adopted：(1) more strict control on the mix proportion of concrete；(2) improved quivering and cure of concrete；(3) using artificially installed deformation joints in the linings；(4) reinforcing the tunnel floor；(5) improved support of connection passes in the separation pillar；(6) supporting the deforming slopes of tunnels to eliminate uneven pressures；(7) grouting (from ground surface or in tunnel) to reinforce the weak surrounding rock.

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STUDY ON VARIATIONAL ADJOINT BACK ANALYSIS OF ROCK MECHANICS PARAMETERS

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2005, 24 (02): 203-203 doi:

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For the parameter back analysis problems in the field of rock mechanics，excessive computational costs and time-consuming grads calculation in grades optimization methods are often a great challenge. A concept of adjoint vector of grads vector is proposed and a variational adjoint method is developed to calculate the grades vector for the parameter back analysis. All grades vectors can be derived at the same time. The formulation for the presented method is simple and the computing time is short. It can be found from the results that the method is feasible and valid. A case study shows that the developed method is reasonable and applicable for practical problems.

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RHEOLOGICAL MODEL AND PARAMETERS IDENTIFICATION
OF ROCK BASED ON PATTERN SEARCH AND
LEAST-SQUARE TECHNIQUES

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2005, 24 (02): 207-207 doi:

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An identification method of rheological model and associated parameters of rock based on laboratory creep experiments are presented. The method is established by using a mixed technique of pattern search and non-linear least-square regression，which can avoid regression divergence when initial rheological parameters are not optimally selected. The method is applied to investigate creeping tests of clay stone samples under uniaxial compression from an engineering projects，and the relevant rheoligical parameters of the samples using Burgers model are achieved. The results show that this model is preferable to the generalized Kelvin’s model.

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STUDY ON TIME-DEPENDENT PROPERTIES AND DEFORMATION PREDICTION OF SURROUNDING ROCK

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2005, 24 (02): 212-212 doi:

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Based on the assumption that the behavior of surrounding rocks conforms to that of Kelvin-Voigt model，a method to determine the parameters related to the time-dependent properties of surrounding rocks is established and the ground displacement of a test tunnel of an underground hydro-power station cavern is predicted by using the measured data. The measured data is revised to consider the space effect of excavation face. The total displacement values are treated by regression to derive the displacement-time curves. The formula to describe the relation between equivalent elastic modulus of the surrounding rock and the displacement values at different moments is also established. The case study shows that the predicted displacements by the method agree well with the measured values，so the proposed method can be adopted in practice.

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ANALYSIS OF THE COMPLETE STRESS-STRAIN RELATION AND DEFORMATION LOCALIZATION FOR INTERMITTENT CRACK-WEAKENED ROCK MASS UNDER COMPRESSIVE STRESSES

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2005, 24 (02): 217-217 doi:

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The crack isolating theory combined with internal variable theory including a micro-to-macro transition is applied to study the localization of deformation and the complete stress-strain relation for intermittent crack-weakened rock masses under compressive stresses. The self-similar model is selected as a basic dissipative mechanism underlying macroscopic inelastic deformation. The closed-form explicit expression for the complete stress-strain relation of rock mass is obtained. The complete stress-strain relation includes the stages of linear elasticity，non-linear hardening，and strain softening. The results show that the complete stress-strain relation and the strength of rock mass depend on the crack interface friction coefficient，the crack spacing，the perpendicular distance between the two adjacent rows，the fracture toughness of rock material，and the orientation of the cracks. Special attention is paid to the transition from distribution damage to localization of damage and the transition from homogeneous deformation to localization of deformation. Theoretical predictions are consistent with the experimental results.

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STUDY OF TWO SHOCK ABSORPTION MEASURES IN TUNNEL

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2005, 24 (02): 222-222 doi:

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Based on Newmark’s step-by-step implicit integration FEM method，the response analyses of a generic tunnel by using viscous-spring artificial boundary technique under various earthquake accelerations and multiform conditions of surrounding rocks are presented. The seismic responses of the tunnel are calculated by changing parameters of surrounding rocks within certain influencing distances to the linings. Two kinds of shock absorption measures，which are setting shock layer and grouting in the surrounding rock，are investigated. The shock absorption effects，applicability，and shock mechanisms are analyzed. The results show that the differential displacements and stresses in the lining of the tunnel decrease and the linings are protected when the two measures are used. It also shows that for weak surrounding rocks，rock grouting is an effective shock absorption measure and the aseismatic capability of surrounding rocks can be improved. For underground structures in hard rocks，the seismic effects on tunnel stability can be ignored even if tunnel is located in earthquake-prone regions，but for important projects. The results provide useful reference for the aseismatic design of tunnel.

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STUDY OF HIGH PRESSURE PERMEABILITY MEASUREMENTS AND APPLICATIONS FOR PRESSURE TUNNELS

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2005, 24 (02): 230-230 doi:

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For the construction of pressure tunnels and underground projects in greater depth，it is necessary to understand the groundwater permeability of the surrounding rocks. Under high water pressure，various weak structures such as joints or cracks inside the rock mass may split or extend，which may lead to permeability change in turn. Therefore，it’s necessary to measure the permeability of surrounding rock under pressures equal to or higher than the designed pressure magnitudes to obtain more reliable permeability information under normal project operation conditions. This paper presents a high pressure permeability measurement technique in boreholes and its application for pressure tunnels.

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PERCOLATION MECHANISM OF FRACTURED COAL ROCKS AS DUAL-CONTINUA

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2005, 24 (02): 236-236 doi:

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Coal rocks are a natural fractured porous media. The pores and fractures have great influence on permeability. This paper presents a new method for estimating percolation probability of the fractured coal rocks as dual-continua，and develops the relationships between percolation probability and permeability of coal rock samples for quantification of the influence of fractures and pores on coal rocks. The results indicate that the relation between the permeability and percolation probability of the coal rocks follows a power function. The results show that the fracture porosity determines the effects of the pore porosity on the samples and the fractures dominate the overall permeability of the fractured coal rocks，which is totally different from the results of conventional concept of porous media.

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STUDY ON THE DOMINANT ORIENTATIONS OF RANDOM FRACTURES OF FRACTURED ROCK MASSES

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2005, 24 (02): 241-241 doi:

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Fractures are important factors that control the stability of rock masses and need to be properly studied as demanded by modern rock engineering. For many decades，scholars at home and abroad have paid much attention to the study of the properties of random fractures，especially the geometrical properties of random fractures. But how to represent the random fractures intuitively that can be easily understood by practicing engineers remains to be a problem.
Based on accumulated experiences during recent years with important rock engineering projects，this paper discusses an accurate representation method for random fractures of fractured rock masses. A data set with 2190 fractures investigated from the field of the Three Gorges dam site is used to be a case study，a conventional method of contour map and scatter plot of Schmidt lower hemisphere projection is shown some shortages of representing the distribution and delineation for the data set，because of the poles of fractures are randomly distributed in the Schmidt lower hemisphere projection.
A new method to delineate the dominant fracture orientation by probability and statistics method applies the rule of right hand to classify the fracture orientations in order to clarify the geometrical features of fractures with more precision without personal judgments. A computer program is developed to carry out the complicated calculation and the visualized diagrams of fractures orientation by right hand rule are represented in the paper so as to be used by practicing engineers.

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RESEARCH OF A SYNTHETICAL METHOD GMEM ON ASCERTAINING SHEAR STRENGTH FOR ENGINEERING ROCK MASS

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2005, 24 (02): 246-246 doi:

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The determination of the strength for engineering rock mass is one of the most important problems in rock mechanics because it is influence on lithology，joint，undergroundwater and temperature field and etc.. This paper considers that the engineering rock mass has the characters of geology，mechanics and engineering，and the above-mentioned three factors should be considered for the determination of strength synthetically. At the same time，this paper puts forward the geology，mechanics and engineering method(GMEM) to ascertain the strength of engineering rock mass that combins experience analogy，grading system of rock mass quality，and connectivity ratio method with estimation of macroscopical geological condition. The GMEM has been applied in many projects，such as the Xiangjiaba hydropower station and etc..

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FUZZY MATHEMATICS METHOD FOR ANALYSIS OF THE WEATHERING DEGREE OF ROCKS

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2005, 24 (02): 252-252 doi:

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By introducing soft coefficients of the elastic modulus and cohesion，the relationship between strength and deformation parameters and the weathering degree of rocks are established. Because the effects of weathering degree are complex and the affecting degrees are different，the weathering degree and the uses of the fuzzy mathematic method to estimate the rock weathering degree are summarized. The method was applied to an open pit mine slope with reasonable results.

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EXPERIMENTAL STUDY ON BEARING PAD

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2005, 24 (02): 257-257 doi:

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The in-situ bearing pad test is an important method for measuring rock mass deformation property parameters with wide applications. The measuring points located inside the plate and the calculating formulae are provided in the rock mechanics test regulations. For the sake of understanding overall deformation property parameter of rock masses，increasing measurement points located outside the plate as presented is needed. The calculation formulae of the deformation property parameters and their applications in practical engineering are also presented.

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COAL AND GAS OUTBURST AREA PREDICTION USING SUPPORT VECTOR MACHINES

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2005, 24 (02): 263-263 doi:

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Support vector machines (SVM) is a machine learn technique sprang up in the middle 90 s of the 20th century based on the structural risk minimization theory. It has many distinct advantages of each technique capabilities，in particular of the generalization ability. This paper presents a development method for coal and gas outburst area forecast on the basis of the SVM technique. Firstly，the character space is divided into three regions according to the optimal classification face of the SVM model and the boundaries of the mixed sample space. The levels of danger，threat，and safety of coal and gas outburst are then constructed with SVM algorithms. In addition，the optimal symbol function of the SVM is converted into the distance function together with the dimension of mixed u1 and u2 levels. The value －1 and +1 are specified on the boundaries of the outburst and no-outburst boundaries of mixed regions，respectively. The danger level index values vary linearly with the D(x) function. This technique was applied to 26 outburst events and 34 no-outburst events from 13–1 coal seam in Panyi coal mine，and a number of parameters and learning arithmetic are achieved. The results indicate that this method can greatly increase the forecacy accurate rate compared with the traditional approaches of D and K indexes. This technique has extensive application in future as a scientific and feasible forecast approach.

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NUMERICAL STUDY FOR WIDE-SLAB EFFECT ON REINFORCED SANDY GROUND

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2005, 24 (02): 268-268 doi:

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In order to obtain a better understanding of the bearing capacity characteristics of reinforced sandy ground with different reinforcement lengths，results from plane strain laboratory model tests are simulated by a nonlinear FEM analysis incorporating an elasto-plastic constitutive model. The constitutive model is developed based on the modified plastic strain energy concept. It is found that the load-settlement relation of the sandy ground and the effect of the reinforcement lengths (i.e.，the wide-slab effect) on the increase of the bearing capacity obtained by the present FEM analysis agree well with those from the physical experiments. The reinforcing mechanism and the progressive failure with developments of shear bands in reinforced sandy ground are also reasonably simulated by the FEM analysis.

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STABILITY OF BOUNDARY PILLARS FOR TRANSITION FROM OPEN PIT TO UNDERGROUND MINING

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2005, 24 (02): 278-278 doi:

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he stability of boundary pillar，which can be found across in mine shifting from open-pit to underground mining，is very important for safe production of underground mine. Based on the practice of Shirengou ore mine from open-pit to underground mining，the stabilities of boundary pillar at representative sections are calculated and analyzed by using the methods of limit equilibrium and numerical simulation. With the application of the limit equilibrium method and consideration of the thickness，span of boundary pillar，height of deposed rock，and obliquity of ore mine，the safety coefficients of all sections of boundary pillar are calculated，respectively. The safe thickness for boundary pillar has been modeled by the RFPA2D (rock failure process analysis)system，including deformation and failure of boundary pillar during caving. At the same time，the failure process of the different sections is simulated. By calculation，the safety and danger section of the boundary pillar is predicted. It validates the designed boundary pillar thickness and offers references to construction.

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DYNAMIC MONITORING AND FEM SIMULATION ANALYSIS OF AN EXPRESSWAY TUNNEL WITH UNSYMMETRICAL LOADINGS

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2005, 24 (02): 284-284 doi:

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FEM calculation results and the time series of in-situ measures for the entrance of Longjin tunnel on the Chong-Zun expressway are presented. A FEM model is established to simulate the deformation behaviors of the tunnel. The anchors are simulated with the anchorage elements，while the cement lining and the steel-arc shelf are simulated with the straight beam elements. The results show that the deformation behavior of the surrounding rock mass is controlled by unsymmetrical loadings during the process of construction. It is proposed that not only the in-situ dynamic measurements but also the analysis of FEM be important for successful construction of the tunnel.

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STUDY OF EXCAVATION METHOD FOR ULTRA-SHALLOW-BURIED LIGHT RAILWAY STATION TUNNELS WITH LARGE SPAN

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2005, 24 (02): 290-290 doi:

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Chongqing Daping light railway station is located in downtown of Chongqing，where there is a dense population as well as numerous buildings. Daping station tunnel has a clear span of 19.8 m，whereas its excavation span and area are 26.3 m and 430.3 m2，respectively，only 4 m overburden and with a surrounding rock of category Ⅲ. In view of complex and unfavorable surface conditions over the station tunnel，such as house buildings and city roads，both of which can′t resist severe shocks or vibrations，it is necessary that small vibrations induced in tunnel construction process and a strict requirement for the surface subsidence amount be favourable. According to the characteristics of large span and ultra-shallow-buried，located in a densely populated city area of numerous buildings，a new method is proposed to use advanced support of large pipe-roof protection and the tunnel section is divided into two parts during the process of construction. The upper part is operated by using two-side pilot drifting method，while the lower part is excavated from the middle to walls，and the arch lining is constructed before the tunnel wall-lining. The method is developed from numerical simulation of the deformation of rocks during the tunnel construction. The application of this method proves to be successful in the construction of Daping light-railway station tunnel.

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FINITE ELEMENT ANALYSIS OF ULTIMATE BEARING CAPACITY OF CIRCULAR FOOTING ABOVE KARST CAVE

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2005, 24 (02): 296-296 doi:

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Finite element method is applied for the analysis of the stability of rock roof above karst cave under the loading of circular footing，and three typical types of rock mass are studied. The determination of ultimate bearing capacity of rock foundation is discussed，and the ultimate bearing capacities of circular footing above karst cave，under different conditions of three different rock mass types，different karst cave width and roof thickness，are obtained. The relationships between bearing capacity and the corresponding influencing factors are analyzed. Some relationship charts for determination of ultimate bearing capacities under different conditions are presented，which are helpful for the design of circular footing above karst cave.

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FUZZY MEASURES ANALYSIS FOR DISPLACEMENTS AND DEFORMATIONS OF JOINTED ROCK SLOPE UNDER INFLUENCE OF GROUNDWATER

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2005, 24 (02): 302-302 doi:

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The predictions of displacements and deformations of rock slopes are important in rock and soil mechanics and engineering. Various approximate methods have been used for such calculations. The displacement or deformation of a rock mass can be regarded as a fuzzy event that takes place at a fuzzy probability. Therefore，the theory of fuzzy measures can be applied to describe the displacements and deformations of rock slopes. Based on the results of the statistical analysis of a large amount of measured data in slope engineering，the fundamental fuzzy model of displacements and deformations of rock slope is established by using the theory of fuzzy measures. The formulas of two-dimensional problems are developed and applied to the predictions of displacements and deformations of rock slopes due to surface excavation. The fuzzy measures models presented are adopted for back analysis using displacement parameters. The agreement of the theoretical results with the field measurements shows that the model is satisfactory and the formulae obtained are valid，and thus can be effectively applied to predict the displacements，the failure of rock slopes due to mining，and the failure of slopes under the influence of groundwater.

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IMPROVED GM MODEL FOR SAFETY MONITORING OF HIGH ROCK SLOPES

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2005, 24 (02): 307-307 doi:

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The conventional GM(1，1) model is highly limited and prone to accumulate systematic error in prediction. The paper traces its error sources and proposes an improved method. This improved model is applied for analyzing the monitoring data from eight successive years of a high rock slope monitoring of the Bikou hydroelectric power station，where the sixth and the seventh years’ data is omitted. A grey safety monitoring model of the high rock slope is established by using the improved GM(1，1) prediction model. By comparing the prediction results of the improved GM(1，1) model with those of the conventional GM(1，1) model and the statistical model，and with those of the mean error，correlation coefficient，and maximum error，it is proved that the modified GM(1，1) model is of high accuracy in safety monitoring and its prediction agrees well with the actual behavior of the high rock slope.

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STUDY ON THE SEISMIC FAILURE MECHANISM OF THE THICK SOFT SOIL FOUNDATION

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2005, 24 (02): 313-313 doi:

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A study of seismic failure mechanism of soft soil sites in Fuzhou is presented. The characteristics of frequency-spectrum structure and response of ground soils，including soft soils and the frequency of ground micro-tremor，were investigated. From the results，it is found that the site soft soil enlarges predominant period of ground micro-tremor to some degree，and the predominant period of ground micro-tremor has a close relationship with the stiffness of the foundation soils. The correlations among the predominant period of ground micro-tremor，the overburden thickness of soils，and the shear wave velocity of overburden，are established. These relations reveal that the predominant period of the ground micro-tremor is positively proportional to overburden thickness，but decreases with the increase of shear wave velocity. In addition，based on the completed measurements of the natural periods of the buildings in the city，using the empirical calculation methods，and approximate calculation methods applied in California，USA，the improved approximate calculation formulae are developed for natural periods of high-rise buildings. The results reveal the seismic failure mechanism in the abundant soft soil sites，and demonstrate the causes of potential seismic failures for some buildings.

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RELATION OF MATRIC SUCTION WITH MOISTURE STATE AND DENSITY STATE OF REMOLDED COHESIVE SOIL

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2005, 24 (02): 321-321 doi:

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Matric suction is relevant with temperature of water-air system，density of pore-water，and relative humidity of pore-air of unsaturated soil. The values of temperature and relative humidity of 23 groups triaxal experimental specimens within different moisture states and density states of a kind of remolded unsaturated cohesive soil are measured through thermo-hygrometer，and then the associated matric suction are computed. Data analysis shows that relation between matric suction and density at different moisture states is of different characteristics. Relation between matric suction and water content is notably nonlinear. Distribution of matric suction looks like a transformed W - type flex surface in the moisture and density state space，in which the axial plan is parallel to the axis of dry density. Its left wing located in the low moisture state steeply raises and presents strong unsaturated soil，the right wing located in the high moisture state levelly stretches and presents weak unsaturated soil，the center part located in the middle moisture state is of a "Λ" type fold and presents typical unsaturated soil. Water-filling pore structure as a new concept has been offered，by which the water-air effect of unsaturated soil can be understood more accurately upon two aspects including pore structure and capillary condensation，so that the variation law of matric suction of unsaturated soil can be suitably recognized.

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RESEARCH ON MODEL CONSTRUCTION OF SUPPORT VECTOR MACHINE AND PRECISION-INFLUEUCING FACTORS OF SLOPE ANGLE DESIGN

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2005, 24 (02): 328-328 doi:

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Based on the structural risk minimization principle，a support vector machine(SVM) algorithm，the best machine learning algorithm in the artificial intelligence field today，is introduced. Two kinds of kernel functions(linear and radial basis function) and two kinds of loss functions (e -insensitive and quadratic) and different penalty parameter C are adopted to program a SVM routine in Matlab. Using the developed SVM model，many influencing factors of slope angle design are analyzed. With continued parameter modification and comparative calculations，a SVM network model with high accuracy of fitting was established. The reliability of this SVM network model is verified by sample testing，where many kinds of accuracy influencing factors of the SVM model are considered. The precision influencing sequence of these parameters is confirmed based on the calculation results，providing reference for similar engineering applications.

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A DISCUSSION ON THE INCLINED ROOF DESIGN OF LONGYOU CAVERNS FOR ENGINEERING SCIENCES

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2005, 24 (02): 336-336 doi:

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An ancient man-made near ground surface rock cavern group was found in Longyou County，Zhejiang Province. The 24 large caverns were excavated 2000 years ago. Its findings attract the attentions of the scholars in the world. Through the field investigation it is found that there are many highlights involved in the excavation of these caverns，such as the inclined roof，the iron-shaped pillars，and the inclined sidewalls and etc.，in which the most noticeable is the inclined roof. In this paper，the detailed field investigation and 3D numerical analysis are carried out to show the engineering scientific problems contained in the inclined roof. The field investigation results reveal that the dip direction and dip angle of the roof are almost coincident with those of the bedding plane. That means the ancients knew very well how to control the direction and the dip angle of the cavern’s roof to sustain the stability of them. The results of the 3D numerical analysis also provide the same conclusion of that. The design of inclined roof can not only improve the stress condition of the surrounding rock but also reduce the settlement of the roof and the lateral deformation of the sidewalls. So，the inclined roof is the best way to solve the shallow buried problem.

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SPECIAL DEFORMATION AND FAILURE MODE OF RIVER BANK SLOPE
—— STUDIES ON MECHANISM OF DEFORMATION AND FAILURE OF BANK ROCK SLOPE AT SETI BRIDGE SITE，NEPAL

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2005, 24 (02): 344-344 doi:

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Seti bridge，located in Pokhara city，Nepal，is one of the key bridges in main national highway network，connecting Kathmandu with Plkhara，and plays an important role in Pokhara city traffic. Its construction started in 1995 and was completed in September 1998. During floods in June 1995，three cracks appeared at left bank. Till now，the largest crack width is about 4 m，threatening the safety of the bridge. In March 2001，a group of seven Chinese scholars investigated the deformation and failure of bank rock slope. Investigation results show that the main deformation mechanisms of the Seti bridge river bank rocks are the combination actions of its peculiar conditions：special meteorological-hydrographic condition (intensive rainfall)，valley topographical features (deep-cutting and narrow valley) and special geological structures (banks consisting of bonded gravel with “easy-scouring” rock stratum underneath，as proved by new investigation results，2002)，and the erosion of the bottom rock strata to form a reentrant by strong water flow. The deformation and failure mechanisms of bank rock slope at Seti bridge site are very special，named as a fracturing-toppling-falling pattern. Under intense scouring actions，easy-scouring strata at the bottom of valley are hollowed out by rushing water. Tensile cracks will then develop in the relatively rigid rock mass overlaid，and induces toppling failure like cantilever due to gravity. The
rock mass among the tensile cracks starts to fall. This pattern of deformation and failure can explain reasonably failure phenomena that appeared in deformation process of bank slope. At present，the inside crack at Kathmandu bank is 17 meters away from Seti Bridge，and the tensile cracks have the possibility to develope，and the crack are threatening the safety of Seti Bridge. Therefore，it is necessary to reinforce both of bank slopes with appropriate measures at bridge site.

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STRUCTURE RELIABILITY ANALYSIS OF UNDERGROUND CAVERN BASED ON RESPONSE SURFACE METHOD

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2005, 24 (02): 351-351 doi:

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Considering the difficulty of setting up the performance function in structure reliability analysis of large complicated underground cavern，a calculation method on the structure reliability that combines 3D non-linear finite element method，response surface method，and JC method，is established. Based on the calculated results that use different quantile values of 8 random parameters by 3D non-linear finite element method and D-P criterion，the reliability function of underground cavern is deduced. Then，the response surface function，the stress component partial derivative function，and the random parameter partial derivative function of both wallrock and the umbrella arch，are also achieved. At last，the reliability index is calculated by JC method. The method is applied to the cavern structure reliability analysis of the underground powerhouse of Yingxiuwan hydropower station in Sichuan province that has been operated for mo re than 30 years. It shows that the value of b is between 1.5 and 4.8，which，as a whole，is on the low side. Most of the low value of b lies in the area of left side of the axial line，where is the main cracking area. By comparing with the monitoring data，it shows that the method can get good precision，high performance，and well practicability. The new method is proved to be a good means in the structure reliability analysis of large underground cavern and other complicated hydrostructures.

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DELAY OF PORE PRESSURE IN OEDOMETER AND ITS EFFECT ON DETERMINATION OF COEFFICIENT OF CONSOLIDATION

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2005, 24 (02): 357-357 doi:

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From common consolidation tests，a new oedometer which can measure the pore pressure from the bottom of specimen is employed. A phenomenon is found that the pore pressure in the specimen inclines to delay. Compared curves of the pore pressure and the displacement，it can be concluded that around the appearance of the of peak value pore pressure，the displacement curve finds its first turn. When the pore pressure reaches its total dissipation，the displacement curve finds its second turn. Because the pore pressure has strong relationship with the displacement，research work is carried out to reveal the cause of the delay. With further experiments under various conditions，it can be found that the side friction and the degree of saturation have strong influences on the delay of pore pressure in the specimen. So the delay rance of pore pressure should be considered in determining the consolidation coefficient，and at last，the measuring relative methods are discussed.