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2009, 28 (07): 0-0 doi:

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RESEARCH ON GAS SEEPAGE LAW IN LAMINATED SALT ROCK GAS STORAGE

CHEN Weizhong，TAN Xianjun，WU Guojun，YANG Jianping

2009, 28 (07): 1297-1304 doi:

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The sealing performance is an important technique and safety index for salt rock gas storage. For the salt rock gas storage containing weak interlayer，it is very possible that the natural gas will escape along the rock layer if appropriate measures are not adopted，which will lead to external permeability of natural gas. Gas permeability mechanism for the laminated salt rock gas storage is very complex. It is key problems to establish the permeability mechanical model and to put forward corresponding numerical method which is suitable for salt rock with weak interlayer based on seepage theory in porous media. It is assumed that the weak interlayer and salt rock are isotropic porous media. The interface between salt rock and weak interlayer is assumed as a fracture with a certain thickness. Based on the related theory，the equivalent-boundary model of the gas permeability is established. This model can reflect the fracture flow which is different from the equivalent medium model，and its computational complexity is less than that of double-permeability model. Combining with the field situation of Jintan gas storage，the pressure distributions of storage with different cyclic pressures for gas filling and gas recovery in five years are studied. The effect of permeability of interface between salt rock and weak interlayer on pressure distribution is analyzed. It is concluded that the effects of permeability on gas pressure distribution are very important. The scientific basis is provided for the design of salt rock gas storage with weak interlayer and reasonable choice of operating pressure.

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DESIGN CRITERIA FOR CONCRETE-LINING HIGH PRESSURE HYDROPOWER TUNNEL AND HIGH PRESSURE PERMEABILITY TEST ON ROCK MASS

ZHANG Chunsheng

2009, 28 (07): 1305-1311 doi:

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The engineering design for concrete-lining tunnels should focus on the investigation and utilization of the surrounding rock geotechnical conditions governed by topography and in-situ stress state，as well as the permeability of rock mass under high water pressure，etc.. Some critical design criteria applied to the design of concrete-lining high pressure hydropower tunnels are discussed，such as the minimum overburden criterion，hydraulic fracturing criterion and minor principal stress criterion，and their application conditions and relations are also discussed. As an illustration，the application of the above criteria to the design of Tianhuangping Pumped Storage Power Station is introduced. Field test method and results of high pressure permeability tests carried out at Tianhuangping pumped storage power station are discussed. At last，the engineering treatments for some locations with comparatively low in-situ stress mainly caused by joint structure are presented.

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康红普，司林坡

KANG Hongpu，SI Linpo

2009, 28 (07): 1312-1320 doi:

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The borehole penetrating method can rapidly and accurately test the uniaxial compressive strength(UCS) of coal and rock mass. Based on the principle of this method，the underground testing apparatus for coal and rock mass strength with small borehole is developed. 34 pieces of coal and rock blocks are tested. The standard samples are drilled from the coal and rock blocks. The uniaxial compressive strengths of the samples are measured；the critical load of the penetrating needle is measured with the testing apparatus in the reserved borehole；and the coal and rock damage patterns on the borehole walls are analyzed. Then the relation between the UCS of coal and rock blocks and the critical load of the penetrating needle is determined. The experiment points out that the forms，depths and scopes of the damage pits caused by the needle in the borehole walls are closely related with coal and rock properties；the higher the coal and rock strength is，the smaller the damage area and the penetrated depth are，and the more regular the pit form is. The formula describing the relation between the penetrating needle critical load and the UCS of coal and rock mass is obtained by the regression of laboratory data combined with underground measurement data. Meanwhile，the discrete property of the critical load and its controlling measures are analyzed；and the influence of structural planes on the coal and rock mass strength and its testing methods are discussed. The in-situ tests are carried out in typical deep coal mining area—Xinwen coal mines. There are great differences among the strengths of roadway roof strata with different lithological characters；and the strata strengths are also different in various coal mines. The coal seam strengths vary and fluctuate considerably along the test borehole because of the broken zone around coal sides，coal heterogeneity and nonuniform distribution of structural weakness planes in coal mass. The supporting designs accord with the coal and rock mass conditions in underground mines on the basis of the in-situ measurement of coal and rock strengths；and the rationality and reliability of the roadway supporting designs are improved remarkably. The stability of the surrounding rock and roadway supporting states are obviously improved. Finally，the present problems of the borehole penetrating method are analyzed；and the improvement proposals are put forward.

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IMPACT OF ORIENTED PERFORATION ON HYDRAULIC FRACTURE INITIATION AND PROPAGATION

JIANG Hu1，CHEN Mian1，ZHANG Guangqing1，JIN Yan1，ZHAO Zhenfeng2，ZHU Guifang3

2009, 28 (07): 1321-1326 doi:

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Hydraulic fracturing is used widely in petroleum industry，which plays an important role in the production of low permeability reservoir. And hydraulic fracturing treatments are greatly affected by the selected perforation parameters. The geometric configuration is a key problem in hydraulic fracturing. The strata are simulated by a triaxial rock mechanics test system on artificial specimens with size of 300 mm×300 mm×300 mm. The fracture propagation mechanism of hydraulic fracturing is studied. Experiments are designed to investigate hydraulic fracture initiation sites，breakdown pressure and geometries，specially the tortuous fracture geometries resulting from fracture initiation and propagation through perforated vertical wellbore. The experimental results show that the tortuous fracture can be generated by using oriented perforation fracturing technology. And a model for prediction of hydraulic fracture initiation pressure from vertical wellbores with perforations has been presented under given in-situ stress condition. To investigate the sensitivity of the results to variable conditions，by changing the perforation angle and the horizontal stress difference，it is found that the breakdown pressure and hydraulic fracture reorientation path are functions of the perforation orientation. To reduce the breakdown pressure and reorientation path，the perforations should be placed with a smaller perforation angle. The effect of micro-annulus near the wellbore on the fracture initiation and its geometry is also discussed；it makes the fracture initiation as from an open-hole and the fracture geometry very simple. The conclusions drawn above provide valuable guidance to the design of hydraulic fracturing treatment and oil engineering practice.

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NUMERICAL SIMULATION OF STRENGTH
AND DEFORMATION CHARACTERS OF ROCKFILL

CAI Zhengyin1，DING Shuyun1，BI Qingtao2

2009, 28 (07): 1327-1327 doi:

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The results from large-scale triaxial test show that rockfill will exhibit strain softening response and dilative behavior during shear process. Whether it will happen depends on the density of the material and its stress state. The lower the effective mean normal stress is，the larger the density is，and the more the strain softening and dilative response are. By introducing state-dependent dilatancy theory of cohesionless soils，a series of numerical simulations of the strength and deformation behaviors of saturated rockfill by triaxial consolidation and drainage test under different relative densities have been conducted. Compared with the simulation results of Duncan-Chang¢s E-B model and Nanshui model，it is found that the theory can reflect the strain softening and dilative characters of rockfill through a unique set of parameters for given materials over a full range of densities and stress levels.

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DEVELOPMENT AND APPLICATION OF SIMILAR PHYSICAL MODEL EXPERIMENT SYSTEM FOR WATER INRUSH MECHANISM
IN DEEP MINING

LIU Aihua，PENG Shuquan，LI Xibing，CHEN Hongjiang

2009, 28 (07): 1335-1341 doi:

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A large similar physical model experiment system for mechanism of deep mining water inrush with high pressure is developed. The system is composed of model box，loading devices of horizontal lateral pressure and vertical pressure，measurement devices and data autorecorder. The dimension of the model box can vary with the practice. It is designed as 1 600 mm in length，800 mm in height and 200 mm in width here. The horizontal and vertical pressures are applied by closed circuit servo-loading devices with a maximum charge of 300 kN. The maximum horizontal displacement is limited in 100 mm，while 1.0 MPa of water pressure can be added to simulate fluid-solid coupling effects. The measurement devices include the stereo microscope to record and measure the development of cracks in the specimen，and the advanced measurement device to monitor and measure the displacements based on digital image analysis. This large similar model experiment system can simulate the complicated mining activities and help to analyze the stresses，deformation(displacements) and failures in surrounding rock. The safety effects of different loading conditions，water pressures and mining engineering and the mechanisms of water inrush caused by mining engineering can be studied. It is certainly a new and valuable modeling and testing research platform for studies of both water inrush in coal mines and related mechanical problems in deep mining engineering.

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APPLICATION OF GEOPHYSICAL LOGGING TECHNIQUES TO INVESTIGATION OF ROCK MASS ENGINEERING IN COAL MINE

YE Genxi1，2，3，HATHERLY P3，JIANG Fuxing1，PAYNE D4，MEDURST T5

2009, 28 (07): 1342-1352 doi:

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The current application of geophysical logging technique to the investigation of rock mass engineering in coal mine，especially the geophysical strata rating(GSR)，is introduced. GSR is mainly based on sonic logging data(density and gamma logs are used simultaneously)；and the formulation relies on a geomechanical understanding of the factors(bedding or fracture) that influence sonic velocity，and does not attempt to estimate rock strength，rather to provide a method for estimating the quality of rock mass quantificationally and comprehensively. Engineering practice indicates that geophysical logging technique with its innate ability has been playing a helpful role in quantitatively identifying the rock mass quality and changes in rock mass，such as delineating the range of soft rock，recognition of key strata，and exploration of potential regions of water inrush. It also comes to the conclusion by comparison that GSR is more reliable than uniaxial compressive strength which is used only in quantitative description of sedimentary rock. Seismic prospecting is also employed to bridge the gap among boreholes and is helpful to understand what is going on there. A new academic thought of geophysically quantitatively describing rock mass quality，namely，it is possible to statically quantitatively describe the rock mass with geophysical logging technique before mining，and dynamically quantitatively describe the rock strata movements associated with mining during retreating with microseismic monitoring or electromagnetic radiation.

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MICRO-PILE COMPOSITE STRUCTURE AND ITS DESIGN THEORY

ZHOU Depei，WANG Huanlong，SUN Hongwei

2009, 28 (07): 1353-1362 doi:

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Micro-pile composite structure has been widely applied to landslide treatment engineering due to its many advantages；and the engineering effect is very evident. But at present，few researches on the anti-sliding mechanism of the structure have been done. In order to provide theoretical support and technique service for the design and construction，the corresponding studies must be urgently conducted. Three types of the micro-pile composite anti-sliding structures have been summarized according to their setting places on the slope，namely，type of slope surface reinforcement，type of slope step reinforcement，type of slope foot reinforcement. Some key problems and applicable conditions are discussed for the design of these structures. Among these structures，the composite structure of micro-pile fixed by the tip beam is usually more adopted in projects. According to the relationship of pile-soil interaction，the anti-sliding mechanism of the composite structure is discussed. The composite structure improves the shear strength of the sliding surface；and the pile-soil system behaves better in anti-sliding effect. The anti-sliding mechanism of the system is not same as the one of the common retaining pile. The anti-sliding effect of the system is achieved by the tensile strength of the micro-pile and the bearing capacity of foundation of soil and pile，but not by the whole bend ability as the common retaining pile. In order to obtain the axial force of the micro-pile，the design theory is put forward according to the method of elastic foundation beam with restriction of transverse deformation. Application of the design theory to a slope project shows that the theory is reasonable and easy.

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RESEARCH ON ACCUMULATIVE DAMAGE EFFECT OF INTERLAID ROCK IN DAMAOSHAN TUNNEL GROUP WITH SMALL CLEAR DISTANCE

LIU Minggui1，ZHANG Guohua1，LIU Shaobo1，LI Qi2

2009, 28 (07): 1363-1369 doi:

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The blasting construction of small clear distance tunnel inevitably causes accumulative damage of surrounding rocks and its mechanical behaviors will be degenerated. Based on dynamic damage variable and internal displacement of surrounding rock，combining with the monitoring results of Damaoshan tunnel，accumulative damage effects of interlaid rock in tunnel groups with small clear distance are studied. Monitoring results of acoustic velocity and internal displacement show that the newly-built blasting construction has caused damage，breakage and slippage of inter-space rock to a certain degree. However，the internal displacement does not cause instability，and surrounding rocks still possess certain strength. By comparing newly-built tunnel with existing tunnel，damage range caused by construction using two side-wall pilot tunnel method is three times more than the range caused by using whole section excavation. Therefore，accumulative damage effect should be brought to high attention during the construction of small clear distance tunnel. Blasting in upper section will lead to activation of the fissures of rock and significant declines of acoustic velocity；and blasting in lower section will lead to vibration of inter-space rock as wall vibration and significant increase of internal displacement，which causes loosing and slippage of rock mass. The slippage will stop till the blasting stops. Both the changing rate of the acoustic velocity and the displacement should be taken fully consideration in the analysis of the accumulative damage range and degree. If only the changing rate of the acoustic velocity is considered，the analytical results will not be correct. The farther the explosion source is，the bigger the damage degree and the displacement of the surrounding rocks are. The accumulative damage effect has distinct nonlinear characteristics.

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EARTHQUAKE DAMAGE EFFECTS OF TOWNS AND RECONSTRUCTION SITE SELECTION IN WENCHUAN EARTHQUAKE ON MAY 12，2008

LI Yusheng，HUANG Runqiu

2009, 28 (07): 1370-1376 doi:

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During Wenchuan earthquake，earthquake damage effects which severely damaged towns mainly include fault dislocation effect，site and foundation effect，amplification effect of ground motion and geological hazard effect. Site selection problem involves with complex factors，such as earthquake faults，geological hazards，national well-being and the people's livelihood，economic development，and so on. It is a complicated system engineering. The basic principle of solving the problems is described as follows. For the towns located in earthquake fault zones and deteriorative geological environment with severe hidden trouble of geological hazard，they must be moved to other places；for the town without severe hidden trouble of geological hazard，damaged seriously but far away from earthquake fault zones，they should be in-situ reconstruction according to the principles of “scientific planning，norms avoidance，reasonable adjustment to the aseismic standards”. During reconstruction site selection，attention should be paid to potential geological hazards，multiplicity of inducing factors and long-term sustainability，and suitability evaluation on geological environment and risk assessment of geologic hazard should be strengthened.

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EARTHQUAKE-INDUCED DAMAGE ANALYSIS OF HIGHWAY BRIDGES IN WENCHUAN EARTHQUAKE AND COUNTERMEASURES

ZHUANG Weilin，LIU Zhenyu，JIANG Jinsong

2009, 28 (07): 1377-1387 doi:

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The results of the investigation on 1 657 bridges damaged in Wenchuan earthquake in Sichuan Province were summarized；and seven types of macro-earthquake damages of highways and bridges were presented. For beam bridges and arch bridge，the main damages were girder displacement，girder falling，pier damage by shear force，pier and girder crushing and cracking，bridge abutment wall and ribbed slab cracking，bridge abutment filler sloughing，arch ring and spandrel cracking，etc.. All of the damage reasons of the bridges were analyzed preliminary；and the influential factors for selections of bridge sites and types were also put forward. The countermeasures were presented at last for girder displacement and pier damage.

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RESEARCH ON STARTING OF MINE DEBRIS FLOW BASED ON ARTIFICIAL SIMULATION EXPERIMENT IN XIAOQINLING
GOLD ORE AREA

XU Youning1，2，CAO Yanbo3，ZHANG Jianghua1，CHEN Huaqing1，YANG Min2，WANG Xianwei2

2009, 28 (07): 1388-1395 doi:

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Following the principle of similarity，using reduced scale structures，taking the slag as a source for straight ramp-start simulation test，the quantitative correlations of the grain composition，slope gradient and the critical water content which are the main influential factors of mine debris flow are studied. The tests indicate when the grain composition is constant，the larger the slope gradient is，the lower the critical water content is. And it is also shown that the water-bearing slag is easier to start than the dry slag. For the slag on the slope，when the saturation is certain，as long as the slope gradient is large enough，the slag will be able to start and form debris flow. When the content of the fine material in the slag reaches 28%，the slag is the most vulnerable to start. The greater the mass of the slag is，the higher the slag heaps，and the easier the slag stars. The slagheap with triangular section is easier to start than that with other sections.

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RESEARCH ON INFLUENTIAL PARTITION AND APPLICATION OF ADJACENT VIADUCT PILE FOUNDATIONS IN XICUN STATION OF GUANGZHOU METRO

WANG Mingnian1，CUI Guangyao1，YU Bo2

2009, 28 (07): 1396-1404 doi:

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Nine groups of viaduct pile foundations are located in the vicinity of Xicun station of Guangzhou metro which is constructed by subsurface excavation method. The minimum clear distance is 2.30 m between the tunnel of Xicun station and pile XJ33. To ensure the use safety of the viaduct，the least squares principle and finite difference method are used to study the influential partition of the pile foundations. The outcome of the influential partition is used for classification of pile foundations. And the concentrated areas of pile foundation settlement of the various types of pile foundations are determined. These results are applied to present the program of reinforcement and the management level of monitoring and measurement of the various types of pile foundations. The results show that the influential partition of the viaduct pile foundation is divided into four regions because of the tunnel excavation of Xicun station. Accordingly，the pile foundations are divided into four categories. The concentrated area of pile foundation settlement of pile type A is 2.0D(D is the diameter of tunnel) section before tunnel face and 3.0D section after tunnel face，1.0D section before tunnel face and 3.0D section after tunnel face for pile type B，and 0.5D section before tunnel face and 2.0D section after tunnel face for pile type C. Nine groups of viaduct pile foundations belong to type A in the vicinity of Xicun station. XJ25，XJ32 and XJ34 are the dangerous piles. These results can effectively control the impact of tunnel construction in Xicun station of Guangzhou metro on the viaduct pile foundation，ensure the construction safety and obtain successful experience. This will provide references to other similar projects.

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RESEARCH ON ANISOTROPIC CHARACTERISTICS AND SIZE EFFECT OF COLUMNAR JOINTED ROCK MASS

ZHU Daojian1，2，YANG Linde1，2，CAI Yongchang1，2

2009, 28 (07): 1405-1414 doi:

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The mechanical properties of columnar jointed rock mass，which is the main composition of dam foundation and surrounding rock of deep cavern at Baihetan hydropower station，are very complex. In order to study the anisotropic characteristics of columnar jointed rock mass，three factors are considered. First，a mixed multi-weakness planes softening constitutive model is built. It can be used to define and describe the mechanical properties and the softening characteristics of multiple oblique joint planes after failure. Second，considering the heterogeneity of the columnar jointed rock mass，a probability model is established through assigning mechanical parameters throughout the numerical specimens by following Weibull distribution. On the basis of sensitivity analysis of probability distribution parameters，combining with the experimental results of rigid bearing plate，the reasonable distribution parameters that fit the structure of field rock mass are computed. Third，column section of jointed rock mass is composed by tetrahedron，pentahedron and hexahedron randomly and irregularly. Voronoi algorithm is used to achieve the randomness of geometric shape and irregularity of arraying order. Taking all these factors into account，the bearing capacity and deformation characteristics in different directions are obtained. The results turn out to be obviously distinct in different directions. At the same time，multiple test blocks with different sizes are analyzed；and the curves of equivalent elastic modulus and unconfined compressive strength in different directions changing with size are acquired. It is shown that the columnar jointed rock mass has obvious size effect；meanwhile the characteristic scale is determined.

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SYSTEM RELIABILITY ANALYSIS OF ROCK SLOPE WEDGE STABILITY BASED ON N-DIMENSIONAL EQUIVALENT METHOD

LI Dianqing，ZHOU Chuangbing，HU Ran

2009, 28 (07): 1415-1424 doi:

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A probabilistic fault tree is presented to model system reliability of rock wedge with multiple failure modes. The versatile 4-parameter b distribution is used to describe the basic random variables in the rock wedge stability model. The n-dimensional equivalent method is employed to perform the system reliability analysis of rock wedge. Reliability sensitivities in three different levels are discussed. An example is investigated to illustrate the proposed method. The results indicate that the failure probabilities of system for rock wedge using the proposed method are fully within the bounds of failure probability obtained from the Cornell bound method. The system reliability of rock wedge can be efficiently evaluated using the proposed method. In addition，the system reliability of rock wedge with correlated multiple failure modes can be intuitively represented by the probabilistic fault tree. The failure probability of system will be overestimated if the correlations between different failure modes associated with rock wedge are not taken into account. The negative correlation between cohesion and internal friction angle has a positive effect on the system reliability of rock wedge. Reliability sensitivity analysis has three levels，namely single limit state function level，single failure mode level and system reliability level. The importance of reliability sensitivity level should be realized due to the significant differences in sensitivity coefficient associated with the aforementioned three levels. Results from sensitivity analysis indicate that the water-pressure parameter and the geometry of rock wedge are significant random variables with higher sensitivity coefficients，which have a significant impact on the calculated failure probabilities of system. Accordingly，to improve the rock wedge stability effectively，a good drainage system for the slope should be designed；and a good structural characterization of discontinuities in the rock mass should be conducted. The proposed conclusions and approaches can form a basis for risk analysis of rock slopes.

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SIMULATION OF FRACTURE PROPAGATION IN LARGE-SCALE RESERVOIR WITH LOW PERMEABILITY AND THIN INTERBEDDED SANDSTONE

YAN Xiangzhen1，SONG Gencai2，WANG Tongtao1，YANG Xiujuan1，LI Yong1

2009, 28 (07): 1425-1431 doi:

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The length/height ratio of fracture is usually smaller than 4. When the large-scale hydraulic fracturing is carried out on reservoir with low permeability and thin interbedded sandstone，because the interlayer is thin and its strength is low，a weak restriction is shown in the height of fracture development. Under this condition，the pseudo-3D model only considering the fluid flowing along the length direction of fracture does not work. So，the pseudo-3D model of predicting the fracture development with 2D flow is built up according to the characteristics of hydraulic fracturing in reservoir with low permeability and thin interbedded sandstone based on linear elastic fracture theory and proper hypotheses. The precise solutions of fracture length and height are calculated by the pseudo-3D model during hydraulic fracturing. The program for fracture parameters is coded based on the pseudo-3D model of 2D flow，which is used to simulate the fracture development during hydraulic fracturing in an actual reservoir with low permeability and thin interbedded sandstone. The results show that the pseudo-3D model of 2D flow has a perfect performance in analyzing the fracture development during large-scale hydraulic fracturing in reservoir with low permeability and thin interbedded sandstone，and can be satisfied with engineering demands.

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RESEARCH ON GRANITE CUTTING AND BREAKING TEST UNDER CONDITIONS OF HIGH TEMPERATURE AND HIGH PRESSURE

ZHAO Jinchang1，WAN Zhijun2，LI Yi3，ZHAO Yangsheng1，DONG Fuke2，FENG Zijun2，LI Genwei2

2009, 28 (07): 1432-1438 doi:

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Drilling issue will happen in high temperature and high pressure environment in the course of geothermal exploitation. The research on the cutting and breaking laws of rock is of great importance to improve the heat of the earth interior borehole efficiency under conditions of different temperatures and confining pressures. In order to gain the experimental effect most approaching the actual project，this experiment utilizes the “20 MN servo-controlled triaxial rock testing machine with high temperature and pressure”and designs precise pressure-adding and revolving system，leading to simple operational control and accurate measurement results. This experiment also utilizes a large-size(f 200 mm×400 mm) granite sample to make experimental condition approach actual project condition，thus serving as a pioneer for such experiments. By studying the cutting and breaking law of granite under high temperature and high pressure，the following results can be drawn. (1) Under high pressure condition(100 MPa)，cutting property of granite increases gradually with the temperature rising；and beyond a certain drilling pressure，cutting speed increases obviously with the temperature rising. Under 755 N weight on bit(WOB) in the experiment，the cutting speed at 300 ℃ increases by 30% to 50% than that at room temperature. (2) Under high pressure conditions(100 MPa)，the unit rock-breaking energy consumption reduces obviously with increment of temperature. Under 755 N WOB，the unit rock-breaking energy consumption at 300 ℃ reduces by 20% to 40% than that at room temperature. (3) In the high temperature and high pressure environments，the cutting speed increases with the rotation speed or WOB. Unit rock-breaking energy consumption increases with the rotation speed increasing，but reduces with WOB increasing. This pattern is basically consistent with that under room temperature without confining pressure. (4) Since granite is damaged gradually within this temperature and pressure range，and the compressive strength goes down slowly. If WOB is very slow，the temperature will have a very small effect on cutting rate and unit rock-breaking energy consumption. WOB needs to exceed a certain value in order to have a good granite cutting effect under high temperature environment. Further study can be conducted in this subject.

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DISPLACEMENT BACK ANALYSIS OF PARAMETER FIELD IN UNDERGROUND ENGINEERING BASED ON EXCAVATION DAMAGED ZONE OF SURROUNDING ROCK

NI Shaohu，XIAO Ming

2009, 28 (07): 1439-1446 doi:

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Due to excavation blasting，the surrounding rock of underground caverns is loosened and its strength lowers. A continuous three-dimensional data field of surrounding rock parameters is employed to describe the different damage degrees of surrounding rock. According to the formation mechanism of excavation damaged zone(EDZ) of surrounding rock，the method to calculate the EDZ induced by excavation blasting in underground caverns is analyzed. By taking the range of EDZ into consideration，a back analysis method based on incremental displacements is put forward. By employing this method，the fields of surrounding rock parameters can be back analyzed. As back analysis of geotechnical engineering involves enormous amounts of computation，the back analysis process is improved by introducing message passing interface(MPI)-based master-slave parallel framework. The parallel computation can be conducted using computer cluster networks，thus considerably reduce the cost and enhance the efficiency of computation. The proposed method is further illustrated with its application to the large-scale underground caverns of Xiluodu hydropower station. The back analysis results are favorable and the reliability and rationality of the proposed method are proven. Based on the surrounding rock parameters field obtained by back analysis，the current anchor support scheme and the stability of the underground cavern are assessed. Also，the stability condition in subsequent excavation is predicted；and the rational recommendations are made for the engineering design and construction，providing the parameters back analysis of underground engineering with a new method.

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EXPERIMENTAL STUDY OF VARIATION LAW OF SATURATED BROKEN MUDSTONE POROSITY DURING CREEP PROCESS

MA Zhanguo1，2，LAN Tian2，PAN Yinguang2，MA Jigang2，ZHU Fahao2

2009, 28 (07): 1447-1454 doi:

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Broken rock shows obvious creep properties. Creep causes the continuous variation of porisity as well as the seepage characteristics. The variation law of saturated broken mudstone porosity during creep process is studied by using the self-developed multiphase coupling creep test device. The results show that during the creep process of the broken mudstone，the porosity has a negative exponential relation with time，and the complete process can be divided into several obvious stages；when the load is the same，the smaller the mudstone particle size is，the smaller the variation of the mudstone porosity is，and the larger the final porosity is. As the load increases，the difference of the porosity caused by the different mudstone particle sizes becomes smaller；under the condition of the same mudstone particle size，the porosity of the mudstone has a quicker variation under bigger loads.

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CAUSES OF RIVERBED DEEP COVER AND ENGINEERING SIGNIFICANCE OF TIGER LEAPING GORGE REACH OF JINSHA RIVER

WANG Qiguo

2009, 28 (07): 1455-1466 doi:

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Tiger Leaping Gorge river reach is in the middle of Jinsha River. It has the topographic and geological conditions for construction of a leading reservoir，and the development benefit is significant. The riverbed is covered by a deep layer with the maximum depth of 250 m. The technical difficulty of constructing high dams and large reservoirs on the deep layer is great. So the research of bed cover and exploration of the feasibility of constructing high dams on the deep cover has great significance for dam site selection. Through a large number of geological survey，exploration，geotechnical test and other investigation results，the profound causes of deep cover are revealed，namely，affected by the new tectonic movement，this area vertically moved evidently and formed the well-known ancient Longpan Basin in the northwest region of Yunnan Province；the Yulong Mountain on the east side of this area has been uplifting constantly since the middle Pleistocene，the Longpan basin has been continuing to accept deposits，nowadays the river bed eventually forms a deep cover. There are eight typical alternative dam sites in this reach，the river bed deposits of two of the dam sites which are located in the upper and the lower narrows of the great canyon reach respectively are relatively shallow(thickness of 40 to 50 m)；the dam foundation should be easier to be dealt with. The river bed deposits of the Shigu，Hongyan and Shangjiang dam sites in the upper reach are the deepest(thickness of 172 to 250 m) according to the current dam construction technology. These dams can only be located on the river bed，the lowest height of these dams should be 250 m；and the technology of building high earth-rockfill dams on these sites will meet or ever exceed the present technology. The depths of the river bed deposits of Longpan，Tacheng and Qizong dam sites are almost the same(about 100 m)；there are two schemes，disposal the deposits entirely or utilization of the deposits，the construction technology of any of these schemes will meet or ever exceed the top grade technology and the technology of damming should be studied. In addition，the study of the development history of the Jinsha River valley，as well as similar projects in future site selection are important scientific and reference values.

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SOLUTION OF FOUNDATION SOIL VIBRATIONS INDUCED BY MOVING LOADS BASED ON BETTI-RAYLEIGH DYNAMIC RECIPROCAL THEOREM

CAO Yanmei，XIA He

2009, 28 (07): 1467-1476 doi:

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Based on the Betti-Rayleigh dynamic reciprocal theorem，the reciprocal property of the Green function is demonstrated；and the analytical solution of soil vibration subjected to moving loads is deduced. By means of double Fourier integral transform，the problem is firstly transformed into wave number-frequency domain，which makes it very convenient to derive the solution and furthermore to analyze the frequency characteristics of soil vibration. By successful application of the dynamic reciprocal theorem，the moving source problem is converted to the fixed source problem with receiver point moving in opposite direction，which greatly simplifies the complex analytical solution of soil/ground vibration induced by a moving load. A computer code for solving the ground responses subjected to the constant moving load and harmonic moving load is developed by using Matlab and is employed to perform a case study. The analytical results show that，for the constant moving load，the ground vibration is of typical low-frequency feature；while for the harmonic moving load，the frequency range of ground vibration is controlled by the Rayleigh wave velocity of the top layer soil；moreover，the Doppler effect appears in the ground vibrations. When the receiver is near the source path，R-wave contributes to ground vibration much more than P- and S-wave；while the receiver is far from the source path，the contribution of P-wave is more obvious.

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GROUND TEMPERATURE AND DEFORMATION LAWS OF HIGHWAY EMBANKMENTS IN DEGENERATIVE PERMAFROST REGIONS

WEN Zhi1，S

2009, 28 (07): 1477-1483 doi:

[PDF] 258 KB (1410)

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The observation data of ground temperature and embankment deformation in the permafrost regions on the Qinghai—Tibet Plateau show that most of artificial permafrost tables under the embankment decline gradually and the ground temperatures of permafrost under the embankment rise universally due to the effects of global warming and human activities. Thus，most of highway diseases induced by thaw settlement come into being. Based on the observation data of ground temperature and embankment deformation at Tangnan of Qinghai—Tibet highway and those at section K369 of Qingkang highway，the rules of transverse uneven and even deformations of embankments are summarized. The ground temperature and embankment deformation characters are analyzed；and the relationship and interaction between ground temperature and embankment deformation are presented. The observation results show that the embankment stability in the permafrost regions depends on the changes of ground temperature and ice content of permafrost under embankment，and the ground temperature status closely relates with the embankment deformation. As for the transverse uneven deformation embankment，the asymmetrical thermal regime results in the enormous difference of the artificial permafrost tables under north and south slopes；and the asymmetrical frozen and thawing state of embankment soil result in the transverse uneven deformation of the embankment eventually. The transverse uneven deformation embankment in degenerative permafrost regions results in great differential deformation between left and right embankment shoulders，which induces the longitudinal cracking disease. As for the transverse even deformation embankment in degenerative permafrost regions，there are little differential deformations between left and right embankment shoulders，thus the embankment deformation has few effects on the stability of embankment and pavement. Due to the engineering geological differences along highway，the undee deformation or local settlement will come into being in the transverse even deformation embankment.

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ASSESSMENT OF ANTI-LIQUEFACTION GROUTING REINFORCEMENT EFFECT OF TUNNEL FOUNDATION BASED ON EARTHQUAKE- INDUCED DEFORMATIONS CONTROL

HUANG Yu1，2，JIN Chen1，2，ZHUANG Zhijing1，2

2009, 28 (07): 1484-1490 doi:

[PDF] 409 KB (1131)

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At present，there are two kinds of theories for anti-liquefaction，i.e. prevention of excess pore water pressure generation and development，and reduction of liquefaction-induced deformations. Up to now，most of researches have paid more attentions to the former，while the latter one has not been fully analyzed. Therefore，focused on the latter theory for anti-liquefaction，by using a cyclic elastoplastic constitutive model，liquefaction analysis of a water intake and outlet tunnel of a power plant in Shanghai is carried out by means of finite element method based on Biot¢s consolidation theory. A numerical simulation method for earthquake-induced liquefaction deformation is proposed under plane strain conditions to assess anti-liquefaction grouting effect. The dynamic responses including displacements，accelerations，and excess pore water pressures of tunnel foundation before and after reinforcement are analyzed. It is proved that the liquefaction deformations of the tunnel foundation can be effectively reduced by the proper anti-liquefaction measures. Some scientific suggestions for aseismic designs of this project are proposed based on the results of numerical simulation，and they can provide good references for liquefiable ground treatment of other similar projects.

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FLUID-SOLID COUPLING CHARACTERISTICS AND STABILITY ANALYSIS OF SOIL-ROCK MIXTURE SLOPE IN RISING AND DRAWDOWN OF RESERVOIR WATER LEVELS

XU Wenjie1，WANG Lichao2，HU Ruilin3

2009, 28 (07): 1491-1498 doi:

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Taking a soil-rock mixture slope in the middle reaches of Jinsha River for example， the fluid-solid coupling and stability characteristics during rising and drawdown of reservoir water levels are studied based on its fine geological structure model. The results indicate that during the initial impoundment period，the deformation of the ground surface is very slow，while the reservoir water level reaches certain elevation it exhibits a trend of sharp rise；the safety factor of the slope stability will decrease；and when the water level reaches a critical one it has the minimum value；hereafter it will rise with the water level rising；the sudden drawdown of the reservoir water level does affect the stability of the slope greatly；and the decreasing value of the safety factor will increase with the amplitude of the drawdown of the water level. All these results will be very useful not only for the practical engineering but also for the theoretical study of the soil-rock mixture slopes in reservoir area.

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RESEARCH ON ACCUMULATED VIBRATION EFFECTS OF SURROUNDING ROCK IN BLASTING EXCAVATING ANCHORAGE TUNNEL FOR SUSPENSION BRIDGE

WU Congshi1，LI Gaohui1，GUO Yunkai1，WANG Qi2，XIAO Bo1

2009, 28 (07): 1499-1505 doi:

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Based on blasting excavation in anchorage tunnel of Aizhai suspension bridge，the development laws of damage degree and loose ring of surrounding rock under different blasting loads are obtained by acoustic wave testing method. The corresponding relation between the damage degree of surrounding rock and the peak particle velocity(PPV) of vibration is discussed. Moreover，the threshold which leads to accumulative damage to rock mass is discussed；and a comparatively complete description of the development of damage degree and loose ring of surrounding rock is given. On the basis of above-mentioned researches，a reasonable control index of blasting vibration velocity is obtained. It is shown that not only the disturbance of single blasting on the surrounding rock should be controlled during blasting construction of anchorage tunnel，but the emphasis should be put on the accumulative vibration effect of surrounding rock induced by frequent short-distance blasting；and the corresponding control measures should be taken. When the PPV of the surrounding rock is controlled in the range of 3–6 cm/s；the maximum thickness of the loose ring of the surrounding rock is about 2.3 m；and the average damage degree of the surrounding rock is 0.15. When the PPV of the surrounding rock is less than 2 cm/s，the accumulated damage degree of the surrounding rock is not obvious，which can be regarded as the threshold of blasting vibration accumulated damage in this project.

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VARIABLE MODULUS ELASTOPLASTIC STRENGTH REDUCTION METHOD AND ITS APPLICATION TO SLOPE STABILITY ANALYSIS

YANG Guanghua1，2，ZHANG Yucheng1，2，3，ZHANG Youxiang2

2009, 28 (07): 1506-1512 doi:

[PDF] 245 KB (1607)

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At present，only the strength parameters are reduced when the strength reduction method is used to analyze the slope stability；moreover，the ideal elastoplastic model is used. This method is mainly utilized to obtain the safety factor of slope stability. In elastic stage，it adopts the linear elastic model and elastic modulus is not reduced，so the nonlinearities of rock and soil are not considered fully before yielding. The deformation calculated by strength reduction method based on the ideal elastoplastic model is smaller. On the basis of the Duncan-Chang¢s model，variable modulus elastoplastic strength reduction method which reduces the elastic modulus in elastic state is proposed；and more practical deformation field can be obtained by this method. The variable modulus is obtained according to the simplified nonlinear constitutive model of soil. By comparing with the theoretical solution for strip foundation and the in-situ loading test results，the rationality of the new method is proved. The method is applied to the calculation of slope engineering deformation，and the relation between deformation and safety factor is hoped to be established to make the field deformation monitoring more reasonable. Meanwhile，it is easier to get the safety factor based on the deformation mutation calculated by the ideal elastoplastic model. It is proposed that the ideal elastoplastic model can be used to determine the safety factor，and the variable modulus elastoplastic model to calculate the deformation field.

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《岩石力学与工程学报》近年初显进步

2009, 28 (07): 1513-1513 doi:

[PDF] 197 KB (795)

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