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2008, 27 (S1): -2590 doi:
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FIELD EVIDENCE AND EXPERIMENTAL RESEARCH ON LOCALIZED
DEFORMATION BANDS IN HIGH-POROSITY ROCKS

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2008, 27 (S1): -2593 doi:
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Field and experimental results of localized deformation bands in high porosity rocks such as compaction bands，shear bands and dilation bands are introduced. The shear bands discussed here are small faults of outcrops in high porosity sandstones with displacements of a few millimeters to a few centimeters. The porosity of compaction bands is lower than that of the wall rocks. The compaction bands have strong weathering resistance and can block the fluid transmission. They bands are correlated to water and petroleum industry，and have practical significance to the storage of nuclear wastes and design of nuclear depots. Further more，they are perpendicular to the maximum principal stress，and correspond to the first shelf of the s-e curves of the symmetric triaxial compression tests under low ambient pressure. From the observation of acoustic emission(AE)，the AE concentration at the lower end of the sample moves toward the center of the specimen with the increase of the differential stress，which corresponds to the formation of the compaction bands. This phenomenon is in agreement with the observation of sample sections under different confining pressures. If keeping on loading，the brittle rocks finally fail. So the compaction bands are localized deformations that appear in the brittle-ductile transition. On the contrary，the porosity of dilation bands is quite bigger than the surrounding rocks. Thus dilation bands are perpendicular to the minor principal stress，accompanied by shear bands. The research of localized deformations has been greatly concerned by geosciences researchers recently，and becomes one of the hot issues in the study of rock mechanics and crust deformation.

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STUDY OF COUPLING MODEL OF FREEZING POROUS MEDIA

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2008, 27 (S1): -2604 doi:
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Based on analysis of the water phase change process in porous media，the volumetric ratio of pore water to pore ice versus temperature is studied. A mathematic relation to describe saturated degree of pore water and pore ice undergoing freezing condition is suggested. Through the introduction of effective pore pressure concept，a coupling model based on theory of porous media is studied to simulate the variation of effective pore pressure under low temperature situation. Formulae to be able to calculate the thermal volumetric dilation coefficient of saturated and unsaturated porous media are employed to describe swelling and shrinkage characteristics of freezing porous media. The comparison results between experimental data and simulated solution validate the correctness of the proposal model in this research. It also indicates that this model could simulate the reasonable solution of effective pore pressure and skeleton stress and describe the swelling and shrinkage deformation feature. Therefore the suggested coupling model is a reasonable and effective approach for the study of the deformation and stress of freezing porous media.

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STUDY ON CONSTITUTIVE EQUATION OF ROCK RHEOLOGICAL MODEL WITH THERMO-MECHANICAL COUPLING EFFECTS

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2008, 27 (S1): -2610 doi:
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In high-level radioactive waste deep geological disposal and deep mining，rock will exhibit rheological behavior under long-term thermo-mechanical coupling effects. In this paper，the rheological characteristics of three common components(elastic component，viscous component and plastic component) under thermo-mechanical coupling effects are discussed and the corresponding assumptions are made. Then，based on Nishihara model，the corresponding creep equation，unload equation and relaxation equation of Nishihara model under thermo- mechanical coupling effects are derived respectively. When the temperature factor is ignored，these equations will degrade to the original Nishihara model equations. These constitutive relations can broadly forecast the rock rheological failure time under specific temperature conditions，and the temperature change of the rock will reduce the rheological failure time. Normally，the greater the rate of temperature change is，the shorter the failure time of rock is. The approximate analysis indicates that the variable magnitude is comparative，namely，the change rate of temperature increase of one order of magnitude，the rock ultimate failure time will be shorted with one order of magnitude.

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ANALYTICAL METHOD OF ROCK MASS PARAMETERS WITH MICROMECHANICAL DAMAGE THEORY

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2008, 27 (S1): -2617 doi:
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Some difficulties are found on the current methods to determine rock parameters. By combination of intactness index of rock mass with microcrack density，the analytical method of rock mass parameters is obtain on the micromechanical damage theory. The Taylor method and the generalized self-consistent method are used combining with practical examples and some statistics；and the method is modified according to calculation results combining with BQ method when the intactness index of rock mass is less than 0.5. The results show that it is reasonable and useful in avoiding artificial influence and experience differences of traditional methods.

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STUDY OF METHOD OF COMPREHENSIVE EVALUATION FOR PARAMETERS OF CONSTITUTIVE MODEL OF ROCK MASS

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2008, 27 (S1): -2624 doi:
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[PDF 299 KB] (1712)

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Due to the limit of single index in the analytical method of sensibility，comprehensive assessment model of attribute recognition based on entropy weight of sensitivity is obtained. The assessment method including various appraisal indexes is used to the global analysis of the sensibility of constitutive models parameters. Also，the method for the sensibility of constitutive model parameters may give a new access. By combing with cohesion weakening and frictional strengthening of brittle rock mass，the assessment method mentioned above is used for the sensibility analysis of constitutive model parameters of surrounding rock mass in the auxiliary tunnel of Jinping II hydropower station. The results show that the main influence factors on deformation and plastic zone of surrounding rock mass are final internal friction angle，initial cohesion and elastic modulus；the next are residual cohesion，critical plastic strain of internal friction angle，initial internal friction angle and critical plastic strain of cohesion；the minor influence factors are Poisson¢s ratio and tensile strength. Based on the results，more attentions should be paid to final internal friction angle，initial cohesion and elastic modulus in similar positive and back analysis and studies in the auxiliary tunnel and diversion tunnel of Jinping II hydropower station.

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RESEARCH ON TRIAXIAL CREEP PROPERTIES AND CREEP MODEL OF COAL CONTAINING GAS

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2008, 27 (S1): -2631 doi:
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[PDF 198 KB] (1304)

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The research on triaxial creep properties of coal containing gas is the important aspect of understanding the interactional relationship between gas and coal in the course of outburst. At present, there are few reports on triaxial creep properties of coal containing gas，so it is necessary to further research triaxial creep properties of coal containing gas deeply. By using self-developed creep experimental apparatus，a series of triaxial creep experiments on coal containing gas have been performed with coal samples which were taken from Songzao Coal Mine in Chongqing. The experimental results indicate that the triaxial creep properties of coal containing gas have a good regularity. In terms of the triaxial creep properties of coal containing gas，a modified Nishihara model under triaxial stress condition has been built by improving the model parameters of Nishihara. Moreover，the creep equations under triaxial stress condition have been deduced from the modified Nishihara model，and each parameter of the equations has been achieved by fitting the experiment results. The prediction by the model is in agreement with the experimental data is experimentally validated. The research shows that the triaxial creep equations from modified Nishihara model can reflect effectually the creep properties of coal containing gas.

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MECHANISM STUDY OF SHEARING SLIPPAGE DAMAGE OF NATURAL FRACTURE IN HYDRAULIC FRACTURING

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2008, 27 (S1): -2637 doi:
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hearing slippage damage and opening mechanism of natural fracture during the process of hydraulic fracturing in naturally fractured reservoir are studied by theoretical analysis，experimental validation and example analysis. theoretical analysis shows that horizontal differential principal stress，approaching angle and coefficient of friction are the main factors that cause fracture shearing slippage damage. In the condition of low horizontal differential principal stress，low approaching angle or low coefficient of friction，shearing slippage damage of natural fracture tend to happen under the influence of hydraulic fracture. The degree of natural fracture opening is determined by horizontal differential principal stress and features of rock mechanics. Experimental results show that after interaction with hydraulic fracture，the previously closed natural fracture opens and the shearing slippage damage happens in the condition of low horizontal differential principal stress or low approaching angle，while in the condition of high horizontal differential principal stress and high approaching angle，the natural fracture is filtered and there is no shearing slippage damage. Fracture opening boundary and shear slippage boundary are given out through example analysis，and the utmost containment of natural fracture is described. The example analysis shows the utmost containment of natural fracture decreases while approaching angle increases.

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RESEARCH ON DEFORMATION AND FAILURE MECHANISM OF THE TALUS SLOPE LOCATED AT LEFT RIVERBANK AHEAD OF THE DAM OF ZIPINGPU HYDRAULIC PROJECT

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2008, 27 (S1): -2642 doi:
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[PDF 392 KB] (1048)

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The stability of the talus slope，which is located at the left riverbank ahead of the dam of Zipingpu hydraulic project，is extraordinarily important during the reservoir operation. Based on field investigation，the geologic background and structure character of the talus slope have been fully analyzed and specified. It is judged that the talus slope is just in the stage of slow creep deformation currently by the evolutionary rule of the slope. The chief controlling stability factors are the reservoir water effect and the earthquake effect under the reservoir working condition. And the mechanism of the reservoir water and the earthquake action to the slope are also analyzed. The paper focuses on the deformation and failure mechanism of the talus slope. The phenomenon of superficial creep deformation and submerged failure would arise and there would be four failure patterns of the talus slope during the reservoir operation. The merits and defects of the yield criterion are discussed，which are Mohr-Coulomb yield criterion and generalized Mises yield criterion used extensively in slope engineering. And the instability criterion is comprehensively analyzed. The specific criterion indexes are put forward by the convergence criteria. And then the location and shape of the most unfavourable slide surfaces are determined by the theory of strength reduction，which are located at the front slope of Dengzhan plateau. The stability of four failure patterns of the talus slope is researched by limit equilibrium method under various work conditions. The research results indicate that the local failure of the front slope of Dengzhan plateau would happen firstly and then the global failure of the talus slope would induce under the reservoir water drawdown conditions. Main attention should be paid to the stability control of the front slope of Dengzhan plateau.

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STUDY ON POST-PEAK MECHANICAL BEHAVIOUR AND STRAIN-SOFTENING MODEL OF THREE
GORGES GRANITE

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2008, 27 (S1): -2651 doi:
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Based on the conventional triaxial compression tests of the Three Gorges granite，the complete stress-strain curves under different confining pressures have been attained. The test results show that the peak and residual strengths increase，and plastic deformation of the Three Gorges granite can be improved with increasing the confining pressure. Based on the stress-strain curves of triaxial experiments，the softening law of physical property parameters is studied，and a post-peak softening numerical model is established by analyzing the relationship between the strength parameters of granite and parameters of post-peak strain softening with elasto-plastic theory and curve-fitting. Conclusion is drawn that cohesion decreases gradually and keeps almost unchangeable with the increasing of strain softening parameter in the strain-softening process of the Three Gorges granite. The post-peak softening model of granite is used in software FLAC3D to simulate the compression tests，and the numerical simulation based on the model approximately matches the triaxial experiments.

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MICROSTRUCTURE AND STRESS-STRAIN RELATIONSHIP
OF CARBONATE ROCK

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2008, 27 (S1): -2656 doi:
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[PDF 478 KB] (1317)

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Generation and development of micro-crack in carbonate rock will affect its mechanical characteristic obviously. Based on triaxial test and stereoscan photograph of carbonate rock consisting of dolomitic rock，limestone，dolomitic limestone，the relationships between stress and strain are divided into tightening phase，linear elastic deforming phase，generation and development of micro-crack phase and fracture phase. Corresponding to these four phases，the change of micro-crack shows the close of original micro-crack，stably sustained linear elastic deforming，new micro-crack generation，expanding and stably developing，and integral breaking. The experiment shows that the micro-crack begins from off-lying to circum of the pore in compression，and then to the pore and rock collapse. The development of micro-crack begins from separation fracture to shear fracture，then to occurrence of separation fracture tracking shear fracture，until fractures are penetrated. The separation fracture and shear fracture are included in initial micro-crack of carbonate rock. The rock fracture begins at the end of micro-crack，which is the stress concentration position after loading. Right round fault，contact point of grain boundary and the micro-crack density increase because of stress concentrating highly. The fracture generates when the stress reaches or approaches to the peak value，and then，crack and strain softening occur successively.

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EFFECT OF NONLINEAR DEFORMATION AT JOINT INTERFACE ON TRANSMISSION AND REFLECTION

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2008, 27 (S1): -2661 doi:
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[PDF 256 KB] (1135)

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Propagation through joint interface of SV wave is a complicated problem，and the stiffness incident angel，nonlinear normal displacement，nonlinear tangential displacement，frequency of incident wave are factors affecting the transmission and reflection coefficient. According to ray theoretical method，the transmission and reflection analytic solution of SV wave propagating through linear deformation joint are attained. Then based on the Lemaitre hypothesis of equivalent effective strain，the Goodman and Duncan models are adopted to study transmission and reflection of wave at joint interface affected by nonlinear normal deformation and nonlinear tangential displacement. The results indicate，if the SV wave is normal incident，only refection SV wave and transmission wave SV are produced；due to the effect of stiffness，the reflection coefficient will decrease and transmission coefficient will increase with the increasing of stiffness；the higher the nonlinear displacement ratio is，the faster the trendy is. The joint interface is like a low filter，the higher frequency will be easily reflected，and the lower frequency will be easily transmitted. If the incident angel of SV wave is under superior limit，the joint stiffness is related with the normal and tangential nonlinear displacements，but the influencing degree of the normal and tangential displacement is much different to every wave field，it is the nonlinear displacement that determines the effective stiffness of joint interface，and eventually determines the transmission and the reflection characterises.

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DEMONSTRATION ON DEPENDENCY OF CONSTITUTIVE RELATIONS OF SOILS WITH STRESS PATHS

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2008, 27 (S1): -2669 doi:
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[PDF 272 KB] (977)

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Based on the triaxial compression tests of clays and sands under different stress paths，it is theoretically proven according to the principle of interaction between plastic volumetric and shear strains that the constitutive relations of soils are dependent on stress paths，and the dependency of stress path is the combination of effects of the interaction between plastic volumetric and shear strains. The dependence of stress path includes not only the effect of pressure sensitivity but also shear-induced dilatancy. The results of triaxial compression tests for clays and sands under three different stress paths show that the shear yield surfaces and volumetric yield surfaces rotate with the change in stress paths. At the same time，the sizes of yield surfaces in the stress space vary with stress paths. This phenomenon is called rotational hardening. The mechanism of yield surface rotation is analyzed and it is explained that the rotational hardening is resulted from the dependency of stress path，which is essentially a reflection of the interaction between plastic volumetric and shear strains.

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STUDY ON SURROUNDING ROCK CONSTRUCTION OPTIMIZATION OF KUIGANG TUNNEL BASED ON FUNCTION ANALYSIS SYSTEM TECHNIQUE

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2008, 27 (S1): -2669 doi:
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[PDF 275 KB] (728)

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The technical-economic view is first adopted to identify the best construction method according to project management objective under certain condition based on value engineering(VE) and function analysis system technique(FAST). Then an appraising model is set up，with expert knowledge and group decision techniques. Finally，the Kuigang tunnel is discussed，which shows that this model is effective for construction scheme optimization and has the value for further study.

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EXPERIMENTAL RESEARCH ON ROCK BREAKAGE EFFECT UNDER REPEATED EXPLOSIONS

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2008, 27 (S1): -2675 doi:
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In order to explore the breakage and damage effect problems of the underground protective engineering in rock under repeated penetration and explosion by precision guided weapons，the contrastive experiments of single-time drilled explosion and secondary drilled explosion have been accomplished. The experimental results show that the explosive crater diameters by secondary drilled explosion and single-time drilled explosion respectively are approximately equal，but the depth and the breaking range of explosive crater of the former is 2 times and 1.66 times of the later under equal total amount of charge. The measure results show that the peak pressures have a large difference at the same measuring points，and the peak pressures of the secondary drilled explosion are higher than those of the single-time drilled explosion for the same measuring points. The calculation results show that the pressure damped exponential of single-time drilled explosion is 1.933，and the stress wave velocity is approximately 4 800 m/s. The conclusions，which has been obtained by calculation according to the stress wave propagation mechanism，shows that the requested thickness of protective layer for secondary drilled explosion is 1.07 times of that for single-time drilled explosion under equal total amount of charge.

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EXPERIMENTAL STUDY OF ROCK UNLOADING STRENGTH PARAMETERS BASED ON MULTIPLE FAILURE METHOD

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2008, 27 (S1): -2681 doi:
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In analyzing excavation engineering，it is of great importance to determine rock strength parameters by unloading stress path. However，strength values determined by conventional unloading tests are often with great divergence. Obviously，among all the factors，divergence of rock specimens is important. To determine unloading strength parameters of rock by a single specimen，multiple failure state method is introduced into unloading stress path；and a special loading procedure based on unloading multiple failure method is put forward for triaxial tests. In conventional multiple failure state tests，it is believed that strain control is the only feasible way to carry out loading control. However，for some confining unloading tests，of which stress-controlled loading approaches are necessary，it is difficult to realize multiple failures by a stress-controlled loading approach. In stress-controlled tests performed by a MTS 815.02 triaxial testing machine for rock mechanics，several critical difficulties such as judging the peak strengths during the tests and controlling the axial deformation during each failure state are investigated；and solutions of these difficulties are proposed. Several multiple failure tests on marble specimens under confining unloading procedures are successfully conducted in the end. It is observed that strength values obtained from this approach matched well with those from conventional unloading tests. It is shown that the proposed approach is feasible and reliable，which not only considers the stress path，but also avoids the divergence of the specimens. It is a practicable and effective method for rock unloading strength parameters determination.

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EXPERIMENTAL STUDIES AND NUMERICAL SIMULATION OF STRESS WAVE PROPAGATION IN ONE-DIMENSIONAL ROCK MASS

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2008, 27 (S1): -2687 doi:
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On the basis of detecting impact load，studies are carried on regulation of stress wave propagation in one-dimensional rock mass by experimental and numerical simulation. These studies include the vibration form of particle in intact rock mass，the effect of different impact loads on particle vibration，the vibration characteristic of particle near discontinuity，and the effect of multi-strip discontinuity on the regulation of propagation and attenuation of stress wave. The experimental results show that the regulation of particle vibration in intact rock mass is obvious，and its vibration frequency is unitary，indicating that the frequency has close relationship to the length of one-dimension rock mass. The experimental results also indicate that the particle vibration near discontinuity is magnified，and it can be attenuated through the crack if the wave length is not larger than the crack width. And with the number of discontinuity increasing，the attenuation of particle vibration is obvious. In addition，the attenuation of stress wave with space increasing is obvious. Multi-scale model of discrete element method is constructed on the basis of primary block discrete element model. The new model is used to simulate the stress wave propagation regulation in jointed rock mass，and is more rational. The result shows that the improved block discrete element model is fitful to simulate the propagation regulation of the stress wave in jointed rock mass.

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EXPERIMENTAL STUDY OF UNLOADING MECHANICAL PROPERTIES OF ROCK UNDER HIGH CONFINING PRESSURE AND HIGH WATER

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2008, 27 (S1): -2694 doi:
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In order to analyze surrounding rock stability of long alignment high overburden diversion tunnel，conventional triaxial compression tests，unloading confining pressure tests at the pre-peak and post-peak and unloading tests under high groundwater pressure on marble，sandstone and slate are conducted. Systematic contrastive studies are made on the strength and displacement in the experiment. The experimental results indicate that unloading confining pressure has important effect on the intensity of rock. The cohesion and angle of internal friction of rock reduce considerably after unloading confining pressure；the reduction is more obvious especially with water pressure. The effect of unloading confining pressure on cohesion is more obvious than that of angle of internal friction. The reduction extent of cohesion is bigger than angle of internal friction after unloading confining pressure. The effect on rock strength at the pre-peak unloading confining pressure is bigger than that at post-peak unloading confining pressure. The confining pressure of rock failure with unloading confining pressure at the pre-peak is higher than at post-peak；the effect on rock strength unloading confining pressure with water pressure is bigger than unloading confining pressure without water pressure. By unloading confining pressure with water pressure，it can weaken the effect of confining pressure on rock，which makes rock failure with higher confining pressure than that without water pressure.

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MOVEMENT RULES OF OVERLYING STRATA AROUND LONGWALL MINING IN THIN BEDROCK WITH THICK SURFACE SOIL

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2008, 27 (S1): -2700 doi:
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Stable structure of main roof couldn¢t be formed because of sliding instability and crushed support during fully-mechanized mining with top coal caving in thin bedrock and thick surface soil. By defining thin bedrock through “three belts” which are decided by strata control，it is found that “three belts” are closely related to mining height and rock mechanical properties. The overlying strata movement rules are studied by laboratory experiment，theoretical analysis，numerical simulation and in-situ measurement. The result indicates that bedrock thickness and mechanical properties and thickness of surface soil are the key influential elements for the stable structure of “stacked layer of blocks”，while the other conditions remain the same. The thick clay in surface soil that owns large permissible bearing capacity can form steady structure with the composition of thin bedrock，so it reduces minimal thickness of bedrock to ensure structure stability. According to the practical condition of the first face in Sima coal mine，the mechanical model of structure which is combined by thick clay and thin bedrock is built. It shows that the immediate roof and top coal can be regarded as “similar zero rigid body” by using plastic and elastic combination body. Through designing the mechanical features of surface soil and change of thickness in bedrock，the rules of the vertical stress，bearing pressure and top coal convergence are simulated and studied，and the minimal bedrock thickness is ensured. The minimal bedrock thickness is about 40 m in loose surface soil condition；when the clay thickness is 40 m，the minimal bedrock thickness is 20 m；and when the clay thickness is 30 m，the minimal bedrock thickness is 30 m. Through the study，it can be deduced that safety mining is feasible at the first face，and it has been proven successfully in mining experiment.

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EXPERIMENTAL RESEARCH ON THERMAL EFFECT OF TENSILE MECHANICAL PROPERTIES OF GFRP REBAR

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2008, 27 (S1): -2707 doi:
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Temperature is an important factor influencing the mechanical properties of glass fiber reinforced plastic(GFRP) material，and it should be considered sufficiently. Based on experiments，the mechanical properties of GFRP rebar at different environmental temperatures ranging from 20 ℃ to 120 ℃ are studied. The load is applied by MTS322 electro-hydraulic servo-controlled testing machine，and the test temperature is controlled by the circumstance box. Twenty six GFRP rebars are adopted in this test，which are 10 mm in diameter and 400 mm in the efficient pull-out length. The following conclusions can be drawn from the experiments. Firstly，during the loading process，white fleck cracks appear on the surface with hard noise caused by damage. The noise becomes louder with the load increasing. Flake crack in a big range is the main failure mode，and the rupture on a section is a rare occasion. Both are brittle failure modes. Secondly，the mechanical properties of GFRP rebar are sensitive to temperature. The ultimate tensile strength，the initial tensile Young¢s modulus，the yield strain and the ultimate elongation ratio all decrease with the temperature increasing，but the elastic modulus after tensile yield is reverse. Thirdly，the stress-strain relationship of GFRP rebar between 20 ℃–80 ℃ is bilinear. With the temperature increasing，the yield point reduces gradually. At the temperatures of 100 ℃ and 120 ℃，the stress-strain relationship is linear. By the analysis of experiment，considering thermal effect，the stress-strain relationship of GFRP rebars and the relationships between correlative parameters and the temperature have been established. A formula has been developed to calculate the ultimate tensile strength of GFRP rebar. The experimental results supply scientific foundations for the GFRP rebars¢ application at different temperatures.

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STUDY ON PHYSICAL MODEL TEST AND DEFORMATION LAW OF
SURROUNDING SOIL FOR SHALLOW METRO STATION CHAMBER

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2008, 27 (S1): -2715 doi:
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[PDF 359 KB] (1209)

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According to conceptual model theory of equivalent material，a large-scale physical model test for excavation of metro station chamber was realized. The excavation process of connection tunnels between metro station chamber and existed double TBM tubes had also been simulated；the ground settlement，soil deformation and displacement of characteristic points around tunnels were also studied. In addition，the influences of the cast-in-place piles to reduce the soil displacement have been simulated. Dynamic mechanical behaviors and deformation laws were obtained. Some conclusions have been obtained. The results may be useful to the construction and expanding excavation of metro station space between existing double TBM tubes.

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STUDY ON FRACTAL CHARACTERISTICS OF SANDSTONE DAMAGE-FRACTURE UNDER CT TEST CONDITION

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2008, 27 (S1): -2721 doi:
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Firstly，cracks located in the CT images scanned at the stages of stress changing from 20.59 MPa to 31.03 MPa are obtained from the images by means of CT data about sandstone under the uniaxial compression condition. The filter designed in the paper is used to pick up cracks，in which the threshold value is determined after sensitivity analysis. Based on these binary images of crack under each loading step condition，the fractal dimension of area and length of the crack in the sandstone are computed by the methods of yardstick，box-counting，island and sandbox. Finally，the relation between the fractal dimension of crack and the loading process is analyzed，and the fractal feature on the damage and fracture of sandstone is discussed through the evolution information of the fractal dimension.

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MODEL EXPERIMENTAL STUDY OF FAILURE MECHANISM AND COUNTERMEASURES OF U-SHAPED HIGH ABUTMENT WITH MASONRY-STONES

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2008, 27 (S1): -2727 doi:
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The cracking problem of high abutment is important in highway construction. Four U-shaped abutment models are built with clay bricks for the contrast study of failure mechanism. There are three models with different structural stiffeners and one is the model of common abutment. When these abutment models are loaded by filling with soil and applying vertically external forces on the surface of the filled soil，the horizontal displacements of the front wall and side wall of the models are measured by dial indicators. Through the contrast analysis of measured displacement and 3D numerical results for four models，a very obvious effect caused by the stiffeners in the abutment model is obtained. The crack loads of the abutment structure with the stiffeners will be improved obviously than the common abutment. If the inside chamfer of the abutment and U-shaped stiffeners are all adopted in an abutment model，the crack loads will be improved more than one time.

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STUDY ON WELLBORE COLLAPSE MECHANISM IN JOINTED ROCK MASSES OF HIGH-DIP-STRUCTURES BEFORE MOUNTAINS

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2008, 27 (S1): -2733 doi:
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There exist abundant oil and gas in the hip-dip structures before mountains in the West China. But borehole caving takes place frequently during drilling in the section of fractured rock masses generated by violent tectonic movements，which severely restricts the profit of exploration and development. This paper sets up the model of borehole drilled in the highly fractured rock masses according to geological situation in the Huoerguosi structure before Tianshan mountains using the software RFPA-flow. The characteristics of stress and seepage around borehole are inquired and the process of wellbore collapse is simulated，also the countermeasures are discussed. The research indicates that stress concentrates around wellbore in the direction of the minor principal stress，however，seepage occurs chiefly on the joint planes around borehole in the direction of the minor principal stress，and water head rises on the joint planes along with seepage process，which results in the collapse of surrounding fractured rock masses. The result that collapse occurs in the direction of the maximum principal stress，showing a reasonable explanation to the complex phenomenon that long axis of borehole exists in the direction of the maximum principal stress on the dip log. The research also indicates that borehole collapse is easy when seepage velocity on the joint planes is decreased，which confirms that improving the plugging performance of drilling fluid is the countermeasure. Lower water head in the hole may cause collapse of rock masses around hole in the direction of the maximum principal stress，however，over-high water head in the hole can also cause collapse of fractured rock masses in the direction of the maximum principal stress，which clarifies that controlling the upper limit of drilling fluid weight is also a necessary countermeasure. The research and result may offer reference for drilling before mountains.

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EXPERIMENTAL INVESTIGATION ON ANTI-FLOATING ANCHOR IN MODERATELY WEATHERED GRANITE

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2008, 27 (S1): -2741 doi:
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Anti-floating anchors have been widely used in China. In the design practice of anti-floating anchors，the design parameters recommended by several current standards change largely without considering the differential mechanical properties of rocks in different areas. On the project of the Great Theatre of Qingdao，the destructive pull-out tests on anti-floating anchors equipped with strain gauges were carried out. The distribution of axial force along the length of anchor and the shear stress between the grout and anchor rod were obtained. The test results indicate that the internal force distribution is not uniform，and no force exists after a certain length. The ultimate pullout resistance and the effective anchorage length of the anti-floating anchors were determined，which may be taken as reference for the design and construction of anti-floating anchors.

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COMPARISON STUDY OF JRC-JCS MODEL AND DIRECT SHEAR TEST

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2008, 27 (S1): -2747 doi:
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Shear strength of structural plane has an important influence on stability of engineering rock mass. It determines the probability of engineering rock mass failure. JRC-JCS model based on directional statistical measurement technology of roughness coefficient of structural plane can consider the effect of geology and environment. For structural planes with few filling or without filling，JRC-JCS model with advantages of low cost，fast estimation and easy manipulation can provide a practical method to obtain the shear strength parameters of structural plane in hard rocks. The model has been applied to fifty rock projects in order to get the shear strength parameters of structural planes. To analyze the reliability of estimating the shear strength parameters of structural planes with JRC-JCS model，the shear strengths of natural rocks with structural plane under dry and saturated conditions are measured by direct shear test and empirical estimation with JRC-JCS model. Then，the test results of shear strength are compared. The results show that the shear strength parameters estimated by JRC-JCS model and direct shear test agree well with each other on the basis of the directional statistical measurement，the analysis of JRC scale effect and the consideration of reduced JRC during the course of shear；and JRC-JCS model can estimate the peak friction angle of structural plane well.

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EXPERIMENTAL STUDY ON ROCK BREAKING MECHANISM OF COAXIAL SWIRLING DUAL-JET

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2008, 27 (S1): -2754 doi:
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[PDF 341 KB] (1232)

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The coaxial swirling dual-jet inherits both the large impact area and deep penetration depth of swirling jet and round jet respectively，which is generated by placing a coaxial round jet at the axis of annular swirling jet. Under high confining pressure，the cavitation incepted by strong shear of the two jets can enhance breaking rock efficiency. Three parameters，nozzle distance，jet pressure and ambient pressure，are studied and the rock breaking mechanism is deduced. The experiments demonstrated that the rock breaking volume increases first then decreases with the increasing of nozzle distance，so an optimal nozzle distance exists¢ which is 13 times of equivalent nozzle diameters. Nozzle distance also has great impacts on the rock penetration depth. With the increasing of nozzle distance，the penetration depth increases first then decreases. The rock breaking area is affected by nozzle distance too. With the increasing of nozzle distance，rock breaking area has almost linear increasing trend. The increasing of jet pressure can largely increases rock breaking volume. When the jet pressure is below than 15 MPa，the rock breaking volume hardly increases；when the jet pressure is over 15 MPa，the rock breaking volume greatly increases. Penetration depth was largely increased with the increasing of jet pressure. The rock breaking area was insensitive to jet pressure. The rock breaking volume and penetration depth will sharply decrease with the increasing of ambient pressure. But the rock breaking area is insensitive to confining pressure. The rock breaking of coaxial swirling dual-jet is a combination of cavitation erosion，jet erosion，shear breaking and pressure pulsation breaking.

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3D COALFIELD SEISMIC INTEGRATED INTERPRETATION TECHNIQUE IN COMPLEX GEOLOGICAL CONDITION

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2008, 27 (S1): -2760 doi:
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General 3D coalfield seismic interpretation commonly uses kinematics information in time domain，and it is not suitable for complex geology condition. If it is applied to complex underground geological structure，the interpretation precision and reliability would be affected because of lack of information. It is an important measure to integrate more information and more subject to increase interpretation precision under complex geological condition. It means that seismic kinematics should combine with dynamics；seismic should combine with geology and well logging，and time domain should integrate with depth domain. The seismic attribute，3D visualization，log constrained seismic inversion，time-depth conversion based on space-varying velocity are the key techniques of 3D seismic integrated interpretation. Taking Huainan coalfield as a case，the torsional structure and neotectonic movement are discovered by 3D visualization technique；collapse column is detected by kinematics and dynamics feature of seismic attribute，and the space variety of coalseam and coal-bearing strata are predicted by logging constrained seismic inversion and space-varying velocity time-depth conversion. According to the discovery of the complex geological structure and the prediction result of coalseam，the coalfield mining condition and reserve can be reappraised. The integrated interpretation techniques use a lot of geological information，so the exploration cost can be reduced under the complex geological condition，and it will become the main technique to solve coalfield complex structure and lithology exploration.

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RESEARCH ON EFFECT OF SUSPENDED CUT-OFF WALL WITH SIMULATION TEST

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2008, 27 (S1): -2766 doi:
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The model test for simulating effect of suspended cut-off wall on preventing seepage failure in two-layer foundation of levee has been carried out in a sandbox. The experimental results for different suspension depths have been obtained. The results indicate that the suspended cut-off wall has significant effects on the prevention of seepage failure as well as reduction of seepage quantity in two-layer foundation of levee which is composed of upper clay and lower silt soil during the stability seepage. For the two-layer foundation of levee，sand spring occurs at the weak positions，then contact erosion occurs at the interface of silt clay and silt. When the water level rises continuously and exceeds the critical water level，the seepage channel develops from downstream to upstream，and runs through the whole soil. At this time，the seepage failure occurs. Research indicates that，under the function of suspended cut-off wall，the condition that seepage failure occurs has been improved，for example，the water level rises greatly，critical apparent hydraulic gradient increases obviously，the seepage quantity reduces distinctly，and the pore water pressure changes evidently. The results show that the suspended cut-off wall can prevent the seepage failure effectively，at the same time，it is constructed easily and acceptable in economy，so it is worth applying in project.

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NUMERICAL CALCULATION OF CFRD BASED ON BINARY MEDIUM MODEL OF ROCKFILL

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2008, 27 (S1): -2772 doi:
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For high concrete faced rockfill dam，the grain crushing is so large in high stress field which may increase the deformation rate of dam body that it should be considered in numerical calculation. Because the traditional constitutive model for rockfill material can not reasonably reflect the effects of grain crushing，the calculation deformation of dam body is much different from its measured deformation. Tianshengqiao CFRD (concrete faced rockfill dam) is the first 200 m class high dam which has abound observation date in the similar of type built dam in China. Based on binary medium model considering grain crushing of rockfill material，the stress-strain behavior of dam body is analyzed by planar finite element method(FEM). Because the dilatancy quantity of dam materials will decrease and their corresponding shrinkage quantity will increase when the grain crushing is considered in numerical calculation，the calculation results of the suggested model is more accurate in qualitative analysis and more reasonable in quantitative analysis. It could be better to be used simulate stress-strain behavior of CFRD，especially high CFRD.

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STUDY ON COMPUTING METHOD OF FRACTALDIMENSION OF RGB IMAGE

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2008, 27 (S1): -2779 doi:
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In calculation fractal dimension of color surface，in order to adequately consider relative information of color surface，an idea that component of RGB images—R(red)，G(green)，B(blue) is recomposed into color vector is presented. By connecting vector endpoint of different pixels to construct a coarse color surface，based on modified projective covering method，the dimension of the surface is computed，and the comparison with traditional fractal dimension of gray-scale surface is made. The result discloses that comparative to computing method of gray surface dimension，by saving R，G，B component of different pixels of RGB image in 3D matrix，the computing method of color surface dimension catches more sufficiently color information of true-color image. Thus，it can better overcome the limitation and defect——lack of consideration towards hue and saturation during the course of dimension computation of gray surface.

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ANALYSIS OF DYNAMIC FACTOR OF SAFETY OF ROCK SLOPE WITH BLOCK ELEMENT METHOD

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2008, 27 (S1): -2785 doi:
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Block element method(BEM) for dynamic analysis is developed and applied to historical analysis of seismic stability of rock slope. Combining the idea of viscoelastic boundary with the theory of BEM，the artificial boundary condition of BEM is formulated，which can eliminate the reflection of the seismic waves on the boundaries of the computational domain. Viscoelastic boundary has the merits of numerical stability and convenience to integrate with computational program. The inertial force of rock block is firstly computed by its acceleration obtained by dynamic analysis，then is decomposed according to supposed sliding mode into sliding force and force perpendicular to the supposed sliding direction，which is used for calculating resistance force. The factor of safety against sliding is defined by the ratio of the resistance force to the sliding force. When the seismic process finishes，the time-history curve of factor of safety against sliding of rock block can be obtained. The application of the intake slope of Xiaowan Hydropower Station demonstrates the capacity of this method.

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STUDY OF ROCK-FALL MOTION ON SLOPE

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2008, 27 (S1): -2793 doi:
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In the design of rock-fall protection project，the proper location and reasonable intercepting height of the intercepting system are most important factors，which directly are concerned with success or failure of the system. There are many factors which can influence the system，but among them the stone motion track on slope plays a key role. Based on the elasto plastic contact theories，the calculation models of restitution coefficient both in normal and tangential impacting directions are studied. Then the fundamental kinematical equation is applied to studying the stone motion characteristics，and the related formulas are deduced. At last，by calculating and analyzing a specific example，the theory is proven to be reasonable.

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DDA WITH STRENGTH REDUCTION TECHNIQUE AND ITS APPLICATION TO STABILITY ANALYSIS OF ROCK SLOPE

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2008, 27 (S1): -2799 doi:
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An extension version of discontinuous deformation analysis(DDA) is presented. In order to calculate the safety factor of a slope，the strength reduction technique is accomplished in the self-developed DDA program. In the extended DDA method，the maximal curvature of the relationship curve of the displacement and the reduced factor is proposed as the failure criterion in the slope stability analysis，which overcomes the drawbacks of the criterion of displacement dramatic increasing. And then，the stability of a rock slope during the falling of the reservoir water level is analyzed based on the failure criterion. The relationship between the safety factor of the slope stability and the speed of the falling of the reservoir water level is obtained. Finally，the excavation sequence of the high slope of Xiaowan Hydraulic Project is simulated using the program and the stability of the excavated slope is analyzed.

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DEFORMATION MECHANISM ANALYSIS OF A CUTTING SLOPE ON 220 KV YANJIN TRANSFORMER SUBSTATION

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2008, 27 (S1): -2807 doi:
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Focused on a cutting slope on 220 kV Yanjin Transformer Substation，the study is carried out to find its movement characters. Through site investigation，deformation investigation and analysis，laboratory test，stress-strain behavior analysis and numerical modelling，three factors are suggested as follows：(1) excavation provides enough opportunity movement；(2) the strength of intensely and completely decomposed mudstone decreases evidently for slaking，softening and argillation in water，and the completely decomposed mudstone is strain softening；(3) V-shaped topography could provide channel for the ground water，and induce adverse hydrodynamic and hydrostatic water pressure. The deformation of cutting slope is retrogressively trigged by excavation，and the weak mudstone controls the slope stability. Slope deformation can be classified into four stages over time：(1) at the first stage，the elastic deformation adjacent to the cutting surface is released due to unloading during excavation；(2) at the second stage，when excavation is almost completed，the slope toe fails because of gravity and concentrated stress induced by excavation；(3) at the third stage，when excavation is completed，cracks appear at crown，and the shear strength of mudstone，which is reduced by groundwater，decreases further due to the increase of shear strain triggered by excavation；and (4) finally，the mid part of the over-layer is tensilely cracked，and the over-laver moves accompanying the slide of underlain mudstone induced by hydrodynamic and hydrostatic pressure，gravity，and dominating action of the softened mudstone. This study suggests that more attention should be paid to the mudstone in the future engineering for its softening characters，and the way of deformation mechanism investigation provides some suggestions for the similar studies.

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INFLUENCE OF APPROACH ON LOCATING PHREATIC SURFACE HYDROUS SLOPE STABILITY ANALYSIS

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2008, 27 (S1): -2814 doi:
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After impoundment of reservoir，there would be a large amount of hydrous slopes，with stability being influenced of the change of the water level. As a common practice，the present slope stability analysis would begin with the determination of phreatic surface，and then the stability would be analyzed. Therefore whether the approach to locate the phreatic surface is appropriate or not is essential to the accuracy of the stability analysis. However the method of roughly generalizing the phreatic surface of the bank slope through experience is commonly adopted，so the correct calculation method is an urgent problem. In this paper，the phreatic surface is calculated through seepage calculation and generalized through experience respectively. Then the effects of these two methods on the stability analysis are compared and analyzed to determine the inaccurately of the method through experience. From the calculation example，the inaccuracy rate through experience is above 10%.

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METHOD OF CHANCE CONSTRAINED ON PROGRAMMING OF SLOPE STABILIZATION

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2008, 27 (S1): -2820 doi:
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[PDF 263 KB] (959)

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There are two aspects influencing on stabilization planning，which are theoretical analysis method and selection of the mechanical property parameters of soil and rock mass. Limit equilibrium theory is one of the normal mathematical approach，in which physics meaning is determinacy，in stability analysis of soil and rock mass. But the result of stabilization computation and the potential slip surface are intensely affected by the mechanical property parameter. The randomness of the mechanical property parameter is only considered in the normal failure-safe analysis model but the restraining characteristic of the determinacy mathematical model and random change of the mechanical property parameter are not contained. The planning of slope stability with method of chance constrained theory means that the restraining conditions of the determinacy mathematical model and randomness of the mechanical property parameter are inverted as the equivalence class of failure-safe analysis model. So the reliability index of slope could be obtained under the condition of the defined slip surface based on searching calculation. In the paper，the analysis idea is shown with an example.

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RESEARCH ON SURFACE EXFOLIATION CHARACTERS AND DIFFERENCE OF FORMATION MECHANISM BETWEEN TWO KINDS OF ROCK MATERIALS

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2008, 27 (S1): -2825 doi:
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For the two kinds of rock materials，grey mediun-grained clay feldspathic sandstone and microlite dolomitic marble，by means of Schmidt hammer test，X-ray diffraction，scanning electron microscope，the formation mechanism of exfoliation and its effect on the mechanical properties of rock surface are analyzed. The results show that the exfoliation has an important effect on the mechanical properties of rock surface. It has an obvious difference of mechanical properties variations between different kinds of rocks with different exfoliation shapes. The flaking and scale exfoliations of the two kinds of rock materials have more effects than granular exfoliation of microlite dolomitic marble on the mechanical properties of rock surface. This difference is caused by the different mineral components and textures of the two kinds of rock materials.

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RESEARCH ON DEFORMABLE CALCULATION METHOD BASED ON THREE-DIMENSIONAL BLOCK DISCRETE ELEMENT

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2008, 27 (S1): -2832 doi:
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[PDF 655 KB] (1471)

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Deformable block discrete element model is studied on the basis of three-dimensional rigid block discrete element method，and corresponding program is developed for this method. Each block element is considered as an elastic body，and finite element grids are generated. Each node displacement in the deformable block is calculated under the condition of force boundary. Jointed elements are constructed to transfer the force and displacement between adjacent deformable blocks. Jointed elements in the method can represent practical joint characteristics and strength in rock engineering. This method reflects the characteristics of continuous calculative method before breakage of structural plane. If the structural plane is broken，the jointed element will change into the normal and shear springs at the preset joint. So it also reflects the characteristics of discontinuous calculation method. In addition，the jointed element has certain thickness，so the calculative parameter can be determined by those of the actual joint. It embodies the improvement to rigid block discrete element method. Compared with rigid block discrete element method，this method can reflect the deformable character of rock，such as Poisson¢s effect of rock mass and the propagation velocity of stress wave in three-dimensional rock mass. Compared with finite element method(FEM)，it presents the jointed characteristics of rock mass more sufficient than FEM，and allows large displacement of element. Moreover，it can simulate the failure evolution process of the structural surface. Compared with the former discrete element model of deformable bodies，it overcomes the complicated calculation induced by finite difference method and is also three-dimensional discrete element model. So it provides an available numerical analytical method for geotechnical engineering.

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RESEARCH ON MECHANICAL CHARACTERISTICS
OF HIGH-STRENGTH REINFORCED CONCRETE SHAFT
LINING IN DEEP ALLUVIUM

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2008, 27 (S1): -2841 doi:
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The alluvium traversed by shaft in mine becomes thicker and thicker along with the development of deeper mine construction. The high-strength reinforced concrete shaft lining is adopted in deep alluvium. For high-strength reinforced concrete shaft lining，its mechanical characteristics are analyzed by experiment and theory. The experimental results show that the ultimate bearing capacity of the high-strength reinforced concrete shaft lining is much great. The factors that influence the ultimate bearing capacity of the high-strength reinforced concrete shaft lining are，in turn，the strength grade of concrete，the ratio of thickness to radius and the ratio of reinforcement. Under the condition of uniformly loading，when the strength of concrete increases 10 MPa，the ultimate bearing capacity of shaft lining increases 4 MPa. However，the effect of the ratio of reinforcement on the ultimate bearing capacity of shaft lining is very small. When the shaft lining comes to failure，there is an inclined crack in the high-strength reinforced concrete shaft lining，and the circumferential reinforced steel bars bend at the inclined crack. The failure of high-strength reinforced concrete shaft lining is compression-shear mode，and the angles between the failure plane of concrete and the direction of the maximum principal stress are 25°–30°. Using the linear softening constitutive model and Mohr-Coulomb strength criterion，the theoretical formula of ultimate bearing capacity is deduced for the high-strength reinforced concrete shaft lining. The results obtained by formula agree well with the experimental data.

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A NUMERICAL TEST METHOD FOR MESOMECHANICAL CHARACTERISTICS OF JOINTED ROCK SAMPLES

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2008, 27 (S1): -2848 doi:
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The nature and property of jointed rocks are very complicated for the various geological actions and a lot of cracks. It is very difficult and costly to carry out physical model test to study the mechanical properties of jointed rocks in depth. Therefore，numerical model test with natural advantage is applied to the research on jointed rocks，but the veracity may be doubted. A new method has been proposed，which considers physical and numerical model tests. The method can take advantage of the two kinds of experiments，facility of physical model test and low cost of numerical test. Based on this idea，a numerical model has been set up，and then its facilities have been validated by the results form special and typical physical model tests. Finally，the numerical model is used to carry out tests on jointed rock samples to study the mechanical properties of jointed rocks. In addition，it has been verified by numerical model test；and the influences of the friction coefficient on crack insides and confining pressure on the first principal stress，deformation，and failure model of jointed rock mass sample，are also discussed.

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PRIMARY RESEARCH ON MECHANISM OF DEEP FRACTURES
FORMATION IN LEFT BANK OF JINPING FIRST STAGE HYDROPOWER STATION

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2008, 27 (S1): -2855 doi:
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At first，the slope geological conditions as well as dam site geostress and deep fractures in the left bank of Jinping first stage hydropower station have been investigated. Then the evolvement and development of Jinping first stage hydropower station valley are simulated by using distinct element codes UDEC and 3DEC；and stress field，deformation and unloading zone distribution of valley are comprehensively analysed. Based on the simulation results and the deformation of present slope，it is considered that the deep fractures at elevation 1 700– 1 850 m at the left bank of Jinping first stage hydropower station are the yield results due to valley erosion to elevation 1 830–1 730 m at the special geological structures，such as soft upside rock and hard underside rock，the dip direction of rock reverse against slope，wide upside and strait underside of valley and the high regional tectonic stress of Jinping first stage hydropower station valley. From the view of engineering geology，the effect of deep fractures at the left bank on the slope stability is different from tectonic faults，and its influence is limited and local. Be sure not to disturb rock masses under elevation 1 680 m is the best way to keep engineering slope safe and to prevent the deep fractures from developing.

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STABILITY ANALYSIS OF SURROUNDING ROCK OF LARGE UNDERGROUND POWERHOUSE CAVERN GROUP

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2008, 27 (S1): -2864 doi:
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Jinping first stage hydropower station is a concrete double-curvature arch dam with a maximum height of 305 m. It has a total capacity of 360×104 kW，the total reservoir capacity is 77.6×108 m3，and the regulating capacity is 49.1×108 m3. It is the highest in the world，and its design complexity is at the world¢s top level. In response to the low surrounding rock classification，developed structure planes，high geostress and massive underground cavern group，the 3D nonlinear elastoplastic damage finite element method is applied to analyze and compute the stability of underground cavern groups to make certain the rationality of the layout of underground cavern group，the sequence of construction and support parameters of surrounding rock. By analyzing and comparing the numerical simulation results and geomechanical model experimental data，it is indicated that the numerical simulation results agree well with the experimental data. The stability of the underground cavern group satisfies the requests of design.

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MECHANICAL CHARACTER ANALYSIS AND IN-SITU MONITORING FOR PORTAL SECTION OF HALF-BURIED TUNNEL

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2008, 27 (S1): -2873 doi:
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Due to the complicated structure and the influence of multiple disturbance of surrounding rock in period of construction，the mechanical behaviors of portal section of half-buried tunnel differ greatly in different construction stages，which brings great difficulties to construction and monitoring. According to the proportion of horizontal and vertical loads borne by the structure，the portal of the half-buried tunnels is divided into three types，i.e. thrust portal，compression portal and combined thrust-compression portal. Numerical simulation is carried out to research the distribution and the developing law of displacement and stress under different conditions. By analyzing the mechanical characters，the weakest positions are detected and the essential monitoring items are also listed in different stages of construction for different types of structures. Based on these results，in-situ monitoring is carried out in four actual highway tunnel engineering. In-situ monitoring results indicate that：(1) the distribution and the developing law of displacement and stress agree with the theoretical results perfectly；(2) the positions and failure modes of structures accord with the theoretical results；and (3) abnormal deformation of structures can be effectively controlled by adopting reasonable measures according to the deformation mechanism of corresponding structure under load. The presented conclusions can provide references for design，construction and in-situ monitoring of similar tunnels.

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RESEARCH ON ROCK QUALITY DETECTION OF DAM FOUNDATION IN GUANGZHAO HYDROPOWER STATION

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2008, 27 (S1): -2883 doi:
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The dam in Guangzhao hydropower station is the highest roller compacted concrete gravity dam in China at present. To check the mechanical indices of rock mass in dam foundation，analyze the reasonability of the survey and design information in early stage is analyzed，and the possibility to carry out optimization about the foundation plane of the 200 m dam in proper condition is considered，entrusted by the owner，Guiyang Hydropower Investigation Design and Research Institute has carried out overall and systematical geological detection and rock quantity research on foundation plane after the foundation was excavated. In this course，geological engineers have adopted ground penetrating radar(GPR)，CT(computerized tomography) of sound wave among holes，the chromatic record of boreholes，deformation modulus tests of boreholes，drilling，water pressure tests，in-situ tests and physico-mechanical properties tests in the laboratory，etc.，getting mechanical parameters information of rock mass in dam foundation. Combined with the geological information，the results are analyzed. According to the results，the rock is hard and rock mass is complete in this dam foundation；karsts are relativly not developed，and the underground water is not so active. The rock mass in dam foundation has enough compressive strength，integrity and homogeneity with enough margin of stability to resist slip and relative homogeneous deformation parameters. Except for the region along fault F1 needing special treatment，the rock mass quality in the dam foundation in the elevation of foundation plane recommended in feasibility study stage and correlative mechanical parameter index can meet the requirement of deformation of the dam foundation.

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SUBSIDENCE CONTROLLING AND CONSTRUCTION SCHEME OPTIMIZATION OF CUTTING ACROSS AND UNDERPASSING AN EXISTING METRO TUNNEL UNDER COMPLEX ENVIRONMENTAL CONDITIONS

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2008, 27 (S1): -2893 doi:
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The Dongzhimen metro station of Beijing Capital Airport line cuts across and underpasses the existing tunnel of subway line 13. This station has two storeys. The upper storey cuts across the existing line 13 subway tunnel，and is built by open-cut method. The least distance between the upper storey and the existing tunnel is only 0.33 m. The bottom storey underpasses the existing tunnel very closely，and is driven by so-called “drift- pile-beam” method. Around this construction area，there are three adjacent foundation pits in the east，west and northwest directions. Among them，the northwest foundation pit of 28 m in depth is the deepest pit in Beijing. All the constructions may induce excessive deformations. Moreover，the underpassed segment of the existing tunnel has two deformation joints which are the most unsubstantial parts of the existing tunnel.The existing line besides each deformation joint may move in the inverse direction，which can make the rails divorced from roadbed. Therefore，differential subsidence control of these two deformation joints and deformation control of retaining walls of these three pits are of great importance during this station construction，but there are few similar examples to be consulted. In order to guarantee normal operation of subway line 13 and foundation pits safety，construction sequences of this station is systematically simulated by using computer program FLAC3D(fast Lagrangian analysis of continua in 3D). The authors put forward an optimized construction scheme that the upper base pit and bottom storey are excavated alternately. In this way，the hunch caused by the upper pit excavation counteracts the subsidence caused by the bottom storey excavation. The numerical simulation results can be provided as the basis for design and construction of this station.

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SEISMIC HORIZON CURVATURE FOR PREDICTING SMALL FAULT IN COALSEAM

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2008, 27 (S1): -2901 doi:
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Small faults in coalseam are one of the important factors that cause coal mine safety accident. It is an urgent and necessary thing for current coal mine safety to predict exactly small faults in coamseam. General seismic interpretation method is suitable for interpreting the fault over 3 m throw，so it is necessary to find new technical method to interpret faults below 3 m throw in coalseam. Seismic horizon curvature is calculated from 3D seismic interpretation horizon and reflects the curving degree to the given horizon at a point. The calculation of seismic horizon curvature is based on the girding horizon，and it is realized through the coefficient of structure surface fitting equation. Curvature attribute of coalseam reflects curving degree of horizon when coalseam was extruded by structure stress. Coalseam faults below 3 m throw on general seismic section have the features such as even tiny variety，twist，weaking abruptly of the amplitude，these tiny varieties show small linear structure on the seismic horizon curvature attribute，so small faults can be predicated according to linear structure abnormity. The length of abnormity and directions represent the continued length and directions of faults respectively. The case shows that predicting small faults with seismic horizon curvature can raise fault interpretation efficiency.

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CHARACTERISTICS OF UNLOADING FISSURES IN DAM¢S BASE OF XIAOWAN HYDROPOWER STATION

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2008, 27 (S1): -2907 doi:
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Xiaowan Hydropower Station is a huge powerstation located in the middle-lower reach of Lancangjiang river. It is a double-curvature arc concrete dam with a maximum height of 292 m，the second highest arch dam under construction in the world. Owning to the narrow，high and steep valley as well as the higher geostress，strong unloading，the development in the dam¢s base during excavation is discussed which worsens the rock mass and leads to a series of troubles. The geological conditions of the dam site，the macroscopical characteristic of the unloading fissures of the base are considered and it finds that：(1) the dip angle of the unloading fissures changes from big to small gradually from the top to the bottom；(2) the unloading fissures in the both banks are inversed in dip direction；(3) the surface of the unloading fissures is almost parallel to the surface of excavation base. Meanwhile，the unloading fissures are classified into three classes as successive fissures，extensive fissures and fresh fissures. Finally，the distribution pattern and scope of the unloading fissures are analyzed. All these are meaningful to understand excavation unloading problem as well as to choose suitable measures to strengthen rock masses.

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MECHANICS AND APPLICATION RESEARCH ON THE FLOOR ANCHOR TO CONTROL THE FLOOR HEAVE OF DEEP SOFT ROCK ROADWAY

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2008, 27 (S1): -2913 doi:
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As the main failure mode in deep adjoining rock roadway，floor heave is one of the most difficult problems to be solved in deep coal mines and other subsurface projects. How to control the floor heave effectively becomes a crucial matter that should be taken into account in supporting engineering. The contrastive studies to control the deformation of floor in lots of cases show that anchors fixed in floor can function positively. By using the method of 3D numerical simulation，the mechanical process of the anchors fixed in floor is studied，and the time effects of their mechanical properties are also analyzed. Based on the analysis results，the work mechanism of the anchors in floor is summarized. The anchors with high flexural rigidity are fixed into the floor in rows，and they can cut off the plastic slip line of the floor，so the deformation of the floor is controlled effectively. Particularly，the technique is suitable for the deep rock roadway of which rock mass structure belongs to blocky structure. Meanwhile，based on the previous studies，this technique is used in a deep roadway engineering，and the asymmetric design method is applied according to the deformation characteristics of floor，which controls the floor deformation successfully and can be as an instructive theory to floor heave control of deep roadway.

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ROCKBURST PREDICTION OF CHENGCHAO IRON
MINE DURING DEEP MINING

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2008, 27 (S1): -2921 doi:
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After 40 years¢ mining in Chengchao iron mine，now it is coming into deep mining. To predict the possibility and intensity of rockburst，the author obtained rocks from the depth underground －430 to －700 m. Based on systematical mechanical experiments of rocks，various prediction criteria for rockburst are brought forward through many testing methods. With the theoretical methods，rocks which have the different possible intensities for rockburst are checked up by the criteria，and some types of rocks in the mine which has high possibility and severe intensity are confirmed. At last，combined with the comprehensive prediction methods in fuzzy mathematics，synthesized prediction upon those criteria is made that the orientation of rockburst and critical depth are ascertained in the mass，which can be the basic theory in the mining design and rockburst prediction.

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DEFORMATION PREDICTION DURING CONSTRUCTION OF CROSS INTERCHANGE TRANSIT STATION

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2008, 27 (S1): -2929 doi:
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With the development of urban railroad transit network in China，the complex construction of interchange station will be a new technical problem for building the whole railroad transit network. In order to provide technical support for safe construction of Dalian road interchange station in Line 8 and Line10 in Shanghai，numerical analysis is used to simulate the whole construction process. With designing theories of deep foundation，the finite element method and ANSYS software，the deformations in main construction cases are calculated. According to the analysis，the conclusions can be drawn as follows：the asymmetric excavation and the asymmetrically chiselling-off of the diaphragm wall are the most dangerous constructions cases；the deformation of the diaphragm wall and ground should be measured during the whole construction，especially，the internal forces of the beam，plane and column in interchange connection should be measured when the diaphragm wall was asymmetric chiselled off. Some reinforcement methods such as ground reinforcement，temporary support should be used if necessary.

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UPPER BOUND LIMIT ANALYSIS BY USING 3D ZERO-THICKNESS INTERFACE ELEMENTS APPROACH

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2008, 27 (S1): -2937 doi:
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The object of this paper is the application of three-dimensional finite element program developed in laboratory，it can consider the multiple planes zero-thickness interface elements and calculate the bearing capacity and simulate the progressive failure mechanism in the cohesive soil. These 3D numerical studies include the ultimate bearing capacity of slope stabilities and shallow foundation. According to the obtained results，the calculation is particularly approached to the upper bound of limit analysis. It shows that the 3D interface elements can be used to predict the bearing capacity of soil，and evidently describe the progressive failure mechanism of slope and foundation stability analysis under the different geometries.

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TESTING RESEARCH ON FREEZING-THAWING CHARACTER AND STRUCTURAL EVOLVEMENT REGULARITY DURING FREEZING- THAWING PROCESS OF AEOLIAN SOIL IN WESTERN AREA OF LIAONING PROVINCE

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2008, 27 (S1): -2946 doi:
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A new device for freezing-thawing test and the application is introduced. By using this device，the typical aeolian soil samples in the western area of Liaoning Province are frozen and thawed under different conditions of temperature gradients，load and water supply. By doing so，the regularity of frost heave and thaw settlement is illuminated. The test results can be drawn as follows：(1) the maximal swelling magnitude and thaw collapse value decrease with the increase of the temperature gradient；(2) not only in the closed system but also in the open system，the external force suppresses the swelling，and the thaw collapse value also decreases with the increase of the load；and (3) the external water supply will increase markedly the ultimate swelling magnitude and thaw collapse value. The displacement caused by freezing and thawing generates and the change of the macroscopic mechanical property and microscopic structure. This is mainly because the structure of the aeolian soil is changed；the bond force between the soil particles is damaged，and the soil particles rearranges. The structure evolvement regularity of aeolian soil in the western area of Liaoning Province during the period of freezing and thawing is studied under different moisture fields and stress fields by using the ice efficiency as the structure parameter.

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STUDY ON NUMERICAL SIMULATION FOR DYNAMIC INTERACTION OF SOIL AND STRUCTURE

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2008, 27 (S1): -2953 doi:
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[PDF 267 KB] (1192)

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Combined with results of theory，shaking table test and numerical simulation，dynamical interaction and aseismic capability of soil-structure system are studied and analyzed based on analysis of theory and calculation. The question of ruined earth pressure cell in test is solved，and the contact pressure between soil and pile is found out by the numerical simulation and distributing law of earth pressure. It is explained and sure that branches and disks of the pile are main components of foundation which can reduce shake and bear dynamic load，so they lighten the impact of seismic waves to structure and consume structural seismic energy fed back to foundation. Phenomena of pulling up on one side and pressing down on the other side in the pile foundation are revealed according to reverse relation of time-history curve of earth pressure from the corresponding measuring points on the sides of the pile foundation under seismic action at the same time. The phenomena are produced because of dynamic interaction of structure-pile-soil，which results in that bearing table shows turn effect. This law not only explains essential reason that the buildings are inclined and toppled in the seismic region，but also illuminates and verifies that the aseismic capability of structure plays greatly in the dynamic interaction system.

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RESEARCH ON THEORETICAL CALCULATION OF LONG-TERM GROUND SETTLEMENT CAUSED BY SHIELD TUNNELING

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2008, 27 (S1): -2960 doi:
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[PDF 287 KB] (1813)

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Post-construction consolidation settlement of soil above tunnel axis caused by shield tunneling is studied. Initial excess pore water pressure，due to stress release by unloading of soil excavation，is triangle-shaped distributed. Assuming that linings are undrained，soil is under single-drainage condition，and thickness of compressed soil equals that of soil above tunnel；theoretical calculation formula of post-construction consolidation settlement is obtained based on Terzaghi’s one-dimensional consolidation theory. Long-term settlements of ground are divided into settlement during construction and post-construction consolidation settlement. Furthermore，theoretical calculation formula of long-term ground settlement is deduced. As shown in analytical calculation，the calculated results are in good agreement with the field data. It is analyzed that long-term ground settlements caused by shield tunneling construction in soft soil of Shanghai are very noticeable. Final settlements of ground can reach above 80 mm，and 80%～90% of settlements are consolidation settlement. Assuming that the earth thickness above the tunnel lining is 5 m，consolidation settlement will be stable after at least 2 years.

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RESEARCH ON INFLUENTIAL FACTORS OF CRACK PROPAGATION DEPTH OF UNSATURATED EXPANSIVE SOILS

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2008, 27 (S1): -2967 doi:
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[PDF 179 KB] (1079)

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Cracks in unsaturated expansive soils influence the engineering properties of soils. The purpose of this paper is to research the tensile crack propagation depth of unsaturated expansive soils. The formula of crack propagation depth based on linear elasticity is put forward，which considers the contributions of effective cohesion and effective internal friction angle at the same time. Then，two expressions are derived from it. One is the expression of the cracking value of matrix suction on ground surface，which can be taken as one of the criteria to estimate the cracking of the ground surface of expansive soils. Another is the expression of the crack propagation depth when the groundwater level has little influence on it. Finally，the relationships between the crack propagation depth and the factors are analyzed，such as effective cohesion，effective internal friction angle，reduction coefficient of effective cohesion，Poisson¢s ratio，matrix suction on ground surface and the groundwater level. The following results can be drawn：(1) With the increase of effective cohesion and effective internal friction angle，the crack propagation depth exhibits a descending tendency. Effective cohesion，however，has a much more serious influence than that of effective internal friction angle. (2) For the different effective cohesions and effective internal friction angles，the crack propagation depth increases as matrix suction on ground surface increases. And with the increase of Poisson¢s ratio and effective cohesion as well as effective internal friction angle，the critical matrix suction on ground surface at crack initiation exhibits an increasing tendency. Effective cohesion has a greater influence relatively. (3) For different effective cohesions and Poisson¢s ratios，the crack propagation depth increases with the increase of the groundwater level. When the groundwater level has minor influence，it increases linearly with matrix suction at the ground surface and decreases as effective internal friction angle and Poisson¢s ratio increase.

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RESEARCH ON YIELD PROPERTY OF SOIL UNDER ROCK-FALL IMPACT

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2008, 27 (S1): -2973 doi:
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[PDF 167 KB] (1154)

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The impact pressure of rock-fall is an important parameter for shield structure design. While not considering the elastoplastic properties of impacted object，the value of impact pressure becomes extremely high and can¢t be used in project design. However，the actual rock-soil materials are all elastoplastic bodies and will produce great plastic deformation under the rock-fall impact. For this purpose，the initial yield pressure should be studied and serve as a basis for judging whether the materials begin to yield or not. Based on the Hertz contact mechanics，under the assumption that the soil obeys the Mohr-Coulomb yield criterion，the initial yield pressure and the corresponding impact velocity of soil are studied. The result shows that the impact velocity of initial yield is very small for the soil，and the cohesion has an obvious influence on it while the internal friction angle does relatively small.

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FINITE ELEMENT ANALYSIS OF BIOT CONSOLIDATION
BASED ON DISTURBED STATE CONCEPT

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2008, 27 (S1): -2978 doi:
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[PDF 207 KB] (904)

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Disturbed state concept(DSC) utilizes constitutive models to depict material responses. The response is obtained by two weight-averaging reference responses values. In DSC，the disturbance factor does not couple with the constitutive function. The incremental form of stress shows conciseness of DSC. DSC superposes disturbance factor on reference responses to revise them to reach actual response. It is the reference response，but not the constitutive model that is rectified by disturbance factor. The essence of DSC is to use regular constitutive models to obtain proper results. The course of rectification of elastoplastic problem results by DSC is the one of combination of DSC and elastoplasticity. The combination of DSC and Biot consolidation is put forward after the combination of DSC and elastoplasticity is accomplished，with the represention of equilibrium function and synthesis function. Water-soil coupled synthesis function group gives the displacement and pore pressure of any time. Detailed formula derivation and finite element analysis are presented. Finite element expression of the synthesis function group is derived based on effective stress principle，continuum condition and equilibrium function. Vertical strain of material is the variable of disturbance factor evolvement function. The strain of each reference response shares the same value. The results show that the material deformation calculated by DSC is greater than that calculated by elastoplastic model，which reveals similarity to results obtained by utility of damage theory.

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PRIMARY-SUPPORTING OPTIMIZATION FOR LARGE-SPAN ROAD TUNNELS IN GRAVEL DEPOSIT LAYERS

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2008, 27 (S1): -2984 doi:
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[PDF 378 KB] (1093)

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Maoshan road tunnel in southern area of Jiangsu Province，located in slope of gravel deposits layers，has the characteristics of large span，shallow overburden. With the parameters of shear strength of gravel deposits obtained from the large in-situ shear test analysis，numerical simulation is conducted to analyze the excavating and supporting processes of the tunnel with elastoplastic FEM. According to NATM，in the process of tunnel construction，polypropylene fibre shotcrete is the main factor embodying the feature of primary-support flexible support. Based on the research on the center cross-diagram(CRD) method construction process applied to shallow-buried tunnels in soft surrounding rock class II，and the analysis of the covariance function of measured deformations of three points：right-upper point(S1)，top(S2)，and left-upper point(S3) and the plastic zone of surrounding rock and inner lining，a research on the rationality of primary-supporting thickness is performed. And it is proposed that the most rational thickness of polypropylene fibre shotcrete is 22–28 cm for the tunnel with buried depth of 26 m. The optimum thickness of polypropylene fibre shotcrete for the typical section of the tunnel is 26 cm. This research result，in addition to the method，can be used as reference in the construction and design of CRD method in slope and shallow-buried tunnels in soft surrounding rock class II.

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TEST ON PHYSICO-MECHANICAL PROPERTIES OF QINGHAI—TIBET SLOPE CLAY UNDER FREEZING-THAWING CYCLES

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2008, 27 (S1): -2990 doi:
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[PDF 185 KB] (1179)

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It has become a common understanding that the structure，physico-mechanical properties of soils could be considerably changed by freezing-thawing cycles. With the variation of engineering properties，the normal running train was disturbed by the decline of subgrade stabilization. In order to study the long-term stabilization of slope in frozen soil area of Qinghai—Tibet Railway，a test was conducted under repeatedly freezing-thawing cycles，aiming at the main physico-mechanical properties of the representative clay. The results show that the physico-mechanical characters of the investigated soils become stable after 10 freezing-thawing cycles，such as water content，density，cohesion，internal friction angle and so on. The stable state is dependent on the original state of the soil sample，and the influence of the original dry density is very important. With the repeatedly freezing-thawing cycles，the cohesion of low density clay increases，but the cohesion of high density clay decreases，and the internal friction angle of the clay changes little. It is suggested that the parameters of soil at stable state should be adopted to estimate the stabilization of slope in frozen soil area.

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STUDY ON PRACTICAL ANALYTIC MODELS FOR
SOIL-STRUCTURE INTERACTION

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2008, 27 (S1): -2995 doi:
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[PDF 360 KB] (1240)

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Relative merits and demerits of existing soil-structure interaction analysis models are discussed，and a new analytic model is presented based on practical engineering application. The three-dimensional elastoplastic bar model is used to simulate the upper-structure，and the contact between soil and base is simulated by using horizontal，vertical and rotary springs and dampers below the base，with different field categories being reproduced by changing the spring and damping parameters. Dynamic soil-structure interaction of a ten-story RC frame building is analyzed by utilizing the model established with the new method，through which effects of several factors，such as the foundation soil¢s shear wave speed，the rigidity of upper-structure，and the earthquake magnitude on seismic response of the interaction system are evaluated，and then the pattern of the energy dissipation under different situations is discussed. Analytical results show that roof displacement does not certainly increase when softer site or stronger rigidity of upper-structure with soil-structure interaction being taken into account，but softer site can decrease the seismic response，and augmenting the rigidity of upper-structure may increase the shear force and the bending moment. Although the change of upper-structure¢s rigidity affects little on energy¢s changing trend of interaction system，damping energy and strain energy of the upper-structure are the main dissipated energy of the soil-structure interaction system under different situations. When the earthquake magnitude changes，there are some different influences on the energy dissipation of the interaction system under different earthquake waves，and the function of damping energy and strain energy may be different.

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RESEARCH ON COMPARISON OF STRENGTH EQUATIONS OF
UNSATURATED SOIL

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2008, 27 (S1): -3005 doi:
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[PDF 229 KB] (1260)

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It is proven that shear strength of unsaturated soil increases as increase of matric suction. However，the mechanism of variation of the shear strength with matric suction isn¢t very clear by now. There are two different types of equation in the shear strength theory of unsaturated soils mechanics，one-stress-state-variable equation and two-stress-state-variable equation. Many practical shear strength equations have been established on the base of the two different types of equations. In order to compare different shear strength equations of unsaturated soil，Luojiashan soil samples are selected for the soil-water characteristic curve(SWCC) test and unsaturated triaxial tests. Based on the tests，the air entry value of Luojiashan soil is 237.7 kPa and the residual water content is 4%. It is shown that，with low suction，the triaxial strength of unsaturated Luojiashan soil is directly proportional to suction. These results certify the applicability of two-stress-state-variable strength theory for unsaturated soil. The triaxial shear coefficient φb for Luojiashan soil is 20.7°. The precisions of the previous equations aren¢t satisfied and further research is needed. With the development of unsaturated soil mechanics，researches on the application of shear strength theory of unsaturated soil should be strengthened.

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EXPERIMENTAL RESEARCH ON SHEAR BEHAVIOR OF
CALCAREOUS SAND

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2008, 27 (S1): -3010 doi:
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[PDF 262 KB] (1154)

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The results of drained shear tests carried out on calcareous sand sample from the South China Sea were presented. The tests reveal that the relation between the stress and strain changes when the confining pressures are changed. Under low pressure，it is similar to the terrigenous sand；and under the medium confining pressure，the mechanical property of the calcareous sand is just analogous with that of the terrigenous sand under high stress level. The particle breakage results in liberation of the close interspace. Thus the volume of strain is much larger than that of quartz sand，which makes almost all the deformation irreversibly plastic during shear process. And the results also indicate that the dilatancy and ratio of stress are closely related to the confining pressures，they decrease as the confining pressures increase.

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RESEARCH ON DISTRIBUTION REGULARITIES OF GRAIN SIZE OF ROCK DETRITUS FROM DISCOID CUTTERS

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2008, 27 (S1): -3016 doi:
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[PDF 441 KB] (1294)

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Tunnel boring machine(TBM) has been widely employed in recent years. In general，for a mixed action of shear，crush and tension，the detritus are formed. Rock detritus dimensions and particle distribution are the key factors of TBM mechanical parameters related to the rock properties，which will influence TBM energy utility and excavation efficiency. They are influenced by cutter spacing，cutter thrust forces and rock characteristics. According to the mechanism of detritus formation，detritus dimensions constitution and its characteristics are discussed. Based on the field TBM tunneling practice，Chongqing Yangtze River tunnel，detritus samples are collected according to rock types and thrust forces magnitude. Then，detritus measuring and screen tests are implemented，and vast data about detritus size are acquired. According to probability statistic theory，detritus dimensions of mudstone and sandstone are matched by normal distribution fitting method. Finally，the measured detritus distributions are calculated and compared with theoretical distribution models(lognormal distribution function and Rosin-Rammler distribution function). Some conclusions for the detritus dimensions，particles distributions and their relations to mechanical parameters are obtained. These conclusions will benefit for improving cutter head layout design and TBM performance.

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RESEARCH ON CONSOLIDATION DEFORMATION OF SAMPLE BY 5 Hz HOLLOW CYLINDER APPARATUS OF ZHEJIANG UNIVERSITY

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2008, 27 (S1): -3023 doi:
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[PDF 287 KB] (936)

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Apparently the ideal apparatus used to simulate soil behavior under principal stress rotation is hollow cylinder apparatus(HCA). The 5 Hz HCA developed by Zhejiang University and GDS instruments Ltd. in England has a combined axial-torsional loading system，which can be used in static and dynamic(at frequency of 0–5 Hz) tests. Accurately measuring hollow specimen¢s deformation is the basis of strain measurement and stress control mode，which is often used in HCA testing. However，after isotropic consolidation，it is not easy to get accurate measurement due to the disturbances in the process of setting-up the sample and the air bubbles between the inner wall and the inner membrane. The formulae for outer and inner radii after consolidation are derived through analyzing the changes of inner cell volume，back cell volume and axial strain by iteration algorithm. Based on the analyses，Tastuoka¢s hypothesis is modified. Comparison between the results with those obtained from Kaman sensors used for local measurement indicates that it is feasible to calculate outer radius by volumetric changes and axial strain. While the test using the amended inner radius can highly improve measuring accuracy，thus the reliability of stress control mode can be also guaranteed.

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TESTING STUDY OF MECHANICAL BEHAVIORS OF FROZEN CLAY IN HEZE DEEP MINING AREA

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2008, 27 (S1): -3028 doi:
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[PDF 280 KB] (971)

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According to mechanical behavior tests using frozen soil samples from three huge thickness clay strata situated between 400 and 700 m deep in Wanfu mine，the following results are obtained：(1) the stress-strain curves of frozen clay mostly show strain hardening and large yield deformation before the peak stress；(2) contrasting mechanical behaviors of frozen clay under frozen temperatures of －15 ℃，－20 ℃ and －25 ℃，the impact of temperature on creep properties of the deep frozen clay is greater than strength，and －20 ℃ is the limit value for freeze state of the deep-seated clay which can effectively control the creep characteristics of deep frozen wall. The relationship between the deep frozen clay mechanical behaviors and frozen temperature reflected in the results of the test is analyzed to be chiefly relative to the water content and structure of deep frozen clay. The soil samples used in the test are under half-solid state in which the bound water is principal part of pore water. Because the frozn temperature of bound water is much lower than that of gravitational water，when the temperature is lower than －20 ℃，the cementation ice content in the frozen soil increases obviously because of the freeze of bound water，and the impact degrees of cementation ice and inter-particle frictional force on strength of frozen soil become stable，and that leads to the rheological property of frozen soil to decrease sharply.

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RESEARCH ON INFLUENCE OF PRINCIPAL STRESS AXIS CYCLIC ROTATION AT LOW SHEAR STRESS LEVEL ON BEHAVIOR OF INTACT CLAY

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2008, 27 (S1): -3033 doi:
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[PDF 344 KB] (916)

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In order to study the influence of principal stress axis cyclic rotation at low shear stress level on clay¢s behavior，a series of experiments of Hangzhou typical intact soft clay were conducted. The experimental results reveal that the stress paths such as principal stress axis cyclic rotation with constant shear stress lower than the limit shear stress bring the variation of samples¢ strain components and pore water pressure into dynamic equilibrium；the stable values of equivalent stiffness and pore water pressure at equilibrium are mainly decided by the tortional shear stress component；and the axial stress component also promotes these two values when the tortional shear stress components are the same. Meanwhile，such principal stress axis cyclic rotation causes the stiffness to be enhanced during the following static shear stage. Especially，when the following stage is triaxial compression one，the strength will arrive in advance observably，and the directions of principal stress increment and principal strain increment become obviously non-coaxial at the initial of triaxial compression，which are mainly caused by the residual strain and changes of soils¢ structure generated in the previous cyclic principal stress axis cyclic rotation. But the static shear strength and critical pore water pressure in the following static shear stages are not greatly influenced by the previous principal stress axis cyclic rotation.

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APPLICATION OF RANDOM FIELD THEORY TO STATISTICS FOR SHEAR STRENGTH INDEXES

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2008, 27 (S1): -3040 doi:
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[PDF 235 KB] (1050)

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In the reliability analysis of foundations，one of the most important problems is how to choose the reasonable statistical method for shear strength indexes of soils. According to the basic assumption of some topics in the soil mechanics，the indexes of shear strength are the parameters describing the trend of average strength of homogenous soils. The mean values and variance of local spatial averaging of soil properties should be used in the reliability analysis. So it is necessary to introduce the random field theory into the statistics for shear strength indexes and to consider the auto-correlation and cross-correlation of the shear strength indexes of soils. The stochastic statistical methods for shear strength indexes are presented based on the traditional statistical methods. Both the auto-correlation of the individual index and the cross-correlation between the indexes can be considered when using the methods. In addition，there is no need to study the auto-correlation function and cross-correlation function of and respectively. The variance of spatial averaging of and can be obtained directly through regression. The process of calculation will be simplified by this means. Finally，by calculating an example of engineering in Tianjin Port，it is proven that the reliability indexes calculated by the stochastic statistical methods agree well with the reliability of practical engineering.

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TEST STUDY OF SOIL STRENGTH WITH DIFFERENT SOAKED PERIODS OF EMBANKMENT OF YELLOW RIVER

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2008, 27 (S1): -3047 doi:
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The soil shear strength is important to analyze the stability of embankment and slope. A series of soil mechanics tests(compression test，quick shear test and unconsolidated-undrained(UU) test are carried out using levee soils of downstream embankment of Yellow River，especially the strength test of the soils with different soaked periods. The change and reducing degrees of strength parameters of clay and soaked silt，and the reasons of strength change and the effect on the stability of embankment are discussed. Because of soaked soil，the compression coefficient of soil obviously increases and the modulus of compression obviously decreases. The compression coefficient of clay samples soaked for 5 days increases 1.46 times at the most than that without being soaked，and 0.64 times for silt samples. At the same time，for the soaked soil，the deformation of clay is geaterer than that of the silt. The conclusion of quick shear test is that the cohesive of clay reduces by 72.6%，silt by 62.8% and internal friction angle changes a little soaked for 5 days because the action of water to soil only destroy the sequence and cement of soil grains，but the soil grain component is not varied. The results of UU test is complex. For the clay samples，c and j decrease quickly with soaked sample，but the time effect of soaked clay is small. However，for the silt，the longer the time that the sample is soaked，the lower the strength of the silt is. It will be the reference to the design and stability analysis of embankment，and the results will be afforded for the management of the Yellow River embankment operation.

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EXPERIMENTAL STUDY OF DYNAMIC STRESS-STRAIN RELATION OF STRUCTURAL SOFT SOIL UNDER TRAFFIC LOAD

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2008, 27 (S1): -3052 doi:
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[PDF 429 KB] (1511)

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Through the dynamic triaxial tests of structural soft soils，the dynamic strain analysis is conducted on the silt soils under traffic load，and the influence of vibration type，vibration frequency，stress ratio，consolidation status of soils are taken into account. The variation rules of the critical dynamic stress ratio of the silt soils and dynamic stress-strain with vibration frequency，confining stress and consolidation status are obtained. Some conclusions can be drawn from the research：(1) there is a critical dynamic stress ratio and a threshold of vibration frequency for structural silt soils under traffic load；(2) there is a turning-point for the dynamic elastic modulus and dynamic shear strain of silt soil under half-sine wave condition.

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3D ANALYSIS OF HIGH ARCH DAM ABUTMENT STABILITY UNDER STATIC AND DYNAMIC LOADINGS

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2008, 27 (S1): -3058 doi:
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[PDF 306 KB] (892)

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According to the principles of static forces for designing and dynamic forces for checking，3D critical block theory is used to identify and describe all removable blocks based on the geological exploration data. Then the corresponding dominative sliding blocks are determined. For the 3D features of the abutment stability problem，the program of 3D rigid body limit equilibrium method is developed to compute and analyze the sliding resistance stability of high arch dam abutments of a hydropower station，nearly 300 m in height，under static and dynamic loadings with several different elevation planes. In dynamic analysis method，the arch dam，reservoir water body and dam foundation are regarded as an integrated system，so that the dynamic interaction between the blocks and dam body can be effectively considered. The results obtained by the method integrating static and dynamic loadings indicate that the arch dam abutments of both sides are stable under static loading with enough margin of safe. While under the action of earthquake，the dam is safe though the factor of safety is not very high. All of these provide significant scientific bases for design and demonstration of high arch dam.

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PARTICLE FLOW SIMULATION OF SOIL UNDER HIGH-SPEED SHEAR

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2008, 27 (S1): -3064 doi:
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[PDF 524 KB] (1325)

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A particle flow model of ring-shear test is constructed by the PFC(particle flow code) in which the soil particles are cohesiveless. Compared the result of simulation test with high-speed ring-shear test，the stress changing tendency of the two tests is similar；the levels of stress are close. The uniformity coefficient of the sand sample in ring-shear test is 1.64 and the particle sample in PFC model is 1.45. The linear contact model among balls is adopted in the simulation test，so the test result is suitable for the cohesiveless soil. The shear boundary can make different kinds of shear zones，so three kinds of boundaries are tested，which are wall，ball-circle and ball- circle and teeth boundary. And the ball-circle and teeth boundary is the one that can make shear zone well proportioned.

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CALCULATION OF ACTIVE EARTH PRESSURE FOR LIMITED SOILS

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2008, 27 (S1): -3070 doi:
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[PDF 217 KB] (1950)

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With the development of underground engineering in cities，people pay more attention to the calculation of earth pressure for limited soils in foundation supporting projects. However，Rankine¢s and Conclom¢s theories based on semi-infinite space assumption are not suitable for calculating the earth pressure of limited soils. Based on the limit equilibrium theory and the hypothesis of planar sliding plane，a formula for calculating the angle of shear failure in limited soils is deduced with the consideration of cohesion force and the width of limited soils. And then，a formula is proposed to calculate the active earth pressure of limited soils exerted against the supporting system. The formula shows that the angle of shear failure of limited soils is no longer the one in Conclom¢s theory. And the angle of shear failure is no long equal to 45°+j/2，but is a variable related to the width of limited soils，the cohesion of soil，the friction angle of soil and the depth. It is found that the angle of shear failure of limited soils increases nonlinearly with the increase of the depth，and decreases with the increase of the width of limited soils and the cohesion of soil. It is interesting that the angle of shear failure in limited soils decreases firstly with the increase of friction angle of soil，but latterly it will increase with the increase of friction angel of soil when it reaches to a certain degree. Finally the calculated results using the deduced formulas for the angle of shear failure and the active earth pressure of limited soils are analyzed by comparison with those of Rankine¢s theory. It proves the present formulas are reasonable.

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UNIT WEIGHT，WATER CONTENT AND SPECIFIC GRAVITY
OF MUNICIPAL SOLID WASTE IN CHINA AND UNITED STATES

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2008, 27 (S1): -3075 doi:
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[PDF 325 KB] (1375)

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In present，landfill is still the most important controlled method for municipal solid waste disposal in China. Correct selection of engineering properties of waste materials is of paramount importance. The properties of waste materials vary within broad ranges，change significantly with time，and are not easily amenable to direct measurement due to heterogeneity and hard inclusions. The components，unit weight，water content，and specific gravity for Chinese and USA waste materials are discussed in detail. The unit weight of Chinese waste is similar with USA waste，but the water content and specific gravity of Chinese waste are greater than those of USA waste. The testing methods for these properties are also presented. Some valuable results are concluded and discussed.

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NORMALIZATION CHARACTERISTIC OF SANDS UNDER TRIAXIAL COMPRESSION AND NUMERICAL MODELING METHOD

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2008, 27 (S1): -3082 doi:
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[PDF 505 KB] (1057)

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Study shows that there is normalization characteristic about the stress-strain curves of mediate-dense sands in the range of routine confining pressure. The triaxial test data are normalized by choosing proper normalization parameters. The neural networks are trained by regarding the normalized data as training samples，and then the constitutive model of sand described by neural networks is obtained. The emulation value of the neural networks agrees with well，which shows that the proposed modeling method is reasonable. It can achieve probabilistic optimization automatically based on all test data by using the modeling method，and can reduce the interference of noise signal，and lower the influence caused by dispersive test data.

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MOISTENING DEFORMATION CHARACTERISTICS OF EXPANSIVE SOIL UNDER TRIAXIAL STRESS STATE

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2008, 27 (S1): -3088 doi:
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[PDF 405 KB] (1038)

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The stage moistening deformation tests are performed for the compacted expansive soil in Ankang using improved triaxial apparatus. The experiment shows that the deformation of the expansive soil is swelling deformation under triaxial stress state with the same stress ratio in the immersion process. The soil deformation appears in specimen¢s every orientation，the deformations in the radial and axial directions behave swelling when stress is smaller. The axial direction expresses the compresses deformation and the radial direction expresses swelling deformation when stress is greater，but the deformation is very little. In moistening shear process，the deformation of the sample is chiefly volumetric expansion and volumetric changes is chiefly lateral deformation，and the axial direction deformation is smaller；the mathematical fittings are done for the experiments data，and the fitting formula has been verified. The results show that the experimental value agrees well with calculation value.

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APPLICATION OF FUZZY PROBABILITY MODEL TO PREDICTION OF CLASSIFICATION OF ROCKBURST INTENSITY

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2008, 27 (S1): -3095 doi:
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[PDF 315 KB] (1175)

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Rockburst is a kind of dynamic instability phenomenon of surrounding rock in underground projects in deep high-geostress zone. The prediction of possibility and classification of rockburst are basic issues in many underground projects. Based on the fuzzy probability theory，a new fuzzy probability model is established to predict rockburst occurrence and its intensity. Some main control factors of rockburst，such as the maximum tangential stress of the cavern wall ，the uniaxial compressive strength and the uniaxial tensile strength of rock，the elastic energy index of rock，are chosen in the analysis. Three factors including ， and are regarded as the evaluating indices. And rockburst intensity is classified as the non-rockburst，slight rockburst，medium rockburst and serious rockburst in the prediction model. In order to assess the index weight scientifically and to avoid the uncertainties while determining the index weight，the fuzzy weight is introduced into the rockburst prediction model. The fuzzy probability model not only holds the merits of classical fuzzy comprehensive evaluation method，but also overcomes its limitations in practice. Rockburst predictions of Dongguashan deep hard rock mine，Qinling Tunnel and an underground hydropower station are performed by this model. Furthermore，23 underground rock projects at home and abroad are also evaluated with the proposed method. The prediction results agree well with the practical records. It shows that the fuzzy probability model is reasonable and effective to predict the possibility and classification of rockburst in deep underground engineering.

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AN ANALYTICAL SOLUTION TO COMPOSITE MODULUS OF COMPOSITE FOUNDATION WITH RIGID-FLEXIBLE PILES

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2008, 27 (S1): -3104 doi:
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[PDF 254 KB] (875)

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Considering the influences of rigid pile length，flexible pile length，rigid pile modulus，flexible pile modulus，soil modulus and replacement ratio on composite modulus of composite foundation with rigid-flexible piles，composite modulus is deduced according to shear displacement method on basis of certain hypotheses. The relationship between parameters and composite modulus is analyzed. Case study shows that the new method is more precise than traditional methods，and there is a reasonable agreement between theoretical solution and measurement result.

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CHARACTERISTICS ANALYSIS OF FOUNDATIONS REINFORCED BY LONG AND SHORT PILES AND LONG-SHORT COMPOSITE PILES

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2008, 27 (S1): -3110 doi:
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[PDF 236 KB] (1095)

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In the process of optimal design of foundation reinforcement for the typical project，by means of finite element analytical method，systematic calculation and analysis have been conducted aiming at raft foundation and foundations reinforced by short pile，long pile，and long-short composite pile respectively. Under the same loading condition，the load-deformation curve of foundation reinforced by short piles approximates to that of natural foundation；and the load-deformation curve of foundation reinforced by long-short composite piles is similar with that of foundation reinforced by long piles. The changing rules of settlement distribution at central cross-section of foundations and at depth of 5 m are same as those of load level-settlement curves. The intensity and range of extensive area of plastic points，which centralizes in the upper soil layers，of foundation reinforced by short piles is similar with those of natural foundation. For the foundations reinforced by long-short composite piles and long piles respectively，the plastic point develops further down to bearing layer；and the distribution and magnitude of the foundation counterforce in the two cases are similar.

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TESTING RESEARCH ON LOAD TRANSFER MODES OF SINGLE AND
MULTIPLE GRAVEL PILES

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2008, 27 (S1): -3116 doi:
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The effect of pile length on the load transfer modes of single and multiple gravel piles is studied using a self-developed two-dimensional experimental apparatus with lever-weight loading systems and directive measurement of pile-bottom pressure by stress ring. In the tests，mechanical-crushed marble stone with an average diameter of 0.75 cm is chosen as the material of gravel piles；and the mixture of manual-disposal Lanzhou loess with certain water contents and Shapotou sand in the volume proportion of 3∶1 is used to be the soil around pile. The test results show that there exists a critical length(more specifically，a critical ratio of pile length to pile diameter). In detail，a majority of top load is borne on the bottom within a short gravel pile under the critical length，but on the top arch within a long one over the critical length，the different load transfer modes result in the different failure modes. The failure of the short gravel pile is induced by the pile plunging into the bottom soil，but the failure of the long one is caused by the shear failure in a triangle region of the lateral soil which induces the swelled failure of the top arch. Additionally，in the case of multiple gravel piles，the top load on each gravel pile can influence the pressure distribution at the bottom of the other piles；the interaction between the piles can accelerate the formation of the top arches，and effectively decrease the critical length consequently. This study indicates that different theoretical formulas should be proposed to calculate the bearing capacity of short and long gravel piles.

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RECTIFICATION AND REINFORCEMENT OF A TILTED BUILDING
BY USING MICRO-STEEL-PILES

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2008, 27 (S1): -3122 doi:
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[PDF 300 KB] (1296)

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An office building is constructed on a backfilled stratum located at the bank of a reservoir. Because of unsuitable ground treatment and great seasonal water level change of the reservoir，the building occurs nonuniform settlement. Making use of the building¢s inverted nonuniform settlement caused by reinforcement，combining the micro-steel-piles which are constructed by stages and areas，the rectification of the tilted building has been successfully conducted；and the foundation of the tilted building has been reinforced. On the basis of engineering practice，a method for reinforcement of building foundation and rectification of tilted building with micro-steel-piles is introduced. The effects of the reinforcement of the building foundation and rectification of the tilted building with micro-steel-piles are also illuminated using the observed data. It is expected that this can provide references for similar projects.

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CONSOLIDATION EXPERIMENT ON EARTHEN ARCHITECTURE SITE
IN ARID REGION

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2008, 27 (S1): -3127 doi:
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Combining the consolidation project of the Gaochang site in Xinjiang Uygur Autonomous Region，silicone-acrylic emulsion has been applied to the consolidation of the samples of the Gaochang site. Tests including chemical analysis，fused-salt analysis，penetration depth，gas permeability，resistance to salt erodibility，unconfined compressive strength，freeze-thaw cycles，wind erosion and analysis of X-ray are carried out. Experimental research reveals that the clay samples treated with the new material have an outstanding effect and can gain good stability against water decomposition，fused-salt，freeze-thaw cycle and wind erosion while the appearance and water permeability nearly keep unchanged. The compressive strength can be improved definitely，thus the soil surface has no incrustation to avoid the soil desquamate. Silicone-acrylic emulsion is an excellent anti-weathering consolidation for earthen architecture site protection in the arid regions of Northwest China.

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RESEARCH ON CONSTRUCTION METHOD OF METRO STATION ADJACENT TO BRIDGE PILES AND REINFORCEMENT
MEASURES FOR BRIDGE PILES

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2008, 27 (S1): -3132 doi:
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Hujialou metro station of Beijing metro No. 10 is designed to be adjacent to the Jingguang Bridge. Restricted by the bridge piles，the metro station structure is divided into two detached tunnels. In the primary design，the cross diaphragm(CRD) method is adopted. In view of the metro station structure adjacent to the Jingguang Bridge piles(the shortest distance between metro main structure and bridge piles is only 2.16 m) and the risk for metro station construction being great，the adopted metro station construction method should ensure the safety of adjacent bridge piles. According to similar engineering construction experience and finite element numerical analysis，the PBA(pile-beam-arc) construction method is adopted. The adjacent bridge pile risk grade is classified according to the bridge piles spatial location. The corresponding reinforcement measures are adopted according to bridge risk grade. The stratum subsidence and bridge pile displacement are measured during construction period. The monitoring result indicates that the PBA construction method for metro station is reasonable and the reinforcement measures for the adjacent bridge piles are effective.

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STUDY ON INFLUENTIAL FACTORS AND MODEL FOR VARIATION OF ANCHOR CABLE PRESTRESS

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2008, 27 (S1): -3140 doi:
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Although the anchor cable is widely used in the geotechnical projects，the prestress variation rules of the anchor cables are still not clear，especially the prestress loss when being locked and lasting of prestress variation of cable in cracked rock are interesting issues. Based on the in-situ monitoring results and analysis of a slope reinforcing case，the prestress loss under being locked，and short-term as well as long-term prestress variation rules are studied. The influence of multi-factor on the anchor cable prestress state is discussed. These factors include the relaxation of the anchor cable，the compression of surrounding rock，the environment change of surrounding rock，and so on. The short-term and the long-term prestress losses are both nonlinear，which can be divided into three stages：remedial loss，long-term loss and periodic variation. The former factors include the friction between anchor cables and surrounding rock，deformation of anchorage system，uneven stress distribution，excavation of the next step slope，the impact action，the effect of group cables，most of which found in the construction term can be retrieved by tensioning again. The long-term prestress loss can be caused by the compression of surrounding rock and relaxation of the anchor cable，which shows the notable interaction effect. Influential factors of the periodic variation include rainfall and temperature change and the variation amplitude is not small and it can return to the former condition. As for the long-term prestress loss of the anchor cable that is trigged by the creep of the materials，a new mechanical model is established and the forecast equation is derived，which presents the interaction of the compression and relaxation. By means of the mechanical parameters and monitoring data of the practical engineering，the stability of the prestress anchorage engineering can be analyzed.

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EXPERIMENTAL STUDY AND MODEL ANALYSIS OF
VISCOSITY OF MALAN LOESS

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2008, 27 (S1): -3147 doi:
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[PDF 258 KB] (891)

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It is of great significance to realize the development rule of geological disasters for study of the viscosity of loess. Lots of shear relaxation tests on Malan loess are conducted；and a simple and practical method is introduced to measure the coefficient of viscosity of Malan loess. On the basis of a viscoelastic solid model with three parameters，the coefficient of viscosity is determined by the measured data obtained from the shear relaxation tests by means of the least squares curve-fitting method. The coefficients of viscosity of Malan loess with different water contents are achieved. The results indicate that，when the water content is 13%－35%，the coefficient of viscosity increases with the water content and the normal stress on Malan loess.

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ENGINEERING APPLICATION OF SETTLEMENT-CONTROLLED COMPOSITE PILE FOUNDATIONS

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2008, 27 (S1): -3153 doi:
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[PDF 238 KB] (978)

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The mechanical mechanism，working behavior and deformation property of settlement-controlled composite pile foundations are analyzed；and the expressions for the pile number of the composite pile foundations are deduced. A new method calculating the settlement of the composite pile foundations，i.e. modified deep foundation layer-wise summation method，is put forward. The foundation settlements of two engineering examples are calculated by the method. The results show that the foundation settlements obtained by the modified deep foundation layer-wise summation method are much less than those of shallow natural foundation. Furthermore，the composite pile foundation settlements accord with in-situ monitoring results，correspond to the practical situation and meet the requirement of current design code of building foundation. Under this condition，the number of the piles can be cut down，and the foundation¢s bearing capacity can exert fully. Consequently，the cost of construction can be saved and the quality of engineering can be more easily assured by the cooperation between the pile and soil.

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A NEW NUMERICAL METHOD FOR MODELING GROUNDWATER LEVEL VARIATION

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2008, 27 (S1): -3159 doi:
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Although there is a vast development of the calculation methods and techniques of groundwater numerical simulation，it has some limitations in theories and practicalities and needs to be further researched and resolved. Therefore，the groundwater modeling process is still permeated with all kinds of uncertain factors. It is one of the largest challenges in this research field to fully utilize and improve the technologies on hand to eliminate the modeling uncertainty，to promote the validity of the numerical simulation process and the reliability of the forecasted results. Based on the traditional groundwater numerical modeling，a new groundwater model to make direct predictions on the groundwater level changes caused by the local stress fluctuations is developed. The variation governing equations related to confined and unconfined aquifers have been developed. It is verified that the simulation process for confined aquifer is as the same as those of traditional numerical simulation process. Otherwise，it is only approximation for unconfined aquifer. The predicted error will be increased as long as the increase of the absolute value of net change. This study introduces an iteration scheme，which can improve the perturbation results. The proposed new modeling reduces the requirements of input data in the modeling processes，and it can also simplify the boundary conditions and，at the same time，introduce the iteration scheme in solving the governing equation. When putting the results into practical use，it will increase prediction accuracy. This research will bring potential contributions to the water resources management and provide guidance for design and construction of geotechnical engineering.

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APPLICATION OF INFRARED PHOTOGRAPHY AND IMAGE PROCESSING TO TUNNEL CONSTRUCTION WITH NEW AUSTRIAN TUNNELING METHOD

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2008, 27 (S1): -3166 doi:
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Digital photography technique is an important method to obtain information of tunnel face in constructing rock tunnel construction with new Austrian tunneling method(NATM). There are lots of dust and fog in constructing rock tunnel with NATM，and the illuminance is always insufficient and uneven since the diameter of dust is much longer than the wavelength of visible light wave but close to infrared. According to the principle of diffraction，visible light could not go through the dust but infrared rays could do. So it is hard to take clear pictures of tunnel face with classical photography technique but possible by infrared photography technique in tunnel construction. The application of infrared photography technology to taking picture of tunnel face for constructing rock tunnel is specified. The possibility and superiority of this method are proven by analyzing in-situ experiments；and the characteristics of infrared photographs of tunnel face are also analyzed aiming at image processing of denoising-illuminance equilibrium-threshold division. In the image recognition step，the Hough transform is used to identify the linear feature of tunnel face picture；and the validity of this method is proven by comparing the recognizing result with monitoring data. Experimental results show that infrared photography is helpful for getting clear tunnel face photograph in rock tunnel construction with NATM：the image processing overcomes the problems of image noise，the overexposure，underexposure in the circumstance of poor illuminance. The recognition of linear feature is on the basis of 3D numeral reconstruction and could provide some critical parameters for rock masses classification.

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RESEARCH ON MECHANICAL MODEL OF THIN PLATE AND SPLITTING FAILURE CRITERION FOR SURROUNDING ROCKS WITH HIGH GEOSTRESS

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2008, 27 (S1): -3173 doi:
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[PDF 343 KB] (1355)

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When the underground caverns of brittle surrounding rock located in high geostress area are excavated，the longitudinal splitting cracks always are found and brittle cracks will appear. The splitting cracks will evolve into large parallel splitting crack groups together with intense deformation such as rockburst，and thus will endanger the safety of engineering. From the perforation mechanism of splitting cracks，the criterion of splitting failure is established based on analysis of stress intensity factor of fracture mechanics and the spread process of splitting cracks. Then the stress state and the splitting range of surrounding rock are evaluated. The splitting rock is regarded as thin plates. According to G. R. Kirchoff ¢s thin plate theory，the applicability of thin plate is verified. The stress and displacement are resolved by elastic thin plate under the condition of basic hypothesis and geostress. The resolution calculations of stress and displacement are settled in theory. Taking Pubugou hydropower station as an engineering case，the criterion is programmed into FISH language and embedded into FALC3D. The splitting failure range is confirmed；and the critical stress and the maximum displacement are calculated by the resolution formulae. The results agree well with the numerical results. It indicates that the splitting criterion can predict the splitting failure range；and the stress and displacement can also be calculated with thin plate mechanical method rather precisely. The method can offer references to evaluating stability of underground engineering and support design with high geostress.

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A RHEOLOGICAL TEST OF SANDSTONE WITH PERTURBATION EFFECT AND ITS CONSTITUTIVE RELATIONSHIP STUDY

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2008, 27 (S1): -3180 doi:
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Large rheological deformation of softening sandstone at great depth is exclusively associated with perturbation. And the study of rock rheology and its perturbation effect becomes especially important. Two new concepts，limit neighbor of rock strength and perturbation effect of rock rheology，are proposed. An experimental result is obtained that the perturbation effect is obvious when the rock sample is in the scope of limit neighbor of rock strength，which indicates that the rock rheology and its perturbation osculate with the rock¢s strain condition；and the perturbation effect is sensitive to the limit deformation. With the concept of limit neighbor of rock strength and perturbation effect of rock rheology，an alternative experimental instrument is developed for studying such a perturbation effect，and it is also used to test some sandstone samples under the conditions of constant axis-loads at different rheological phases. Some perturbation time and cumulative deformation curve of sandstone rheology at different phases are achieved for studying the rule of rock rheology and its perturbation effect. Finally，the factors of perturbation effect and a rheological constitutive equation for sandstone at different rheological phases are presented to simulate the perturbation effect. The constitutive equation can be used to calculate the rheology and its perturbation increment of the same rock；and the stability of surrounding rock can be analyzed.

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NEW THEORY FOR SHEAR RHEOLOGICAL ANALYSIS OF PILE¢S BEARING PERFORMANCE

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2008, 27 (S1): -3186 doi:
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[PDF 246 KB] (958)

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This paper presents theoretical as well as experimental results on the bearing performances of the pile-soil system. To sufficiently consider the time effect of geomaterials and the spatial effect of the pile-soil system on pile¢s bearing performance，a rheological theory of soil for the pile foundation is proposed. Based on the rheological theory，an improved analytical model of pile-soil system is established to analyze the mechanism of spatiotemporal effect on the pile¢s bearing capacity. Some analytical and semi-analytical solutions of the time and spatial effects of single pile¢s bearing performance are obtained. This new theory can be used to predict various behaviors of pile foundations，such as the controlling of foundation settlement. In addition，the theory can also be used to validate the construction quality of foundation and to compute the load-displacement relationship of pile，which can supplement the current foundation test technique.

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EXPERIMENTAL RESEARCH ON PROPAGATION AND COALESCENCE PROCESS OF THREE-DIMENSIONAL FLAW-SETS

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2008, 27 (S1): -3191 doi:
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A team of transparent specimens using a type of casting resin are employed，which has brittle fracture properties of rock-like material under frozen environment. The primary flaws in samples are made of three thin aluminum films. The propagation and coalescence process of three-dimensional(3D) flaw sets were observed. The experimental results show that wrapping wing cracks individually initiate and grow from every pre-existing flaw end at the beginning of fractures. Then the interaction roles between the flaws gradually become stronger and stronger，and principally，the secondary cracks are induced to extend towards the direction opposite to wing crack. This type of crack is so called wrapping anti-wing crack(against wrapping wing crack). The whole specimens will be broken off by the coalescence fracture of wrapping wing and anti-wing cracks. Furthermore，the distribution type of 3D flaws will greatly affect some parameters of growth and coalescence of 3D cracks. Especially，the initial growth angle of crack will change by about 10°. Finally，the primary fractured pattern and mechanism of 3D flaw sets are discussed in this paper.

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FUZZY RECOGNITION FOR ROCK CUTTABILITY BASED ON SHIELD DRIVING PARAMETERS

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2008, 27 (S1): -3196 doi:
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Based on shield driving data at Chongqing Yangtze River tunnel and fuzzy diagnosis principle，rock cuttabilities are studied. Point load strength tests of representative mudstone and sandstone in field are carried out. Thrust force and penetration rate(PR) of shield corresponding to the representative mudstone and sandstone are recorded by data acquisition and storage system of shield. Based on multivariate regression analysis，corresponding prediction models of penetration rate are developed，and then the attribution spaces of shield penetration rate are constructed and divided according to rock properties. Rock cuttabilities are flagged by corresponding PR of shield. Making use of fuzzy diagnosis principle，difference between PR in a rock sample and PR in representative rock is defined as a conception of distance. The correspondence between PR and normalized distance is developed. Membership of PR in a rock sample to PR in representative rock is acquired subsequently. Consequently，recognition function for rock cuttabilities is constructed. The rocks along the tunnel are characterized as alternation of mudstone，sandstone and mudstone containing sandstone. These rocks are all subordinate to the range of soft rock to medium hard rock，and the scope of their hardness is not too wide. So the rock cuttabilities are divided into three levels as soft，medium soft and medium hard，based on which the rock cuttabilities along the tunnel is recognized. Results of the rock cuttabilities are beneficial supplements for engineering geology surveying reports during construction；and these results have provided scientific references for predicting the cutter wear and deciding the time of the cutter exchange. When the shield is advancing，accuracy control of shield has too been improved.

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SKEWNESS DISTRIBUTION AND COUNTERMEASURE OF GROUND SETTLEMENT DUE TO ASYMMETRICAL EXCAVATION IN URBAN SHALLOW LARGE-SPAN DOUBLE-ARCH TUNNEL

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2008, 27 (S1): -3203 doi:
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Many practical measures indicate that the settlement distribution of ground surface and vault，plastic zone in surrounding rock masses，and stresses in the middle wall are remarkably asymmetrical，i.e. skewness distribution. The position of maximum subsidence always lies toward the initial excavation side and the ground settlement curve is steeper on the initial excavation side while gentler in the subsequent side. A few empirical formulae such as the one based on the Weibull distribution by fitting the ground settlement curve have been proposed to estimate the skewness. However，the mechanisms of the skewness settlement have not been reasonably analyzed. The issue through a detailed case study based on monitoring data，numerical simulation and back analysis for an urban shallow large-span double-arch tunnel，which is constructed using CD/CRD methods，is considered. Furthermore，specific countermeasures were proposed，i.e. grouting to ground loss，stopping-water- heavy-curtain to limit range of skewness，non-isoparametric supporting to regulate time-space effect. To guarantee the safety of the underground pipelines and ground buildings，risk threshold values and control criteria are put forward based on an integrated approach of time-space effect and structural integrity level.

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SIMULATION AND PREDICTION RESEARCH OF ENCLOSURE STRUCTURE DEFORMATION FOR AN OPEN-CUT METRO STATION

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2008, 27 (S1): -3210 doi:
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[PDF 460 KB] (1284)

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Based on the detailed analysis of the geotechnical investigation report of an open-cut metro station， the numerical simulation has been performed for the metro station using the finite difference program FLAC3D considering the main structures of the metro station，the initial ground stress，the construction process and the physical and mechanical parameters of the stratum. The results show that the enclosure structure and the internal bracing can stably support the surrounding rock. Several suggestions for the construction have been proposed；and the stable values have been predicted for the monitored displacements of the enclosure structure during the construction process. Meanwhile，by monitoring the displacements of the metro station，the stable displacements of eight monitoring points on the enclosure structure have been obtained. Comparing the values and the change tendency of the displacements，it shows that the stable monitoring values of enclosure structure are smaller than the predicted ones by the numerical simulation，but the change tendency of the deformation is consistent. Therefore，the validity of the FLAC3D program is proven in the aspects of estimating the stabilization of the surrounding rock and predicting the displacement in the foundation pit；and an effective and dependable method of the displacement prediction for the similar follow-up projects has been provided.

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ANALYSIS OF SLOPE STABILITY AND ITS INFLUENCE ON DAM SITE SELECTION OF KALA HYDROPOWER STATION

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2008, 27 (S1): -3216 doi:
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The Kala hydropower project，with an installed capacity of 1 080 MW，is located in the middle reach of Yalong River in Liangshan autonomous prefecture，Sichuan Province. The river section where the dam is located is mainly composed of consequent strata of sandstone and slate. The valley slopes are intercalated with hard and soft rock stratum，with well developed erosion gullies and strong physical geology process. Within the 16 km-long river section，9 large landslides with a total volume of 772.05×106 m3 are developed. Due to the steep river banks，the rapid river flow，the narrow valley and the large landslides，any landslides might result in serious reservoir sedimentation or river blockage，and thus endanger the dam and other project structures. Therefore，the stability of these landslides and their influences become the critical factors for the selection of dam site. Stability analysis for the landslides is carried out based on the studies of the geology background，and stability of typical landslide is calculated with limit equilibrium method；potential influences on the project in case of landslide failure are studied based on the analysis and calculation of the landslide scale and their possible surges. Finally，following the principle of “first avoiding then treating”and with the comprehensive considerations of the water power utilization and construction condition of the project，recommendation on dam site selection and suggestions for the subsequent works are proposed.

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ABUTMENT STABILITY ANALYSIS OF ARCH DAM BASED ON 3D NONLINEAR FINITE ELEMENT METHOD

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2008, 27 (S1): -3222 doi:
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The rigid-body limit equilibrium method can not reflect actual stress distribution in rock mass，and finite-element-based strength reduction method also has some problems in judging convergence in abutment stability analysis of arch dam. To solve these problems，multi-grid method is adopted to establish structural grid for finite element computation and slip surface grid for computing factor of safety of slope stability，respectively. Factor of safety of any slip surface or sliding block can be easily worked out from the stress result calculated by finite element method，and consequently combine nonlinear finite element method and limit equilibrium analysis. A perfect elastoplastic incremental analysis method based on Drucker-Prager criteria is considered in nonlinear finite element computation；elastoplastic computation has good convergence for both small step size and large step size，and it can increase computation precision to some certain extent. The method has been implemented in TFINE，a nonlinear finite element method program. Based on analyzing influence of interpolation method and grid density on accuracy of computation results，it is applied to abutment stability analysis of an arch dam. The contrastive analysis with results of the rigid-body limit equilibrium method demonstrates that the computation results are larger then those of the rigid-body limit equilibrium method，however，it is better in accordance with practical conditions when nonlinear stress adjustment in calculation is considered.

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STUDY ON KEY TECHNIQUES FOR CONSTRUCTION OF METRO CROSSING TRANSFER STATION

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2008, 27 (S1): -3229 doi:
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The metro transfer stations are increasing with the network formation of Shanghai urban rail traffic. The technical problems，such as the burying depth of stations increasing，excavating adjacent to stations in operation，rebuilding metro station structures，often appear in metro stations construction. Based on the metro crossing transfer station in Dalian Road，Siping Road in Shanghai，the calculation parameters of various soil strata are gained by comparing the monitored and computing data. The key construction cases，including the foundation pit excavation for the new station crossing the existing station，chiseling diaphragm walls of the interchange section of the transfer station，and the structural force-bearing system transition of interchange connection，are simulated by FEM with soil transversely isotropic elastoplastic model and thin-layer element interface model. The different effects on the operation station are compared when symmetrical excavating and asymmetrical excavating in the deep foundation pits beside the existing station are considered. The impact of chiseling on the both side diagram walls in interchange connection of the exiting station is studied；and the regularities of deformation and internal force variation of the transfer station caused by above construction cases are analyzed. The calculation results indicate that symmetrical excavation and symmetrically chiseling diaphragm walls of the interchange section are safer to structures of the transfer station than that of asymmetrical excavation. Finally，some suggestions are given for the using station and around environmental protection.

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STUDY ON REASON AND SPATIAL-TEMPORAL DISTRIBUTION CHARACTERISTICS OF DEBRIS FLOW IN LONGNAN
AREA ALONG G212

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2008, 27 (S1): -3237 doi:
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The national highway No.212(G212)(Lanzhou—Chongqing) is a main link to connect northwestern region to southwestern region in China. The mountains area along G212 in Longnan is one of the most famous areas for debris flow. Therefore，in order to ensure proper construction and safe operation of the G212，reason and spatial-temporal distribution characteristics of debris flow in Longnan area along G212 are considered. The research area is located in the northeastern fringe area of Qinghai—Tibet Plateau，drape strip of west Qinling. Complicated geological structure，instable faults，fragmentized rock，intensely new structural activities，mass and concentrative rainfall，asymmetric vegetation coverage and improper human activities provide necessary preconditions for debris flow disaster. Firstly，through consulting literatures and field investigation，the engineering geological environment is analyzed，which includes geological structure，stratum and lithology，engineering geological rocks，terrain and physiognomy，new structural activities，rainfall，vegetation and human activities. Then，based on the understanding of the mechanism of landslides in this area，the spatial and temporal characteristics of the debris flow distribution are studied by investigating typical debris flow gullies and linking the engineering geological environment. Debris flows mainly exist in the Bailong River，Min River(the first-level branch of Bailong River) and Beiyu River. The distribution characteristics of time are discussed from three aspects：daily period，month period and age period. Among of them，debris flow appears in July and August based on month period. The results can provide some references to the route selection and proper approaches and measures to deal with geological disasters.

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ANALYSIS OF STRATUM DEFORMATION INDUCED BY OVERLAPPING TUNNELS CONSTRUCTION IN SHALLOW DEPTH

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2008, 27 (S1): -3244 doi:
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Overlapping tunnels will influence each other during construction stage，and will result in a series of problems such as ground subsidence controlling，particularly for watery and weak surrounding rocks in shallow depth. Based on the in-situ information of stratum displacement of Guomao—Laojie overlapping tunnels in Phase I of Shenzhen Metro，basic movement characters of stratum induced by overlapping tunnels in watery and weak surrounding rocks were analyzed. The notable characteristics in construction are to possess a large ground surface subsidence，outburst of stratum deformation，high loss ratio of the stratum，large curvature and slope of the ground surface subsidence. The loss ratio of the stratum is as high as 9.2%，which is much larger than that of common tunnels constructed in normal stratum. The mechanisms and major influential factors of stratum deformation are also explored considering host medium and engineering conditions. Subsequently，corresponding technologic measures of how to control the large deformation in stratum of overlapping tunnels are proposed. The measures were also applied to the construction in Phase I of Shenzhen Metro，and a good effect has been achieved. The research result can provide reference to controlling the stratum deformation induced by overlapping tunnels construction in the similar stratum.

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STUDY ON STRESS-STRAIN PROPERTIES OF ROCKFILL MATERIALS UNDER DIFFERENT STRESS PATHS IN NUOZHADU PROJECT

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2008, 27 (S1): -3251 doi:
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Based on the testing data of the triaxial consolidation tests on the upstream main rockfill materials used to build the dam in Nuozhadu hydropower station under different stress paths，the shear strength and stress-strain properties are studied and the stress-strain parameters of the rockfill materials are obtained. The Nuozhadu hydropower station is located in Lancang River，Yunnan Province. Several conclusions are drawn after an analysis of the properties of the stress-strain under the special stress paths that the stress-strain properties are controlled by the stress paths and the rockfill materials and the actual stress paths are consistent with the assumed stress paths in the triaxial consolidation test. It is found that there is a great difference for the rockfill materials¢ deformation moduli under the different stress states. According to the data of the triaxial consolidation tests，the strength parameters and the deformation moduli of the rockfill materials under different stress paths with a constant stress ratio are figured out. The stress state is one of the main influential factors for the rockfill materials strength and it has close relationship with strength. The relationships among the stress state，the cohesion and the frication-angle，strength parameters are discussed. All these researches are significant for establishing the mechanical constitutive relations of the dam and analyzing the dam¢s stability in Nuozhadu hydropower station

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NUMERICAL INVESTIGATION ON SIZE OF DAMAGE PROCESS ZONE OF CONCRETE STRUCTURES

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2008, 27 (S1): -3261 doi:
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Gradient-dependent damage model is widely used in the simulation of mechanical behaviours of concrete structures，which have localization phenomena. With the principle of nonlocal energy dissipation，the characteristic length of a gradient-dependent damage model should be the distance of two material points whose damage evolution processes can affect each other. Numerical simulations were performed on the evolution of damage process zone of concrete structures，and the size and evolution of damage process zone were studied. The adopted geometrical model is four-point-shearing beam，and ABAQUS/EXPLICIT software are taken as the numerical tools. The main results include：(1) The length of a complete damage process zone is between 0.042 1 and 0.061 2 m for the given double-notched beam，which is 0.15 m in width and 0.40 m in length. Variation of size of damage process zone is caused by variation of strain states，which are shearing dominated at beginning of deformation and tension dominated at the end of deformation. (2) Secondary damage process zone appeared at the end of deformation，and its size is about 0.036 7 m for the given structure. (3) For the single-notched beam with four-point shearing loads，which is 0.10 m in width and 0.44 m in length，the size of damage process zone is 0.047 3 m during deformation process. These results can be referred as the value of the characteristic length of a gradient-dependent damage model.

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STUDY ON ABUTMENT PRESSURE RULE OF OVERLYING STRATA SPATIAL STRUCTURES BASED ON MICROSEISMIC MONITORING

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2008, 27 (S1): -3274 doi:
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As the mining depth increases，many hazards related to the deep overburden collapse such as pressure bump，coal and gas burst will appear，which are caused by the movement of overlying strata. A study of the abutment pressure rule of overlying strata spatial structures is the theoretical basis of controlling the hazards. In this paper，the overlying strata from longwall face to the Earth¢s face as multilayer spatial structures are considered. Based on microseismic monitoring，the movement rules of multilayer spatial structures are studied and the computing models of abutment pressure are set up. The rule of abutment pressure is also analyzed and the computation formulae are gained by using the elasticity theory. The computation results are compared with the results of field microseismic monitoring. Field experiments in Huafeng coal mine show clearly that this method is useful for the prediction of abutment pressure and can provide accurate theoretical basis for controlling the mining hazards caused by the movement of overlying strata.

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APPLICATION OF TRANSFER COEFFICIENT METHOD TO SCHEME DESIGN OF LANDSLIDE TREATMENT WITH SLOPE CUTTING

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2008, 27 (S1): -3281 doi:
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[PDF 243 KB] (1176)

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Slope cutting is a traditional method in landslide treatment. The key issue of slope cutting project is to make it most economical and can maintain stability. In practical engineering，unbalanced thrust force method is used to calculate driving force and residual driving force of slope-sliding blocks，then the optimal dimension and location of slope cutting are searched under the condition that the quantity of the residual driving force of shear outlets of landslide is less than or equal to zero，but its computation is considerably tedious. In allusion to the problem，using the idea of transfer coefficient method，the concept of residual sliding resistance force is introduced and optimal dimension and location of slope cutting can be obtained only after residual sliding resistance force of slope-sliding blocks is calculated. This method doesn¢t need to carry out searching calculation. It is simple and convenient in calculation. The calculation process is as follows：based on the anticipated factor of safety，residual sliding resistance force is calculated inversely starting from the last slide block. The residual sliding resistance force is transferred upwards one by one between the blocks. When the residual sliding resistance force of a block is negative，let it be zero in the next calculation until residual sliding resistance forces of all blocks are achieved. If the residual sliding resistance force of some block is negative，the block is the one that needs to be removed and the quantity of the negative force is the load of the block which needs to be eliminated.

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ANALYTICAL STUDY ON ROCK PROPERTY OF LONG-DEEP TUNNEL WITH CSAMT METHOD

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2008, 27 (S1): -3286 doi:
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[PDF 302 KB] (964)

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In geophysical exploration work for deep-long tunnel，the issue is mainly concentrated on bearing conditions of potential unfavourable geologic body near the area of tunnel line. As for deep-long tunnel，the unfavourable geologic bodies mainly include fault and fractures，and because of distinct electric differences between unfavourable geologic body and surrounding medium，the controlled source audio frequency magnetotelluric(CSAMT) method is used to detect such unfavourable geologic bodies. CSAMT method has been adopted for the study on rock property of tunnel line about rebuilt railway in southwestern area. Based on related standard or literatures on CSAMT method，the data are firstly introduced. With the effective data，indoors data processing can be done. The much attention is paid on the analysis of typical apparent resistivity frequency curves，especially on unfavourable geologic body. The electric response of these unfavourable geologic bodies can be known and the differences between normal stratum and those containing unfavourable geologic bodies can be determined. Smoothing process can be done on original data and then processed data can be inverted. With the comparison between inverted data and original data，the fitness curves can be obtained. It is the fitness information that can help us determine the effect of inversion results. If the fitness data are too large to get correct inverted data，processing flow would return to smooth processing and should change parameters to invert again till getting correct result. Combined with geologic information of relative boreholes，the geologic interpretation can be carried out，and inverted results can also be verified. The study results show that CSAMT method is effective in exploring unfavourable geologic bodies and it is applicable for the analysis of rock property of tunnel line. Therefore，CSAMT method is an instructive guide for tunnel construction.

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GEOLOGICAL GUARANTEE AND CONSTRUCTION CONTROLLING TECHNIQUE OF MAIN ROADWAY CROSSING FAULT ZONE
WITH 435-m FALL

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2008, 27 (S1): -3292 doi:
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[PDF 313 KB] (1103)

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Taking safe construction of the main haulage roadway drilling crossing a 435-m fall and 140-m wide fault zone as engineering background，a study of engineering geological guarantee and construction controlling technique of roadway are performed. Based on the fault rocks，scraping characteristics of rock core shear-sliding surface，water conductivity，recent activities of the faults and regional geological analysis，it is found that roadway construction will not be subjected to fracture water outburst. The key construction technique lies in successful control of head-on hollow roof rock collapse. Under this point，grouting of chemical serum should be chosen as a precaution. Once the roadway is formed，it is important to control large-scale water seepage caused by argillitization of broken loose mudstone and keep long-term stability of roadway. So combination of lag-grouting of controlling rock mass weakened by fracture water and high-intensity pretension supporting to prevent continuous rheological deformation is advocated. As a result，two supporting schemes were considered：as long as self-stability of the roof rock is allowed，the stepwise bolting with anchorage cables installed at key area will be adopted；otherwise，the pre-grouting，spraying，shedding and bolting scheme will be selected instead. Process controlled project is highlighted by dynamic use of advancing pre-grouting，spraying，shedding and bolting to guarantee the roadway¢s safe construction.

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SELECTION OF INITIAL PREDICTION TIME FOR LANDSLIDE WITH VERHULST INVERSE FUNCTION MODEL

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2008, 27 (S1): -3298 doi:
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[PDF 318 KB] (1023)

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It is a key problem to select the initial prediction time with Verhulst inverse function model in landslide study. Generally，there is a problem of selecting by quantitative calculation method in that the independent variable of logarithm function in the model may be negative. The predicted data of accumulated displacement and relative displacement are calculated with all ，and all predicted -curves are formed. The initial prediction time can be selected with analyzing the predicted curves and monitoring curves. The selecting principles are as follows：(1) the predicted displacements can be calculated on points n and n+1 of the monitoring list；(2) the curve configuration of predicted accumulated displacements is similar to the monitoring curve；and (3) the dispersion between the monitoring relative displacement and its predicted value on the point n is the least. The experimental results of several groups of measured data show that the precision of critical sliding time can be obtained within one time interval；and the method to choose is effective.