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2011, 30 (S1): 2593-2593

[PDF] 257 KB (843)

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STUDY OF RELATIONSHIP BETWEEN JOINT ROUGHNESS COEFFICIENT AND STATISTICAL PARAMETERS

WU Yuexiu1，LIU Quansheng1，2，LIU Xiaoyan1

2011, 30 (S1): 2593-2598

[PDF] 352 KB (1589)

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The previous methods for measuring joint roughness coefficient JRC are based on ten standard joint profiles，their errors are large and are disturbed by human factor. Besides，the effects of sample size which is used to scatter the rough joint profile on JRC and statistical parameters are not considered. In order to avoid the measurement error of JRC of ten standard joint profiles，size，the study is conducted from the perspective of numerical simulation of rough joint by considering the range of JRC and the effect of sample. Joint projection height is assumed to accord with the truncated normal distribution；the projection profile of joint is generated with the projection height and sample size of each segment；and rough joint with a certain trace is generated finally. According to Barton′s straight edge method，JRC is measured. Each statistical parameter is calculated；and the relationships between JRC and statistical parameters are fitted with different sample sizes. The results show that：the regression functions between JRC and RMS，CLA are linear，the regression functions between JRC and MSV，Z2，Rp，SF are exponential and the related coefficients are very large. The effect of sample size on results is significant；and it is advised that sample size should be close to the particle size of rock mass. Because that MSV，RMS and CLA can only reflect the average value of projection height of rough joint，while they cannot reflect the effect of weights of various projection heights on JRC. Therefore，it is suggested that Z2 and SF should be adopted to evaluate the value of JRC.

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STUDY OF RELATIONSHIP BETWEEN POISSON′S RATIO AND ANGLE OF INTERNAL FRICTION FOR ROCKS

ZHANG Nianxue1，SHENG Zhuping2，LI Xiao1，LI Shouding1，HE Jianming1

2011, 30 (S1): 2599-2609

[PDF] 453 KB (2678)

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Based on relationship between Poisson′s ratio and angle of internal friction for pure tensile failure，the relationship between Poisson′s ratio and angle of internal friction for pure shear failure is deduced；the shear，brittle shear，plastic shear and tensile failures as well as creep deformation distribution zones are defined by Poisson′s ratio and angle of internal friction. Based on the analysis of test data，the linear boundary lines for tensile shear and shear tensile failures are determined；the semi-empirical formulae of brittle shear failure criteria are established. According to the semi-empirical formulae，Poisson′s ratio and angle of internal friction and shear strength of single rock specimen can be calculated easily；the mesoscopic failure modes of rock can be zoned. By comparing with the results of triaxial compression tests，the mechanisms for different rock failures are explained. The case study demonstrates that it is practical to use the Poisson′s ratio to calculate shear strength of single rock specimen. The classification of rock failure zones can be used in prediction of failure modes and failure types.

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PHYSICAL SIMULATION STUDY OF SIMILAR MATERIALS FOR ROCKBURST

LI Tianbin1，WANG Xiangfeng1，2，MENG Lubo1

2011, 30 (S1): 2610-2616

[PDF] 338 KB (828)

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According to the test results of physico-mechanical properties of similar materials with various mixture ratios，a type of similar material with the most obvious tendency of rockburst is selected to produce a large-size model and to perform the physical simulation test of rockburst. The physical simulation test is carried out by means of opening hole simulating tunnel after model loading，combined with a typical section of diversion tunnel in a hydropower station. The study results show that，under the condition of natural stress state in the model boundaries，the arch crown，spandrel and side walls of tunnel respectively produce the obvious catastrophic phenomena of stress and strain；and the acoustic emission counts of surrounding rock also increase rapidly after tunnel excavation，showing the clear features of rockburst. The spalling，buckling and cracking phenomena of surrounding rock appear in model under over loading conditions. It is concluded that the tunnel in the hydropower station will mainly occur the tensile rockburst with the patterns of spalling，buckling and cracking.

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STUDY OF MECHANICAL BEHAVIOR RESPONSE OF SALT ROCK UNDER CYCLIC LOADING

GAO Hongbo1，2，LIANG Weiguo1，XU Suguo1，ZHANG Chuanda1，YANG Xiaoqin1

2011, 30 (S1): 2617-2623

[PDF] 306 KB (970)

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To study the mechanical behavior of salt rock under cyclic loading，the uniaxial compression tests were conducted with thenardite，bedded thenardite and rock salt specimens respectively. It is demonstrated that the strength of thenardite under cyclic loading is lower than that under monotonic loading. The strength of bedded thenardite with calcium mudstone is higher than that of pure thenardite. However，the strain at the point of peak strength is less than that of the later because of the hard interlayer effect. Different from other rocks，at the initial period，the loading and unloading curves almost overlap each other. With the development of loading stress and cyclic time，the phenomenon of the plastic hysteresis loop during unloading period occurs slightly，but the loop area is small. During the later period，the Young′s modulus in the unloading process is larger than that in the loading process to certain extent due to the slight plastic hysteresis. For the bedded thenardite，the Young′s modulus is larger than that of pure thenardite because of the effect of the hard interlayer. Simultaneously，it is found that the recovery of plastic deformation of the bedded thenardite is larger than that of pure salt rock during the unloading process. The Young′s modulus of salt rock，on the whole，is almost consistent during the cyclic loading even with slight plastic recovery hysteresis at the later period with stress and cyclic number development. The common phenomenon of Young′s Modulus decreasing with yield stress in yielding and damaging periods for general rock material does not happen for salt rock. From the point of energy theory view，the strength decrease magnitude of rock during cyclic loading is relative to cyclic time and accumulated area of the hysteresis loop. In the tests，the loading and unloading curves are almost overlapped and the hysteresis loops are small，therefore the strength decrease magnitude is also less. Consequently，it could be deduced that the strength of the surrounding salt rock in a salt cavern storage will be less affected by cyclic injection and withdraw. However，strong pressure fluctuation could make energy accumulated in rock mass，thus the strength and longevity of the cavern are inevitably harmed.

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NOMOGRAPH FOR DETERMINATION OF PITCH PROPERTY OF DISCONTINUITY TRACE ON ROCK EXCAVATED SURFACE

LIU Ming，HUANG Runqiu

2011, 30 (S1): 2624-2633

[PDF] 801 KB (913)

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By analyzing the intersection of discontinuity with slope surface，the classification of discontinuity and its trace in orientation with respect to slope is made. The feature triangle，with structure manifest，operation easy and relation simple，to determine intersection type of discontinuity with slope and pitch property of its trace is proposed by the comparison of planar projection with stereographic projection for them. By the concurrent and collineation principle of the orientating variables(elements of attitude)，the nomograph to determine pitch property of discontinuity trace is drawn，with which to illustrate the distribution of various intersection properties in the value space. The application of this nomograph should be helpful to collect and check on the locating and orientating data of discontinuities，and authentic evaluation of the structure of rock mass.

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STUDY OF NONLINEAR VISCOELASTO-PLASTIC RHEOLOGICAL MODEL OF SANDSTONE WITH WEAK PLANE

ZHANG Zhiliang1，2，XU Weiya1，2，WANG Rubin1，2，ZHANG Yu1，2

2011, 30 (S1): 2634-2639

[PDF] 292 KB (777)

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The sandstone with weak plane is sampled from the compressive zone of the left bank dam foundation of Xiangjiaba hydropower station. Shear rheology tests are carried out for the rock by using CSS–3940YJ rock shear rheology testing machine. The test results show that the sandstone is the typical soft rock，and the rock shows significant metastable rheological property under the constant shear stress. When the stress reaches a certain level，the accelerative creep damage of rock occurs after the primary creep and metastable creep. The nonlinear rheological component is improved according to the shear creep behavior of the sandstone with weak plane，and it is equivalent to Newton dashpot when the stress is less than threshold as well as nonlinear viscoplastic component when the stress exceeds threshold. By connecting the improved rheological component and generalized Kelvin model in series，a new four-component nonlinear viscoelasto-plastic rheological model of rock is proposed，which can fully reflect the metastable and accelerative creep properties of rock material. The model has advantages of simple structure and few parameters. The constitutive equation of this rheological model is deduced；and the nonlinear creep property of rock is carried out based on the theoretical analysis. The shear rheological parameter identification of the rock is carried out based on the proposed model，and the method of parameter identification is mainly investigated when the stress level exceeds the threshold. The comparisons between calculated results of nonlinear rheological model and tested results show that the proposed nonlinear viscoelasto-plastic rheological model is available and reasonable.

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APPLICATION STUDY OF NONSTATIONARY NISHIHARA VISCOELASTO-PLASTIC RHEOLOGICAL MODEL

PAN Xiaoming1，2，YANG Zhao1，2，XU Jiancong1，2

2011, 30 (S1): 2640-2646

[PDF] 326 KB (956)

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Based on Nishihara model by introducing the nonlinear Bingham viscoplastic component and adding a Kelvin component，a new nonlinear viscoelasto-plastic rock rheological model(nonstationary Nishihara model) is proposed，which can fully reflect the global rheological property of rock material. Rock viscoplastic rheological parameters nonlinearly change with time under high stress level. According to the UMAT format requirement of ABAQUS and plane strain or stress finite element theory of nonstationary Nishihara viscoelasto-plastic rheological constitutive model，the corresponding UMAT codes are programmed. The numerical test results show that the establishment of nonlinear viscoelasto-plastic rheological model can uniformly describe creep process under different stress states，which demonstrate the extensive adaptability of the model. Using the nonstationary Nishihara viscoelasto-plastic model，the rheological numerical analysis is applied to rock slope. Under the large load on the top of slope，the slope vertex enters into the accelerated creep stage firstly；while the midpoint and end point of slope are under a low stress state or the viscoelastic stage，the displacement tends to be a constant value finally. These results indicate that the developed model is correct and reliable，and will have good application prospects.

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STUDY OF ROCK DAMAGE CONSTITUTIVE MODEL AND DISCUSSION OF ITS PARAMETERS BASED ON HOEK-BROWN CRITERION

SHI Chong 1，2，JIANG Xinxing1，2，ZHU Zhende1，2，HAO Zhenqun1，2

2011, 30 (S1): 2647-2652

[PDF] 313 KB (928)

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Based on Hoek-Brown criterion and hypothesis of rock particles obeying Weibull random distribution，the damage parameter is modified reasonably considering the characteristic of rock post-peak softening. The three-dimensional damage constitutive model reflecting the whole process of rock fracture is established；and the test is conducted to verify the validity of model. The test results show that the model results are in good agreement with test results. On this basis，the influences of Weibull distribution parameters and Hoek-Brown criterion parameters on the rock damage constitutive model are discussed；and it will provide good reference to the engineering applications.

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EXPERIMENTAL STUDY OF PHYSICO-MECHANICAL PROPERTIES OF FAULT MATERIALS FROM SHENXIGOU RUPTURE OF LONGMENSHAN FAULT

LI Bixiong1，2，DENG Jianhui2

2011, 30 (S1): 2653-2660

[PDF] 728 KB (925)

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Mechanical property of fault gouge is the weakest in the geological materials composing the fault. In order to understand the influences of physico-mechanical properties of fault gouge on the characteristics of ground motion near fault and the damaged styles of structures，the direct shear tests on undisturbed samples of fault materials containing fault gouge from Longmenshan fault are conducted using conventional soil test method in laboratory；and investigations into natural fault material structures and mineral distributions are carried out. The slice identification results show that，mineral composition of black fault gouge is similar to that of gray breccia and the color of black is caused by limonite. The basic physical property test results show that the grain size of black gouge is smaller than that of gray gouge，distribution of grain size is very inhomogeneous，and the specific gravity of black gouge is less than that of gray gouge. Direct shear test results show that shear strength of fault materials with low void ratio is higher than that with high void ratio；and the peak shear stresses are larger for these specimens with high water content compared to those of specimens with low water content but the same void ratio. The maximum shear stresses do not appear until the shear tests stop，instead，the entire shear displacement is characterized by strain hardening or perfectly plastic behavior. The shear strength reaches the lowest for those specimens with shear zone in the interface between different layers.

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STUDY OF CREEP DAMAGE VARIABLE OF MICA-QUARTZOSE SCHIST BASED ON MICROSCOPIC TEST

CHEN Wenling1，2，3，ZHAO Fasuo1，2，3，GONG Hujun4

2011, 30 (S1): 2661-2666

[PDF] 726 KB (847)

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Triaxial creep characteristics of mica-quartzose schist are obtained by triaxial creep test. The polarizing microscope and scanning electron microscope are used to observe the radial and axial slices of mica-quartzose schist for three triaxial creep stages，which are no forces stage，the upcoming accelerative creep stage and the creep damage stage；and the microstructure change of mica-quartzose schist during triaxial creep process is observed. The effect of microstructure change on mica-quartzose schist is attributed to the damage variable and change in porosity. The relations of macro-stress and macro-strain with damage variable and porosity are established by statistical damage theory and simplified mechanical model，and the creep damage variable is deduced. The variation of the creep damage variable in the whole creep curve of mica-quartzose schist is analyzed；and the corresponding relationship between the creep damage variable and microstructure change of each creep stage is studied；the creep failure is interpreted from the perspective of creep damage. The creep damage variable is also simplified according to the whole creep curve in order to use conveniently.

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STUDY OF CORRELATION BETWEEN FRACTAL DIMENSION AND RQD OF THREE-DIMENSIONAL JOINTED ROCK MASS

XU Liming，WANG Qing，CHEN Jianping，ZHOU Fujun，TAN Chun

2011, 30 (S1): 2667-2674

[PDF] 324 KB (909)

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Firstly，the three-dimensional network simulation technique is used to establish the model of randomly distributed discontinuities in the statistical homogeneity zone of rock mass structure. The structure of jointed rock mass is regenerated on the screen of computer. Then，the fractal dimension of three-dimensional jointed rock mass is calculated by using fractal theory. The three-directional scanlines which are parallel to x，y and z axes respectively are set in the three-dimensional network model of jointed rock mass to obtain the rock quality designation(RQD). By analyzing the data of fractal dimension and RQD，it is found that the RQD decreases with the increase in the fractal dimension，which have a good linear relationship. The formulae of fractal dimension and RQD under different thresholds of three-dimensional jointed rock mass are deduced. Based on the slope of the linear relationship curve between fractal dimension and RQD，the most reasonable threshold is determined.

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ANALYSIS OF ENERGY DISSIPATION IN PROCESS OF UNLOADING CONFINING PRESSURE FAILURE OF ROCKS

ZHU Zeqi1，SHENG Qian1，XIAO Peiwei2，LIU Jiguo3

2011, 30 (S1): 2675-2681

[PDF] 394 KB (1002)

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Based on the analysis of energy transformation between testing machine and rock specimen，the energy dissipation law in process of unloading confining pressure failure and the relationships between energy and rock specimen deformation and confining pressure are analyzed comprehensively. The study results show that the energy dissipation is greatly related to the failure characteristic of rock specimen and confining pressure. The energy dissipation of ductile failure is greater than that of brittle failure. For the same failure mode，the energy dissipation obviously increases with the increasing confining pressure. Two unloading confining pressure tests show that the energy dissipation of rock specimen presents nonlinear relationship with time，while the energy dissipation of rock specimen presents linear relationship with lateral deformation. Under the same lateral deformation level，the greater the confining pressure is，the greater the energy dissipation is，and the rock specimen presents more brittle characteristic.

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EXPERIMENTAL STUDY OF INDICES FOR EVALUATING SMALL DISTURBANCE IN UNDERGROUND-CROSSING CONSTRUCTION

CHEN Bao，XU Shengwen，PENG Fangle，LI Qiufang，YE Weimin

2011, 30 (S1): 2682-2689

[PDF] 392 KB (778)

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In order to control the soil disturbance caused by construction passing beneath highly dense building districts and to ensure the construction influence within small disturbance domain，the determination of indices for evaluating small disturbance and investigation on their variations under different stress paths during underground-crossing construction have become crucial issues. From the perspectives of stress disturbance and strain disturbance，the shear modulus，pore water pressure and critical stress state surface are chosen as main indices for small disturbance evaluation. The curves of modulus，pore pressure and stress vs. strain for undisturbed soil are obtained by laboratory tests to quantitatively analyze the changes in stress and strain under different stress paths induced by underground-crossing construction. The results indicate that the shear modulus decreases sharply as strain increases in a small strain domain，but the change ranges of shear modulus are different under different stress paths. Meanwhile，a slight change in strain may lead to an evident change in pore pressure. Moreover，according to the failure surface and the definition of disturbance ratio，a critical stress state surface may be specified for the control of small disturbance in underground-crossing construction.

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STUDY OF MECHANICAL PROPERTIES OF JINTAN SALT ROCK BASED ON DIRECT SHEAR TESTS

YAO Yuanfeng，YANG Chunhe，JI Wendong

2011, 30 (S1): 2690-2696

[PDF] 385 KB (896)

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A series of direct shear tests are carried out by using testing machine RMT–150C to investigate the characteristics of salt rock in Jintan gas storage. The shear stress of dilatancy and failure characteristics are deeply analyzed by considering the salt rock as a kind of polycrystalline polymer. The results show that shear failure of salt rock is ductile failure，and the shear displacement corresponding to ultimate shear strength is generally 4–6 mm；the shear displacements of several specimens even reach 7–8 mm. The whole curves are relatively flater，the shear strength is not very clear，which is mainly due to the grain dislocation alternatively. Finally，the shear strength parameters c and is 3.16 MPa，44.7°，respectively. The residual strength and the normal stress is basically a positive correlation，and the residual strength is much higher，about 50%–80% of shear strength which indicates a strong bearing loading capacity for salt rock only by friction. Salt rock shear dilatancy occurs before the residual stress and after peak stress，and the initial stress of shear dilatancy is close to the stress for termination under much higher normal stress. Shear failure section of salt rock is not a plane but a fracture zone. It can be seen that part of the section has clear scrape which is similar to the“plow effect”. This will help to improve the shear capacity of salt rock. The results also have great reference for understanding the mechanism of Jintan salt rock and investigating the stability of underground gas storage.

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STUDY OF STRESS SENSITIVITY AND ITS INFLUENCE ON OIL DEVELOPMENT IN LOW PERMEABILITY RESERVOIR

LIU Renjing1，2，LIU Huiqing2，ZHANG Hongling2，TAO Ye3，LI Ming2

2011, 30 (S1): 2697-2702

[PDF] 244 KB (1385)

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To deeply research the stress sensitivity of low permeability reservoir，the strong stress sensibility of low permeability reservoir is theoretically proved based on the capillary bundle model with varying diameters. The effects of effective stress，pore structure，stress loading mode on permeability are studied by laboratory experiments with varying fluid pressures，while keeping confining pressure steady. The effects of stress sensitivity on oilfield development under different formation conditions are studied by numerical simulation. The results show that：The effect of stress variation on porosity is very small，but its influence on permeability is very large. Comparing with high permeability reservoir，stress sensitivity of low permeability reservoir is stronger. Stress sensitivity is closely relative to effective stress，pore structure and stress loading mode. The stress sensitivity increases as the permeability decreases，the effective stress and the stress loading velocity increase. There exists permanent damage on permeability while the effective stress reduces，and the permeability cannot recover to the initial value. The producing pressure drop of the production well has a good exponential relationship with stress sensitive coefficient. The stronger the reservoir′s heterogeneity is and the lower the average permeability is，the larger the stress sensitivity is，and thus its effect on oil production is larger. However，the effect of rhythmicity on stress sensitivity is small. These results have guidance to develop low permeability reservoir reasonably.

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INFLUENCE OF MICROCRACKS ON STRENGTH PARAMETERS OF ENGINEERING ROCK MASS

FAN Lei，ZHOU Huoming，ZHANG Yihu

2011, 30 (S1): 2703-2709

[PDF] 282 KB (726)

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By analyzing the tip stress field of compressive-shear microcrack，the initiation strength of rock mass containing crack is estimated. The results show that the initiation strength of rock mass has a relationship to the angle between microcrack and the orientation of the maximum principal stress and confining pressure. When the confining pressure increases，the initiation strength increases，but the initial angle will decreases. Only when the angle between the microcrack and the orientation of the maximum principal stress is in a certain range，the microcrack has an effect on the initiation strength of rock mass，and this range will reduce with the increasing confining pressure. Furthermore，the microcrack needs high applied force to keep propagating. Therefore，the failure of shallow engineering rock mass is mainly controlled by the penetrated cracks. The influence of microcracks on the mechanical behaviour of rock mass can be neglected when using the numerical methods.

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STUDY OF COMPACTION CHARACTERISTICS AND STRENGTH RECOVERY OF ROCK IN EXCAVATION DISTURBED ZONE

LEI Ming，HASHIBA Kimihiro，FUKUI Katsunori，OKUBO Seisuke

2011, 30 (S1): 2710-2719

[PDF] 418 KB (668)

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To investigate time-dependence behaviors of compacted specimens，loading rate-dependency of the specimen in uniaxial compression was investigated in this study. A rock specimen was，at first，completely fractured and then compacted in a steel cylinder. After pushed out of the cylinder，the compacted rock specimen was loaded in the alternating loading rate test，in which a single rock specimen was loaded at two alternating loading rates with a predetermined strain interval ，to obtain two stress-strain curves corresponding to the two loading rates to investigate the loading-rate dependency accurately. It was found that strength recovery was remarkable for Tage tuff，Kimachi sandstone and Kawazu tuff，the uniaxial compressive strengths increase with the maximum axial load in the compaction test. But strength recovery was poor for Sanjome andesite under the testing conditions. In the alternating loading rate test，stress fluctuated with alternating loading rates through the whole test. For the four rocks，when the maximum axial load in the compaction test was large，loading-rate dependency of uniaxial compressive strength of the compacted specimens was found to be consistent with the intact ones. When the maximum axial load in the compaction test was small，the extreme values ， of parameter n of loading rate-dependency were calculated. Parameter n of the intact specimen lied in the maximum and minimum ，and did not differ too much. The results indicate that it is expectable for strength recovery to occur for rocks in the excavation disturbed zone after properly being supported for a long time. And time dependency of fractured rock around an underground opening was similar to that of the intact surrounding rock mass. It will be reliable to use the same parameters in the constitutive equation for rocks in the intact and excavation disturbed zones，to simplify numerical simulation of the time dependency behaviors of underground structures.

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PRELIMINARY RESEARCH ON COMPLETE TRACE LENGTH DISTRIBUTION BASED ON AREAL SAMPLES

ZHANG Guoqiang1，2，DENG Jianhui1，2，FEI Wenping1，2，ZHANG Ru1，2

2011, 30 (S1): 2720-2729

[PDF] 403 KB (758)

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A sampling window method is adopted to estimate the origin moments of trace length for the Poisson disc joint model，and the origin moment equations of trace length are deduced from the complete trace intersected with the circular and rectangular sampling windows. When the rectangular sampling window covers the maximum trace length of the infinite sampling window，the three trace number equations are proposed to estimate the number of the traces. On this basis，the concentric sampling window method is proposed to estimate the appropriate sampling window size which not only covers the maximum trace length of the infinite sampling window，but also contains the appropriate number of complete trace length samples. Based on the mathematical characteristics of the Poisson point process，when the joint diameter distribution is continuous，the approximate form and constraints of polynomial of the trace length distribution are proposed in the infinite sampling window. If the appropriate rectangular sampling window size was verified by concentric sampling window method，an estimation method is proposed to estimate the complete trace length distribution. The maximum trace length of the infinite sampling window is inferred by using the small step searching algorithm. The origin moment equations of trace length are tested for accuracy by theoretical solutions of two cases. To check the validity of concentric sampling window method and complete trace length distribution inference method，an case is simulated by Monte Carlo method，and their results are compared with theoretical solutions.

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EXPERIMENTAL RESEARCH ON INFLUENCE OF TEMPERATURE ON MECHANICAL PROPERTIES OF COAL CONTAINING METHANE

XU Jiang，ZHANG Dandan，PENG Shoujian，LIU Dong，WANG Lei

2011, 30 (S1): 2730-2735

[PDF] 312 KB (1201)

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By using the self-developed triaxial servo-controlled seepage equipment for thermo-fluid-solid coupling of coal containing methane，the triaxial compressive tests on moulded coal containing methane are conducted under different temperatures；and the influences of temperature on deformation and mechanical properties of coal containing methane are studied. The results show that the deformation of coal containing methane increases with the increase in temperature under the same stress conditions；the axial，radial and volumetric strains have different trends in different temperature ranges，the changing speed of radial strain will exceed that of axial strain when temperature exceeds 60 ℃. The failure angle increases slightly with the increase in temperature. The compressive strength，residual strength and elastic modulus decrease gradually with the increase in temperature，but their trends are different in different temperature ranges. Poisson′s ratio increases at the beginning，then it decreases as temperature increases. It concludes that the temperature plays an important role in the deformation and mechanical properties of coal containing methane；the increase in temperature will weaken the strength of coal containing methane generally；the changing trends of deformation and mechanical properties of coal containing methane are different in different temperature ranges. The results will provide a certain referential value for deep mining and roadway support.

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STUDY OF BURSTING LIABILITY OF COAL AND ROCK

QI Qingxin1，2，PENG Yongwei2，3，4，LI Hongyan1，2，LI Jiqing2，3，4，WANG Yougang2，3，4，LI Chunrui2，3，4

2011, 30 (S1): 2736-2742

[PDF] 279 KB (1464)

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Based on the experimental data，the data of bursting liability of coal and rock are analyzed. According to the problems existing in the industry standard of bursting liability of coal and rock，the uniaxial compressive strength(UCS) of coal selecting as a new index to evaluate the bursting liability of coal is put forward，and the criterion is also involved. The applicability of previous bursting liability index of roof rocks is analyzed. The new formula and its new index and criterion for bursting liability of roof rocks are deduced based on the freely supported beam model. The relationships between the brittleness index，moisture content，etc. and the bursting liability are analyzed. The results show that the UCS of coal can be used as the index to evaluate the bursting liability of coal. The calculated results of bending energy index based on the freely supported beam model are consistent with actual condition.

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EXPERIMENTAL STUDY OF PORE EVOLUTION LAW DURING DISSOLUTION-RECRYSTALLIZATION FOR GLAUBERITE

LIU Zhonghua1，2，HU Yaoqing1，XU Suguo1，LIANG Weiguo1，YANG Dong1，ZHAO Yangsheng1

2011, 30 (S1): 2743-2748

[PDF] 393 KB (856)

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The glauberite samples are scanned at various dissolution-recrystallization times by using the high-precision micro-CT test system μCT225KVFCB；and the evolution laws of dissolution-recrystallization are studied from the meso-scopic perspective with X-ray attenuation coefficient. The results show that in the dissolution-recrystallization process，the porosity of glauberite increases gradually；the total specific surface area decreases gradually；the mean pore diameter，the specific surface area of passage and the largest passage increase at first and then decrease. These results have great significance for the implementation and control of the in-situ dissolution mining of glauberite deposits.

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ANALYSIS OF CALCULATION METHOD OF VERTICAL PRESSURE IN LOOSE ROCK MASS AND RESEARCH ON DIVIDING LINE STANDARD FOR DEEP- AND SHALLOW-BURIED TUNNELS

QU Xing，LI Ning

2011, 30 (S1): 2749-2757

[PDF] 343 KB (1059)

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Calculation of the rock pressure is still primarily based on the loose media theory，but the existing criteria cannot clearly define which class of surrounding rocks is the loose rock mass，producing the negative values in the calculating results. Meanwhile，the division of deep- and shallow-buried tunnels as an important issue is not still a final conclusion. Taking the rectangular tunnel with arch crown as the analysis object，the comparative analysis is carries out，and the difference of several methods of shallow-buried tunnel lies in stress analysis method，application of shearing strength theory and method for transforming lateral pressure of wedge body into earth pillar pressure. The basic condition of tunnel shape which can make sure to not produce negative value is obtained by using the formulae of Terzaghi，Xie Jiaxiao and Bierbaumer. Considering the advantages and disadvantages of existing division methods of deep- and shallow-buried tunnels comprehensively，the dividing line standard of deep- and shallow-buried tunnels is proposed which is between M. M. Promojiyfakonov law and Bierbaumer law. Taking the hole span as criterion，the fitting formula of correction factor which can consider comprehensive impact of cavity is built，and the rock mass mechanical parameters are considered in process of formula establishment.

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STUDY OF CREEP PROPERTIES OF SALT ROCK WITH LOGGING DATA

LIU Wei1，XIAO Lizhi1，XIE Ranhong1，ZHU Yuqing2

2011, 30 (S1): 2758-2763

[PDF] 279 KB (736)

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Based on five logging data，the crossplot and caliper vector techniques are introduced to build the logging evaluation method with multi-parameter，for example，caliper，caliper difference，borehole cross-sectional area，caliper integral(borehole vertical-sectional area)，borehole volume. Four crossplot methods clearly show the first stage and the second stage of creep under certain underground geological conditions. The first stage of creep is after 30 days. In this period the slope of creep curve and creep velocity are larger，and the creep velocity presents the trend of attenuation. The slope of creep curve and the creep velocity become smaller，and creep goes into the second stage. It demonstrates that the logging data can better evaluate the creep properties，and it can provide effective reference for the future running stability analysis of Jintan gas storage.

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STUDY OF STRENGTH REDUCTION METHOD CONSIDERING MATERIAL DEFORMATION AND FAILURE CHARACTERISTICS

ZHANG Qiang，GE Xiurun，WANG Shuilin，LI Chunguang

2011, 30 (S1): 2764-2769

[PDF] 351 KB (872)

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Based on post-peak progressive failure process of material，the slope and dam foundation asynchronous strength reduction method conforming to the geotechnical materials deformation and failure law is proposed. And the calculation method of asynchronous reduction ratio is given based on Mohr-Coulomb criterion. Meanwhile，considering the different dilatancy properties of rock mass with different stress states and plastic deformation，the user subroutine USDFLD is compiled using the field variable interface of ABAQUS program. Then the dilatancy angle will varies with the minimum principal stress and plastic shear strain. Finally，an example is analyzed. The results show that：(1) At the working state of hydropower station，the stress level of the potential sliding surface stress is enhanced significantly，and it changes the dilatancy characteristics of rock mass on sliding surface. The factors of safety of dam foundation are obviously different from those with associated and non-associated dilatancy angles. (2) The factor of safety decreases significantly with the increase in asynchronous reduction ratio. Therefore，only considering the geotechnical materials′ real deformation law and failure process can correctly represent the factors of safety of slope and dam foundation. The analysis can provide meaningful results for the optimization design and stability estimation of large scale slope and dam foundation engineering.

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EXPERIMENT AND CALCULATION MODEL FOR ESTIMATING EFFECTS OF ANCHOR-ROOT AT BOTTOM OF FULL-LENGTH BONDED BOLT

LIU Bo1，2，LI Dongyang1

2011, 30 (S1): 2770-2776

[PDF] 375 KB (654)

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Installing the anchor-root at the bottom of full-length bonded bolt in rock foundation could not only strengthen the anti-pullout capability of bolt anchorage system but also reduce the bolt length. A series of laboratory and in-situ tests are carried out to study the behavior of anchor-root. Two groups of bolts with different lengths are tested for comparing the curves of axis force along the depth，and one group of anchor-root bolts is installed for tests. The relationships between the installation location of anchor-root，the anchorage length，the bolt diameter，the shear stiffness between bolt and mortar are studied. The experiment results show that because the load transmits from the top to the bottom，the anchor-root plays the role when the small load is applied on short full-length bonded bolt. On the basis of curve characteristics of bolt axis force，an assumption that the anchor-root role is equivalent to anchorage length added is proposed，and the calculation model is established. Compared with measured data，this model can be used to predict the effect of anchor-root at the bottom of full-length bonded bolt.

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EXPERIMENTAL RESEARCH ON ANTI-PENETRATION AND ANTI-EXPLOSION PROPERTIES OF GREEN ULTRA-HIGH PERFORMANCE FIBER REINFORCED CEMENT-BASED PROTECTIVE MATERIALS

SHE Wei1，ZHANG Yunsheng1，SUN Wei1，FANG Qin2，RONG Zhidan1，ZHANG Wenhua1，LIU Jianzhong3

2011, 30 (S1): 2777-2783

[PDF] 389 KB (898)

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A series of ultra-high performance engineering protective materials with compressive strength higher than 100 MPa is prepared by utilizing composite mineral admixtures(20%–50% mass replacing portland cement)，polycarboxylic type high performance water reducer(water reducing ratio 40%)，short and fine steel fibers on normal shaping and curing condition. Based on the empirical formula，the properties of anti-penetration and anti-explosion of target specimens with different compressive strength(C100，C150，C200) are investigated. The experimental results show that the green ultra-high performance concrete(GUHPC) has excellent performance in anti-penetration and anti-explosion，especially in the C200 target specimens. The corresponding energy dissipation per meter，coefficient of penetration and coefficient of explosion cavity radius are 516 kJ/m，0.389 mm2•s/kg and 0.051 m/kg1/3，respectively. Its ability of anti-explosion is equivalent with reactive powder concrete(RPC)，in addition，the performance of anti-secondary explosion and spalling resistance is excellent.

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EXPERIMENTAL RESEARCH ON EFFECTS OF GAS SATURATION ON ACOUSTIC WAVE VELOCITY OF CARBONATE ROCK

ZHU Honglin，LIU Xiangjun，LIU Hong

2011, 30 (S1): 2784-2789

[PDF] 195 KB (1186)

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The variations in the P- and S-wave velocities，the ratio of P-wave velocity to S-wave velocity(Vp/Vs) of carbonate rock with different gas saturations are studied by using the experimental methods. The results show as follows：(1) With the increase in gas saturation，the P-wave velocity and Vp/Vs both show a decreasing tendency，while S-wave velocity is almost unaffected. (2) The acoustic wave frequency has some influence on the acoustic wave velocity and Vp/Vs. The main distribution of Vp/Vs is varied with different frequencies，general rule is that Vp/Vs when Sg = 0% is greater than that when Sg = 100%. (3) Completely regarding water-saturated rock as the water zone，with the increase in gas content in water zone，the Vp/Vs will begin to decrease from the background value，the sharper decline illustrates transition from the water zone to the gas zone. Meanwhile，combining with the decreasing character of P-wave velocity，the theoretical basis for indicating gas zone utilizing acoustic logging data is settled. (4) Although Vp/Vs can offer some reference for identifying gas zone of carbonate rock，other relevant parameters must be combined to accurately assess the reservoir in practical application.

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EXPERIMENTAL STUDY OF BOND-SLIP RELATIONSHIP BETWEEN BOLT AND MORTAR AND THEORETICAL SOLUTION TO FAILURE PROCESS

LIU Bo1，2，LI Dongyang1，DUAN Yanfang1，JIN Guangling1，TIAN Ning1

2011, 30 (S1): 2790-2797

[PDF] 359 KB (845)

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To research the bond-slip relationship between the bolt and mortar for rock foundation，the pullout test for short bolt in laboratory and uplift test for long bolt in field were carried out respectively. In laboratory，6 kinds of mortar were mixed to analyze the effect of the compressive strength and sand ratio of mortar on bold-slip relationship. Then，the best mix proportion is presented. Based on the local deformation theory，a mathematics model is built，and it can describe the change process of bolt-mortar interface undergoing elastic，plastic softening and slip when the long bolt is subjected to the uplift load. The model was applied to analyzing the field test data. The results show as follows：(1) The effective anchorage depth is a constant value if uplift load is less than elastic ultimate load，or it will increase. (2) The attenuation degree of axis force with depth will slow because the interface plastic softening and cracking occur in top of bolt. Finally，the calculation formula of effective anchorage depth increasing with the increase in uplift load is presented.

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EXPERIMENTAL STUDY OF VENTILATION PROPERTY AND PARAMETERS OF CUBIC ARRANGED CEMENT BALLS

TONG Gangqiang，LI Dongqing，ZHANG Mingyi

2011, 30 (S1): 2798-2802

[PDF] 206 KB (728)

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The block stones are widely used in Qinghai—Tibet railway construction due to the characteristics of good ventilation and heat transfer ability. It plays a positive effect on cooling permafrost. The air flow law inside the block stone layer has become a hot issue. But the particle size and shape of block stones are all irregular，and the packing methods are also random. Therefore，if directly conducting the ventilation experiment with block stone layer，the results obtained are accidentally and uncertainly. In order to avoid all above disadvantages，the permeability and inertial resistance coefficient of layer of cubic arranged cement ball with different diameters are studied by using wind tunnel tests. The diameters of balls are 0.15，0.20，0.25 and 0.30 m，respectively，and the porosities of cubic arranged cement balls were all 0.476. Results of the wind tunnel tests show that the internal pressure gradient of the cement ball layer has a good nonlinear quadratic curve relationship with the seepage velocity. The permeability and the inertial resistance coefficient are related to the diameter of cement balls. With the increase in the diameter of cement balls，the permeability increases and the inertial resistance coefficient decreases.

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NUMERICAL ANALYSIS FOR VISCOELASTO-PLASTIC RHEOLOGICAL PROPERTY OF INTERLAYERED ROCK MASS

XIONG Liangxiao1，2，YANG Linde2

2011, 30 (S1): 2803-2809

[PDF] 254 KB (1296)

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The uniaxial creep tests on greenschist from auxiliary tunnel at Jinping II hydropower station are carried out. Taking the interlayered rock mass composed of greenschist and marble as subject，the numerical analysis for uniaxial compression creep test on interlayered rock mass is conducted by using FLAC3D. The experimental and analytical results show that the failure strength of interlayered rock mass decreases with increasing dip angle of marble interlayer when the dip angle is smaller than 60°，while the result will be quite on the contrary when the dip angle is larger than 60°. Reuss model or Voigt model is applicable for forecasting the failure strength of interlayered rock mass when the failure strength ratio between marble and greenschist is small.

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STUDY OF CREEP PARAMETERS OF MICA-QUARTZOSE SCHIST DURING TRIAXIAL CREEP TEST

CHEN Wenling1，2，3，ZHAO Fasuo1，2，3，GONG Hujun4

2011, 30 (S1): 2810-2816

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The variation law for the creep parameters of mica-quartzose schist—elastic modulus and viscosity coefficient during triaxial creep process is obtained by the triaxial creep test. The elastic modulus has different variation laws before and after the yield stress，the relation between viscosity coefficient and time has three types at different stress level. By scanning electron microscope test，the micro-structural changes in major components in mica-quartzose schist during triaxial creep process are derived from observing the radial and axial slices of mica-quartzose schist which made from three creep stages，respectively，and the three stages are no force stage，the upcoming accelerated creep stage and creep damage stage. On this basis，a reasonable micro-scopic interpretation for variation in creep parameters during triaxial creep process is given. The study shows that variation in creep parameters during triaxial creep test for mica-quartzose schist has a good correspondence with the micro-structural changes，the macro variation in creep parameters is an external behavior of internal micro-structural changes of mica-quartzose schist. The function reflecting the actual law of creep parameters variation is established，and then the creep model is derived，which can be an approach to describe the upcoming accelerated creep stage of rocks.

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STUDY OF CHARACTERISTICS OF LOW FREQUENCY CRUSTAL STRAIN WAVES RECORDED IN TIANSHAN MOUNTAINS

JIANG Jingxiang，GAO Ge，YIN Guanghua，LI Jie，WANG Zaihua

2011, 30 (S1): 2817-2825

[PDF] 557 KB (709)

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Based on 24 years′ observation of 4-component borehole strainmeter in Tianshan Mountains，Xinjiang Uygur Autonomous Region，China，the low frequency strain waves prior to major earthquakes are analyzed. Among the 144 earthquakes with M≥4.0，it is found that the low frequency strain waves appeared obviously prior to 39 earthquake events. The major findings about the characteristics of the strain waves can be summarized as follows：(1) The range of the strain wave period is 3–16 days，centered at 3–7 days；(2) The amplitudes of the strain waves are between 10－7 and 10－5，with a majority at 10－6；(3) With the increase in the magnitude of the earthquake，a series of characteristics of the strain wave could present as follows：① more complicated waveforms；② increased percentage of strain wave record，from 17% for magnitude ranging from 4.0 to 4.7，to 100% for magnitude greater than 7.7；③ increased epicentral distance of strain wave record；④ longer duration of strain wave，from several days prior to small earthquakes to several years prior to great events；⑤ longer precursory interval prior to the pending earthquake. Comprehensive understanding of the characteristics of the low frequency strain wave prior to major earthquake provides the practical significance for disastrous earthquake forecasting.

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STUDY OF GPR MODEL EXPERIMENT FOR DETECTING COASTAL EMBANKMENT

SONG Hua，WANG Lizhong

2011, 30 (S1): 2826-2833

[PDF] 684 KB (897)

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In order to analyze the application of ground penetrating radar(GPR) in coastal riprap embankment，the model experiment is conducted. The experiment is carried out under different depths of saltwater. Then，through comparing the measured results with those obtained by numerical FDTD analysis for verification，the target reflection interface can be distinguished in waveform figure；the depth and shape image of riprap bottom boundary are investigated after calculating travel time difference and velocity. According to influence of saltwater on GPR signal，the experimental results indicate that the GPR is effective to identify the riprap bottom boundary of coastal embankment without saltwater. When model is submerged by seawater，the dielectric coefficient and electrical conductivity of media increase significantly. Moreover，the detecting error increases with the submergence depth and the interface image appears fuzzy. By using the linear characteristic of influence lines obtained from the forward simulation，the error of model experiment is corrected. Therefore，it can provide the basis for GPR application in coastal embankment.

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EXPERIMENTAL RESEARCH ON DISTRIBUTION CHARACTERISTICS AND INFLUENTIAL FACTORS OF P-WAVE VELOCITY FOR ROCKS IN NORTHEAST REGION OF SICHUAN PROVINCE

WANG Guibin，YANG Chunhe，GUO Yingtong，MAO Haijun

2011, 30 (S1): 2834-2842

[PDF] 250 KB (901)

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Mineral composition，microstructure，temperature and confining pressure condition of rocks are crucial factors for determining the P-wave velocity of rocks. 49 kinds of rocks are chosen from the carbonate and sand-shale formations of the important exploration area in northeast region of Sichuan Province. The P-wave velocity is determined under the conditions of room temperature and no confining pressure，room temperature and confining pressure，high temperature and confining pressure. The distribution characteristics and influential factors of P-wave velocity for the rocks in northeast region of Sichuan Province are systematically analyzed. The average values and variation ranges of P-wave velocity for sand-shale formation and carbonate formation are given. Many mathematical models are used to determine the relationship of buried-depth and density with P-wave velocity for sand-shale formation，carbonate formation and whole formation respectively. The optimal regression equation is determined. The main influential factors of P-wave velocity are discussed for sand-shale formation and carbonate formation. The qualitative and quantitative relationships of temperature，confining pressure and formation with P-wave velocity are established；and the primary mechanism is discussed simply. After a comprehensive analysis，it can be realized that the deposition of sand-shale formations is continuous. The microstructure of carbonate formation is complicated and it plays an important role in acoustic response.

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STUDY OF HIERARCHICAL RECOGNITION THEORY OF HAZARD SOURCE OF ROCKBURST

PAN Junfeng，LAN Hang，MAO Debing，XIA Yongxue

2011, 30 (S1): 2843-2849

[PDF] 352 KB (796)

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The potential hazards existing before occurrence of rockburst is pointed out by combining the theoretical analysis and field cases. The concept of generalized hazard source is introduced into the rockburst monitoring；and the area between energy accumulation and damage initiation is defined as the hazard source of rockburst. Then through further analysis，the hazard source of rockburst has three elements，i.e. triggering element，potentially dangerous element and development trend element. The only objective of rockburst monitoring is to recognize the hazard source of rockburst in time and accurately. The spatial-temporal state when the hazard source of rockburst generates is analyzed. In order to avoid the generation of blind area，the hierarchical recognition of hazard source of rockburst in spatial-temporal state is proposed；and the application model is established. According to the coal mine field，coal face field and local area，the hierarchical recognition of hazard source of rockburst in Huafeng coal mine，China，is conducted by using monitoring technologies of microseisms，acoustic emission and mining-induced stress. Practice in Huafeng coal mine proves that the hierarchical recognition theory of hazard source of rockburst can not only improve the field monitoring efficiency，but also guide the rockburst forecast effectively.

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NONLINEAR DYNAMIC RESPONSE OF MARBLE TO REPEATED SHOCK WAVE

XI Jun1，YU Yong2，XI Daoying2

2011, 30 (S1): 2850-2857

[PDF] 241 KB (810)

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The experimental research on the propagation of repeated shock wave through dry and water saturated marble has been performed by means of Hopkinson bar. The results suggest that impact modulus varies with stress and strain. When repeated shock stress in dry marble is less than yield stress，the dynamic modulus reduces with the increase in distance or time of wave propagation. Due to the modulus of unloading is larger than one of loading，the unloading wave pursues the loading wave，resulting in the narrowing of stress wave and the amplitude decreasing continuously. With the increase in the number of shock，the modulus of dry marble becomes larger，dispersion and amplitude of attenuation decrease，stress wave gets narrow and the impact compaction effect appears. When the shock stress in water saturated marble is larger than yield stress，the modulus and the properties of stress waveform are similar to ones of dry marble. With the increase in the number of shock，the experimental results show that waveform gets longer and scattered，the residual strain increases. These are inverse to the results in dry marble. It is because that shock exceeding yield stress causes crack growth and new crack initiation，volumetric expansion and modulus decrease in water saturated marble. All these results are helpful to the design and construction of large projects，especially for the defense engineering.

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IN-SITU TESTING STUDY OF ACCUMULATIVE FORMATION LANDSLIDE REINFORCED BY MICROPILE GROUP

ZHU Benzhen1，SUN Shuwei1，2，ZHENG Jing1

2011, 30 (S1): 2858-2864

[PDF] 287 KB (830)

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In-situ test on micropile group for reinforcing accumulative formation landslide was carried out. The monitoring data indicates the deformation mode of landslide was very complicated，which went through several stages as shallow sliding，deep sliding and temporary stable. The deformation of subgrade is controlled by micropile group well ensuring the safety of traffic. There is a great difference in the load sharing ratio among different rows of micropile. During the displacement of the landslide mass reaches its maximum value，the front row of micropile resist the maximum value of load，followed by the rear row of micropile，while the middle row of micropile resist the smallest value of load. As the landslide tends to be stable，the load sharing ratios among different rows of micropile tend to be uniform. Besides，comparing the testing results with the theoretical results，it was shown that elastoplastic load-displacement curve method can well reflect the lateral force characteristics of micropile group under landslide thrust. Fixed micropile head will induce the stress concentration at the top and cause the larger bending moment of micropile within the range of 2 m beneath ground. Therefore，the hinged bearing between micropile and the rigid capping beam may be adopted.

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SOLUTION OF VECTOR SUM FACTOR OF SAFETY OF SLOPE BY THREE-DIMENSIONAL METHOD OF COLUMNS

LUO Xianqi1，YUAN Heng2

2011, 30 (S1): 2865-2870

[PDF] 196 KB (741)

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Through dividing the potential sliding body into slices and introducing several reasonable assumptions to forces acting between columns，the static equilibrium analysis is conducted for the columns and the sliding body，and the anti-sliding forces between columns and the normal force acting on sliding surface are thus calculated. On the basis of the definition of the vector sum factor of safety，a three-dimensional method of columns is proposed. It is indicated through some examples that for planar sliding surfaces and symmetrical sliding surfaces the factor of safety based on the definition of vector sum is in agreement with that based on the strength reduction. If the sliding surface is more complicated，the former is usually less than the latter.

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INTERACTION MECHANISM BETWEEN SURROUNDING ROCK AND SUPPORT BASED ON SPATIAL EFFECT OF EXCAVATION FACE

HOU Gongyu

2011, 30 (S1): 2871-2877

[PDF] 316 KB (879)

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According to the principle of excavation-induced unloading and the spatial effect of excavation face，the concept of secondary release of surrounding rock elastoplastic deformation is put forward. The mechanical model is established based on spatial effect of excavation face and secondary release of surrounding rock elastoplastic deformation. The interaction between surrounding rock and support is studied. The solution to interaction between surrounding rock and support in equilibrium is derived by introducing two necessary compatibility conditions which are stresses compatibility and displacement compatibility on the acting surface(contact surface) of surrounding rock and support. Design method of support structure is established based on spatial effect of excavation face and coordination of surrounding rock-support.

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DISCRETE ELEMENT SIMULATION OF DEFORMATION AND MOVEMENT MECHANISM FOR TANGJIASHAN LANDSLIDE

CAO Yanbo1，DAI Fuchu1，XU Chong1，TU Xinbin1，MIN Hong2，CUI Fangpeng3

2011, 30 (S1): 2878-2887

[PDF] 1357 KB (1313)

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Earthquake is considered as one of the main factors of the generation of a landslide which always causes severe disasters. Taking Tangjiashan landslide，a typical bedding rockslide triggered by the Ms 8.0 Wenchuan earthquake，as the study site，and discrete element numerical simulation is carried out to simulate the initial and subsequent movement of the rockslide. It is found that under seismic loading，stress concentration occurred first at the top of the slope and then expanded from the top towards the toe along the sliding plane，sheared out from the toe in the end and resulting in failure of the slope. The simulation of the subsequent movement of the slope shows that the movement mode of Tangjiashan landslide is starting-up→high-speed sliding→colliding down→self-stabilizing. It also shows that some blocks of the surface exhibit horizontal throwing and vertical jumping under seismic loading. Topographic amplification effects are also observed from both acceleration and velocity of the monitoring points of the slope，indicating that the amplification factor of horizontal acceleration exceeds that of vertical acceleration，and the amplification factor of horizontal velocity exceeds that of vertical velocity. By contrasting the amplification effect of structural plane and the underlying bedrock，it is found that there was a high acceleration when the landslide was at the stage of starting-up，and it also shows that the existence of persistent structural plane plays a controlling role in the dynamic response of the rock slope.

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EXPERIMENTAL STUDY OF MECHANICAL PROPERTIES OF INTERFACE BETWEEN PILE AND MACADAM SOIL IN ACCUMULATIVE LANDSLIDE IN THREE GORGES RESERVOIR AREA

CHEN Jing，LI Shaojun，MENG Fanzhen，MIN Hong

2011, 30 (S1): 2888-2895

[PDF] 356 KB (979)

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Due to the influence of water level change and seasonal rainfall in the reservoir area of Three Gorges，the mechanical properties of interface between anti-sliding pile and macadam soil are very important for the reinforcement design and safety operation of accumulative landslide. Based on a typical macadam soil landslide，a series of shear tests on interface mechanical properties are conducted under the conditions of various water contents，macadam ratios and shear rates. Accordingly，the functional relationship of shear strength parameters and water contents，macadam ratios is built. The change characteristics of mechanical properties of interface between pile and macadam soil are discussed. The results indicate that the shear strength，inner friction angle and cohesion decrease as the water content increases. However，for the increment in macadam ratios，the cohesion will decrease gradually，but the shear strength and inner friction angle of interface decrease firstly and then increase after a critical value，the change trend obeys parabolic relation. Besides，different shear rates have obvious influence on the parameters of shear strength；the shear strength will increase when the shear rates are promoted. The experimental results will not only provide significant data for the reinforcement design on macadam soil slope stabilized by anti-sliding piles，but also contribute a lot to the interface constitutive model and long-term stability analysis of reinforcement engineering.

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COMPARATIVE STUDY OF THREE CALCULATION METHODS FOR SLOPE FACTOR OF SAFETY

LIU Jie1，LI Jianlin1，2，WANG Lehua1，LUO Shiwei1，ZHU Min1，ZHOU Jifang2，ZHAO Zongyong1

2011, 30 (S1): 2896-2903

[PDF] 348 KB (1260)

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In view of the widespread use of the limit equilibrium method and the strength reduction finite element method(FEM) for calculating the slope factor of safety，the gravity proportion automatic loading method based on changing the gravitational acceleration is proposed；and the advantages and disadvantages are pointed out by comparing their computation principles and results of each method. The analytical results indicate that the slope factor of safety calculated by using the gravity proportion automatic loading method increases much more rapidly than that using the strength reduction FEM，and it is also higher than the result calculated by limit equilibrium method to a certain extent. The factor of safety calculated by the gravity proportion automatic loading method is the most sensitive to the slope geometry variation，so it is superior to the other two methods on quantization of the slope factor of safety. When the single-layered slope angle is less than 45°，the limit equilibrium method is the best. If adopting the FEM methods，the layering process of the slope is needed. For three-layered slopes，the limit equilibrium method and the gravity proportion automatic loading method are recommended，the strength reduction FEM is not suitable. In addition，the calculating time for the limit equilibrium method is the shortest. For five-layered slopes，the calculating time for the strength reduction FEM is 10 times of the gravity proportion automatic loading method；and the discrepancy has a improving tendency with the increase in the slope layer number.

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ANALYSIS OF PSEUDO-STATIC SEISMIC STABILITY FOR THREE-DIMENSIONAL SLOPE

HU Cheng1，2，LU Kunlin1，ZHU Dayong1，XU Qiang2

2011, 30 (S1): 2904-2912

[PDF] 619 KB (752)

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On the basis of the three-dimensional(3D) slope stability analysis of the modification of normal stresses on 3D slip surface，the solution to the factor of safety of the 3D slope subjected to the 3D earthquake is derived by using the method of pseudo-static analysis. The influences of the two-dimensional(2D) and 3D pseudo-static analysis methodS on factor of safety are compared. The influential law of 3D earthquake on the factor of safety under symmetrical slip surface condition and asymmetrical condition are discussed，respectively. Then the effect of the volume of slip mass，asymmetrical extent and parameters of soils on the factor of safety are also analyzed. Finally，the relative errors of factor of safety under 3D earthquake and only the horizontal earthquake are studied. Results show that the horizontal earthquake is uppermost influencing factors，the next is the vertical earthquake，and the lateral earthquake is the weakest. The 3D solution has a better agreement with practice and a higher degree of accuracy.

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YIN Guangzhi1，2，3，LI Xiaoshuang1，3，WEI Zuoan1，2，LI Yaoji3，WANG Qingsheng3

2011, 30 (S1): 2913-2923

[PDF] 464 KB (888)

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Based on the gently inclined medium thick phosphate layer of the deep part of the east mining section of pithead #6 of Jinning phosphate mine of Yunnan phosphate chemical group Co.，Ltd.，the similar simulation model experiment for the transition from open pit to underground mining is carried out by using the mine pressure plane stress similar simulation experimental frame in College of Resources and Environmental Sciences，Chongqing University. The experimental results show as follows：(1) Affected by the underground mining，the stress distribution of the top，lumbar and bottom of open pit slope has readjusted；with the expanding of mining range，it presents a dynamic change trend that being in compression，then the compressive stress increases，finally being in tension in whole. Because of the supporting protective effect of boundary pillar，the vertical sink of open pit slope is very small after underground mining. (2) After the extraction of underground phosphate，a abutment pressure zone in a certain area of roof which is behind and in front of the underground goaf is formed；but in the area of roof which is close to upper side of underground goaf，a roof stress-relaxation zone appears. And at the same time，in the area of floor which is close to lower part of underground goaf，a floor stress-relaxation zone appears. The stress-relaxation zone expands gradually and the roof abutment pressure zone moves forward dynamically with the advance of extracting along the inclination extension of phosphate layer. (3) Due to the influence of mining，the roof and floor surrounding rocks near the goaf both have different degrees of deformation，the roof strata have different degrees of subsidence and the roof strata have different degrees of rising. The maximum subsidence point of roof and the maximum rising point of floor are located in the centre of underground goaf which is a little close to the lower part，and they moves forward dynamically with the advance of extraction. And the integral shapes of subsidence curve and rising curve of rock stratum are both tend to be bowl shape when the underground mining of phosphate reaches fully mining. Taking the goaf as center，with the increase in the distance from it along vertical and horizontal direction，the deformation of roof and floor strata are both monotone decreasing. (4) When the mining advances to the fault fracture zone and its influence region，the fault fracture zone is activated，it appears slipping and shear fracture along faulted interface. The experimental results have great significance for field engineering of the gently inclined medium thick phosphate layer of the deep part of the east mining section of pithead #6 of Jinning phosphate mine of Yunnan phosphate chemical group Co.，Ltd. and similar mines transition from open pit to underground mining.

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FIELD TEST STUDY OF GRANITE SOIL HIGH SLOPE REINFORCED BY PRESTRESSED CABLES

LIU Yongjiang，YANG Jing

2011, 30 (S1): 2924-2930

[PDF] 255 KB (886)

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Granite soils are widely distributed over the South China. With the development of highways，there have been more and more granite soil high slopes along highways. The prestressed cables frame is a common method to reinforce the granite soil high slopes. Through field test on a actual slope of Shantou—Jieyang highway，the internal force distribution and the counterforce endured of frame，the transferring rules of anchoring force in the soil，and the tensile force distribution rules of each section of cable. The results are very valuable to guide the design and construction of similar projects.

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RESEARCH ON MECHANISM AND MONITORING AND EARLY-WARNING TECHNOLOGY OF LANDSLIDE IN LUOSHAN MINING AREA

TAO Zhigang1，2，ZHANG Bin1，2，HE Manchao1，2

2011, 30 (S1): 2931-2937

[PDF] 422 KB (1264)

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With the scale extending of mining，the landslide in Luoshan mining area has became more and more serious(405.2×105 m3)，which are being threatened to the sustainable safe mining of the underground mineral resources，such as molybdenum，gold and so on. First，in order to predict its landslide disaster early and guide the mining，the origin of Luoshan landslide is analyzed by utilizing the theories of mining and engineering geology. The results show that the weak geologic structure and unreasonable mining sequence and concentrated regional rainfall mainly caused those landslides. Then，a kind of new idea that uses mining theories to control landslide is put forward，and mining sequence is adjusted timely，which is from the slope top to the slope toe，making the slope more stability. Finally，based on the sliding criterion that sliding force is greater than the anti-sliding force is the necessary and sufficient conditions for occurrence of landslide，the principle and method for sliding force remote monitoring is presented；and a kind of systemic landslide remote monitoring network is established in Luoshan landslide mass. After 10-month site test，the landslide mass tends to be stable；and it shows that the method of using mining to control landslide is scientific and practical.

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NUMERICAL VERIFICATION OF EARTH-ROCK DAM SLOPE FAILURE DURING SHAKING TABLE TEST

KONG Xianjing1，ZHU Yalin1，2，ZOU Degao1，3，LI Yongsheng1

2011, 30 (S1): 2938-2945

[PDF] 342 KB (873)

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The seismic stability of earth-rock dam is studied through shaking table test and numerical simulation. The dynamic behavior，failure mode，stability and reinforced performance of the soil dam slope during earthquakes are discussed. An elastoplastic analytical method is applied to simulating and analyzing the dynamic failure process of soil dam slope under earthquake. The permanent displacements of earth-rock dam in different cases are studied. In addition，the stability of dam slope，the depth of slip surface and the effectiveness of reinforcement are investigated by using the quasi-static method. The comparison between the calculated results and results obtained from shaking table tests shows that they are close and definitely verified each other. The study also shows that the top of dam is the vulnerable part；and cracks normally appear near this part under earthquake. The reinforcement and the gentle slope also can decrease the permanent displacement of dam slope. The reinforcement can obviously enhance the overall stability of dam without increasing the volume of the soil dam. The reinforcement has more advantages than the gentle slope.

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WU Yue1，LIU Dongsheng2，LU Xin1，SONG Qianghui1，WU Yingxiang1

2011, 30 (S1): 2946-2953

[PDF] 410 KB (870)

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Based on the situation that the quantitative degree for assessing the vulnerability of element at landslides risk is low，the quantitative assessment method of the vulnerability is discussed. Through analyzing the failure process of element at risk impacted by the landslide mass，it is considered that the impact energy translates into the deformation energy of element at risk gradually，which is caused by impact force work in process of element at risk impacted by the landslide mass. Because of plastic deformation，the deformation energy dissipates progressively；then it leads to the destruction and collapse of element at risk. Vulnerability is defined quantitatively as a function of impact kinetic energy and the deformation energy of structure. The quantitative function is deduced. Based on this function，the quantitative vulnerability assessment model for typical element at landslide risk is established by using energy method to calculate velocity of landslide debris for the simplified case. This quantitative model accords with the principle of landslide mechanism. It is a new way for vulnerability quantitative assessment.

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ANALYSIS OF SEISMIC REVIEW OF BIKOU ROCKFILL DAM WITH EARTH CORE

ZHU Sheng1，2，SHI Gaofeng1，2，ZHOU Jianping3

2011, 30 (S1): 2954-2962

[PDF] 645 KB (724)

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Some damage phenomena appear in Bikou earth core dam after “5.12” Wenchuan earthquake. With the bedrock motions at Wenxian seismic station(062WIX)，the input acceleration time-history is obtained from the relationship of free-field peak ground acceleration(PGA) and fault distance in Wenchuan earthquake. The dynamic parameters of dam soils are determined by comparing with the information of large-scaled laboratory triaxial experiments of other projects based on their physical and mechanical characteristics. Based on TSDA program for three-dimensional finite element dynamic analysis，the permanent deformation and the pore water pressure of core dam are close to the recorded data；the maximum acceleration along the dam axis is scaled up in amplitude only by a factor of 2.36 at the dam crest，and the dynamic response of cut-off walls is also weak. Because Bikou dam is located on the hanging wall of fault，and high-frequency componet of the bedrock motions had developed，although the earthquake lasted much longer，the dynamic response is weaker than that under the standard seismic waves synthesized by design response spectrum according to “Specifications for seismic design of hydraulic structures”. From the results of seismic review，it could be found that the core dam built by the modern technology of heavy vibration has good seismic behavior；and the current seismic theories and methods for earth dam are basically feasible.

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STUDY OF GROUTING UPLIFTING FOR EXISTING BUILDINGS TRAVERSED BY TUNNEL AND ITS APPLICATION

PENG Zhengyong

2011, 30 (S1): 2963-2969

[PDF] 387 KB (904)

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Subsurface excavation tunnel at Punan section of phase I project of Xiamen airport road is a shallow-buried，large-span and soft rock tunnel，the surrounding construction environment is complex. Building #34 is a key protection object during tunnel traverses buildings. According to the structures，foundation rocks and surrounding environment of building #34，the ground tracking grouting method is adopted to protect buildings during construction by systematically analyzing the reliabilities and operabilities of various building protection schemes. The sleeve valve pipe grouting is adopted for building #34 according to grouting test results of buildings #104，#105. Monitoring points of building subsidence and crack development have been set in order to control the subsidence and crack development of building #34 and guide the construction timely. Monitoring results show that grouting uplift can control houses subsidence effectively. Finally，the total subsidence value of each monitoring point is controlled within 25 mm；the differential subsidence of each monitoring point is controlled within 1‰. The building #34 structures are in control state when tunnel traverses. Therefore，the grouting uplifting is a very important method to protect existing buildings traversed by tunnel. This study results will provide some references for similar tunnel projects.

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STUDY OF ACTIVE EARTH PRESSURE ON RETAINING WALL SUBJECT TO TRANSLATION MODE CONSIDERING LATERAL PRESSURE ON ADJACENT EXISTING BASEMENT EXTERIOR WALL

YING Hongwei1，2，HUANG Dong1，2，XIE Xinyu1，2

2011, 30 (S1): 2970-2978

[PDF] 400 KB (833)

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In the case of retaining wall adjacent to existing basement and the backfill?s width is limited，it is not strict to use classical Coulomb or Rankine theory to calculate the active earth pressure. The results obtained from finite element method(FEM) show that when the retaining wall translates and the backfill is under fully active limiting state，the sliding soil wedge does not break away from the adjacent basement exterior wall；the lateral pressure from the basement exterior wall cannot be neglected. It also shows that multiple slip surfaces occur in the backfill if the backfill?s width is very small. The earth pressure above the intersection point between the last slip surface and the retaining wall or the adjacent basement exterior wall is approximately equal to the Coulomb active earth pressure. Based on the numerical results，a new theory model to calculate the earth pressure for limited soils is presented. The solving method for calculating the active earth pressure coefficient and the first slip surface inclination are provided. Using the horizontal differential element method，the theoretical formulae of the distribution of active earth pressures on retaining wall and the relative height of the application point of the resultant earth pressure are obtained. Comparisons of the calculated results with solutions obtained from the proposed method，the classical earth pressure theories，the other existing methods and FEM show that the proposed method can provide a good prediction of active earth pressure under this situation. It is shown that，the active earth pressures? distribution for limited soils is nonlinear. If the wall-soil friction angle 0°， increases，but and decrease with the increase in the aspect ratio of backfill ；and when ，the results are the same from Coulomb formulae. If 0°，， and are coincident with Rankine theory.

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OPTIMIZATION ANALYSIS BY KEY BLOCK THEORY FOR CONSTRUCTION PROCEDURE OF EXTRA LARGE-SPAN DOUBLE-ARCH TUNNEL

CHEN Xiaoxiang1，2，XIA Caichu1，3，BIAN Yuewei1，3，XU Chongbang1，3

2011, 30 (S1): 2979-2985

(780)

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According to different joint collecting areas，the revealed rock joints are collected and described finely during construction of central drift of Jinjishan multi-arch tunnel with eight traffic lanes based on the probabilistic method. Then the key block theory is adopted to predict the possible unstable blocks during construction progress of the main tunnel. In the meanwhile，the geometric and mechanical parameters of the key blocks are defined to analyze the influences of construction procedure on the unstable blocks. Furthermore，by comparing and analyzing the safety factor of the key blocks in different construction procedures，the design optimization analysis is performed. The results show that：(1) During the construction procedure of the main tunnel of Jinjishan multi-arch tunnel，the blocks located in the side surrounding rock mass are stable. (2) The key blocks with considerable volume in the top surrounding rock mass may be formed. (3) The numbers and the volumes of the key blocks may decrease in the construction procedure with excavating the right side drift first of the double-side drift method. The research results provide guidance for safety construction of Jinjishan multi-arch tunnel with eight traffic lanes.

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A CASE STUDY OF ROCK MASS ENGINEERING OF UNDERGROUND POWERHOUSE AT XILUODU HYDROPOWER STATION

FAN Qixiang1，2，WANG Yifeng2

2011, 30 (S1): 2986-2993

(893)

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The underground powerhouses′ rock masses at Xiluodu hydropower station are discontinuous and anisotropic damage influenced by the inner beddings of the basalt. The elasto-plastic damage theory is used to analyze the stability of surrounding rock. A good construction organization and technological are executed to control the rock excavation damage in order to ensure the rock beam forming. Moreover，the safety monitoring feedback is implemented for the location of geological defects，and the monitoring results are used to estimate the surrounding rock stability. Through reviewing the rock mass engineering practice process of a typical underground powerhouse such as the complex geological conditions，stability analysis，excavation and support procedures，and safety monitoring analysis，a number of insights for the design concept and implementation of the project are put forward，which can provide direct reference for the giant underground powerhouse engineering.

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MONITORING ANALYSIS OF FISSURE DEVELOPMENT EVOLUTION AND HEIGHT OF OVERBURDEN FAILURE OF HIGH TENSION FULLY-MECHANIZED CAVING MINING

ZHANG Yujun1，2，LI Fengming3

2011, 30 (S1): 2994-3001

(784)

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Taking Wangpo mine as the experimental mining，by borehole flushing fluid leakage and drilling colour television system，the height of overburden failure caving and fissure development evolution are monitoring. And then，the digital analysis and similarity simulation experiment of fissure development evolution are carried out. The research results show as followings：(1) The overburden failure height of high tension fully mechanized caving mining Wangpo mining is from 94.00 m to 104.92 m. (2) The main distribution characteristic of rock fissure is that the evolution of fissure is mainly with the high angle even vertical to the rock strata；the fissure evolution amount is square increasing with the buried depth；and the fissure width is normal distribution approximately with the fissure amount. (3) The fissure cluster region focus on before and after the coal wall；and the fissure density distribution curves of overlying strata are high at both ends，low of the middle，such as saddle-shaped.

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ANALYSIS OF DEFORMATION MONITORING AND MECHANICAL BEHAVIORS OF BIG PIPE-ROOF FOR SHALLOW-BURIED LARGE-SPAN TUNNEL TO UNDERPASS HIGHWAY

LI Jian1，TAN Zhongsheng1，YU Yu2，NI Lusu1

2011, 30 (S1): 3002-3008

(840)

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Wenxiang tunnel is a shallow large-span loess tunnel in Zhengzhou—Xi′an Special Passenger Railway；and the mechanical behaviors of big pipe-roof are studied. The longitudinal deformations of the pipe-roof before the underpass section are monitored by strain gauges fixed in the pipe-roof. Based on the monitoring results，the mechanical behaviors and function mechanism of long scale pipe-roof are thoroughly analyzed. Furthermore，a new double-parameter elastic foundation beam model of pipe-roof in shallow tunnels is build and its boundary condition gets analyzed. By model calculating with deflection curve equation and calculation of longitudinal strain，the evaluation of mechanical behaviors of the pipe-roofs in Wenxiang tunnel is performed successfully. The measured values and the calculation results are consistent well. The research results show that：(1) In front of the excavating face about 15m，the pipe roof starts to bear the load；and after the excavating face about 15 m，its force tends to be stable. The longitudinal deformation of the whole pipe-roof is groove-shaped distribution and its largest force is at the excavating face. (2) Simultaneously，the results also indicate that the mechanical behaviors of pipe-roof relate to the location of the excavation face，the footage of the tunnelling cycle，the mechanics parameter of both pipe-roof itself and surrounding rock，and so on. (3) The conclusions from calculation model can be used as theory basis in the design parameter optimization of construction and the construction scheme selection of pipe-roof；and the application effect has been verified in deformation monitoring at underpass section.

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RESEARCH ON SURROUNDING ROCK LOOSE ZONE OF TUNNEL UNDER UNSYMMETRICAL LOADING WITH GROUND PENETRATING RADAR AND ITS APPLICATION

GUO Liang1，LI Juncai1，ZHANG Zhicheng2，CHENG Shoujin2

2011, 30 (S1): 3009-3015

(748)

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Based on test principle of ground penetrating radar(GPR)，the application feasibility for detecting the surrounding rock loose zone is verified. By using ground penetrating radar of LTD–2100 to monitor Fubang tunnel，we can get the results that：the thickness of surrounding rock loose zone in a tunnel under unsymmetrical loading is larger than that of traditional in geological bedding strata，the loose range at larger pressure side is more apparent than the other side，and the position with maximum loose range usually appear at the spandrel or vault. According to the monitoring results，the lining design program and accident removal countermeasures for the tunnel under unsymmetrical loading in geological bedding strata are proposed. And combining with actual measurement in field，the feasibilities of operation and application，which utilize ground penetrating radar to detect the surrounding rock loose zone are discussed. It could be verified the feasibility of testing surrounding rock loose zone with ground penetrating radar，which could also provide an effective guidance for the excavation and support construction of Fubang tunnel.

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STUDIES OF REPAIR AND SUPPORTING TECHNOLOGY OF LARGE SPAN DYNAMIC MINING PRESSURE ROADWAY

WU Yongping1，2，GAO Xicai1，2，XIE Panshi1，2，LI Chao1，ZENG Youfu1，2

2011, 30 (S1): 3016-3021

(760)

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According to the supporting problem of large span and dynamic mining pressure roadway in the Dafosi colliery of Binchang Co. in Shaanxi Province，the deformation and failure characteristics of roadway in complex surrounding rocks are analyzed based on the special engineering geological conditions and affections of dynamic mining pressure；and the analysis results indicate that the main reasons of supporting failure are local tectonic stress，soft rock mass in floor，dynamic mining pressure and explosion shock loading. Taking the 40106 haulage roadway for example，a repair scheme considering the complementary control of cable anchor，strengthen monomer point column and angle bolt is determined and is applied to engineering practice on the integrative idea. The field observation results show that the floor heave and the roof crush of large span can be controlled effectively by decreasing the span of the roadway，strengthening roof and sides and increasing bolts in sidewalls and floor corner of roadway.

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IMPROVEMENT OF ANT COLONY ALGORITHM FOR PREDICTING UNEVEN SETTLEMENTS OF SHIELD TUNNEL IN SOFT SOIL AND ITS PARAMETERS SELECTION

WEI Kai1，2，GONG Quanmei2，ZHOU Shunhua2

2011, 30 (S1): 3022-3031

(816)

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According to monitoring settlement data，the law of the uneven settlement of shield tunnel in soft soil and its causes are analyzed；and then the leading information with regulation is obtained. Together with the auxiliary information with great randomness，it can be used to improve the previous prediction model based on ant colony algorithm. The principle for selecting partial parameters in the prediction model is preliminarily conferred by an instance. The results show that：(1) The leading information with regulation is considered to have something to do with the amount and cumulative settlement of positions with significant settlement in the vertical sedimentation tank，and the distance between the positions with significant settlement and the positions with non-significant settlement. (2) The improved prediction model is clear in calculation process，simple in formula，easily to use and has high prediction accuracy；and its maximum error can be controlled about 0.5%. (3) The influence of match between evaporation coefficient of pheromone and the total number of ants on prediction accuracy is relatively significant；whereas the correction function reflecting auxiliary information has a little role when there is no random factor；based on these，a reasonable process of parameter selection in the model is given.

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DISPLACEMENT CHARACTERISTICS ANALYSIS OF SURROUNDING ROCK IN UNDERGROUND POWERHOUSE CHAMBERS AT PUBUGOU HYDROPOWER STATION DURING CONSTRUCTION

HUANG Qiuxiang1，2，DENG Jianhui1，SU Pengyun3，WANG Dikai3，YOU Ping4

2011, 30 (S1): 3032-3042

(857)

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Based on the monitoring data statistical results，the surrounding rock mass displacement magnitude distribution and spatial distribution in underground powerhouse chambers are analyzed. Taking the generator chamber for example，by means of geological information combining with excavation and construction progress， the effects of geological factors and excavation factors on the displacement are analyzed from the aspects of displacement，in-depth laws and strain rate，and the interaction between the two kinds of factors are analyzed. The research results show that：(1) The large displacement positions concentrate in the rock-anchored beam site and downstream side walls. (2) The effect of faults on upstream parts is not obvious，and the displacements are quite different between with or without faults zone. The nearby cross-site construction has a great impact on downstream displacement of surrounding rock，and the construction factors enhanced the impact of geological factors. (3) The displacement is the result of a variety of factors，and the geological factor and excavation factor are the main reasons of displacement appearing and development. (4) The law that the displacements of positions of poor geological conditions are larger is not entirely correct，and the inappropriate construction would intensify the effect of structural surface to cause a great displacement. Even in the case of non-structural surface，the inappropriate construction can also cause large displacement of surrounding rock. (5) Generally speaking，the displacement of locations with faults crossing performs as "open" displacement，and the displacements in the structure of surface area with faults crossing are different obviously. The law that the impact of faults on displacement is complex and diversity，and it has relations with the faults? intensity and location. The blasting is one of the primary means of excavation，and its technical study has a great academic value and economic significance.

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STUDY OF MECHANICAL BEHAVIOURS OF CONSTRUCTION INTERACTION FOR SHALLOW UNDERWATER TUNNELS WITH SMALL CLEAR SPACING

YUE Jian，LENG Wuming，ZHAO Chunyan

2011, 30 (S1): 3043-3051

(776)

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In order to save land and link the existing roads on the banks conveniently，the underwater tunnels with small spacing may be designed to cross the river. During the period of construction of the underwater tunnels with small spacing，the constructing interaction of the twin tunnels is the key factor affecting the stability of the tunnel engineering. Based on the Liuyanghe tunnel which is the underwater small-distance road tunnels by shallow-burying and hidden-digging method，the constructing interaction of the twin tunnels is studied. Firstly，the three-dimensional finite element model is established to analyze the reasonable lagging distance between the twin tunnel excavated faces. Then，the pore water pressure，surrounding rocks pressure，internal force in steel arch and secondary lining，the axial force of anchor，ground surface settlement，crown settlement，convergence and water level are monitored during the period of construction. At last，based on the measured data，the deformation and stress properties of surrounding rocks and supporting system are analyzed；and the mechanical characteristics of constructing interaction between the twin tunnels are also studied. The experiences and conclusions presented can provide design，construction and monitoring references for similar projects.

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BACK ANALYSIS OF SURROUNDING ROCK STABILITY BASED ON EXCAVATION PROCESS OF UNDERGROUND POWERHOUSE AT LAXIWA HYDROPOWER STATION

YAO Xianchun1，LI Ning1，2，CHEN Lijing1，SUN Hongchao3，JING Maogui4

2011, 30 (S1): 3052-3059

(753)

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The excavation size of Laxiwa underground powerhouse is huge；and its surrounding rock is mainly brittle hard granite rock. Moreover，the mountains are high；the slopes are steep；and the valleys areas are narrow in the area plant. Except that，the regional stress field values are high and the high stress fields distributions are complex，which are extremely detrimental to the stability of the cavern. In order to estimate the stability of surrounding rock and supporting long-term safety of underground plant after excavation，based on back analysis model of excavation and the change laws of displacement measured by multipoint extensometers at different depths from the tunnel wall，the tunnel surrounding rock is divided into loose rock zone，transition zone and stability zone. And then，rock mass mechanical parameters were back analysed and calculated by using the measured displacement increment on each layer caused by excavation and the objective function of its mean square error. When excavating underground powerhouse each layer，the mechanical parameters and ground stress parameters near rock mass were obtained. Combination of ground stress parameters and mechanical parameters，the follow-up analysis of the stability of surrounding rock of excavation plant was evaluated and predicted. Also a standard is presented to determine the stability of surrounding rock of Laxiwa underground plant. The standard for subsequent control of underground plant monitoring deformation provides a basis for effective guidance of the plant supporting design and excavation construction.

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RISK ANALYSIS OF DOUBLE SHIELD TBM CONSTRUCTION ACCIDENT INDUCED BY TUNNEL DEFORMATION

WEN Sen1，XU Weiya2

2011, 30 (S1): 3060-3065

(858)

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Tunnel boring machine(TBM) is widely used in deep tunnel at present；and the accidents caused by tunnel deformation become more and more common. Therefore，it is very necessary to analyze the risk of accidents induced by tunnel deformation in advance. Considering the mutual effect of tunnel face and shield rear support，convergence-confinement method and risk analysis theory are applied to calculate the pressure imposed by surrounding rock on shield. Meanwhile，according to the magnitude of pressure imposed on shield，the specific influence of tunnel deformation on TBM construction is estimated；and the consequence of accidents risk is divided into five ranks. Deformation risk evaluation matrix for TBM is proposed by the combination of occurrence probability with consequence rank；and then the risk rank can be determined by the proposed evaluation matrix and existing risk acceptance criterion. In the end，the risk analysis of double shield TBM construction accident in west route of South-to-North Water Transfer Project is conducted by using the research results.

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ANALYSIS OF REASONABLE EXCAVATION SEQUENCE AND STRESS CHARACTERISTICS OF PORTAL SECTION OF SHALLOW TUNNEL WITH UNSYMMETRICAL LOADINGS

LIU Xiaojun1，2，ZHANG Yongxing1，2

2011, 30 (S1): 3066-3073

(779)

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The portal section of shallow tunnel with unsymmetrical loadings is a typical three-dimensional problem，the main initial geostress of which is gravity stress. The relatively real initial geostress can be obtained by accurately simulating the topographical and geologic conditions，which can increase the reliability of the calculation result. Analysis of three-dimensional simulation in the excavation process of portal section of shallow tunnel with unsymmetrical loadings of Laozhai tunnel in Guizhou province of Xiamen—Chengdu Expressway is conducted by using the fast Lagrangian analysis of continua in 3 dimensions(FLAC3D) program. Comparing excavated shallow part firstly with excavated deep part firstly by the annular pilot heading conservation core soil method，the changes of deformations and stresses of rock mass and supporting structure of Laozhai tunnel in different excavation sequences are obtained. Actual tunnel excavation sequence is optimized by comparison；and the rationality of excavation scheme is explained by the method of released load and the method of principal stress trace. Finally，through analyzing and calculating the measured data of three measured sections in site，the stress characteristics of surrounding rock and supporting structure of Laozhai tunnel portal section are obtained. The analysis results can provide technical guidance for the design and construction of Laozhai tunnel and the tunnel which has the similar topographical and geologic conditions.

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DEVELOPMENT OF DATABASE SYSTEM FOR UNDERGROUND POWERHOUSES OF HYDROPOWER PROJECT AND ITS APPLICATION

HU Tianqing1，2，XIAO Ming1，2，XIONG Qingrong1，2

2011, 30 (S1): 3074-3080

(762)

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Based on the rich engineering data of hundreds of underground powerhouses which are accumulated by our team，SQL Server 2005 is used as design tool and C# programming language is selected as front-end development tool to develop the database system of underground powerhouse，achieving the purposes of data storage，retrieval，statistics，analysis of significant design parameters of underground powerhouse and the results of stability analysis of surrounding rock. Engineering data of hundreds of projects are stored in the database，including engineering description，geological conditions，geostress field，size of powerhouse，supporting design，excavation scheme design，back-analysis，seepage field analysis，stability analysis of surrounding rock，etc.. The system realizes the functions of engineering analogue method，data analysis of underground powerhouse design and surrounding rock stability analysis. Taking underground powerhouse of Huangdeng hydropower station on Lancang river in Yunnan province for example，related engineering by using characteristic parameters of underground powerhouse is obtained to retrieve the database. With the empirical supporting parameters，the supporting parameters design of main powerhouses are achieved. Lastly，the rationality of the design is verified by 3D elastoplastic finite element software. At the same time，the system can help to deepen the understanding of all kinds of laws of underground powerhouses by adequately exploring various kinds of digital information where the rich data of underground powerhouse are contained. The system also have laid foundation for the design of expert database system of underground powerhouses which can contribute to establish a comprehensive and systematic method of surrounding rock stability analysis as well as the forecasting of underground engineering.

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TIME-DEPENDENT DEFORMATION STUDY OF UNDERGROUND POWERHOUSE OF JINPING I HYDROPOWER STATION

CHENG Lijuan，LI Zhongkui，GUO Kai

2011, 30 (S1): 3081-3088

(842)

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Because of the huge scale and complicated geometry condition，the stress redistribution and surrounding rock deformation of underground powerhouse of Jinping I hydropower station perform strong time-dependence. The factors influencing surrounding rock?s time-dependent behaviour are concluded as the excavation process and rheology of rock mass；and the latter is studied a lot. The rheological theory for rock mass is briefly introduced and discussed at the beginning. Then，taking a typical monitoring section as an example，the monitoring data of the section are analyzed. Based on the analysis，some suggestions about support are provided. The monitoring data also imply that damage area of the caverns contributes the primary time-dependent deformation. Finally，the time-dependent back analysis method based on displacement is studied. The concrete idea and ways of numerical implement of this method are discussed in detail. And the method is applied to the typical section to testify its rationality. The research results show that the time-dependent back analysis method is effective to simulate the time-dependent behaviours of surrounding rock.

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STUDY OF TYPICAL BLOCKS IN VAULT OF THREE GORGES UNDERGROUND POWERHOUSE

XIA Lu1，LI Maohua2，CHEN Youhua2，WANG Jiaxiang2，YU Qingchun1

2011, 30 (S1): 3089-3095

(754)

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The stability of block is one of the key geological issues in the underground powerhouse caverns in the Three Gorges Project. Large-scale blocks can be easily developed due to enormous excavated surface associated with large spans and high side walls in underground caverns. The basic analysis process of GeneralBlock software is presented. First，the 3D block model is set up by GeneralBlock in order to identify and analyze the associated stability problem of rock block in vaults. Based on the modeling results，design and construction of effective reinforcement in accordance with combination of different types of rock blocks are put into practice. In addition，system monitorings for bolts，cables and blocks are set up. The safety monitoring results show that the deformation of block is less than 2 mm，and the stress of anchor bar and loss rate of cable remain stable. These outcomes indicate generally an effective reinforcement.

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ANALYTICAL SOLUTION FOR COMPOSITE GROUND WITH GEOSYNTHETIC ENCASED STONE COLUMN UNDER TIME-DEPENDENT LOADING

ZHANG Yiping，WANG Yang

2011, 30 (S1): 3096-3102

(834)

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Aimed at the composite ground with geosyntetic encased stone column(GESC)，an analytical solution for its consolidation under time-dependent loading is developed. In this solution，not only the flow at radial and vertical directions within column and soil are considered，but also the deformation at radial and vertical directions of column and soil are included. Base on the general solution，the consolidation for GESC composite ground with ramp loading and trapezoidal additional stresses in depth is carried out，and compared with the existed solution by degenerated to ordinary stone column composite foundation. The comparisons show that the consolidation velocity obtained from this paper is slower than that of the previous solution since the presented method includes the complete volumetric strains of the column and the surrounding soil.

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STUDY OF SURROUNDING ROCK PRESSURE CHARACTERISTICS OF SHALLOW EXCAVATION THREE-ARCH METRO TUNNEL IN LOESS REGION

LAI Hongpeng，LIU Miao，XIE Yongli

2011, 30 (S1): 3103-3111

(775)

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In order to precisely understand the rock pressure variation laws of three-arch metro tunnel and its supporting system in construction period in loess region，a large scale field testing relying on the route No.2 of Xi?an metro construction site is conducted. The variation laws of contacting pressure of surrounding rock and initial supporting system，contacting pressure of initial supporting and secondary lining，and surrounding rock pressures of each construction stage are monitored. The research results show as that：(1) The surrounding rock pressures of each part of initial support in earlier excavation chamber are larger than that of later excavation chamber. (2) The pressures in vault and in bottom of invert are larger with the excavation span. (3) The stress of bottom of mid-partition between left and right lines is the largest due to the upper soil load. (4) The stress of the initial supporting system increases after the secondary lining construction. (5) The loading proportions of the initial support and secondary lining are 52.81% and 47.19% respectively，and they can be adopted as 50% in the design stage. (6) The surrounding rock pressure of each part in earlier excavation is increasing with the other chamber′construction later.

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STUDY OF NONLINEAR STATIC AND DYNAMIC COUPLING INTERACTION OF SOIL-UNDERGROUND STRUCTURE CONSIDERING INITIAL STATIC STRESS

ZHUANG Haiyang1，WU Xiangzu2，CHEN Guoxing1

2011, 30 (S1): 3112-3119

(825)

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According to the limitation of existed methods used to analyze the earthquake response of soil-structure dynamic interaction，the nonlinear static and dynamic coupling interaction of soil-underground structure theory and calculation model are developed. Based on the model，the earthquake response and damage mechanism of subway station with two layers and three spans are analyzed，respectively. The research results show that：(1) Under the static and dynamic coupling loadings，the damage orders of subway station members are obtained in detail. The lower surface of middle slab near to the lateral wall is damaged firstly；and the severely damages take place on the ends of middle columns. The lower surface of the top slab near to the lateral wall，the upper surface of bottom slab on the side span，and the upper surface of top slab near to the middle column are damaged in turns. (2) As a whole，the ends of middle columns and the bottoms of lateral walls are damaged more easily and severely. The members of subway station are almost damaged by tensioning or compressing respectively when weak earthquake ground motion is inputted. However，when the earthquake ground motion become stronger，these members are damaged by tensioning and compressing simultaneously. (3) At the same time，the subway station may be damaged more easily and severely by near field earthquake.

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NUMERICAL TEST INVESTIGATION ON UNLOADING ROCKBURST PROCESSES

HUANG Zhiping1，2，TANG Chun?an1，MA Tianhui3，TANG Liexian4

2011, 30 (S1): 3120-3128

(747)

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In order to explore the mechanism of rockburst induced by unloading，the process of instability failure under unloading is exhibited by rock failure process analysis software(RFPA2D). Taking the example of basic mechanical parameters of the granite，firstly，the two-dimensional numerical test of uniaxial loading failure for the square numerical specimen is simulated；and then，for the same specimen，the surrounding rock unloading test under the condition of bidirectional load is simulated. The numerical test results show that：(1) There is a large differences on the rock failure mechanisms and failure modes between the uniaxial loading test and unloading instability test. (2) The progressive microcracks propagation is dominant in failure process of uniaxial loading test；and the microcracks concentrate on the local fracture plane. Before the main fractures induced，Acoustic emission(AE) phenomenon which is the omen of many microruptures appears；and it is the typical rockburst mode of instability induced by the progressive failure. (3) The brittle characteristic during the rock unloading failure in the biaxial test under confining pressure is more evident. The unloading failure is mainly released by sudden，high energy density. At the same time，it shows intense dilatation failure characteristics along the unloading direction；and the failure mode is large-area shear fracture combined with local tension fracture. On the contrary to the uniaxial loading，there is nearly no omen of any microfracture before the main fracture；and it is the typical failure mode of transient rockburst.

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EXPERIMENTAL INVESTIGATION ON THRESHOLD PRESSURE GRADIENT IN SATURATED/UNSATURATED FLOWS IN ULTRA-LOW PERMEABILITY RESERVOIRS

XIE Quan1，2，HE Shunli2，JIAO Chunyan2，ZHU Huayin3，FU Chunyan4，LEI Gang2

2011, 30 (S1): 3129-3134

(733)

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According to the investigation argument between Chinese researchers and oversea scholars on threshold pressure gradient characteristics in ultra-low permeability reservoirs，with full diameter from Triassic outcrop by means of fully-automatic flooding system of AFS300TM provided by Core Lab in USA，an unsteady approach to test the threshold pressure gradient of saturated and unsaturated flow in the ultra-low permeability cores is proposed. The threshold pressure gradient in the saturated and unsaturated flows are analyzed with the investigation on the pressure variation from downstream and upstream of the rock cores. The experimental results indicate that the threshold pressure gradient doesn′t exist in the ultra-low permeability rocks with saturated flow of normal brine and kerosene. And the capillary force caused in the interfaces of the fluids in the unsaturated flow is the basic reason of obvious threshold pressure gradient. Moreover，the dynamic effect of capillary pressure is observed in the unsteady state flow experiments from ultra-low permeability rocks.

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STUDY OF LONG-TERM DEFORMATION CHARACTERISTICS OF SAND AQUIFERS FOR LAND SUBSIDENCE CAUSED BY GROUNDWATER WITHDRAWAL

WANG Fei，MIAO Linchang

2011, 30 (S1): 3135-3140

(717)

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The field monitoring data of land subsidence in Yangtze River delta area demonstrates that the deformation in the aquifers accounts for a large proportion of the total settlement and develops with time. There are many parameters in the existing sand creep models；however，it is difficult to obtain relative accurate parameters. According to the creep characteristics of sand，the Singh′s soil creep model was adopted to calculate the long-term deformation of aquifers in this study. This model assumes that the creep rate and time present linear relationship in the double logarithmic coordinates. There is only one parameter m needed in this model，which stands for the line slope of the creep rate and time elapse in the double logarithmic coordinates. The statistical results of the existing sand creep test data show that，the values of m are 0.9–1.1. The sensitivity analysis of m shows that the different values of m in the range of 0.9–1.1 cannot affect the creep deformation significantly. Therefore，the value of m can be assumed as 1 when specific test data is not available. Two cases of Changzhou and Shanghai are given to demonstrate the effectiveness of Singh′s model and accuracy of the proposed method in long-term deformation of sand aquifers calculation.

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MODEL TEST OF VACUUM PRELOADING WITH CONTROLLED VENTILATION AND ITS MECHANISM ANALYSIS

ZHU Ping，SUN Liqiang，YAN Shuwang，JI Yucheng

2011, 30 (S1): 3141-3148

(657)

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With the development and construction of Binhai New Area，more and more lands are formed by the reclaimed soil with a water content of more than 80%. The vacuum preloading method is the conventional used method to improve the reclaimed soil. Therefore，how to reduce the cost for soil improvement has become an urgent problem to be solved. An improved vacuum preloading method in which the air is introduced at some stages during the period of vacuum preloading. The model test is designed and performed according to the concept of this method. A parallel model test with the conventional used vacuum preloading method is also carried out for comparison. During the tests，the settlement，pore pressure and vacuum pressure in the soil are obtained. The results show that the proposed method is more effective than the conventional vacuum preloading and it can reduce the reinforced time and is cost-effective. Finally，the mechanism of the proposed method is also studied.

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PERMEABILITY OF BENTONITE-SAND MIXTURES AS BACKFILL/BUFFER MATERIAL IN HLW DISPOSAL UNDER SWELLING CONDITIONS

ZHANG Huyuan，ZHAO Tianyu，LU Yiting，ZHANG Ming

2011, 30 (S1): 3149-3156

(699)

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The Gaomiaozi bentonite(GMZ001 Bentonite) from Inner Mongolia was mixed with quartz sand at different sand mixing ratios of 0%，10%，20%，30%，40% and 50%. The soil specimens were prepared by compacting the mixtures under a pressure of 20 MPa using an electronic compression press. The permeability coefficient and the swelling volume of the mixtures under confining pressure of 300 kPa were determined using a flexible-wall permeameter. Test results show that there is no significant change in permeability coefficient of GMZ001 bentonite-quartz sand mixtures within the sand mixing ratios ranging from 0% to 50%. These mixtures can therefore meet the requirement of impermeability for backfill/buffer materials. In order to better understand the influence of sand mixing ratio and dry density on the permeability coefficient，the effective clay dry density (ECDD) is adopted. It can be seen that there was a good linear-attenuation relationship between the logarithm value of permeability coefficient and ECDD of bentonite-sand mixtures. Based on the results of compaction test，it can be proved that the permeability coefficient of GMZ001 bentonite-sand mixtures is a single-value function of sand mixing ratio. Thereby，the permeability coefficient of GMZ001 bentonite-sand mixtures can be predicted by the function under different mixture compaction conditions，hoping that this result could provide a theory basis for the optimization and design of the bentonite-quartz sand as buffer/backfill materials.

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RESEARCH ON MECHANISM OF DREDGED CLAYEY SOIL IMPROVED BY DYNAMIC DRAINAGE CONSOLIDATION METHOD

WANG Shanshan1，2，LI Lihui1，LIU Kai3，HU Ruilin1，YU Wenlong1

2011, 30 (S1): 3157-3164

(714)

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To study the mechanism of dynamic consolidation with drainage on dredged clayey soil，the model test is conducted by self-developed large-scale indoor model equipment and the dredged clayey soil from Tianjin is selected as research object. It is focused on monitoring and analyzing the dynamic variation in pore water pressure in tamping process. The model test results indicate that the water content of soil descends，density and shear strength of soil appear significant growth after consolidation. To make up the defect of model tests，numerical simulation is conducted by FLAC3D to discuss the dynamic response characteristics of dredged soil under impact loads. The instantaneous hammer-soil contact stress，displacement of soil skeleton and dynamic variation in pore water pressure are mainly studied. The results of model test and calculation both indicate that the pore water pressure appears sharp increase at the hammer-soil touching moment，and it can be divided by three phases of increasing-stable-descending. The calculation results also show that the contact force doesn?t reach the maximum value at the hammer-soil touching moment. The contact force varies with ramming times and appears several bounces in tamping process. It is also found that the peak pore water pressure and peak displacement are delayed with the increasing depth and radial distance from center of the hammer bottom.

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CHARACTERISTICS OF EQUIVALENT STRESS OF STRUCTURAL FLUID OF UNSATURATED LOESS UNDER COMPRESSION

CHEN Cunli1，CHU Feng1，GUO Juan2，CAO Chengming3，DONG Yuzhu1

2011, 30 (S1): 3165-3171

(680)

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The compression tests are conducted on Xi?an intact and remoulded as well as artificially structural loesses under different moisture contents. Based on the principle of equivalent deformation，the equivalent stress of structural fluid is ascertained by using compressive stress difference between unsaturated and saturated loesses which have the same dry density and consolidation void ratio. The characteristics of equivalent stress of structural fluid are investigated. The research result indicates that the relationship between equivalent stress of structural fluid and stress as well as degree of saturation on Xi?an intact and remoulded as well as artificially structural loesses is power function，which is the same as that on the loess of other regions qualitatively. The variation regularity of equivalent stress of structural fluid is successfully universal. The changes of structural property and moisture content of loess as well as stress can be reflected by the equivalent stress of structural fluid；and the parameters of power function equation of equivalent stress of structural fluid are relative to moisture content and structural property as well as dry density. The equivalent stress of structural fluid under the condition of coupling of stress and moisture is calculated by the power function equation. Furthermore，effective stress and the compression curves of effective stress of unsaturated loess can be obtained.

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CENTRIFUGAL MODEL TESTING STUDY OF EXPLOSION- INDUCED CRATERS AND PROPAGATION OF GROUND SHOCK IN CLAY

MA Liqiu1，2，ZHANG Jianmin1，2

2011, 30 (S1): 3172-3178

(775)

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Previous research results indicate that chemical blasting is a phenomenon induced by volumetric effect. 1/N3(N for centrifuge acceleration) for blasting centrifuge model energy scaling can be confirmed according to the phenomenon. Centrifugal model tests on explosion-induced craters and propagation laws of ground shock in clay are investigated by using Tsinghua University?s 50 g•t geotechnical centrifuge. Measured acceleration waveform are presented，and the recorded results are also analyzed. Some certain understandings about explosion-induced craters and ground shock propagation in clay are obtained. Coriolis acceleration has no obvious effect on the forming process of the crater；on the contrary，Coriolis acceleration has effect on the ejection of crater and its distribution. The volume of crater has distinct relationship with gravity acceleration，small-scale modeling must increase gravity acceleration. The results prove that the geotechnical centrifuge is a good apparatus for blasting.

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DISCUSSION ON QUANTITATIVE PARAMETERS OF LOESS STRUCTURE

TIAN Kanliang1，2，MA Jun3，LI Yonghong1，2

2011, 30 (S1): 3179-3184

(806)

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The structure of loess is determined by the link structural strength and friction structural strength between loess particles. To quantitatively describe loess structure is to quantitatively study the variation laws of link structural strength and friction structural strength of loess. Therefore，some new and reasonable structural parameters of the structural loess are suggested for different loading states，such as the loess structural parameters based on the deformation conditions(i.e. link structural deformation potential parameter mp1，friction structural deformation potential parameter mp2 and structural deformation potential parameter mp)，the loess static structural parameters based on the strength conditions(i.e. link structural static strength potential parameter mε1，friction structural static strength potential parameter mε2 and structural static strength potential parameter mε) and the loess dynamic structural parameters based on the strength conditions(i.e. link structural dynamic strength potential parameter mγd1，friction structural dynamic strength potential parameter mγd2 and structural dynamic strength potential parameter mγd). Moreover，the rationality，stability and wide applicability of the proposed structural parameters are discussed.

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STUDY OF Q3 LOESS MICROSTRUCTURE CHANGES BASED ON IMAGE PROCESSING

GU Tianfeng1，2，WANG Jiading1，2，GUO Le1，2，WU Dalei1，2，LI Kaichao1，2

2011, 30 (S1): 3185-3192

(686)

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Loess geological disaster is closely related to its microstructural characteristics. For the issues now existing in quantitative analysis of scanning electron microscope(SEM) image，the microstructural characteristics of intact and cyclic loaded Q3 losses are studied. Firstly，noise reduction and segmentation method in the scanning electron microscope(SEM) image processing are discussed. A SEM image analysis method is presented by applying Lee image enhancement algorithm to image noise reduction and applying the fuzzy C-means clustering method to gray-scale image segmentation. With the presented SEM image analysis method，the pore area，pore size，roundness，shape ratio and other parameters of Q3 losses before and after cyclic loading are calculated. The results indicate as follows：(1) Large pores number of loess decreases，loess particles gradually arrange densely，and their contact relationship changes from point contact to surface contact under dynamic stress by analyzing the appearance features of SEM images. (2) The deformation produced by cyclic loading is mainly due to damage of large pores by analyzing pore area and its number changes. (3) Loess pores get a directional feature and the features change after damage of soil structure due to cyclic loading by analyzing loess pore directional distribution characteristics. (4) Based on the study of pore shape distribution characteristics，the soil particles may rotate and narrow pore of loess changes greatly，which resultantly result in the damage of pore connectivity. The study can provide basis for soil macroscopic deformation mechanism.

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ACCUMULATED STRAIN AND CRITICAL DYNAMIC STRESS OF FROZEN SILT AT HIGH TEMPERATURE

JIAO Guide1，2，MA Wei1，ZHAO Shuping1，CHANG Xiaoxiao1，YANG Shuguang1

2011, 30 (S1): 3193-3198

(755)

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Dynamic uniaxial compressive tests on Qinghai artificial frozen silt are carried out with different dynamic stress amplitudes at the steady temperature of －0.95 ℃. The relationships between accumulated strain and vibration times for frozen silt at different dynamic stress amplitudes under two kinds of frequencies are obtained. The results show that accumulated strain increases with the increasing vibration times. The relation curves of accumulated strain and vibration times can be classified into three types，i.e. failure type，stable type and critical type. When vibration times is same，the higher the dynamic stress amplitude is，the larger the accumulated strain is. The strain rate decreases with time at the beginning and the logarithm of strain rate is linearly related to the logarithm of time. With the increase in vibration time，the strain rate of failure type curve reaches a minimum value and then increases，while the strain rate of stable type curve fluctuates in certain range. The higher the vibration frequency and dynamic stress amplitude are，the larger the strain rate is. The higher the vibration frequency is，the lower the critical dynamic stress is.

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ANALYSIS OF MEASURED SETTLEMENT OF SUPER-LONG PILES AND PILE GROUPS IN ZHEJIANG FORTUNE FINANCE CENTER

ZHANG Zhongmiao1，2，WANG Zhijie1，2，ZHANG Qianqing1，2

2011, 30 (S1): 3199-3207

(879)

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Static load test results and measured settlement of foundation show that the shaft compression accounts for a considerable part of the total settlement of a super-long pile under designed working load；and the super-long pile works as an end-bearing friction pile under the maximum load. Side friction resistance of the super-long pile shaft gradually occurs from the top to down of soil layer. The measured data also indicate that the ultimate relative displacement between pile and soil for fully mobilizing side friction resistance is found to be 14–18 mm in sandy silt and 17–19 mm in silty clay，respectively；and the shaft resistance softening is observed when the pile-soil relative displacement is larger than the threshold of slip displacement. Furthermore，the settlement of pile-group foundation increases with the increasing load. The whole building settles down simultaneously and the settlement is small when the load is small(below the 5th floor)；the settlement of the core tube is larger than that of the outer parts as the load reaches a certain value(above the 30th floor). At the completion of this building，the differential settlement is small and the whole building deformation is compatible. It can be noted that the settlement ratio of pile group effect reaches a maximum value，and then slowly decreases with the increasing load at the pile head.

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EXPERIMENTAL STUDY OF CONSOLIDATION OF SOFT CLAY USING ELECTRO-OSMOSIS METHOD

JIAO Dan1，2，GONG Xiaonan1，LI Ying1

2011, 30 (S1): 3208-3216

(727)

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A laboratory tests programme of soft clay with axisymmetric operative condition under different initial conditions and power conditions was conducted on the self-made electro-osmosis consolidation apparatus. Electric current，electric potential，drainage，shear strength，moisture content and settlement were monitored in the electro-osmotic process. After analyzing and comparing the consolidation characteristics of soft clay，conclusions can be obtained as follows：(1) Electro-osmosis method can effectively improve the soft clay foundation through reducing moisture content，improving shear strength and reducing post-construction settlement and so on. (2) The electro-osmosis effect of soil with higher voltage and higher moisture content is better than that of soil with lower voltage and lower moisture content. (3) Comparing with continual current，intermittent current can increase electro-osmotic effect and has higher electric energy efficiency when moisture content and voltage are similar. Moreover，it can lead to more uniform treating effect after electro-osmosis. (4) Electro-osmosis also brings negative impacts including electrode corrosion which is less under lower voltage or intermittent current.

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ACCIDENT ANALYSIS OF DYNAMIC COMPACTION IN GROUND IMPROVEMENT OF AN INDUSTRIAL PARK IN ZHEJIANG PROVINCE

ZHANG Zhongmiao1，2，ZHANG Qianqing1，2，WANG Huaqiang1，2

2011, 30 (S1): 3217-3223

(855)

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An accident which is caused by the dynamic compaction in ground improvement of workshop #1 in an industry park in Zhejiang province，is analyzed；and the measures for reinforcing independent bearing platform and site ground are proposed. The analysis shows that the large discrepancy in the thickness of fill layer，the substratum with relatively low strength in deeper depth，the limitation of reinforcing depth of dynamic compaction，and some parts of this site with insufficient ramming energy are all the main causes of the accident. Therefore，the dynamic compaction is not suitable to be alone applied in ground improvement of a site with a large discrepancy in the thickness of the same soil layer and the substratum with relatively low strength at deeper depth. After the entire independent bearing platforms have been adjusted to a unified elevation，piles are used to reduce the settlement of independent bearing platforms；and the ground of the site can be reinforced by cement slurry in order to eliminate its post-construction settlement in the thicker soil layer.

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NONLINEAR ANALYSIS OF HIGH-RISE BUILDING SUPERSTRUCTURE-PILE-SOIL MASS INTERACTION CONSIDERING CONTACT EFFECT UNDER SEVERE EARTHQUAKE

WU Chenghao1，2，YAO Qianfeng1，YAN Hongxia1，3，LI Jitao1

2011, 30 (S1): 3224-3233

(692)

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In order to study and predict nonlinear seismic response of high-rise buildings better under earthquake especially severe earthquake，the Jiannanchun hotel，located in Mianzhu city of Sichuan province，which endured Wenchuan Earthquake，is selected for research object. Superstructure-pile-soil mass three-dimensional finite element physical model is established by the popular finite element software ABAQUS. Different dynamic characteristics of superstructure caused by varied inter-pile soil and bearing layer soil are discussed via comparing the vibration characteristics and dynamic responses of superstructure upon rigid subgrades and pile-soil foundation. Conclusion is drawn for the influences of inter-pile soil and bearing layer soil on dynamic characteristics of superstructure thereby. Meanwhile，the influences of nonlinearities of superstructure，soil mass and pile-soil contact on nonlinear responses of the interaction system are considered. Comparison between time-history analysis results of dynamic elastoplasticity and disaster investigation performed after Wenchuan Earthquake indicates that the ability of anti-collapse of superstructure of high-rise buildings considering interaction effect meets the actual circumstances better than traditional design method. Results of finite element model matching site investigation well show that software ABAQUS is greatly applicable for severe nonlinear interaction problem analysis of high-rise buildings；and it can be guidance for engineering practice. Besides，the proposed method supplies important theoretical basis for engineering practice.

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PARAMETER IDENTIFICATION OF SOIL PROPERTIES IN SHAKING TABLE TEST ON LIQUEFIABLE SOIL-HIGH-RISE BUILDINGS SYSTEM

LI Peizhen，LIU Yanmei，CUI Shenglong，LU Xilin

2011, 30 (S1): 3234-3244

(743)

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Based on the shaking table tests on liquefiable soil-high-rise buildings interaction system，the site liquefaction mechanism and dynamic characteristics of liquefiable soil during earthquake excitation were analyzed by using parameter identification technique to study the acceleration and water pore pressure records. The time-history curves of cyclic shear stress and shear strain in the soils were evaluated from the acceleration records in the soil by one-dimensional shear beam model. These time-history curves were used to estimate variation in dynamic shear modulus of soil and material damping characteristics with shear strain amplitude. Shear wave velocity，effective stress path and shear strain of pile and soil were discussed further. The analysis result shows that：Under the stronger earthquake excitation，the soil stiffness increases with the increasing depth；the stress-strain loops are rounded and show larger hysteretic damping characteristics for large earthquake excitation；the ratio of pore water pressure to vertical effective consolidation pressure goes up obviously；the increasing pore water pressure has influence on shear wave of soil；soil stiffness and shear strength both decrease with the increase in pore water pressure. Soil stiffness calculated from measured accelerations is consistent with that obtained through independent laboratory tests；but the material damping calculated from measured accelerations is much larger than that measured in laboratory tests，which is smaller than the equivalent damping associated with hysteretic damping. The shear strains in the soils inside and outside the pile group were found to be compatible. However，the amplitude of the shear strain outside the pile group is larger than that inside the pile group. The parameter identification technique of soil properties is useful for studying liquefaction field and practical seismic design of structure in liquefaction field.

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MODIFIED MOBILIZABLE STRENGTH DESIGN(MSD) METHOD ON DEFORMATION PREDICTIONS OF FOUNDATION PIT

WANG Haoran1，2，WANG Weidong1，3，HUANG Maosong1，2，XU Zhonghua3

2011, 30 (S1): 3245-3251

(848)

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Firstly，the mobilizable strength design(MSD) method for predicting deformation induced by excavation is introduced. The method cannot only use the strain-stress curve of site soil but also take the effect of heterogeneity and anisotropy of soil on undrained strength of soil into account. Then，after considering the undrained anisotropic shear strength of K0 normally consolidated soft clay and bending strain energy of retaining wall，the MSD method is modified. A numerical example is calculated by the modified MSD method in the end. The results calculated by the modified MSD method are compared with those calculated by finite element method(FEM) based on the MIT–E3 constitutive model and normal MSD method. It is shown that the results calculated by the modified MSD method are closer to those calculated by the FEM，which proves that the modified MSD method is more suitable for calculating deformation induced by excavation.

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INDOOR MODEL TEST OF PILE FOUNDATION USING SEDIMENT AT PILE BOTTOM

MEI Guoxiong1，2，HU Chengbo2，MEI Ling2

2011, 30 (S1): 3252-3259

(700)

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CONSOLIDATION ANALYSIS OF STONE COLUMN-REINFORCED COMPOSITE GROUND BASED ON TWO-DIMENSIONAL ELASTIC DEFORMATION

LU Mengmeng1，2，XIE Kanghe3，ZHOU Guoqing1，2，LI Ying3

2011, 30 (S1): 3252-3259

(805)

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Firstly，the two-dimensional elastic deformation behaviour of composite ground under the influence of excess pore water pressure is analyzed. Analytical solutions are obtained for the volumetric strain，stress and displacement within the column and surrounding soil，respectively. Based on the results of the two-dimensional deformation analysis，solutions are developed for the consolidation of composite ground by comprehensively considering an instantly applied load，the combined flows along both the radial and vertical directions and three possible variable patterns of horizontal permeability of soil in distributed area. Finally，the consolidation behaviour of composite ground with two-dimensional deformation is investigated. The analysis results show as follows：(1) The degree of consolidation of composite ground predicted by the present solution with two-dimensional deformation is less than that calculated by the previous solution with only the vertical deformation under the same calculation conditions. (2) The column-soil stress ratio predicted by the present solution increases gradually during the consolidation process；but unlike the results predicted by the previous solution with one-dimensional deformation，it will not go up to the column-soil compressive modulus ratio but cease increasing at a smaller value. (3) Unlike the traditional solutions with one-dimensional deformation，the column-soil stress ratio at the initial moment predicted by the present solution with two-dimensional deformation is not equal to zero.

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RESEARCH ON BASE GROUTING EFFECTS OF PILES IN SURAMADU STRAIT AREA OF INDONESIA

HUANG Ting，GONG Weiming，DAI Guoliang

2011, 30 (S1): 3269-3274

(816)

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To research the influence on pile bearing capacity after base grouting in Suramadu Strait area of Indonesia，the static load tests on four test bored piles of Suramadu Strait Bridge are conducted before and after base grouting under compression. The long-distance displacement sensors and strain gauges are adopted. Consequently，the pile displacement and axial stress along the shaft are obtained. Based on the test results，the comparative analysis of bearing properties of piles before and after base grouting are made. The test results show that after grouting，the tip resistances increase by 24.70%–40.98%；the lateral frictional resistances increase by 9.2%–32.1%，and the ultimate bearing capacities of piles increase by 16.61%–33.65%. The base grouting effects of piles are obvious. Because of poor penetration ability of soil in this area，not only tip resistances are improved after grouting，but also lateral frictional resistances are improved. By comparing lateral frictional resistances along pile shaft，it is found that the slurry penetration height along the shaft has a certain range. The result indicates that the quantity of mortar intrusion has more influences on the slurry penetration height than grouting pressure on it. Therefore，the quantity of mortar intrusion should increase appropriately in practical engineering design. The research results have been directly applied in the design of bridge foundation and can provide references for similar projects.

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ANALYSIS OF RESIDUAL STRESS ON PILE-BASE POST GROUTING PILE

ZOU Jian1，2，ZHANG Zhongmiao1，2，LIN Cungang1，2

2011, 30 (S1): 3275-3280

(708)

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Theoretical analysis and field tests on pile-base post grouting pile were carried out to study the generation and dissipation of residual stress and their effects on bearing behaviour of pile. Generation and dissipation of residual stress were observed for a long time by means of embedding earth pressure cells at pile tip and reinforcement stress gauges at pile shaft. The observation results show that during pile-base post grouting，high pressure grout produces a bidirectional force inside the confined spaces of pile tip，where the pile tip and pile tip soil are preloaded. Because of the bidirectional force，pile tip soil is preloaded and there will be negative friction along the bottom of pile shaft. However，within 24 hours after grouting，the permeation and pressure filtration of injected grouts will lead to the decrease of this bidirectional force and the dissipation of residual stress. 24 hours later，the residual stress remains at a constant value. So before loading test，there are still negative friction along the bottom of pile shaft and the pile tip soil is preloaded. By preloading the pile tip soil and not changing the value of side friction resistance，the existence of residual stress can improve tip resistance；and thereby enhances the ultimate bearing capacity of post grouting pile as well. If the residual stress was neglected and the reading of reinforcement stress gauges was taken as zero reading assumption，the side friction resistance of pile will be overestimated and its tip resistance will be underestimated.

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ANALYSIS OF STABILITY OF BORED PILE HOLE-WALL

WANG Yungang1，2，ZHANG Guang1，HU Qi3

2011, 30 (S1): 3281-3287

(805)

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By the methods of finite element numerical simulation and finite element strength reduction，the influences of soil properties，relative density of mud，hole depth and hole radius on the stability of bored pile hole-wall are analyzed. The analysis results are shown as follows：(1) The major problem of stability of bored pile hole-wall in clay is hole shrinkage. The poorer the properties of clay are or the deeper and bigger the hole are，more serious the phenomenon of hole shrinkage is. The dense mud can reduce the size of hole shrinkage effectively. (2) The major problem of stability of bored pile hole-wall in sand is collapsing and the relative density of mud is the major influencing factor. When plastic zones appear in the hole-wall soil，the soil is easy to be destroyed and the failure will spread to all around the plastic zone；finally，the hole collapses. In order to prevent collapsing，the relative density of mud should be heavy enough to make sure the lateral pressure of mud is not less than static lateral pressure of soil. The research results can provide references for the design and construction of bored piles in soft soil.

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INFLUENCE OF COUPLE STRESS ON INTERFACES BOUNDARY LAYER EFFECT OF LAYERED ROCK MASS WITH INCLUSION

ZHANG Dunfu1，WANG Xiangyu1，2，LI Shucai1

2011, 30 (S1): 3288-3294

(627)

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The effect of material microstructure is not included in the traditional continuum theory. The microstructure size of rock material is usually above millimeter scale. Under high strain gradient condition，the bending deformation of layered rock mass is remarkable. Interfaces boundary layer effect of layered rock mass with inclusion is studied by adopting couple stress theory and finite element method. The results of the typical elasticity theory and the couple stress theory are compared. The results show that the absolute values of stresses and strains within interfaces boundary layer decrease. Under couple stress theory，the transition region of shear strain emerges near interfaces boundary layer. The abrupt change of the shear strain is relieved，but the shear stress is no longer continuous. The size of the region is influenced by the characteristic length，not by the second shear modulus，posion?s ration and elastic modulus.

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WATER INRUSH MECHANISM STUDY OF FAULT ACTIVATION INDUCED BY COUPLING EFFECT OF STRESS-SEEPAGE-DAMAGE

LI Liping1，2，LI Shucai1，SHI Shaoshuai1，XU Zhenhao1

2011, 30 (S1): 3295-3304

(820)

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Based on investigation analysis and classification statistics of massive cases of water inrush geological hazards in mining activities，catastrophe evolution mechanism of water inrush of retarded type for filling fault has been researched；the variation characteristics of fault occurrence，filling ability and water conductivity due to mining effect have been analyzed；the physico-mechanical characteristics of filling medium effect on water inrush channel formation of fault activation have been analyzed. Taking the filling fault under pressure water for example，the mechanical characteristics and seepage properties of filling medium at elastic region and strain-softening zone with different distances from the aquifer have been analyzed；and the function of water effect on filling medium strength has been adopted to the constitutive relation of shear stress and deformation，in order to establish the swallowtail catastrophe model of water inrush for filling structure slipping；and the main influencing factors of catastrophe evolution path have been derived from the bifurcation set of system potential function. For the filling fault above the pressure water，the seepage damage characteristics of filling medium for its failure process have been analyzed. Considering the double failure criterion of compression shear and tension shear，and the coupling equation of stress and seepage damage which is suitable for the damage description of pre-and post stages has been adopted，in order to get the catastrophe evolution process of floor cracks evolution，activation process of fault filling medium and formation of water inrush passage. Through the simulation analysis of water inrush of fault activation with different dip angles and fault throws，the coupling effect of stress and seepage damage have been analyzed；and four typical styles of water inrush paths have been put forward by accurately locating the different evolution paths of water inrush. The conclusions can provide reference for the study of the mechanism of water inrush and its control.

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WEATHERING CHARACTERISTIC AND MECHANISM OF SEDIMENTARY PYROCLASTIC ROCKS AT THE BOTTOM OF EMEISHAN BASALT

XU Zemin

2011, 30 (S1): 3305-3318

(748)

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The spheroidal weathering of sedimentary pyroclastic rocks which deposited at the bottom of Emeishan basalt is intensive. The weathering extent is stronger evidently than that of the overlying basalt. The saprolited crust have spongy microtexture and are characteristic of high porosity，high intrinsic permeability，high specific water capacity，low specific yield and low density. Both of the sedimentary volcanic clasolite have a homothetic chemical composition. Also，the changes of chemical composition in the weathering process are nearly the same. The temperature fluctuation in vadose zone can form to tiny slot between different clasts. The condensated vapor water in the tiny slot dissolve the limestone clast firstly，and then a sponginess crust occur，whose water absorbability and storativity are stronger than other saprolized crusts. The liquid water which has been absorbed and stored in the sponginess crust can both ensures the dissolution of the pyroclasts in the crust itself and supports the spread of the weathering front. The weathering process of basic calcareous sendimentary pyroclast can be divided into two stages which can not be separated absolutely. In the first stage，limestone clasts are mainly dissolved and basaltic clasts are dissolved in second stage.

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STUDY OF DEFORMATION CHARACTERISTIC OF ROCK MASS WITH MULTIPLE PERSISTENT CRACK SETS

HAN Jianxin1，2，LI Shucai1，LI Shuchen1，TONG Xinghua1，LI Wenting1

2011, 30 (S1): 3319-3325

(609)

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Natural rock mass usually contains multiple parallel distribution of persistent crack sets. It is important to study the deformation and deformation characteristic of rock mass with parallel distribution of persistent crack in engineering design and stability analysis of surrounding rock mass. On the assumption that rock is isotropic linear elastic body and the stress-displacement relation of crack is linear stiffness relation，the computational model of deformation of rock mass with multiple persistent crack sets is presented by the method of Mohr?s circle of stress. On this basis，the rock mass with cracks are equivalent to anisotropic continuous mass. Equivalent elastic modulus and equivalent poisson?s ratio are put forward. The effect of material parameters and geometry parameters of rock and crack to the equivalent elastic modulus and equivalent poisson?s ratio of rock mass with cracks is studied. The model can comprehensively consider the effect of material parameters and geometry parameters of rock and crack to the deformation of rock mass. So the model has some reference value in predicting deformation and stability of rock mass.

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INVESTIGATION ON MIXED-MODE FRACTURE CRITERION OF SURFACE CRACK IN ROCK-LIKE MATERIALS

LI Mingtian1，2，LI Shucai1，ZHANG Dunfu1，YANG Lei1，SHAO Dongliang1

2011, 30 (S1): 3326-3333

(721)

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Direct tensile experiments of rock-like materials with surface crack have been carried out. And the influences of the inclination angle of the surface crack on the peak strength and fracture process have been analyzed. Because the inclined surface cracks are under the mixed mode I，II，III loading conditions，in order to study the fracture criterion of the surface crack the stress intensity factors of the front of half-circular surface crack are calculated according to fracture analysis code–3D(FRANC3D). And the law between I，II，III mode stress intensity factors and the orientation angle are analyzed. Then the initial angles are predicted according to the minimum strain energy density criterion，the maximum circumferential stress criterion and the revised maximum circumferential stress criterion. The contrast with the experimental results show that the revised maximum circumference stress criterion，which included mode–III stress intensity factor is fit to predict the initial angle of the inclined surface crack.

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STUDY OF OPTIMIZATION OF DESIGN PARAMETERS FOR UNDERGROUND GAS STORAGE IN SALT ROCK

WANG Baoqun1，2，ZHANG Qiangyong1，LI Shucai1，YANG Chunhe3

2011, 30 (S1): 3334-3340

(713)

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The influences of geometrical parameters，surrounding rock parameters and the height of casing shoe under various geological conditions on the stability，impermeability and serviceability of the underground gas storage in salt rock were studied based on the numerical simulation. And then the optimization criteria of design parameters for underground gas storage under various geological conditions were presented. In salt domes and thick salt layers，central expansion cylindrical cavity should be adopted in order to minimize the damage of the salt rock. In the same geological conditions，the top expansion cylindrical cavity should be adopted in order to decrease the cavity shrinkage and ground settlement. And in thin salt layers the best shape to ensure the stability of cavity was ellipsoid with the axial ratio of 7/3. The reasonable pillar spacing in the salt dome and thick salt layers should exceed three times of the chamber diameter，and two times in thin salt layer. The minimum thickness of roof should ensure salt cavity did not leak，collapse and the ground did not subside heavily under the maximum allowable internal pressure. The top of the casing shoe should be located outside the allowable influence range of salt creep in order to make sure the impermeability of the cavity.

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RESEARCH ON ROCK ENVIRONMENTS VIBRATION RESPONSE INDUCED BY METRO TRAINS IN ROCK MEDIA

ZHANG Bo1，2，LI Shucai1，2，ZHANG Dunfu1，2，XUE Yiguo1，WANG Xiping2

2011, 30 (S1): 3341-3347

(698)

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The visco-elastic artificial boundary was analyzed to be suitable for the layer rock. Taking the Qingdao metro line #3 as the studying subject，the computation model was constructed to study the effects of rock elastic modulus，tunnel depth as well as tunnel lining thickness on the rock environmental vibration response induced by the metro train. The results show that the variations of rock elastic modulus at different depths generate different effects on the rock environmental vibration response. There is only one amplification zone of vertical acceleration at the free surface of rock environment with great elastic modulus，where the acceleration amplification zone is at the tunnel upward of free surface. The vibration effects of metro trains on free surface increase with the decrease of tunnel depth. The tunnel lining thickness has few effects on the rock environmental vibration response induced by the metro train.

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GROUND SETTLEMENT DEFORMATION CHARACTERISTIC STUDY OF SHALLOW LARGE-SPAN TUNNEL IN CONSTRUCTION PROCESS

LI Xinzhi，LI Shucai，LI Shuchen

2011, 30 (S1): 3348-3353

(739)

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According to Mulingguan tunnel of Qingzhou to Linshu highway，the monitoring of ground settlement deformation characteristic on the shallow large-span tunnel in the construction process was carried out，the excavation methods of the three-lane span shallow tunnel were discussed and tunnel ground settlement deformation characteristic under the three-level seven-step parallel tunnel excavation was analyzed. Through field test discovered in the process of the pile roof and before the excavating face，the ground had occurred beforehand settlement displacement. The key step influenced ground deformation near the tunnel center line was first and middle step，then the key step influenced ground deformation near the tunnel arch shoulder was down and last step，it showed that with the tunnel excavation depth increases，the range and depth of its impact on both sides of the tunnel extension. The impact of tunnel excavating face on ground settlement focused on the excavating face within 1 times of the hole diameter D，afterward excavating face one D，the deformation gradually slowed down，and the eventually ground settlement distribution appeared abnormal skewness to the first excavating tunnel. Three-dimensional fast Lagrangian element method was applied to simulate the excavation of shallow large-span tunnel tunnel. The distributions of ground settlement were obtained and the result was in good agreement with that of in-situ monitoring test，the conclusions can provide a reference for other similar projects.

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STUDY OF DEFECTS CHARACTERISTICS AND REPAIR METHODS OF OLD TUNNEL IN COLD REGION

YUAN Chao，LI Shuchen，LI Shucai，LI Wenting

2011, 30 (S1): 3354-3361

(727)

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According to the characteristics of old in-use tunnels of Shenyang—Dandong railway，an investigation on defects like water leaking has been carried out by sketch of tunnel damage and ground penetrating radar(GPR) scanning. The features of defects such as tunnel lining cracking，surface corrosion，water infiltration，freeze-thaw，lining vacuousness，collapse and rockfall of the entrance，etc. are studied and analyzed carefully. The degradation mechanism of tunnels is briefly analyzed from the physical factors and chemical factors. Based on the above， combining the relevant data and operating characteristics of the railway tunnel in cold regions，the flow chart of tunnel maintenance and the main repair methods are given. And these methods are carried out in the Fenshuiling tunnel maintenance works at last. The paper provides theoretical basis for integrated maintenance of tunnels and contributes to the guidance for engineering practice.

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FORWARD OF TRANSIENT ELECTROMAGNETIC METHOD FOR GEOLOGICAL PREDICTION IN TUNNELS BASED ON FIELD-CIRCUIT COUPLING AND ITS ENGINEERING APPLICATION

SUN Huaifeng1，LI Shucai1，SU Maoxin1，XUE Yiguo1，ZHANG Yongwei1，2，ZHANG Wenjun1

2011, 30 (S1): 3362-3369

(771)

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Analytical solutions in homogeneous half-space are joined as initial conditions in almost all the forward of transient electromagnetic method(TEM)，no problem when the model has an analytical solution. However，it is not suitable for TEM advanced geological prediction in tunnels with a homogeneous whole space because of the excavation. According to Maxwell equations and on the basis of 3D transient eddy current field equations and circuit equation，we establish a field-circuit coupling model based on vector magnetic potential formulation. Node method is used during the time discretization；and a Galerkin form time discrete equation is established. The model achieves the goal of using voltage as excitation source in 3D forward of TEM，which makes the 3D forward much nearer to the actual situation. The famous smoking effect in TEM is simulated based on the field-circuit coupling method. Comparison between the simulation results and the analytical values show that the numerical simulation is consistent with the practice. Two models with and without consideration of effects of seawater are established and analyzed according to Qingdao subsea tunnel. The field-circuit coupling method is used and the effects of the seawater above the tunnel are collected.

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FIELD TEST STUDY OF REINFORCED SOIL WALL ON SOFT GROUND

CHEN Jianfeng1，GU Jianwei2，SHI Zhenming1，WANG Yanling3，CHU Weihong3

2011, 30 (S1): 3370-3375

(597)

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A field test was conducted on a geogrid-reinforced soil wall(RSW) with wrapped face on soft ground. Such items as settlement at the original ground surface，lateral and vertical displacement at the RSW toe，lateral displacement at the RSW face，vertical earth pressure in the RSW and lateral earth pressure along the back of the RSW face and reinforcement strain were analyzed. The working behaviour and the stability of the RSW were discussed. The test results show that the failure of the RSW on soft clay exhibits external instability；the wall surface shows bulging and the maximum lateral displacement occurred at the middle of the full height of the wall；the maximum strain occurred at 0.8 H(H is wall height) distance from the wall surface and ‘0.3H’ method used to predict the location of slip surface and maximum strain is not applicable to the RSW on deep soft clay. The results can be referred for the research，design and construction of the similar projects in the future.