As the key position of tunnel seismic design，the portal section is extremely vulnerable to foundation failure and structure damage. The longitudinal distances of 100 m in portal section of Galongla tunnel are selected as the prototype to conduct large-scale shaking table test. The research results are shown as follows：(1) The soil around tunnel has obvious amplification effect on the input seismic waves with the frequency near the predomination frequency of soil；and also it has filtering effect on the input seismic waves with high frequency. (2) The tunnel vibrates synchronously with the surrounding soil；and it doesn?t show its own natural vibration frequency. The inertial force has little effect on underground structure?s seismic response. So the key point of tunnel?s anti-seismic research is failure prevention of surrounding rock under the earthquake；and the main purpose of structure?s aseismic design is to reduce the structure damage from the failure of its surrounding rock. (3) The absorbers and aseismatic joints don?t change the spectrum characteristics of lining；but they can increase the peak acceleration of lining. So，the damping effect should not be judged by the acceleration magnified coefficient at these places. The research results have important application value to aseismic design and shock absorption design of tunnel.

According to the cracks discovered in the embankment of Xiaowan arch dam，two functional cable models are built to simulate the stress field under the conditions of pulling of prestressed cable and secondary grouting. The feasibility of anchoring in the embankment，and the effects of anchoring on the stress around anchorage region and the performance of crack surfaces are studied by combining integer model and sub-model；and the effect of chemical grouting on reinforcing shear strength of cracks is analyzed. The results indicate that：the anchoring scheme of 400 t is superior to the 100 t；the maximum tensile stress around bonded length is about 0.2 MPa，which plus current stress may not cause new cracks. The anchoring and chemical grouting can enhance the shear capacity of crack surfaces to some extent；and its effect becomes distinct as the water level rising up. The compression shear yield zones in some cracks appear in the high water level，and large tonnage of anchoring or other measures are suggested to strengthen these areas.

The underground powerhouse in Xiangjiaba Hydropower Station has a huge scale，with the characteristics of complex structure，complicated geologic condition，large support quantities and big construction disturbance. Based on a large number of studies，the construction procedures and supporting parameters for underground caverns，especially the main powerhouse，are determined. The strict managements and controls are adopted in the construction；and a real-time monitoring and dynamic analysis system which integrates design，research and construction is established. The measured displacements in the rock masses of underground powerhouse are small and develop stably after excavation，with the maximum magnitudes of 13.36 mm in roof and 6.74 mm in walls，which are smaller than the design values of 20.4 mm in roof and 62.5 mm in walls；and they are smaller than ones of similar underground powerhouse. The principles and procedures of design，construction and management in construction of the Xiangjiaba underground powerhouse complex are summarized，so as to provide some references for the similar large underground powerhouse projects.

A self-developed meso-shear test equipment for coal rock containing gas is introduced. It is composed of main structure，loading system，gas-charging system，crack observation system and acoustic emission system. The equipment has the following features：(1) The shear mechanical tests for coal based on the fluid-solid coupling can be carried out，which provides reliable experimental means to study the mechanism of coal and gas outburst from micro level. (2) It has good airtightness，which can guarantee adequate adsorption of gas on coal sample. (3) The lateral loading system is designed，so both restrictive and non-restrictive shear tests can be carried out. (4) It has diverse methods to test experimental data. The curve of shear load and shear strain，images of meso-cracks and acoustic emission signal can be acquired synchronously. (5) From the view of its overall design，the equipment has simple structure，low processing cost，good reliability and easy operation. By using the equipment，non-restrictive direct shear tests under the gas pressures of 0.5，1.0 and 2.0 MPa are carried out. Shear load-shear stain curve and meso-evolution of shear plane cracks are obtained. Based on the test results，the mechanical processes of the formation，extension，penetration and instability are analyzed. The experiment results show that the equipment has good practicality and reliability，and it provides new test means to study the meso-shear mechanical characteristics of coal.

In order to study the effect mechanism of high pressure water injection on the methane desorption characteristics of coal，a series of experiments have been designed and conducted. Combining the connected porosity and pore size distribution law determined by the press mercury test and the residual mass of water in coal samples after water injection experiments finished，the difference of methane desorption law has been confirmed. The results show that：(1) Under the same methane absorption pressure of different coals，the larger porosity is，the better methane desorption capacity is. (2) The methane desorption capacity is mostly affected by the methane equilibrium absorption pressure of the same coal. The larger absorption pressure is，the better desorption capacity is. (3) According to the pore size distribution law and increment of water in coal mass samples，the critical pore size of coal sample is calculated under different water injection pressures. The critical pore size affects directly the methane desorption capacity；and the smaller pore size is，the lower desorption rate is. (4) The relationship of methane desorption rate and the critical pore size of water flowing into coal by data fitting accords with the Langmuir law function.

Because of lack of internal energy dissipation law of landslide in the sliding and impact processes，we can not calculate the impact energy precisely. In order to solve this issue，the landslide models are designed and constructed according to the similarity principle. The measurement system of friction coefficient is made up of photoelectric sensor and electronic timer；and the measurement system of impact force is made up of dynamic soil pressure sensor and dynamic strain acquisition instrument. A measurement method of impact energy is proposed for the situations of perfect elastic collision and completely inelastic collision. The impact energies of landslide mass with the same weight and different particle sizes are tested. The results show that the impact energies decrease markedly with the particle size decreasing. And the reasons are that：the internal energy dissipation of landslide mass increase with the particle sizes decreasing；and the friction coefficient between the landslide mass and sliding path increases also，which adds to the friction energy dissipation. Based on the experiment analysis，two methods are proposed to calculate the impact energy，which provide reference for the further research，under the condition of unknown internal energy dissipation mechanism. The comparison with the existing method indicates that：for the landslides composed of all kinds of particle sizes，the result of method ignoring the inner energy dissipation is bigger than the proposed two methods；and the differences increase with the particle size decreasing.

To choose the best borehole coupling medium and improve the seismic exploration excitation effect，the calculation methods of explosion load and transmitted wave specific energy based on the theory of elastic wave are built. The analytical solutions are calculated by program in Matlab；and the graphics are drawn for the comparative analysis. Then，the field experiment is conducted in typical carbonate rock site；and the experimental data are analyzed by the way of energy analysis based on the power spectrum. The theoretical calculation and experimental results show that：(1) When the coupling medium of decoupling charge is water，the seismic wave energy is the biggest，the frequency is the highest，and the signal-to-noise ratio is the lowest. (2) When the coupling medium of decoupling charge is air，the seismic wave energy is smaller than that of water，the frequency is the lowest，and the signal-to-noise ratio is the highest. So，in order to gain a good seismic excitation effect，the air should be used as the coupling medium of decoupling charge in seismic exploration，and the seismic wave energy can be made up by increasing the total charge.

The growth and dissipation process of pore water pressure in rockfill dams during construction period is very complex. Based on the monitoring data of Pubugou corewall，the characteristics and forming mechanism of pore water pressure during the construction period are analyzed. In addition，the comparative analyses between Pubugou dam，Xiaolangdi dam and Lubuge dam are made. The results show that：(1) The growth and dissipation modes of pore water pressure in Pubugou corewall during the construction period contain four modes which are delay-response mode，immediate-response mode I，immediate-response mode II and no-response mode. (2) The immediate-response mode II is the main growth and dissipation mode. (3) The essence of delayed response of piezometers is the process that the soil around the piezometers changes from nonsaturated state to saturated state. (4) The permeability coefficient of soil is the determinant factor of the delay response of piezometers. (5) The immediate-response mode I is the result of the more high water content in local corewall；so，in order to avoid the immediate-response mode I，the water content of corewall should keep uniformity during the construction period. (6) Filling rate has significant effects on pore water pressure of the delay-response mode and immediate-response mode II；and the effect on the immediate-response mode I is not obvious. The heterogeneity of gravelly soil should be paid high attention during the design and research stages of rockfill dams of gravelly soil corewall.

Through a single crack，the main cracks appeared in the wall and imbedded near the wall of cavern are simplified as a half infinite plane with a fringe crack and one with a crack near the free edge for chilled liquefied petroleum gas(LPG) storage cavern respectively. To explore the influence mechanism of temperature decreasing on crack propagation，firstly the effect of rock parameters change caused temperature decreasing on the crack propagation is analyzed. Secondly，the effects of temperature boundary type，intensity and velocity of temperature decreasing，and angle between crack and wall on the temperature fields，stress fields and the stress intensity factors(SIF) of cracks with different lengths are researched. Finally，as a tentative research，the inhibition action of the ground stress on crack propagation during the temperature decreasing of crack is taken into consideration through the principle of superposition；and the relationship between the of temperature storage medium and the ground stress of cavern is analyzed under the condition of the existent crack non-propagating.

Based on field investigation for tunnels at Jinping II Hydropower Station，four primary failure types of deep buried marble are classified and their failure mechanisms are analyzed：(1) The first one is tensile slabbing rockburst. The rock mass near tunnel wall is slabbed due to unloading of excavation；at the same time，the elastic strain energy is stored in the slabs. Then，when the strain energy is stored sufficiently，the energy is released suddenly and the rockburst occurs. (2) The second one is tensile slabbing spalling. The rock mass near tunnel wall is slabbed due to unloading of excavation. Then，the slabs bend to inner of the tunnel and break. At last，the instabilities of slabs appear and they collapse down from the tunnel wall. (3) The third one is shear rock burst. A potential wedge of rock is formed in the rock mass near the tunnel wall because of the shearing action；and at the same time，the elastic strain energy is stored in the wedge. Then，the wedge is pushed out from the tunnel wall and the rockburst occurs when the shear stress on the potential shear surface exceeds the shear strength of the rock mass. (4) The last one is shear spalling. A wedge of rock is formed in the rock mass near the tunnel wall. Then，the wedge is detaching gradually from the tunnel wall，and at last，the wedge collapse down from the bottom of the tunnel. The four failure types may occur separately or combinatorially. The occurrence frequency of tensile failure is higher than that of shear failure. The failure classification of deep buried marble is useful for understanding the failure mechanisms of depth buried and intact hard rock mass and tunnel support design.

Probability relation between trace length and diameter of rock discontinuities applicable for semi-trace scanline sampling needs to be studied. And five kinds of possibilities are assumed as follows：endpoints of chords are distributed randomly on circumference；midpoints of chords are distributed randomly on a circular diameter；midpoints of chords are distributed randomly in sector；midpoints of chords are distributed randomly both on sectorial arc and diameter；midpoints of chords are distributed randomly on sectorial diameter(generalized model)，five models of probability relations between untruncated-uncensored semi-trace length and diameter are acquired. Theory and practice demonstrate that the former four models are not applicable or not quite applicable for semi-trace scanline sampling；while generalized model is quite applicable. The five models supply a gap in previous knowledge of relation between the probability densities of untruncated-uncensored semi-trace length and diameter. When diameters follow uniform distribution pattern，a new diameter algorithm of generalized model is proposed. The new algorithm is applied to Wenchuan earthquake successfully and worth popularizing.

Based on the displacement monitoring data and displacement evolution of landslide，total displacement can be divided into trend term displacement which is controlled by its own geological conditions and periodic term displacement affected by external factors such as rainfall，water level changes，and so on. Then the displacement prediction model of landslide can be established by time series analysis. Double moving average method is used to separate the trend term displacement and periodic term displacement of landslide. On this basis，GM(1，1) grey model is used to forecast the trend term displacement；and autoregressive(AR) model is used to forecast the periodic term displacement. Total displacement is obtained by adding the calculated predictive displacement value of each sub-stack. Taking Bazimen landslide in the Three Gorges reservoir area for example，it is shown that the result could better reflect the development trend of landslide under external factors，based on the comparative analysis of the measured and predicted displacement-time curves. The results demonstrate that the established landslide displacement prediction model is feasible and effective in the landslide displacement prediction.

Based on the Mohr-Coulomb failure criterion，a formula to calculate the factor of safety for landslide under coupling condition of earthquake and rainfall is deduced by introducing the inertia force of ground motion and groundwater factor. Then，by applying frequency analysis of physical and geometric parameters of slip mass and Monte Carlo simulation，a method to estimate sliding probability of landslides under coupling condition is developed. Consequently，the theoretical matrix，which considers influences of ground motion，slope angle，soil type and groundwater factor on sliding probability of landslides synthetically，is established to assess the risk probability of landslides under coupling condition. The earthquake，in fact，is a small probability event. For thinking over the occurrence probability of actual earthquake in any certain research region，it is better to calculate the repeated probabilities of ground motion according to its background seismicity. By the reoccurrence probabilities of ground motion，the above-mentioned theoretical matrix could figure the actual risk probability of landslides associated with earthquake events in any interesting region. According to the two kinds of theoretical matrixes，the probabilistic assessment for regional susceptibility of landslides under coupling condition should be achieved by GIS，data of digital geological map and high-precision DEM in a certain research region. As the case of Kitakyushu City，Japan，the procedure is applied to investigate the regional susceptibility of landslides under coupling condition in this city and the probabilistic assessment results are provided in the end.

Inspired by the flysch which was given by Hoek in RocLab software and based on the field work and lab experiment，a quantitative diagram of the geological strength index(GSI) for granite based on mineral structure and drilling is established；of which the process is as follows：(1) Mineral structure，rock core length and joint condition of rock are introduced in this diagram to help the quantitative study of GSI. (2) Try to use the typical picture of field core to substitute the sketch drawing given by Hoek. Combining with characteristics such as rock quality designation of core，core recovery ratio and rock structure and so on，the pictures are described. According to Hoek-Brown formula，elastic modulus E of granite is calculated by the proposed diagram of GSI. Comparison between the calculated result and that given by the exploration firm is conducted；it is also shown that the results fit each other very well and the minimum error of E between them is 0.11 GPa. Therefore，the new GSI diagram is scientific and it can be widely used in drilling engineering to estimate the parameters of granite.

First of all，the feasibility of using a universal distinct element code(UDEC) to simulate stress waves propagation in rockmass has been validated. Then，the study about the rules of stress waves crossing fractures which have various attitudes has been conducted. The three main fractures in Longmenshan region affecting the stress waves propagation are used as an example to validate the rules of stress waves crossing fractures and illustrate the shock isolation effects and the hanging wall effects of the large-scale fracture. The main research results can be summarized as follows：(1) The dynamic responses of the earth?s surface beside the fractures are anomalous compared with that on the fractures；and the dynamic responses of the earth?s surface on the side of hypocenter will be more seriously than that on the other side. (2) With the increasing of fractures attitudes from 0° to 90°，the shock isolation effects of fractures on stress waves firstly will increase and then will decrease；and the dynamic responses caused by transmitted waves will be weaker with the increasing of the amount of fractures. (3) Wenchuan—Maoxian fault and Guanxian—Anxian fault are not coseismic fault；so they have shown good shock isolation in the process of Wenchuan earthquake. Compared to the condition without faults，the vertical peak ground accelerations of hanging wall surface of Wenchuan—Maoxian fault and foot wall surface of Guanxian—Anxian fault decrease 38% and 47% respectively. (4) Because of the faults reflecting the earthquake waves，the dynamic responses of earth?s surfaces of the hanging wall and footwall of Yingxiu—Beichuan fault are serious compared to the state without faults. The vertical peak ground accelerations of the hanging wall and footwall surface of Yingxiu-Beichuan fault increase 41% and 32% respectively. The above research results reflect the shock isolation effect and hanging wall effect of fractures.

Influences of the two important geometrical parameters of joint inclination angle and joint connectivity rate of a joint set，on uniaxial compression strength，elastic modulus and stress-strain curves of rock mass with non-persistent open joints，are investigated systematically by conducting uniaxial compression tests on gypsum specimens with a set of preexisting open flaws. It is found that：(1) With the increasing of joint connectivity rate，the ductility of axial stress-axial strain curves increases，and they change from single-peak curves to multi-peak curves. (2) At the same joint inclination angle，the peak strength and elastic modulus of specimens decrease with the increasing of joint connectivity rate，which can be estimated by two kinds of power functions respectively，where their parameters are varied with joint inclination angle. (3) When joint connectivity rate is not very large，the peak strength and elastic modulus of specimens are varied with the joint inclination angles in the similar way，i.e. they are the highest at the joint inclination angle of 90°  while they are the lowest at the joint inclination angles of 30° and 60°. When joint connectivity is very large，the peak strength and elastic modulus of specimens are the highest at the joint inclination angle of 90°，while peak strength is the lowest at the joint inclination angle of 45° and the elastic modulus is relatively lower below 60°，respectively. Through further analyses for failure process of the specimens，it is revealed that the jointed rock mass macroscopic mechanical properties affected by joint inclination angle and joint connectivity rate are governed by microscopic damage mechanism，such as closure and friction of the preexisting joints，stress concentrate in the rock bridge and induce crack initiation，propagation and their coalescence with the preexisting flaws to form the final failure planes or shear bands.

With a view to water inflow of the fractured fault zone occurred in the Qingdao Jiaozhou bay subsea tunnel construction and via theoretical analysis，laboratory and field test as well as practical application，the experimental investigation on general cement paste，ultrafine cement paste，specially made sulphoaluminate cement paste and cement-sodium silicate double liquid are all conducted；and the necessity of advance pre-grouting with the material of ultrafine cement is obtained. Moreover，the key parameters of grouting have been ascertained and confirmed in practice，i.e. the grout diffusion radius is 1.5–2.0 m，the terminate pressure in grouting is 3–4 MPa，the reinforced ply of grouting is 5–6 m. Through the experimental comparison of multistage forward grouting，multistage retrograde grouting and one-off grouting，the optimal grouting method is determined；i.e. adopting the multistage forward way of one-off full hole grouting. In the construction process，a system of coordinating informationized hole-drilling grouting equipments is probed and developed with the three-boom drill jumbo and top-speed pulper for slurrying，high-pressure grouting pump for grouting and grouting recorder automatically logging the grouting parameters. By implementing the strategy of drilling and grouting conducted at each deployed position simultaneously，drilling and grouting operated on a parallel basis，a highly efficient and informationized advance pre-grouting is thus realized. The grouting effectiveness is mainly focused on the hydraulic discharge of drilling holes(according to the design requirements，hydraulic discharge per linear meter should not exceed 0.15 L/min and local discharge shall be no more than 3 L/min)，and assisted in packer test of hole，which are further supplemented by tunnel seismic prediction(TSP) geophysical prospecting comparison，drilling TV analysis，excavation and tunnel face analysis as well as P-Q-T curve analysis. By the practical grouting for 31 stages，the above mentioned materials，parameters and grouting methods are all proved to be feasible and reliable.

The stress relaxation test of saturated silty mudstone under triaxial compression is carried out on the RLJW–2000 rock microcomputer-controlled rheology servo test system by step loading method. Based on the test results，the stress relaxation of silty mudstone is divided into three stages；and the variation laws of stress relaxation rate，radial strain，volumetric strain and relaxation modulus with time are investigated under different strain levels. Moreover，the variation law of stress-strain tautochrone is analyzed. The triaxial stress relaxation properties of silty mudstone is systematically revealed，which provide the fundamental materials for the establishment of silty sandstone?s relaxation models. Burgers model is selected to describe the stress relaxation properties of silty mudstone. Based on the LM-NLSF method，the model parameters under different strain levels are obtained. Comparing testing curves with theoretical curves，it is shown that Burgers model is suitable to describe the stress relaxation properties of silty mudstone；and the obtained parameters have certain practical value.

Characteristics of displacements evolution in aspects of time and space in instability process of fault rockburst are inspected and analyzed by using the digital speckle correlation method. The test material is a kind of Fangshan granodiorites and the specimens are loaded by a large-scale double-axis test machine；the specimen surface speckles images in instability process of fault rockburst are recorded by adopting high speed cameras. The analysis results show that：(1) Fault rockburst is associated with confining pressure. Fault rockburst needs to meet certain confining pressure conditions；and fault will slick steadily when the confining pressure is lesser. (2) Peak stress and stress drop increase in the process of fault rockburst when confining pressure increases. (3) There are interval sliding characteristics of displacement evolution in fault rockburst；and the time of interval sliding increases with the increasing of confining pressure. The sliding distance and velocity at the first sliding are both greater than that at the second sliding. (4) Fault displacement evolution displays space differences characteristics in instability process of rockburst；and sliding value will increase with the increasing of the distance between observation point and loading end.

The tangent modulus method of undisturbed soil is used to calculate the nonlinear settlements of soil foundation and pile foundation separately；and the nonlinear relation P-S(load-settlement) curves of the soil foundation and pile foundation are obtained. Supposing that the soil foundation and pile foundation are acted independently，simultaneously considering that the settlements of soil foundation and pile foundation are equal，then we can obtain the load acting on the soil and pile by the P-S curves. Then，by controlling the settlement value and adjusting the thickness of cushion，the relative stiffnesses of soil and piles can be matched to make the best use of the bearing capacities of soil and pile foundation；and the settlement of the composite foundation can reach the desired aim. Consequently，the design of combination foundation can reach the perfect optimized condition. Finally，the implementation process of the method is explained by the case study.

Taking the foundation pit of Minzhi station in metro line 5 of Shenzhen city for example，the internal force and deformation characteristics of unsymmetrical-loaded foundation pit?s enclosure structure are systematically studied based on field test；and the stability of retaining structure about the horizontal displacement and internal force of diaphragm wall is evaluated reasonably. The results show that the deformation of top of the diaphragm wall inclined towards the inside of the enclosure structure with shallow excavation depth；and the displacement of the diaphragm wall near railway is larger than that of the diaphragm wall far from railway due to the load from train and unsymmetrical bed. However，the deformation of top of the diaphragm wall far from railway moves towards the outside of the enclosure structure after the excavation depth up to threshold；and the deformation increases with the increasing of excavation depth. Moreover，under the same conditions about construction procedure and excavation depth，the moment of the diaphragm wall near railway is larger than that of the diaphragm wall far from railway；also the maximum moment position of the diaphragm wall near railway is deeper than that of the diaphragm wall far from railway. According to the stress pattern and displacement of unsymmetrical loaded foundation pit，different supporting parameters on both sides of foundation pit should be considered differently. Therefore，the test conclusions can provide reference for the design and construction of foundation pit.

The bearing behaviors of vertical pile and inclined piles with inclination angles of 5°，8°，10° and 15° are contrasted according to model test. Effects of inclination on the bearing capacity of single plastic tube cast-in-place concrete pile(TC pile for short)，pile-top settlement，pile shaft horizontal displacement，bending moment along pile shaft，skin friction and the ratio of tip resistance to load on pile top are analyzed. The model test results show that：(1) Effects of pile inclination on the bearing capacity and pile-top settlement are not apparent when the inclination angle of TC pile is less than 8°；but for the inclined piles with inclination angles of 10° and 15°，the reduction of bearing capacity of single pile is significant. (2) Horizontal displacement and bending moment of pile shaft mainly occur in the upper one third of pile length；and both go up with the increase of load and inclination angle. (3) Skin frictions of vertical pile and each inclined pile first increase and then decrease with the increase of pile depth；and the mean values of ultimate skin frictions increase slightly with the increase of inclination angle；and the bearing ratio of skin friction is large. (4) Tip resistance and the ratio of tip resistance to load on pile top go up with the increase of load and fall with the increase of inclination angle. The Origin software is applied to fit the curve between ultimate bearing capacity and inclination angle with Sigmoidal function. The formula is obtained to calculate the ultimate bearing capacity of inclined pile. Based on the field data，the range of correction factor is gained.

Cyclic triaxial-torsional coupling shear tests are performed on Nanjing?s saturated fine sand，of which the relative density is 50%，under three-directional anisotropic consolidation state by the hollow cylinder apparatus；and step loading is employed to simulate the effect of wave loads with variable amplitudes more realistically. Influences of initial principal stress direction angle，initial deviator stress ratio and initial intermediate principal stress parameter on the relationship between residual pore water pressure and accumulative lost energy are investigated respectively. The results show that with the same accumulative lost energy，the residual pore water pressure decreases with the increasing of initial principal stress direction angle and initial deviator stress ratio；while it increases with the increasing of initial intermediate principal stress parameter. The empirical formula between residual pore water pressure and normalized accumulative lost energy is established preliminarily.

The three-parameter viscoelastic constitutive model is applied to describe the creep properties of geogrids at low stress levels. Combining with the creep tests results of geogrids，the model parameters are obtained by using the utmost optimization method. It has been proved that the three-parameter viscoelastic model of geogrids can relatively accurately reflect the two-stage attenuation creep properties of geogrids at low stress levels. Then，one constitutive model of reinforced soil considering viscoelasticity of geogrids is suggested. The stress and strain formulas of reinforced soil when soil is in the elastic and plastic stages are obtained. The study results show that stress of geogrids is not only associated with the external forces that reinforced soil bears，the properties of geogrids and soil，but also with the reinforcement layer spacing and working time. When soil enters into the plastic state，geogrid mainly displays creep properties with its stress changeless，which leads to the increase of strain of reinforced soil with time. As time goes by，geogrid displays stress relaxations；and its stress as well as the stress of soil would decrease. The stress relaxation values of geogrids placed in soil are smaller than that placed in air. Moreover，the stiffness coefficients E2，viscosity coefficient   of geogirds and the internal friction angle   of soil affect the time required for the reinforced soil arriving at plastic state which is called Tp most.