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2007, 26 (10): -0 doi:
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GEOLOGICAL ORIGIN AND STABILITY EVALUATION OF SIWANCUN LANDSLIDE IN LUDING COUNTY

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2007, 26 (10): -1945 doi:
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Siwancun landslide locates at 1 km downstream of the dam site of Luding Hydropower Station and its stability has great influence on the dam design，construction and operation. In order to evaluate its stability，detailed geological investigation and tests are carried out；geological origin and evolution are analyzed，and a geological structural model is established. The landslide is a high-speed one induced by earthquake dated back to 17.2±2 ka B. P.，i.e. the late period of Late Pleistocene by ESR method. The landslide dammed Dadu River experienced at least 3 secondary slides after dam break. The present landslide fills is of broom-shaped，around 700 meters long，800 meters wide and the maximum depths of 137.62 m. The total volume is about 5.0×107 m3. Its toe extends into the bed of Dadu River. At its front，the bank slope is steep with a slope of 40°，while the middle and rear parts of the slope are gentle. The slide fills are mainly composed of boulders and granular soils of granite and diorite origin，with good permeability. No deformation is evidenced during site investigation. Three-dimensional stability evaluation is carried out using the strength reduction technique and limit equilibrium method；and the factors of safety are 1.49 and 1.42，respectively. It is shown that the landslide is stable.

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STUDY ON CRACKING AND STABILITY PROBLEMS OF HIGH ARCH DAMS ON COMPLICATED FOUNDATIONS

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2007, 26 (10): -1951 doi:
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The stability of arch dams and their cracking mechanism have been discussed. They are concerned with thermal variation，rigidity weakening due to earthquake and seepage effects. Cracking and propagating micro- mechanism and marco-cracking yield condition in the dam surface and jointed rock mass are analyzed；then，a mechanical failure model for arch dams is proposed in account of total stiffness between dam body and rock foundation. It is shown that the fractures and rupture of dam and foundations are key process in analyzing stability of dams. By employing proposed numerical model，based on Xiluodu arch dam with complicated rock foundation，the dam cracking process in up-down stream surfaces under different water pressures，and the relation between point safety and water pressure in the interface between dam and foundation are analyzed. The numerical results show that the proposed numerical model and methods have good fitness in hydraulic design.

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UNDERGROUND WATER AND ITS TREATMENT STRATEGY
IN AUXILIARY TUNNELS OF JINPING HYDROPOWER PROJECT

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2007, 26 (10): -1959 doi:
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The Jinping Hydropower Project(Jinping I and II)，which is under construction，is located in the Jinping bend of Yalong river，with a total capacity of 8.4×106 kW. Jinping I is characterized by the 305 m high double-curvature arch dam，and Jinping II by the four headrace tunnels which is 17 km long each，with very high pressure and large quantity underground water. The project is scheduled to run in 2012. The Jinping auxiliary tunnels (2×17.5 km) serve as the access tunnels between Jinping I and Jinping II，and also as the exploratory and construction adits for the headrace tunnels of Jinping II. The hydrogeological condition is complicated in the area where Jinping auxiliary tunnels pass through. The technical issues encounted in the construction of the auxiliary tunnels include large quantity and high pressure blowing water，ventilation during the tunnel excavation，and rockburst and the treatment. Since the tunnel construction started in 2003，unexpected large quantity of blowing water with high pressure was encountered and have been controlled. The several cases of large quantity and high pressure gushing water and their characteristics are presented，geological focasting methods adopted in the process of the auxiliary tunnel construction are explained，and the technical route of water treatment is analyzed，and then the treatment measures and suggestions are recommended. The gushing water issue encountered in the Jinping auxiliary tunnels is complicated，and the experiences and methods accumulated during construction could benefit the future construction of the headrace tunnels of Jinping II and some other similar tunnelling projects.

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STUDY ON UNLOADING NONLINEAR MECHANICAL CHARACTERISTICS OF JOINTED ROCK MASS

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2007, 26 (10): -1968 doi:
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According to stress characteristics，rock mass may be divided into the loading rock mass and the unloading rock mass respectively. The rock mass of the permanent shiplock of the Three Gorges Project is studied with the self-developed triaxial test equipment based on the geometric similarity and the gravity similarity，the similarity of mechanical properties of material，the similarity of rock mass structure，the similarity of boundary force，and the similarity of excavation process simulation. The 250 mm×250 mm ×250 mm samples are made by the baritic powder，the iron powder，the gypsum，the water and so on；and the geometric scales of the sample are 3，9，27，81 respectively. For the sample with scale of 27，the structural planes are included with dipping angles being 8°，36°，52°，82°，and 90° respectively with the unloading direction vertical to the shiplock axis. Study on the relationship between stress and strain of jointed rock mass under loading and unloading conditions，the anisotropy of unloading rock mass(relationship between stress and strain，tensile strength，deformation modulus)，the size effect of unloading rock mass(tensile strength，compressive strength，Poisson¢s ratio，deformation modulus)，the rheological property of unloading rock mass，and the strength criterion of unloading rock mass are also conducted. The research indicates that different structural plane directions affect rock mass unloading evidently. With the size increasing，the tensile strength，compressive strength，deformation modulus，Poisson¢s ratio and anisotropy of the rock mass decrease. The rheological property of rock has direct relationship with rock mass tensile stress magnitude. Finally，the rock mass material constants m，s of Hoek-Brown criterion are obtained to describe rock mass strength.

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ANAYSIS OF ANTI-SLIDING STABILITY OF SYNCLINE STRUCTURE ON RIGHT ABUTMENT OF DANJIANG CONCRETE ARCH DAM

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2007, 26 (10): -1976 doi:
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The unstable rock body with syncline structure on the right abutment of Danjiang arch dam are analyzed under the thrust from arch dam. Firstly the seepage through the foundation and abutment as well as the thrust from arch dam are calculated by finite element method. Then the three-dimensional limit equilibrium method is used to calculate the anti-sliding safety factors under different working conditions. Finally，the number of reinforcing cables needed to meet the specification requirement of anti-sliding safety factor is evaluated；and the influence of dip direction of cables on safety factor is analyzed too. The results provide theoretical basis for the anti-sliding design of the syncline rock structure.

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STUDY ON SURROUNDING ROCK STABILITY OF LONGTAN TUNNEL BASED ON IN-SITU MONITORING MEASUREMENTS

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2007, 26 (10): -1982 doi:
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Longtan tunnel is located on the section from Baishiping Town to Enshi City，Hubei Province，of Hurong(Shanghai—Chengdu) highway. It is about 8.6 kilometers long，the second longest highway tunnel in China，and its depth is about 530 meters. It is designed to penetrate the strata consisting of developed karst caverns，faults，and fractures caused by tectogenesis. So the initial stress in the surrounding rock is high；and the geological conditions along the tunnel are very complicated. It is a very typical deep and extra long tunnel under complicated geological conditions. To study the stability of this tunnel，many in-situ measurements on the surrounding rock have been taken. Through the in-situ measurement，the distribution characteristics of the internal displacements，the bolt axial force and the contact pressure between lining and surrounding rock are studied. And the influencing factors are analyzed in detail. Based on the analyses of the measurement，some useful conclusions are drawn to the stability of the tunnel；and some suggestions are made to modify and optimize design and construction scheme. This study will offer some useful references for construction of tunnels in the similar geological conditions.

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PERFORMANCE ASSESSMENT：A RISK-INFORMED APPROACH TO SAFE ISOLATION OF NUCLEAR WASTE IN DEEP GEOLOGICAL MEDIA

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2007, 26 (10): -1991 doi:
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Performance assessment(PA) is the application of risk assessment in the field of nuclear waste geological disposal. PA was initially adopted as a measure to quantitatively demonstrate the performance of both natural and engineered barriers of a repository，which eventually leads to building a safety case. The ultimate guidelines for PA are the principles and standards that are recognized and accepted by international communities. In practice，PA virtually links major parts of a repository program including waste characterization，disposal concept，site selection and characterization. This places PA in the unique position of the nuclear waste management program：PA can be used as a decision-making tool to aid repository program planning and management in order to meet the programmatic goals cost effectively. The article introduces PA from the top-down viewpoint and covers topics of methodology，modeling，and uncertainty. Finally，the authors provide some specific suggestions to Chinese scientists.

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RESEARCH ON MESOSTRUCTURE DYNAMIC DAMAGE CHARACTERISTICS OF EXPANSIVE RED SANDSTONE WITH
DIGITAL IMAGE PROCESSING TECHNIQUE

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2007, 26 (10): -2007 doi:
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The red sandstone of Hongshanyao Hydraulic Project in Nanjing has characteristics of microdilatancy and is easy to be weathered and wetted. By using the advanced equipments such as SEM，X-radial diffraction instrument，rock mechanics testing machine of MTS81503 and so on，a lot of mesostructural pictures of red sandstone with different water contents are obtained；and the gray level thresholding is done with these images. The paper puts forward the digital image processing technique to deal with gray distribution pictures of red sandstone in different dynamic damage stages with different water contents. Further studies on the mesostructural changes of red sandstone in different damage states with different water injection times and crack propagation are discussed quantitatively. The aim of this paper is to bring forward a reliable research method to analyze and evaluate quantitatively the expansive deformation failure mechanism of expansive red sandstone with time. The research results have momentous reference value for foundation treatment design and construction of Hongshanyao Hydraulic Project in Nanjing.

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SOME ISSUES IN DISCONTINUOUS DEFORMATION ANALYSIS FOR GEOTECHNICAL ENGINEERING

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2007, 26 (10): -2014 doi:
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Some key problems including energy dissipation，convergence criterion and simulation of construction procedure for geotechnical engineering in discontinuous deformation analysis(DDA) method are discussed. A linear viscous-type resistance is used to absorb the kinetic energy of the block system；and the equilibrium equations to contain damping term are derived by minimizing the total potential energy. The mechanism of the energy consumption by damping force is discussed；and three types of convergence criteria including displacement criterion，velocity criterion and acceleration criterion are defined to ensure convergence to the correct result for quasi-static analysis. According to the features of DDA，the problems of the excavating load and bolting load in the analysis of geotechnical engineering are studied. Two new algorithms to simulate sequential excavation for rock masses have been developed and implemented into the DDA program. Three typical numerical examples are calculated to demonstrate the capability of the DDA with the new extensions. The computational results show that the improved DDA has not only high accuracy and good convergence performance，but also is easily applied to practical engineering.

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EXPERIMENTAL STUDY OF 3D GEOMECHANICAL MODEL ON GLOBAL STABILITY OF DAGANGSHAN DOUBLE CURVATURE
ARCH DAM

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2007, 26 (10): -2027 doi:
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Aiming at the engineering geological problems of the Dagangshan arch dam，by three-dimensional geomechanical model test，the whole failure process and mechanism of the arch dam and abutments from loading to failure are studied. The model simulates the discontinuous rock body of dam foundation，the mechanical properties of rock and the entire double curvature arch dam. The model considers the various factors influencing the stabilities of dam foundation and abutment during test，including overloading as well as strength-decreasing of weak structural planes in the rock mass of the dam foundation. A kind of model test material called temperature analogous material whose strength varies with temperature in the process of experiment is adopted to simulate the decrease of the weak structural planes. Then，the comprehensive method considering both overloading and strength-decreasing is successfully applied to the model. The displacement fields of arch dam under the pressure of normal pool level and overloading after strength-decreasing are obtained. The deformation characters of dam and abutment and relative displacements of internal fault for typical measurement points are obtained，and the overall developing process of displacement and crack before arch dam and foundation destabilization and its failure mechanism are revealed. The safety evaluation on the model experiment indicates that the strength reserve coefficient K1 and overloading coefficient K2 are 1.25 and 4.0–4.5 respectively，and the global safety factor for the dam foundation and abutment is 5.0–5.6. The slope stability can be evaluated by synthetically analyzing test data，and the reinforcing measures for the weak areas of dam abutment are advised.

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BASIC PHYSICO-MECHANICAL PROPERTIES AND TIME-TEMPERATURE EFFECT OF DEEP INTACT ROCK FROM BEISHAN PRESELECTED AREA FOR HIGH-LEVEL RADIOACTIVE WASTE DISPOSAL

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2007, 26 (10): -2034 doi:
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[PDF 337 KB] (1392)

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Physico-mechanical property is one of the important aspects for site selection，design，construction and performance assessment of high-level radioactive waste(HLW) disposal. Through a nationwide screening and comparison，Beishan area，a Gobi desert in Gansu Province，is considered as a suitable candidate for HLW geological repository in China. The dominant lithology in Beishan area is porphyritic monzonitic granite and tonalite，with high homogeneity. The deep intact rock of Beishan area has the properties of high density，low porosity，high mechanical strength，low strain and high brittleness. The strain and acoustic emission behavior of granite under constant loading with different temperatures(room temperature，50 ℃，90 ℃) and confining pressures (0，10 and 30 MPa) are studied through creep test. The results indicate that the effect of temperatures and confining pressure on the mechanical property is significant. When the confining pressure is 10 and 30 MPa respectively，the elastic modulus increases with temperature increasing to about 70 ℃，and then decreases a little with the temperature increasing higher；the crack damage stress linearly decreases and Poisson¢s ratio linearly increases separately with the temperature increases. The steady state creep strain rate increases and the time to failure response at the same stress ratio reduces with the temperature increasing. The time to failure increases rapidly as the constant load decreases. The axial creep strain increases and time to failure of granite at the same stress ratio increases rapidly when confining pressure increases.

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GENERAL METHODOLOGY OF SPATIAL BLOCK TOPOLOGICAL IDENTIFICATION WITH STOCHASTIC DISCONTINUITIES CUTTING

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2007, 26 (10): -2043 doi:
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[PDF 534 KB] (1445)

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Based on the topology principles and literatures，the “oriented” theorem is extended and the “closed”theorem is brought forward. The former means edges，loops and blocks are all of orientations. The latter means every edge in a block is attached to two loops with directions being converse in the edge. All loops are used twice times during block identifications；and the total volume of all positive and negative blocks is zero. Then，by procedures of 3D discontinuities network simulation，intersecting lines and primary loops analyses，deleting isolated loops，relative loop analysis，and closed block identification，the general method of spatial block topological identification is put forward. The criteria of validity check are presented simultaneously. Case studies and validity examinations show that the method can correctly and effectively search a great number of blocks(including concaves) with complicated figures formed by numerous finite discontinuities，and indicate that the method is universal and reliable.

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NEW SUPPORTING METHOD FOR SHALLOW-BURIED CAVERN BASED ON MINING METHOD AND ITS ENGINEERING APPLICATION

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2007, 26 (10): -2049 doi:
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In order to meet the requirements of maintaining the original condition of rock face of underground cavern，avoiding heavy excavation to protect ground environment，and reducing support cost of large-span shallow buried cavern，a new supporting method for shallow-buried cavern based on the mining method is presented. It is a built-in method that some crisscross small tunnel sheds are embedded in the overburden layer. So the supporting system of interaction between the surrounding rock and supporting structure is formed. The surrounding rock can display its self load-bearing capacity in the shallow-buried cavern according to this method. And the self load-bearing capacity is controllable in some degree. The method is applied in a large-span shallow-buried cavern，which locates in a tourism spot. The monitoring data reveal that the method is feasible and the proportion of rock self load-bearing reaches forty-seven percent.

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RESEARCH ON DISTRIBUTION RULE OF SHALLOW CRUSTAL GEOSTRESS IN CHINA MAINLAND

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2007, 26 (10): -2056 doi:
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Through collecting the measured geostress data from about 400 drillings up to now in China mainland，450 groups of data with less local influence are selected. The trend of the vertical stress，the maximum and the minimum horizontal principal stresses with depth are established；and the results are compared with the world-wide corresponding regression analysis results. The dispersed point charts of ratios of the maximum and the minimum horizontal principal stresses varying with depth in China are established；and the change rules of the ratios with the depth are studied. As the difference between the maximum and the minimum horizontal principal stresses is great，especially in shallow positions，the ratios of the maximum horizontal stresses to the vertical stresses reflect the horizontal tectonic stress better than the average horizontal stress. The geostress statistic analysis method of Hoek and Brown，which uses the ratio of the average horizontal stress to the vertical stress to study the change rules of geostress with depth，is improved. The dispersed point charts of the ratio of the maximum horizontal stress to the vertical stress and the ratio of the minimum horizontal stress to the vertical stress with depth in China are established；and the corresponding regression analysis is also done. The distribution rules of geostress in China mainland is systematically summarized；some statistic forms are used firstly；and the research results can provide references to the study of macroscopic distribution characteristics of geostress in China mainland and for engineering constructions of related industries.

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RESEARCH ON INFLUENCE OF SHIELD TUNNEL CONSTRUCTION ON DEFORMATION AND SECONDARY INNER FORCE OF CONSTRUCTED PARALLEL TUNNEL

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2007, 26 (10): -2063 doi:
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[PDF 560 KB] (1982)

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Taking the assembly lining structure of shield tunnel as object of study，the continuum material model with the tunnel circumferential and longitudinal stiffness being discounted is introduced based on equivalent deformation principle. With the Dali interzone of the project Guangzhou metro line 3 as research background，laboratory model test and 3D finite element analysis are both applied to the research on the influence of shield tunnel construction on the constructed parallel one. The longitudinal secondary，longitudinal additional axial force and bending moment，circumferential deformation，circumferential secondary axial force and bending moment of the constructed tunnel brought by the newly parallel one are investigated. Factors such as surrounding soil，clear distance，jacking force，etc.，are also discussed in the distribution and variation of displacement and secondary inner forces of the constructed tunnel during shield tunnel construction. The results indicate that the influence of the newly constructed tunnel mainly occurs on the hance of the constructed tunnel close to the new one，that it is necessary to keep a certain clear distance between two tunnels in the weak stratum and that the jacking force of the shield should be controlled in a certain range，according to surrounding soil，clear distance，possible displacement，relative deformation and secondary inner forces.

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MEASUREMENTS AND APPLICATION OF IN-SITU STRESS AND RELATED ROCK MECHANICAL PARAMETERS OF SURROUNDING ROCK OF AIR-CUSHION SURGE TANK AT A HYDROELECTRIC PROJECT IN WEST SICHUAN

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2007, 26 (10): -2070 doi:
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In order to demonstrate the design scheme of the air-cushion surge tank for a hydroelectric project，the hydraulic fracturing technology is adopted to define the in-situ stress and related rock mechanical parameters of rock mass surrounding the high pressure cavern. The measurement results show that the minor principal stress in the rock mass around the high-pressure cavern is 5.6–7.9 MPa and nearly horizontal，the jacking strength is about 6.0–8.0 MPa，and the permeability under pressure of 7.0 MPa is less than 1.0 Lu. Therefore，the rock mass for the cavern is of good rock mechanical performance and a good pressure-cavern place. But there exist some tensile fissures in the rock mass of high-pressure cavern，which have poor bearing capacity，good connectivity and severe water permeability，and are a huge hidden trouble for the non-supported high-pressure cavern construction. The effective high-pressure grouting measures can improve the integrity of rock mass structures and enhance the high-pressure sealing function，which is the key for the construction of the project.

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RESEARCH ON GEOGRIDS REINFORCED SOIL RETAINING WALL WITH CONCRETE RIGID FACE BY FIELD TEST

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2007, 26 (10): -2077 doi:
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The field test of geogrids reinforced soil retaining wall with concrete rigid face is done in the Ganzhou—Longyan Railway main line of China. The test includes the measurement of the basement pressure and lateral pressure of the reinforced soil wall，the tensile force of the reinforcement and the lateral horizontaldisplacement of wall. The basement vertical pressure of the reinforced soil retaining wall is nonlinear along the reinforcement length；and the maximum value is in the middle of the reinforcement and reduces gradually to the two ends. The testing lateral pressure of the reinforced soil wall is nonlinear along the height and the value is less than the active lateral earth pressure. The tensile strain along reinforcement at the upper wall is a distribution of single peak，but the tensile strain along reinforcement at the lower wall is twin peak values. The potential fracture plane at upper wall is similar to“0.3 H”method；but the potential fracture plane at lower wall is near to the active Rankine earth pressure theory. The maximum lateral displacement of the wall face during construction is at lower position of wall；and the maximum lateral displacement of the wall face after construction is at top of the wall. These test results can be used for references in future studies and designs of geogrids reinforced soil retaining walls.

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EXPERIMENTAL RESEARCH ON CRITICAL PERCOLATION GRADIENT OF QUICKSAND ACROSS OVERBURDEN FISSURES DUE
TO COAL MINING NEAR UNCONSOLIDATED SOIL LAYERS

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2007, 26 (10): -2084 doi:
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[PDF 355 KB] (1265)

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Concrete blocks with fissures of different sizes are adopted to simulate mining fractured rock mass，and the clay，silt，coarse sand and gravel are used to compose 7 kinds of soil samples with different particle size distributions. Then，the types and mechanisms of the seepage deformation and failure of the unconsolidated soil layers across the caving zone and water flowing fractured zone within overburden，and the relationship among the critical percolation gradient of unconsolidated soil layers while seepage failure across mining-induced fissures from above to bellow vertically，soil particle size distributions，physico-mechanical properties and the widths of fissures are studied in laboratory tests by reequipped seepage meters. The results show that the silt，coarse sand and gravel with small amount of clay are easier to quicksand，and pipe and quicksand occurs frequently while d50 is less than 1/10 of the width of fissure. When the critical percolation gradient is larger than 1，the critical percolation gradient of soils with same particle size distributions is in direct proportion to the unit weight and cohesion，in inverse to the liquid index. The wider the fissures are，the smaller the critical percolation gradient for the same soil sample is when seepage failure deformation occurs across fissures，and the critical percolation gradient decreases exponentially with the extension of the width of fissures. Moreover，the relationship among the volume of quicksand and the width of fissure，and the initial water level are also studied in tests，and the results indicate that the volume of quicksand increases linearly with the width of sand inrush mouth in the same initial water head，and increases with the initial water head in the same size of sand inrush mouth，but the sand content in the quicksand decreases with time. So it can be deduced that the initial water level and width of fissures are the key factors controlling the amount of the quicksand in mine working face.

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ANALYSIS OF INFLUENCING FACTORS OF SHIELD TUNNELING PERFORMANCE IN COMPLEX ROCK STRATA

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2007, 26 (10): -2092 doi:
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The purpose of mechanized shield tunneling is to increase its penetration rev and penetration rate. According to literatures，the main factors relating to shield tunneling performance are geological conditions，mechanical parameters and their compatibility. The shield tunneling performance of Chongqing Yangtze River tunnel in alternative of mudstone and sandstone bed is discussed. Based on field shield excavation tests and rock point load strength tests，shield cutter penetration rev，penetration rate and their influencing factors are studied. Using the collected in-situ data，the statistical relationships between shield tunneling performance and rock strength，cutter head thrust force and torque are analyzed by means of regression analysis. Simultaneously predicting models of penetration rev and penetration rate are established. The higher the rock strength is，the lower the cutter penetration rev and penetration rate are；and their relationship can be expressed by power function. As the cutter penetration increases，the cutter head torque increases linearly. Thought checking the shield tunneling characteristics in the two strata，the shield tunneling performance is found higher in the mudstone，but higher torque value is required. However higher thrust force is required in the sandstone if the efficient excavation is to be acquired；and the required torque is lower than that in the mudstone. This can be attributed to higher strength of the sandstone and its shallow penetration of the disc cutters.

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FAILURE MODEL TEST ON DEEP ANTI-SLIDING STABILITY OF
WUDU RCC GRAVITY DAM

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2007, 26 (10): -2097 doi:
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Based on the geological simplification of the typical sections and dam foundation of Wudu RCC gravity dam，the 3D geomechanical model test on stability against deep sliding in the condition of natural foundation of this dam is performed. In the physical model，the conditions of landform and geology including rock mass，fault and joint of the typical monoliths are simulated. According to the mechanical parameter of the rock mass and weak structural plane，materials suitable for the geological condition of Wudu project are developed. The overloading method is used. As a result，the deformation behaviors of the dam，dam foundation and the main fault are analyzed；the failure process，shape and mechanism of the dam and foundation are discussed；the controlling factors influencing the stability of dam foundation are disclosed and the safety factor and failure mechanism of the typical dam sections are achieved. Thus，the reinforcement measure for the dam foundation is discussed. The presented research results provide references to safety evaluation and design of this dam.

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STUDY ON MARBLE UNLOADING MECHANICAL PROPERTIES OF JINPING HYDROPOWER STATION UNDER HIGH GEOSTRESS CONDITIONS

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2007, 26 (10): -2104 doi:
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The Jinping Hydropower Station is a large-scale national key project，of which the diversion tunnels are deep-buried. Especially the tunnels are located in a high geostress area；so it is of significance to study the variation laws of unloading mechanical properties under high geostress conditions. To simulate the tunnel excavation unloading effect，a series of triaxial unloading tests and a special designed multiple failure state unloading tests are carried out. The results show that under high geostress conditions，the unloading properties of marble specimens are as follows. (1) Under same initial stress conditions，stress needed in axial compression failure is more than that in confined unloading failure. Confining pressure reduction is prone to cause rock failure. (2) From the very beginning of unloading，the lateral deformation increases remarkably；and dilatancy presents prominently. Moreover，if the deformation caused by initial axial compression is disregarded，the volumetric deformation increasing is dominated by lateral deformation. (3) During the unloading stage，the relationship between Poisson¢s ratio rises up；and the confining pressure could be well described by biquadrate. The deformation modulus declines indistinctly at first，while as failure approaching，even little confining declination would cause large decreases. (4) Shear strength parameter c under unloading conditions is 14% lower than that under conventional compression conditions；while j is greater than that about 23%. These conclusions reveal the unloading properties of marble under high geostress conditions and offer important references for stability analysis of deep-buried tunnels.

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MECHANICAL CHARACTISTICS OF SANDSTONE AFTER HIGH TEMPERATURES

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2007, 26 (10): -2110 doi:
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The laboratory tests are done for studying on the mechanical properties of Jiaozuo sandstone after undergoing different high temperatures. The temperature varies in the range of 20 ℃，100 ℃，150 ℃，200 ℃，400℃，600 ℃，800 ℃，1 000 ℃ and 1 200 ℃. The scopes of this study include apparent shape，peak stress，peak strain， modulus of elasticity，Poisson¢s ratio and stress-strain curve of sandstone. The degradation mechanism of sandstone in high temperature is discussed briefly. The test results show that high temperature leads to the changes of apparent shape for sandstone，the temperature does not obviously affect the mechanical properties and heating reinforces some mechanical indexes of sandstone in the temperature ranging from room temperature to 400 ℃. When the temperature is above 400 ℃，the mechanical properties of sandstone present deterioration with the increase of temperature，and the peak stress and modulus of elasticity sandstone decrease in different extents. The peak strain of sandstone increases by a big margin before 800 ℃. The deformation of sandstone increases generally with the rising of temperature. The Poisson¢s ratio of sandstone presents increasing before 600 ℃，and then decreasing as the temperature increases. Thermal stress，changes of minerals formation and microstructure due to temperature result in the changes of mechanical properties and degradation of sandstone.

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STUDY ON DAMAGE MECHANISM OF SANDSTONE UNDER HYDRO-PHYSICO-CHEMICAL EFFECTS

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2007, 26 (10): -2117 doi:
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A series of tests on evolution of the porosity，pH value，as well as the mineral composition of sandstone under different water flow environments are conducted；and the micro- and meso-mechanisms of hydro- physico-chemical damage of sandstone are analyzed. Accordingly，a method is suggested，by which the secondary porosity individually induced by hydro-chemical interaction can be separated from the total secondary porosity through introducing the test value of secondary porosity of sandstone specimen under distilled water environment. And thereby，a representation of damage variable demonstrating the hydro-physico-chemical effect of sandstone is provided based on the variety of secondary porosity. Moreover，the CT scanning tests on the sandstone specimen with hydro-physico-chemical interaction of 180 days are carried out. The study reveals that the hydro-physical damage is mainly affected by the transfer and diffusion of cement materials，and debris in and around the pore of rock，and closely related to the hydro-chemical damage by the ion concentration and pH value in water solution. The varieties of mechanical behavior of sandstone induced by the hydro-physicochemical interaction are dominantly resulted from the secondary porosity，which can be divided into two parts，respectively caused by the hydro-physical and hydro-chemical effects. The comparison of the calculated damage values and CT values demonstrates that the representation of damage variable of sandstone is feasible.

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CAUSES ANALYSIS OF CRACKING OF ROCK-BOLTED CRANE
GIRDER IN AN UNDERGROUND POWERHOUSE

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2007, 26 (10): -2125 doi:
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Rock-bolted crane girder is a widely used structure in underground powerhouse nowadays. In hydropower projects longitudinal crack between rock-bolted crane girder and surrounding rock masses can hardly be found. Aiming at the cracking phenomenon in an underground powerhouse，detailed analysis of the cracking mechanism is made based on geology，monitored data and construction process. It is concluded that the cracking initiates between late October and early November，2006；differential deformation caused by vein faults in the surrounding rock and excavation is the major cause leading to the cracking while the development of the differential deformation cannot be effectively controlled by support measures. So considering the discontinuous characteristics of rock masses，it is important to make detailed geological investigation and to forecast possible differential deformation on the sidewalls during construction period，so as to take effective support measures and assure the safety of the girder.

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STABILITY ANALYSIS OF SLOPE AND DAM FOUNDATION BASED ON VECTOR METHOD SAFETY FACTOR

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2007, 26 (10): -2130 doi:
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Sliding is a vector concept. The vector analysis method(VAM) of slope and dam foundation stability is put forward on the basis of vector method safety factor. It studies the overall stability of the sliding mass， determines the calculating direction θ according to the tendency direction toward sliding of the whole sliding mass，defines the vector method safety factor F(θ) in terms of the vector characteristics of forces against and driving sliding in θ，and analyzes the stability of slope and dam foundation with F(θ). As the loads and sliding surface of slope and dam foundation are given，the real stress distribution of the sliding surface can be calculated by finite element method. The opposite direction of the sum of the static sliding fractional forces along the sliding surface is θ；and the formula of F(θ) is directly derived from the real stress distribution of the sliding surface and the Mohr-Coulomb criterion，not requiring redundant assumptions. The definition of F(θ) based on the force vector analysis is clear in physics and mechanics. Because the formula of F(θ) is an explicit expression and is simple to calculate，it is convenient to apply VAM to engineering. As a verification，F(θ) is solved by applying VAM to two standard testing slopes of ACADS；and the results are almost the same as those by ACADS. By applying VAM to the dam section #3 foundation stability analysis of the Three Gorges Project，the results are coincident with qualitative analysis—finite element strength reduction method simulating the gradual damaging process of the dam foundation. These case studies show the feasibility and the engineering practicability of VAM.

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EXPERIMENTAL STUDY ON MICROSTRUCTURE OF STRENGTH PROPERTY OF RED SANDSTONE

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2007, 26 (10): -2141 doi:
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In order to discuss the microstructural mechanism of strength property of red sandstones，the microstructural changes of red sandstone under load are tracked by using optical testing systems；the unconfined compressive strength of corresponding rock specimen is measured and the comparable quantitative parameters are extracted. By using multilinear regression method，the correlations between unconfined compressive strength and microstructural parameters are analyzed. Then the microstructural elements closely linked with unconfined compressive strength of red sandstone are filtered and the evolutionary characteristics of prominent microstructural elements are analyzed. The findings indicate that under uniaxial compression，the red sandstones at first experience structural intensification and then structural degradation until they are failed；the unconfined compressive strength of red sandstone is mainly related with compaction rate，pore distribution and connecting condition of mineral grains；and the above factors have a more notable impact on the unconfined compressive strength of red sandstone with the increase of weathering；with the increase of load，the grains area ratio and Euler number decrease，the pore develops towards centralization or collectivization，and the red sandstones gradually lose their resistance to deformation.

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STUDY ON SITE MONITORING AND STABILITY OF LAYERED
SURROUNDING ROCKS OF UNDERGROUND POWERHOUSES
OF HYDROPOWER STATION

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2007, 26 (10): -2148 doi:
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The comprehensive stability of the rock mass produced by couple factors in complex geological environment is analyzed. By several measurements，the displacement and dynamic relaxed area at grottos¢ intersection of the underground powerhouses are researched on site tracing monitoring. And the displacement of the rock mass is calculated by finite difference method. The comparison analysis of the tracing monitoring and calculated result shows that the calculated values agree well with the measured data. Therefore，the research results present important reference for studying on the failure characteristics，mechanical behavior，deformation laws and relaxed area of the similar layered composite rock mass；and they have great theoretical significance for determining some control indexes. The research results have reference to the design and construction of the large underground powerhouses.

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MODEL EXPERIMENTS ON SEEPAGE FAILURE OF
DEEP FOUNDATION PIT CONSIDERING INFLUENCE OF
FOUNDATION PILES IN SANDY SOIL

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2007, 26 (10): -2153 doi:
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Using home-made seepage and seepage failure test apparatus，model experiments in different conditions were carried out. Based on the analysis of water head and soil deformation results，the seepage failure problem of deep foundation pit in uniform sandy and silty soil is investigated. The results demonstrate the seepage failure modes in deep foundation pit in uniform sandy and silty soil. Combined with numerical simulation and model experiments，the mechanism of seepage failure is analyzed based on the change of soil stress. Moreover，the effect of foundation pile on seepage failure and the effect of seepage on the deformation and stress of foundation pile are studied. According to the research，the plastic strains firstly appear on the foot of the supporting structure. Seepage failure takes place when the plastic zone joints together；and the failure model is wedge type in uniform soil. Influenced by cohesion，the water head difference in silt is more than that in sand when seepage failure takes place. Influenced by piles，the water head difference of seepage failure also increases.

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本刊2007年增刊1被EI收录论文(155篇，收录率为100%)题录

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2007, 26 (10): -2161 doi:
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本刊2007年增刊1被EI收录论文(155篇，收录率为100%)题录