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2009, 28 (10): -0 doi:
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SOME ADVANCES IN ROCK BLASTING DYNAMICS

QIAN Qihu

2009, 28 (10): -1968 doi:
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[PDF 743 KB] (1809)

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The principles of rock blasting dynamics and related engineering applications in the recent years are reviewed. The main issues are covered in blasting cave range，various determination methods for failure zones，theories of short-wave and weak-wave in near-field of cave blasting，the movement in plastic regions and mechanical parameters in far-field，and rock fracture under blasting for underground works. The laws of blasting effects in uniform media in indoor test are also introduced，which include heterogeneous and homogeneous characteristics of geostress，fissure，and shllow-buried cave in laboratory simulation or experimental test. The actual rock blasting tests are touched in failure effects of near-field，seismic effects in far-field，and irreversible deformation regions. The latest similarity research results in underground blasting，shallow-buried blasting (throwing and directional blastings) are also presented. In addition，engineering applications of rock blasting dynamics in various fields are briefly introduced. Filnally，some ideas and prospects are proposed for later research in rock blasting dynamics.

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LIMIT EQUILIBRIUM METHOD BASED ON NUMERICAL STRESS FIELD
AND ITS APPLICATION TO ENGINEERING

ZHU Dayong1，LU Kunlin1，TAI Jiajia2，CHEN Juxiang1

2009, 28 (10): -1975 doi:
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By using numerical method，the stress distribution can be reasonably obtained，but it is not easy to obtain the factor of safety. With limit equilibrium method，the factor of safety can be readily derived，but its precision is limited due to over-assumptions. From the stress field by numerical analysis，the normal stress distribution over the potential slip surface is calculated，with which the factor of safety is satisfied with the whole equilibrium conditions by using the method of normal stress modification. Such a limit equilibrium method based on numerical stress takes full advantages of the numerical analysis and the limit equilibrium with theoretically yielding more reasonable solution for the factor of safety. This method has been applied to the stability analysis of the deep foundation of Wudu reservoir dam and the computational results are shown to be satisfactory by comparison with the conventional limit equilibrium method and the strength reduction FEM，which has been adopted in the design of dam foundation treatment.

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ANALYSIS OF INTERFACIAL SLIP MESOMECHANICS IN ANCHORAGE SECTION OF PRESTRESSED ANCHOR CABLE

YOU Chun¢an1，ZHAN Yubao2

2009, 28 (10): -1976 doi:
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Based on the test of interfacial mechanics of prestressed anchorage segment，the interfacial deformation laws and the failure conditions under different loads are studied. The test results show that anchoring strength is related to anchorage length but not with proportion relationship. When anchorage length reaches a constant value，the increase of anchoring strength is limited although with further increase of anchorage length. Under the condition，the strength of sand pulp is fixed，and the higher the sand-bearing capacity in the anchorage body is，the larger the anchoring strength is. The process from elastic deformation to plastic slip and up to debonding failure is studied on the mesoscopic level. It is demonstrated that anchorage body interfacial layer is a material with a certain thickness and special mechanical properties，whose mechanical properties are related to property of rock-soil body and closely to the material fabric of grouting body. So the mechanical properties of interfacial body will be effectively promoted based on the research on composition and mixture ratio of grouting materials，by which the anchoring strength will be improved. Deformation of one point on interface of anchorage body can be divided into three stages，i.e. elastic deformation，plastic-slipping deformation and debonding deformation. Because of the debonding effect of interface layer of anchorage body，the nearer it is to proximal end of load，the larger shear stress the anchorage body will bear. Within the whole anchorage system，the main stressed area is plastic-slipping zone；and the stresses born by elastic zone and debonding zone are relatively smaller.

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PREDICTION OF WATER INFLOW IN TUNNEL BASED ON STOCHASTIC FINITE ELEMENT OF UNSTEADY SEEPAGE

WANG Yuan1，2，WANG Fei1，2，NI Xiaodong1，2

2009, 28 (10): -1994 doi:
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In prediction of water inflow in tunnel，the water inflow is generally random because of the spatial variability of permeability in rock mass，so the random analysis of prediction of water inflow is necessary. Thus, the spatial variability of permeability in rock mass is described by regarding permeability tensor as three- dimensional anisotropic random field，and vector separable local average method is adopted for discretion of random field. Then the stochastic finite element governing equations of three-dimensional unsteady seepage are deduced based on random variational principle in first order perturbation method. Furthermore，the three- dimensional unsteady random seepage field can be derived and the formulas of mean and standard deviations of flow rate are deduced combining with the first order Taylor series stochastic finite element method. Finally，some programs are developed for proposed method；and an example for stochastic prediction of water inflow is given. The results indicate that the proposed method is feasible.

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INVESTIGATION ON MECHANICAL PARAMETERS OF WATER-ROCK INTERACTION

LU Yingfa1，2，SUN Hui2，LI Jianlin1，WU Xinxing1

2009, 28 (10): -2005 doi:
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The processes are very complex for the coupling of water-rock interaction，and the sensitivity of water to porous media material cracks should be focused for the research of fundamental mechanical properties of rocks. The conventional used test methods are true and pseudo triaxial tests；and the theories and measure technologies of ture and pseudo triaxial tests are also analyzed. The mechanical parameters are obtained by ture and pseudo triaxial tests with/without water pressures. The idea that the triaxial test is only suitable for the isotropic porous media materials is proposed；and the hexahedron sample of 5 cm×5 cm×10 cm is proposed to conduct the triaxial test to understand the anisotropic mechanical behaviors of porous media materials. The obtained testing methods of anisotropic Biot coefficient and mechanical parameters under different stress states are proposed by using the influences of unloading water pressure on porous media materials. The testing results show that variational trends of anisotropic Biot coefficient in the different directions are not the same. The testing method of limit yield stress is suggested：the limit yield stress is equal to the deviatoric stress corresponding to the maximum water pressure of curve between deviatoric stress and water pressure. The testing results also show the Skempton coefficient disperity is significant；and the mechanism of water pressure action is different under various injections and drainages. It is crucial for damage mechanics and civil engineering to research water-rock interaction.

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RESEARCH ON NONLINEAR VISCOELASTO-PLASTIC
CREEP MODEL OF ROCK

SHE Chengxue

2009, 28 (10): -2011 doi:
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By using the creep strength theory of rock and the Kachanov damage theory，the relationship of damage with time is firstly proposed. By establishing the relationship of the damage and the viscoplastic rheological parameter，the nonlinear rheological parameter expression is put forward including the factors of time and loaded stress. By incorporating the parameter expression into the Nishihara model，the new nonlinear creep model is established for describing the total three-stage of creep process. When the loaded stress is larger than the long-term strength of rock，the damage occurs，and the rheological parameter begins to present nonlinearity changing with time. By compiling program of the model into finite element method code，the numerical tests are conducted，showing that the proposed creep model can properly describe the creep failure process for soft and hard rocks. It can describe not only the nonlinear failure of the soft rock，but also the abrupt failure of hard rock in the tertiary stage of creep demonstrating the extensive adaptability of the model to different kinds of rocks. The comparison of tests and calculation for marble and rock salt samples respectively further demonstrates the correctness of the model. Obviously，the achieved results show that the proposed nonlinear creep model will find good application to practical engineering.

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DYNAMIC CENTRIFUGE TESTS OF SEISMIC RESPONSES OF PILE FOUNDATIONS IN INCLINED LIQUEFIABLE SOILS

WANG Mingwu1，TOBITA T2，IAI S2

2009, 28 (10): -2012 doi:
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The problem of seismic performances of pile groups found on the inclined liquefiable soils is a nonlinear and complicated problem because the seismic responses of pile groups are influenced by the pile-soil interaction and lateral spread. Two cases of 50 g centrifuge tests are conducted to investigate acceleration，displacement，bending moment and excess pore water pressure responses of pile groups on the inclined liquefiable soils during earthquake. The scenario input motions with peak shaking amplitudes of 3.64 and 9.68 m/s2(at prototype scale) are adopted in centrifuge tests. A rectangular rigid container is used in two cases. The inclined soil profile is comprised of saturated silica sand resting on stiff bedrock. The fluid material is simulated by deaired motolose solution of 50 times of the viscosity of water such that the deposit has the prototype permeability of sand. The model of pile foundations consists of structure supported by a 2 row×2 row piles，10 times in diameter spacing pile group. Moreover，the results from centrifuge cases are compared. The failure mechanism of pile groups in laterally spreading soils during earthquake is also discussed；and a good result is achieved. It is found that the lateral displacement and bending moments of pile groups are much larger in laterally spreading soils than those in non-liquefiable soils. The location for the maximum bending moment during shaking and residual bending moment transfer further down with the liquefaction and lateral spread of soils. The proposed dynamic centrifuge test is applicable and reliable for simulating seismic performance of pile groups on the inclined liquefiable foundation. These results for insuring the aseismic stability and aseismic safety of pile group in the inclined liquefied soils are potentially very significant.

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DISCUSSION ON SEVERAL ISSUES OF SEEPAGE STABILITY OF DEEP FOUNDATION PIT IN MULTILAYERED FORMATION

CONG Aisen

2009, 28 (10): -2023 doi:
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[PDF 319 KB] (1516)

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The issues of seepage analysis and design aspect of anti-seepage body in the design of deep foundation pit are concerned. It is shown that the importance of the seepage calculation of deep foundation pit should be focused on. The limits of current support standards for design and construction of deep foundation pit are pointed out. The basic requirements for foundation pit are provided and related countermeasures are also proposed. With three-dimensional finite difference method，the basic seepage characteristics of deep foundation pit are given；and the minimum embedded depth into soil(rock) of the underground continuous diaphragm wall is determined. The achieved results show that the proposed measures are feasible and they can provide references to similar engineering cases of deep foundation pits.

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STUDY OF SHAKING TABLE TEST OF SQUEEZED BRANCH PILE-SOIL-HIGH-RISE STRUCTURE INTERACTION SYSTEM

QIAN Deling1，XIA Jing1，LU Wensheng2，XU Yanfei1，LI Jianquan1

2009, 28 (10): -2030 doi:
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[PDF 326 KB] (1238)

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Shaking table test of dynamic interaction of squeezed branch pile-soil-high-rise structure system is designed and carried out，which reproduces the earthquake damage phenomenon of pile foundation and frame structure. The seismic response of dynamic interaction system，the seismic effects of squeezed branch pile and the difference of aseismic capability between single-span and double-span frame structure are studied based on the shaking table test. The test phenomenon，natural frequency，damping ratio，vibration mode，displacement response，acceleration response at the top of superstructure of the system are calculated and analyzed. The test results show that the influence of interaction on structural dynamic characteristics and seismic response is large，the resistant effects of compression，tension and torsion of squeezed branch pile are obvious，the aseismic capability of double-span frame structure is superior to that of single-span frame structure，which is good consistent with collapse phenomenon of many single-span buildings under Wenchuan earthquake. Maximal displacement of structure under excitation of the Shanghai artificial-wave is larger than that of El Centro wave under the same condition，which means the damage of structure not only is related to magnitude but also to the waveform of the seismic waves. The results will have important significance in aseismic design and prevention of seismic disaster.

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INFLUENCE OF POROUS STRUCTURE PROPERTIES ON MECHANICAL PERFORMANCES OF ROCK

YANG Yongming，JU Yang，LIU Hongbin，WANG Huijie

2009, 28 (10): -2031 doi:
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[PDF 544 KB] (1855)

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Using principle of statistics and FLAC3D，the three-dimensional porous structural models of sandstone are reconstructed. On the basis of the 3D porous structural models，the influences of porous structure parameters(pore number，pore radii distribution and space position distribution) on mechanical performances of sandstone are explored through a number of Brazil disk split tests with different pore distribution characters parameters by means of numerical simulation. The results indicate that porosity affects the failure states of disk models greatly. When the porosity is smaller，the tensile failure is main failure mode. When the porosity is larger，the tensile failure and shear failure act together. With the increase of porosity，the tensile strength decreases with exponential distribution. The split failure region of disk model is larger with the smaller pore radii distribution parameters. The pore radii distribution has some influences on tensile strength of disk model with smaller porosity. The influence of pore space position distribution on disk model failure mode is mainly concentrated in the place of crack occurring. It does not change failure mode and crack number of disk model. The effect of pore space position on tensile strength of disk model can be ignored. The achieved results disclose the intrinsic mechanisms of deformation and failure of rock and supply references for studying the influence of porous structure parameters on physical-mechanical performances.

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STRUCTURAL ANALYSIS OF PERMEABLE TUNNEL WITH RIBBED ARCH BEAM

YU Fei1，CHEN Shanxiong1，CHEN Xiuhe2，ZHANG Sheng2，WANG Fei2

2009, 28 (10): -2047 doi:
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[PDF 848 KB] (1099)

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Based on the analyses of stability control factors of shallow-buried tunnel adjacent to mountain and the disadvantage of traditional design scheme，a new type of tunnel structure，permeable tunnel with ribbed arch beam，is presented. Combining pre-reinforcement of the vault slope with cross-mounted pipe-shed and ribbed arch beam structure，a reasonable and complete supporting system is formed；and the excavation scope of the tunnel reduced significantly and no ventilation system and lighting system is needed. This tunnel structure comprehensively reflects the design idea of engineering safety，environmental protection，energy conservation and landscape coordination. With practical engineering，the design principle and structural characteristics of this tunnel are expounded；and the characteristics of stress and deformation and the schemes of excavation and reinforcement are analyzed by numerical simulation method. The analytical results reveal that the relaxed region of tunnel surrounding rock can be determined，and the cross-mounted pipe-shed is designed to reinforce the vault slope. By comparative analysis of different excavation schemes，the optimal construction program is suggested that is suitable for the cavern rock firstly and the integrated concrete in the ribbed arch beam and the tunnel-lining，which can lower the stress level of the tunnel structures and homogenize the stress distribution. The permeable tunnel with ribbed arch beam has been built successfully，so as to verify the reasonability of above-mentioned research results and the construction scheme of this kind of new tunnel.

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RESEARCH ON CONCRETE FAILURE PROCESS UNDER UNIAXIAL TENSION BASED ON STOCHASTIC DAMAGE MODEL

LIU Zhiguang，CHEN Jianyun，BAI Weifeng

2009, 28 (10): -2058 doi:
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[PDF 356 KB] (1032)

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A one-dimensional stochastic mesomechanical damage model is adopted to study the failure process of concrete specimen subjected to uniaxial tension. A balance is taken into account between the dissipated energy in damage evolution and the released elastic strain energy of the specimen during the loading process. The stability analysis of the failure process is conducted；and a stability criterion of the failure process for uniaxial tension test of concrete is derived based on energy principle. The critical state is defined according to the criterion，which is a transition from uniform damage to local damage；and the state is different from the peak stress state and lags behind it. The instable failure process of concrete specimen is accompanied by stress significantly decreased and it indicates that the specimen will fail in a brittle manner，while the stable failure process shows more ductility. Theoretical analysis indicates that the stress-strain curve shape，which includes a sudden decline in stress，is not only affected by the material heterogeneity but also by the length of the test specimens. To describe the heterogeneity，it is regarded that the material failure strain is given by a homogeneous，lognormal or Weibull random distribution. Finally，the failure processes of several concrete specimens under uniaxial tension are simulated with different lengths.

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INSTABILITY MECHANISM AND PREVENTION OF ROADWAY UNDER CLOSE-DISTANCE SEAM GROUP MINING

FANG Xinqiu1，2，GUO Minjiang1，2，LU Zhiqiang1，3

2009, 28 (10): -2067 doi:
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During the process of close-distance seam group mining，mining roadway in the lower seam is affected by coal pillar in the upper seam and the adjacent working face¢s mining. Due to the severe roadway roof caving and floor heave in the working face E12505 in Cuijiazhai coalmine，the field measurement，theoretical analysis and numerical simulation are adopted to study the mechanism of roadway¢s instability. The result shows that，when the upper pillar is narrow，the roadway is under the lower levels of the pillar and the protecting pillar is not wide enough，thus the roadway is easily damaged after the adjacent working face¢s mining. It is suggested that the distance between the roadway and the upper pillar is 25 m，and the protecting pillar is 20 m，so that the roadway can be stable in strengthened support. The industrial tests have been conducted at working faces E12611 and E12504，and good results have been achieved.

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PERMEABILITY AND MESO-STRUCTURE CHARACTERISTICS OF BEDDED SALT ROCK

ZHOU Hongwei，HE Jinming，WU Zhide

2009, 28 (10): -2073 doi:
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[PDF 478 KB] (1314)

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Salt rock，as a medium with extremely low permeability，has been widely used for oil and gas underground storages and high-level radioactive waste disposals in many countries. Twenty standard salt rock samples with dimensions of 25 mm in diameter and 50 mm in height，taken from the Yunying salt mine in Hubei Province，are tested by the automated core measurement system and the X-ray industrial CT to obtain their permeability characteristics and meso-scale structures. The test results indicate that the porosity of salt rock samples is less than 0.25% and the permeability is as low as 10－16–10－18 m2，and all decrease gradually with the increase of confining pressure in general. The mechanism of very low permeability subjected to meso-structure of salt rock is revealed by the X-ray industrial CT tests. It is shown that the salt rock is very compact at the meso-scale，and there are very few micropores and microfissures in pure salt rocks；and interlayer in salt rock is even more compact than that of pure salt rock，resulting in a shielding effect on permeability of bedded salt rock. Moreover，the effects of confining pressure and seepage lead to an obvious decrease in permeability. And the decrease of permeability agrees well with the decrease of porosity along with confining pressure.

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STUDY OF SOIL DISTURBANCE CAUSED BY SUPER-LARGE DIAMETER SLURRY SHIELD TUNNELLING

YUAN Dajun1，YIN Fan1，WANG Huawei2，HUANG Qingfei1，XIAO Heng1

2009, 28 (10): -2080 doi:
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[PDF 288 KB] (1524)

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Based on the Nanjing Yangtze River slurry shield tunnelling project，the investigations on the subsidence，horizontal displacement of soil，earth pressure and pore water pressure are conducted by setting up corresponding equipments. Then，the underlying laws，influential range，and influence degree for soil disturbance exerted by different stages of slurry shield tunnelling are analyzed. In addition，according to the stress variation in soil，the relevant mathematical relations between stress disturbances degree and distances are proposed；and it is found that the shield driving can affect stress disturbance of soil(disturbance degree is larger than 5%) at a range of 16 m from shield(approximately the hole diameter). After that，based on field test data，the Peck formulae are improved by establishing the mathematical model of hydraulic pressure on kerf，the synchronous grouting pressure，and ground subsidence. The model gives better prediction on subsidence caused by slurry shield tunnelling. Finally，with careful consideration on shield tunnelling data，some measures to reduce soil disturbance are also presented.

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PRACTICE OF COMPREHENSIVE EARLY-WARNING GEOLOGICAL PREDICTION ON AQUIFER FAULT IN QINGDAO KIAOCHOW BAY SUBSEA TUNNEL

XUE Yiguo，LI Shucai，SU Maoxin，ZHANG Xiao，ZHAO Yan，LI Weiteng

2009, 28 (10): -2087 doi:
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[PDF 653 KB] (1364)

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Taking Qingdao Kiaochow bay subsea tunnel for example，the principle is integrated by geology，geophysical exploration，and core drilling. The technology system of geological disaster，geological prediction in subsea tunnel construction is established. The result of comprehensive geological prediction is optimized. The concrete forecasting process in putting into effect in subsea tunnel is exactly predicted；and a fairly good predicting effect is achieved. The above-mentioned practice has certain lessons and guiding significance to similar projects.

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MODEL TEST ON DISPLACEMENT FIELD OF DOUBLE-ROUTE METRO CONSTRUCTED WITH HORIZONTAL FREEZING METHOD

CAI Haibing1，2，CHENG Hua2，PENG Limin1，YAO Zhishu2，RONG Chuanxin2

2009, 28 (10): -2095 doi:
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[PDF 469 KB] (1212)

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Aiming at horizontal freezing engineering of double-route metro，an integrated model experiment system is established based on similarity theory. Frost heaving and thawing settlements of the metro are analyzed by model test under freezing wall¢s intensity is guaranteed. Experimental results indicate that the connecting time of freezing wall ties up with frost heaving of soil，and strong moisture migration makes frost heaving of soil comparatively larger for prior freezing of uplink tunnel. Two thawing modes are contrastively analyzed in the test. In forcible thawing condition，thawing settlement phenomenon of soil is not obvious，and thawing settlement of near ground in forcible thawing condition is only 47 percent of thawing settlement of near ground in natural thawing condition. The phenomenon shows that the forcible thawing mode can reduce thawing settlement of soils.

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DAMAGE DEFORMATION CHARACTERISTICS AND ITS STRENGTH CRITERION BASED ON UNLOADING EXPERIMENTS OF GRANITES

LU Yinghui1，LIU Quansheng1，2，HU Yunhua3

2009, 28 (10): -2103 doi:
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[PDF 343 KB] (1265)

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Two different unloading tests of granites from the Dagangshan Hydropower Station at Dadu River have been carried out. In order to analyze rock failure mechanism，the damage laws of mechanics and strength parameters，the failure strength criterion during the process of unloading，the conventional triaxial compression tests of granites have been also performed. The results show that：(1) The characteristics of intense rebound deformation，distinct dilatancy and brittleness failure of rock have been observed in two different unloading tests. (2) Compared with the deformation modulus in conventional triaxial compression tests，the deformation modulus at the beginning point of unloading has been degenerated；the relationship between damage factor and initial confining pressure is approximately linear，but little damage is found in the Poisson¢s ratio. (3) During unloading stage，the Poisson¢s ratio rises up continually，and the variation law with the confining pressure can be well described by exponent relation；deformation modulus varies hardly，but at the failure point，it decreases rapidly. (4) In the two different unloading tests under high geostress，the Mogi-Coulomb envelope can match stress circle very well. (5) In the two unloading tests，shear strength parameters have been evaluated by Coulomb laws，and it is founded that the cohesion c decreases，but the inner friction angle increases during unloading；and the variation is dependent of the unloading style. These conclusions have revealed the unloading mechanical properties of granites under high geostress and provided reliable theoretical reference for the numerical simulation about excavation and design for the stability analysis of large-scale hydropower projects in West China.

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ANALYSIS OF DYNAMIC AND FRACTURED PHENOMENA FOR EXCAVATION PROCESS OF DEEP TUNNEL

LI Shuchen1，2，QIAN Qihu2，ZHANG Dunfu1，LI Shucai1

2009, 28 (10): -2112 doi:
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[PDF 535 KB] (1496)

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Tension-compression alternating regions can be formed around the rock mass during excavation process. The zonal disintegration phenomena may be brought when the geostress is too large. In order to interpret the tension-compression alternating and zonal disintegration phenomena，the dynamic mechanical model and calculation model of tunnel excavation are presented based on dynamic characteristics of tunnel excavation unloading. And the equilibrium physical equation，geometric equation and boundary condition equation are derived，which are satisfied by the disturbance stress，disturbance strain and disturbance displacement caused by the excavation unloading. Trial function of displacement is assumed considering the practical displacement constraints condition，and integral-variational equation group of the surrounding rock；and its modal matrix is induced by Hamilton time-domain variation principle considering time-domain variation and constraint conditions. The steady-state response of discrete vibration equation group is obtained using Duhamel integral in setting excavation unloading path and zero initial condition. By matrix transformation，the solutions of surrounding rocks disturbance stress，strain and displacement are obtained. The analyses of examples show that the theory and method can correctly reflect the dynamic process caused by excavation；and they effectively simulate the zonal disintegration phenomena of the rock mass.

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EXPERIMENTAL STUDY ON DYNAMIC MECHANICAL PROPERTIES OF AMPHIBOLITES UNDER IMPACT COMPRESSIVE LOADING

LIU Junzhong1，XU Jinyu1，2，LU Xiaocong1，ZHANG Lei1，WANG Zedong1

2009, 28 (10): -2120 doi:
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[PDF 393 KB] (1249)

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In order to investigate rock dynamic compression mechanical properties with strain rate varying from 40 s－1 to 150 s－1 on amphibolites，the specimens are subjected to axial impact with different projectile speeds by using the split Hopkinson pressure bar(SHPB) of 100 mm in diameter and a thin red copper circular plate as pulse shaper；and the consistence of experiment is discussed to consider the effect on experimental result of size of the samples. The wavy curves of samples，dynamic compressive strength，dynamic strength increase factor，and the relationship between specific energy absorption and strain rate are also analyzed. Experimental results show that the dynamic compressive strength and specific energy absorption of amphibolites are strain rate dependent，and the strain rate effect can be expressed by linear approximations. The failure strain of rock increases with the strain rate；and the relationship between dynamic strength increase factor and logarithm of average strain rate is approximately linear，but no relations can be seen for the initial elastic modulus of amphibolites with strain rate. Testing and consistence of case verification experiment show that the SHPB test results of amphibolites are acceptable. The experimental method and conclusions can be used to analyze the dynamic capabilities of other brittle materials.

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STUDY OF METHODOLOGY OF PLATE-LOADING CREEP TEST OF ROCK MASS

XIONG Shihu，ZHOU Huoming，ZHONG Zuowu

2009, 28 (10): -2127 doi:
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[PDF 306 KB] (1208)

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Laboratory results can hardly reflect the rheological properties of engineering rock mass because of the size-effect of samples and the difference between test conditions and work state of engineering rock mass；so in-situ creep tests were carried out in some important hydropower projects；and the in-situ plate-loading creep test is applied more often. But in the test method，there exist some shortages，so it is suggested that the generalized five-parameter Kelvin model can be accepted to describe the rheological properties of rock mass；and the single-stage loading manner with load level being consistent with engineering load is suggested. The creep deformation equation based on generalized five- parameter Kelvin model of rock mass under plate-load is deduced；and it is found that the results agree with elastic deformation equation when t = 0 or t→∞. Finally，test examples，of which creep model and its parameters are inversed using nonlinear least squares curve fitting method，are given to demonstrate that the magnitude of the correlation between generalized five-parameter Kelvin model and test curves is superior to that of generalized three-parameter Kelvin model.

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INTELLIGENT ANALYSIS MODEL OF SLOPE NONLINEAR DISPLACEMENT TIME SERIES BASED ON GENETIC-GAUSSIAN PROCESS REGRESSION ALGORITHM OF COMBINED KERNEL FUNCTION

LIU Kaiyun，LIU Baoguo，XU Chong

2009, 28 (10): -2134 doi:
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[PDF 199 KB] (1457)

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Compared with support vector machines(SVM)，Gaussian process(GP) holds many advantages such as easy coding，self-adaptive acquisition of hyper-parameters and prediction with probability interpretation. Herein，the Gaussian process regression(GPR) is adopted to analyze the slope displacement time series. A combined kernel function of GPR(CKGPR) obtained by additive single standard covariance functions is putted forward to overcome poor generalization ability of single kernel function. At present，the hyper-parameters of GPR are achieved by maximizing likelihood function of training samples based on conjugate gradient algorithm. However，the conjugate gradient algorithm has the shortcomings of too strong dependence on initial value in optimization effect，showing the difficultly in determination of iteration steps and easily falling into local optimum. On the basis of above-mentioned results，genetic algorithm(GA) coded in decimal system is used to optimize the hyper- parameters of GPR with the combined kernel function，and then the GA-CKGPR algorithm can be formed；and the corresponding code is programmed in Matlab. From the analytical results of Wolongsi slope displacement time series，it can be concluded that the GA-CKGPR algorithm can obviously improve the prediction precision than those of GA-SVR and standard GA-GPR algorithms，so it can be utilized in slope displacement analysis and meanwhile can be served as a reference for similar projects.

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UNIFIED HARDENING MODEL FOR SOILS

YAO Yangping，HOU Wei，LUO Ting

2009, 28 (10): -2151 doi:
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[PDF 720 KB] (1822)

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Unified hardening(UH) model is an elastoplastic model system proposed based on the Cam-clay model，which includes two basic elements，namely，transformed stress method and unified hardening parameter. The model is combined with strength criteria by adopting the transformed stress methods on the basis of the SMP criterion，the Lade¢s criterion and the generalized nonlinear strength theory. The model，to which the unified hardening parameter is introduced，is able to describe many mechanical behaviors，including strain hardening and softening，stress dilatancy，over-consolidation，inherent anisotropy，structure，creep compression，asymptotic state and so on. Fewer parameters required in the model are determined by the conventional triaxial test. The model not only develops the Cam-clay model but also is easily exploited in the engineering software. Therefore，its application to engineering appears to be highly promising.

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DISCUSSION ON “NEW COMPUTATION METHOD FOR SOIL FOUNDATION SETTLEMENTS”

MEN Kai

2009, 28 (10): -2153 doi:
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[PDF 121 KB] (1022)

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DISCUSSION ON “NEW COMPUTATION METHOD FOR SOIL FOUNDATION SETTLEMENTS”

JIAO Wuyi

2009, 28 (10): -2156 doi:
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[PDF 140 KB] (1209)