In order to study the free charge migration law of different types of coal and rock samples during the process of tensile failure，the charge monitoring system for coal and rock tensile instability and failure is developed under the frame of the Brazil disk splitting test. The mechanical characteristics and free charge migration law are obtained through the real-time monitoring process of sandstone，mudstone and coal samples during tensile instability and failure. The results show that there exist free charges during the tensile process of coal and rock mass. Charge signal abnormal area is corresponding to the stress mutation process in the samples splitting test；and the free charges produced by coal is richer than that produced by sandstone and mudstone during tensile failure. Compared with sandstone and mudstone，the residual strength of coal after fracture still makes the charge signal have larger fluctuation. Charge induction law is different between tensile and compression failure of coal and rock. One of the important reasons for the abnormal charge signal is the damage localization caused by crack propagation under the tensile stress during the tensile instability and failure of coal and rock mass.

On the basis of analyzing destructive mechanism and reinforcement mechanism of coal roadway sidewall，concept design of protecting the roof by strong sidewall is put forward by means of establishing mechanical model of coal roadway，analyzing relationship between supporting force and Mohr circle，researching the width of limit equilibrium zone in sidewall and mechanism of roadway energy dissipation；and the theory of strong support for coal roadway sidewall is also theoretically demonstrated. FLAC3D is used to analyze surrounding rock?s mechanical response caused by coal roadway excavation and clarify influences of sidewall bolt on sidewall strength. So the theory of strong support for coal roadway sidewall is demonstrated through numerical simulation. Finally，theory of strong support for coal roadway sidewall is applied to coal roadway supporting design of Malan and Guandi mines. Good results have been obtained in these practices. The study results show as follows：(1) Improving the support strength of sidewall can not only enhance the bearing capacity of sidewall on the roof，but also reduce the width of limit equilibrium zone in sidewall as well as generalized span of roof. (2) Increasing strength ratio and stiffness ratio between the sidewall and roof can decrease quantity of plastic hinges in sidewall，which makes reasonable mechanism of roadway energy dissipation，ensuring the overall stability of coal roadway. (3) Using the concept design of protecting the roof by strong sidewall to support roadway which has lower strength in sidewall than roof can form the well function mechanism of protecting roof by strong sidewall，as well as the reasonable mechanism of roadway energy dissipation，which ensure the safety of coal roadway. (4) Increasing diameter，length，density of sidewall bolt can effectively control the deformation of surrounding rock and decrease limit equilibrium zone. (5) Both numerical simulation and field application indicate that improving the strength of sidewall can improve the overall stability. Theory of strong support for coal roadway sidewall has good applicability in engineering practice.

A series of tests on characteristics of acoustic emission(AE) and seepage have been performed on gas-filled coal under conditions of conventional triaxial path and unloading confining pressure path. The difference in characteristics of AE and seepage of coal during failure process under two paths is studied. The results show that characteristics of AE and seepage change with stress paths. In the two paths tests，stress，gas flow and AE signal of gas-filled coal have good correlations；and the curve of gas flow has the similar change rules. The suffering point of gas flow lags in conventional triaxial path，but also an obvious and direct correspondence exists between the suffering point of gas flow and starting point under the unloading confining pressure path. Compared with the conventional triaxial path，the cumulative damage is bigger under the unloading confining pressure path. The curve slope of AE cumulative ringing from unloading confining pressure starting point increases obviously，and experiences a sharp increase in failure point. In the two paths tests，AE amplitude curves have different variations；and AE amplitude curves of gas-filled coal show a bimodal state bounded by the starting point under unloading confining pressure path.

Aiming at the support crushing accidents during the faces mining out of the upper 1-2 goaf-side coal pillar in panel of coal seam 1-2 of Shigetai coal mine，the mechanism and its prevention measures are researched based on the field measurement，simulation experiments and theoretical analysis. The results show that when the cut-hole of the lower seam was set under the upper coal pillar，the working face would go through the mining stage from the area under the coal pillar to that under the goaf，which was called the mining out of the upper goaf-side coal pillar. In the mining process，two situations exist in the support crushing by the influence of the cut-hole position. If the distance between the cut-hole and the upper coal pillar boundary is larger than the first breaking step of the key stratum(KS) above the pillar，the periodic breaking block of the KS and its broken block at the side of goaf near the pillar boundary will form an unstable three hinged structure when mining out of the pillar；and the excessive load caused by the relative rotary motion of the structure is the fundamental source for the support crushing. If the distance is between the first breaking and periodic breaking step of the KS，the KS will present the cantilevered breaking state when mining out of the pillar；and the support crushing is caused by the excessive load due to its long breaking span. Meanwhile，when the KS breaking span is more than 1.7–1.9 times the length of its periodic broken step，the risk level of the support crushing will be obviously higher than that in the former situation. The simulation experiments and engineering practices show that the support crushing accident during the mining out of the upper goaf-side coal pillar can be effectively controlled by reducing the distance between the cut-hole and coal pillar boundary，so as to prevent the breaking of the KS above the pillar.

Based on the technical requirements of surrounding rock fissure testing in geomechanical model test，a fissure testing scheme with fracture wire is put forward；and the fracture wire materials are sifted. Through contrast test，graphite wire is chosen finally. This material can basically crack synchronously with model medium and satisfy the test requirements. The graphite wire is applied to the Huainan coal mine；and the occurrence and development processes of surrounding rock fissures are obtained. This technique can provide reference for fissure testing in similar experiments.

Explosion load test system of digital laser dynamic caustics is used to analyze the dynamic fracture effect of blasting crack with different charging structures. Mechanism of directional fracture blasting with slotted cartridge is studied and the difference of dynamic energy release rate between principal crack and secondary crack is compared. The results show that the blasting effect is best when the decoupling coefficient ?1 = 1.67. The propagation velocity and dynamic stress intensity factor of principal crack show a downward trend in the mass，and is up to a smaller peak in the mid- and late-expansion processes. As the buffer layer between explosive product and blasting hole wall，the plasticine medium transfers energy well. The dynamic energy release rate values of secondary crack as a whole is less than that of two principal cracks.

The evolution characteristics of deformation fields and temperature fields are inspected and analyzed by using the digital speckle correlation method and infrared thermal imager. The test material is a kind of coal and the specimens are loaded by uniaxial test machine. The analytical results show that：(1) The deformation field evolution of coal specimen is divided into two phases：initial uniform deformation evolution to deformation localization at pre-peak loading stage，and deformation concentration in the localization band at post-peak loading stage. (2) The temperature evolution of coal specimen is divided into two phases：temperature rises due to internal particle spacing change caused by thermo-mechanical coupling effect at pre-peak loading stage；temperature decreases due to the tensile-shear effect and the sliding effect of deformation localization band at post-peak loading stage. (3) The temperature change is obvious in the deformation and destruction process of coal specimens；and the temperature evolution characteristics are similar inside and outside the deformation concentration band. The temperature increases at pre-peak loading stage and decreases at post-peak loading stage. The temperature inside the deformation localization band is higher than that outside the deformation localization band.

Based on the characteristic of gangue，a PFC3D model with contact-bond nonlinear constitutive behavior is established to simulate the triaxial compression tests of gangue. Different gradation projects of particle assembly are designed on the basis of Talbot?s theory；and gradation particle model is generated by using Fish language. The numerical simulation of triaxial compression test of gangue is conducted. The stress-strain curves，volumetric strain curves and microcracks propagation curves under different confining pressures are compared to verity the strength and deformation regulations of gangue with different gradations from mesoscopic view. The study result shows that optimal gradation of particles will improve the peak strength of gangue assembly and decrease its compressibility. The simulation results would be helpful for the optimal design of gangue backfill material in coal mining.

Cyclic impact tests on sandstone under different axial and confining pressures are conducted with a modified three-dimensional split Hopkinson pressure bar(SHPB)，in order to analyze the impact resistance of sandstone with cyclic impact number and to research the effect of axial and confining pressures on dynamic fatigue mechanical properties. Confining pressures are set as 4，8，10 and 12 MPa，and four levels of axial static stresses are 49，84，105 and 125 MPa，respectively. Incident waves in input bar are approximately constant，and incident energy is 230 J. The results show that total cyclic impact number will decrease with the increase in axial stress when the confining pressure is constant. The total cyclic impact number has an increasing trend with the increasing confining pressure when axial compression is constant. With the increasing cyclic impact number，dynamic peak stress，deformation modulus at loading stage and elastic strain decrease，whereas dynamic peak strain and residual strain increase. Rock dynamic peak stress has a good negative linear correlation with average strain rate. When the confining pressure is constant，the absolute values of linear-fitted slope of dynamic peak stress and average strain rate increase gradually with the increase in axial stress；and when the axial stress is constant，the bigger the confining pressure is，the smaller the absolute values of linear-fitted slope is. Decreasing axial compression or increasing confining pressure is able to improve rock resistance to cyclic impact loads when the rock is under three-dimensional static stress.

An analytical method for stability analysis of hydraulic rock slope incorporating microseismic monitoring and stress field analysis，was established. The initiation，propagation，extension，interaction and coalescence mechanisms of microcracks during the progressive failure processes of the left bank slope at Jinping I hydropower station were investigated using realistic failure process analysis code in three dimensions(RFPA3D). The whole instability failure mechanism of rock slope was revealed. The spatial evolution regularity of stress field and microseismicity of the rock slope during progressive failure processes were discussed；and research method was thus formed to reveal macroscopic rock mass structures failure from mesoscopic damage evolution processes. The comprehensive researches show that the weak structure planes such as faults F5，F2 and lamprophyre X are one of the key factors controlling the failure modes of the left bank slope. The potential sliding surface and its acoustic emission of the rock slope obtained by RFPA3D are in good agreement with the trend of spatial macro evolution of rockmass microcracks captured by microseismic monitoring system.

The slip zone of large-scale landslide in the Loess Plateau has been identified as red clay rock of Upper Pleistocene. However，there are few studies about the structural characteristics and formation mechanism of the slip zone. Herein，the fabrics and structural characteristics of clay rocks are introduced based on drilling core analysis，surface survey，X-ray diffraction and scanning electron microscope. Meanwhile，stress-strain test，residual strength test and slip zone creep experiment are also implemented. The formation mechanism of interbedded shear zone in the large-scale landslides is therefore analyzed. The results indicate that the main slip zone consists of rich-developed approximately horizontal shear plane. Plastic deformation and shear deformation break out together with the changes of soil structures in the slip zone. As for the mode of motion，block sliding prevail. It is also found that clay rocks suffer more fissures after evolving into soil of slip zone. The average water absorption velocity reaches 2.7 g/h and the penetrability is promoted. Under such a condition，the water absorption velocity of the standard rock sample in unit period accounts for 1.5 times of original rocks；the specific activity is 0.83. It is better than original rocks in terms of specific surface area and activity. Furthermore，structural changes of original rocks are accompanied by strength attenuation. According to test results，the conhesion of peak strength for original clay rocks with water content of 19.1% is 613 kPa，and the internal friction angle is 26.7°. In Boji mountain，the conhesion and internal friction angle of residual strength of slip zone is 8.79 kPa and 17.2°，respectively；the conhesion and internal friction angle of long-term strength of slip zone is 57.4 kPa and 20.47°，respectively.

The action mode and space-time evolution laws of surrounding rock pressure are the core contents of tunnel supporting structure design，which are hot issues in underground engineering research. Based on the summary of main types and influencing factors of tunnel surrounding rock pressure and the statistical analysis of surrounding rock pressure of 91 monitoring sections in 44 tunnels，the population distribution characteristics of surrounding rock pressure and their relationships with surrounding rock grade and buried depth of tunnel are studied. Then the variation law of rock pressure and lateral pressure coefficient with the increase in buried depth is discussed. Based on the statistical analysis of field monitoring data of rock pressure，the basic law of rock pressure time-history is studied. Three stages including rapid growth-slowly growth-settle out is put forward；and the rapid growth stage is mostly the time during unsupported or without effect of support after tunnel excavation. Finally，the distribution laws of rock pressure along the tunnel and the feature of nonuniformity coefficient are discussed. The results offer some references for analyzing the pressure mechanism of tunnel surrounding rock and perfecting the design method of supporting structure.

Based on the basic principle and method of fluid mechanics，heat transfer and dynamics of air，a cold temperature field model is deduced. The impact of surrounding rock tunnel ventilation is considered in this model. This model includes：temperature control equations of surrounding rock，air temperature field control equations in tunnel and wind flow control equations of turbulence field. On this basis，numerical analysis method is used to discuss the temperature field change law of surrounding rock and thermal insulation measures of Galongla tunnel in Tibet under the condition of ventilation. The study results show that：before tunnel excavation，there is a clear temperature fluctuation in the shallow mountain changing with the change of season；and the apparent change appears at the depth of 18 m. When rock depth is more than 18 m，the temperature fluctuation amplitude of rock mass with the change of season is less than 0.5 ℃. Due to ventilation effect，the temperature of surrounding rock presents the adverse conditions of below 0 ℃ within the scope of inlet and outlet sections of tunnel at the most coldest month(January) after the breakthrough of tunnel. Further research shows thats：at the inlet section of 600 m and outlet section of 400 m in Galongla tunnel，heat preservation material such as phenolics with the thickness of 6 cm is laid on secondary lining surface，which can effectively prevent the Galongla tunnel lining and rock from freeze-thaw damage.

Evaluation of blasting damage degree and range of rock mass is important in the blasting parameter design and structure support. Based on the comprehensive analysis of the current methods in studying rock mass damage caused by blasting，the nuclear magnetic resonance(NMR) detection technique is introduced. Beginning with studying the essential reason of blasting damage，the porosity and T2 spectrum distribution are regarded as the criterion，as well as the NMR images，the range of rock mass blasting damage is quantificationally analyzed. Combined with the ultrasonic testing and rock mechanics strength measurement techniques，the NMR results are discussed and compared. In addition，the relationship between the NMR characteristics and rock mass strength has been discussed，which conform to exponential distribution. And a prediction mathematical model of uniaxial compressive strength is established based on the NMR results. The results show that the practicability and accuracy of NMR are better，which opens up a new technical method for studying the blasting damage of rock mass.

Impulsive wave events generated by landslides have the sudden and catastrophic characteristics，for which investigation information is very limited；so prototype physical experiment study is a good method in this condition. Taking impulsive wave event of Gongjiafang slump mass in Three Gorge reservoir area for the prototype，a big physical similarity model with the length of 24 m，width of 8 m，height of 1.3 m，is established，which is the first prototype model on main stream after the reservoir impounding. The model similarity ratio is 1∶200. Marble grit(d50 = 1.47 mm) is used to simulate cataclastic rockmass in the test，using 15 wave gauges，high-speed cameras and run-up instruments to monitor wave process；and six sets of impulsive wave tests with the variable of impulse velocity into water in the front of the landslide are conducted. The comparison between test results and investigation results show that the test method can be used to study or forecast impulsive wave generated by similar cataclastic rockmass failure. After analyzing a series of test data，waves interactive process is showed firstly with the help of the gauge data，for example，wave chasing，superposition and reflection wave superposition. The data also finely portrait the wave propagation and run-up decay ratio in the riverway. Through this prototype model test，the improvement direction of the experiment on impulsive wave generated by cataclastic rockmass failure is discussed. The method used in this paper can offer references for impulsive wave generated by cataclastic rockmass failure，and the results obtained can provide great technical support for forecasting impulsive wave generated by other similar slopes of Three Gorges reservoir area.

The sizes and connectivity of the pores in porous media such as rock and soil are randomly distributed at microscopic level. Due to this characteristics，the flow of fluids in the porous media is significantly different from the flow characteristics in the ideal single pore model. As important features of seepage，capillary hysteresis and air entrapment generally occur in the porous media experiencing cyclic change of water content. Based on the analysis of drying/wetting progress in the porous media，a theoretical model of seepage is developed，in which the effect of air entrapment is taken into account in the soil-moisture retention constitutive relation. A numerical analysis method is developed and implemented into the computer code. The model can be used to simulate the unsaturated seepage in porous media with the effect of air entrapment under arbitrary change of water content. By comparing the numerical results with measured data，it is shown that the effect of air entrapment is significant to the fluid distribution. The effects of capillary hysteresis and air entrapment should be taken into account in unsaturated seepage analysis in order to accurately predict the soil-moisture state of porous media.

When slurry shield tunneling，slurry pressure can?t be set easily under complex conditions，such as channel erosion of the riverbed. If it wasn?t dealt with carefully，slurry fracturing or even slurry eruption would happen，which had negative effect on project security or led to project accident. In order to observe slurry fracturing propagation phenomenon and analyze its mechanism，in-situ slurry fracturing apparatus was made for the first time and in-situ tests were carried out. Based on these，a slurry fracturing propagation model was established；and a calculation method for upper limitation value of slurry pressure set to prevent slurry fracturing was given. The results suggest that mechanical properties of slurry fracturing propagation are not only related to stratum properties，but also related to the chosen slurry properties. When properties of stratum can?t be changed easily，increasing slurry bulk density and viscosity is beneficial to prevent slurry fracturing propagation during tunnel excavation. The phenomenon of slurry pressure reduction after slurry fracturing is beneficial to prevent slurry fracturing propagation. The slurry pressure should not be increased hurriedly after it becomes lower because of slurry fracturing；otherwise，not only the slurry pressure couldn?t be added，but also it leads to slurry fracture stretch more quickly，which speed up slurry eruption. Anti-fracturing ability of slurry and stratum would mostly become smaller and smaller during slurry fracturing propagation. Therefore，the first step to prevent slurry eruption is to prevent slurry fracturing；and the upper value of slurry pressure should be limited.

Due to progressive blocking of cement grains within the soil matrix，filtration of grout plays a significant role during grout dispersion process. The influence of filtration on the grout dispersion in gravel is studied. The injectability criterion of the grout is first summarized. Then the linear filtration law is introduced into the mass balance relationships of water，cement and soil to develop a cement grout dispersion model in spherical coordinates with account for filtration. The comparison between model results and experimental data proves the validity of the given model and the necessity of considering the phenomenon of filtration. In addition，the influences of filtration on permeation grouting under different injection durations and water-cement ratios are also studied. The results reveal that the penetration resistance increases gradually due to grout filtration，leading to the increase in grouting pressure with time. For grout with smaller water-cement ratio，the grouting pressure is larger and the influence of filtration is more obvious.

Fiber reinforced polymer(FRP) is a new composite material with excellent mechanical properties and corrosion resistance. It is a significant way to solve the durability problem of anchor rod by substituting this polymer for steel bars. Using anchor-rod-structure specimen made from glass fiber reinforced polymer(GFRP) bars with fiber grating installed internally，loaded by hollow hydraulic jack，monitored by grating sensing technology，this paper focuses on the failure mechanism of large-diameter sand-coated GFRP rebar in the frame beams under the condition of anchoring. Research shows that in the experiment，in terms of tensile force and average bond strength，this large-diameter(25 mm) GFRP rebar has reached the design strength of ribbed steel with the same diameter. The most reasonable thickness of frame beam varies from 30 to 40 cm. Transient loading cycles have no obvious influence on GFRP rebar interface-bond state；the degradation of rod body interface-bond state will occur under sustained loads，and it continues to develop and expand to the deeper part. Moreover，the greater the load applied is，the deeper the depth extended to is and the faster the degradation proceeds. Optical fiber grating monitoring technology is an effective method to find and observe the interface-bond state degradation process.

According to the established calculation formulae of geological strength index(GSI) and disturbed factor D for rock masses estimated by ultrasonic velocity of rock mass，the rock mass mechanical parameters are predicted by Hoek-Brown criterion based on ultrasonic velocity(the method of rock mass ultrasonic velocity for short). Then，taking Lancang River cross domain engineering slope rock mass of China—Myanmar oil and gas pipelines(domestic section) for example，based on the rock physico-mechanical parameters which were obtained by laboratory test and the wave test data，the rock mass mechanical parameters can be assessed according to the method of rock mass ultrasonic velocity and the Hoek-Brown criterion. It is shown that the calculation results of the method of rock mass ultrasonic velocity accords well with that of the method proposed by E. Hoek. The rationality of the method of rock mass ultrasonic velocity is further explained by numerical results. In addition，the proposed method provides a new approach to determine the mechanical parameters of rock mass，when test data are scant.

A high steep hill with river valley near National Road G213 is used as a prototype. A full process from initial deformation to sliding of the slope during ground shaking is simulated by a new discrete element method—continuum-based discrete element method(CDEM). Combining with shaking table test results，seismic landslide responses of accumulation body of the high steep slope are analyzed. The analytical results are as follows. The stress concentration phenomenon appears at the top of the accumulation body firstly；and then some tension failure points and shear failure points appear there，which expands toward the toe of the accumulation body from the top of that along the accumulation body-bed rock structural plane. At the same time，the number of tension failure points gradually increases. At last，the toe of the accumulation body-bed rock structural plane breaks；and then the accumulation body shears out from the toe，which results in the landslide. The starting time of landslide and the arrival time of peak ground acceleration(PGA) are synchronous or the former lags behind the latter slightly. In the high steep area，based on the input seismic wave，regardless of on the slope or inside the slope，peak acceleration is amplified as elevation increases. Generally speaking，amplification of the vertical peak acceleration is larger than that of horizontal peak acceleration；and the amplification of peak acceleration on a slope is larger than that inside the slope. In the river valley topography，based on the input seismic wave，regardless of the river valley or the backsides，peak ground acceleration is also amplified as elevation increases. There are some influence scopes of river valley on acceleration amplification effect. In this scope，the amplification of the horizontal peak ground acceleration is larger than that of the vertical peak ground acceleration. The amplifications of accelerations have obvious directivity of topographic effects，which are related to the gradient of bank sides. Distribution of acceleration amplification effect is nonuniform in river valley；and the smaller the distance to bank sides is，the stronger the acceleration amplification effect is.

In order to investigate the regularity of crack propagation under blasting dynamic loads，polymethyl methacrylate(PMMA) plates are employed to make samples containing a single crack and a borehole. The borehole is designed along the quadrant of a circle centered at one crack tip with radius of 60 mm. A detonator inside the borehole is fired to produce dynamic stress waves. The effects of incident angles of stress waves on crack initiation angles and propagation angles have been studied experimentally. The results show that：(1) As incident angle is 0°，crack initiation angle is 0°，i.e. the cracks propagate along the crack surface plane；(2) As incident angle is greater than 15° and less than 75°，wing-cracks occur along the pre-existing crack tips；(3) The wing-crack property is related to the incident angle of stress waves；(4) As incident angle is greater than 75°，new developed cracks are very small.

Numerical model of rock joint was generated and direct shear tests at different normal stresses were conducted using PFC2D. Shear behavior of the rock joint，along with development and evolution law of microcracks at different normal stresses were examined. It is shown that the shear behavior of simulated joints corresponds well to that observed in real joints；and the dependencies of shear strength and peak dilatation angle on normal stresses conform well to predict results of the JRC-JCS model. Compressive contact force mainly concentrates nearby asperities on both sides of the joint plane. The larger the normal stress is，the more concentrated areas of confact force will appear，and the higher the concentration degree is. As normal stress continues to enhance，the developing rate of microcracks within the specimen gradually increases；and the proportion of shear cracks to the total number of microcracks gradually enlarges；but they still far less than the tension cracks. The distribution characteristics of compressive contact force on joint surface are consistent with the development law of microcracks in the specimen. Shear failure of joint under external load results from convergence and correlation of microcracks in the joint plane；and the effect of compression induced tensile cracking plays a dominant role in the process of joint shear failure.

A new non-contact cyclic wave load generation system for centrifuge model test is developed. Through computer controlled load device，the system can simulate storm wave load on breakwater in deep water. The system solves the problems accounted in previous study such as difficulty in energy dissipation，generating additional constraint and mass，and applying of reversal load that is hard to be carried out. Then a new measuring and controlling system is developed for dynamic centrifuge model test，which contains four functional modules：high speed data acquisition，low pass digital filter for signal noise and interference removal，modified proportion integration differentiation(PID) load control and signal generation control. The system also optimizes load control and data acquisition functions in dynamic centrifuge test. The feasibility of non-contact wave load generation system is verified by suction caisson breakwater centrifuge model test. Test results show that the device can apply wave load accurately and steadily，and can adjust load amplitude randomly. Cyclic displacement characteristics of suction caisson breakwater under wave load are as follows：accumulated value and amplitude of dynamic tilt angle both increase；horizontal displacement amplitude increases notably；while accumulated value of vertical displacement increases significantly. Suction caisson breakwater has oscillation-rock coupled motion mode.

When the vacuum preloading method is applied to improve dredge fill，adequate bearing capacity needs to be provided for the large-scale spile machine installation equipment. A new technique is developed，in which the dredge surface is filled with a certain thickness of silt sand to provide enough bearing capacity to support the spile machine installation performance. A small-scale model test is carried out to intuitively identify the availability of crust improving the bearing capacity of foundation；and bearing characteristics and mechanism of foundation with crust are discussed. Finite element analysis is performed by PLAXIS software，in which the development of the plastic zones and displacement fields can be obtained. The calculated bearing capacity is compared with the analytical solutions achieved by Vesic formula. The contribution of a crust layer with silt sand to the bearing characteristics of foundation in rigid upper layer and soft lower layer is discussed，which can provide the technique with solid theoretical basis.

In order to study the influence of pile spacing on the structural properties of piled-raft foundation，model tests of piled-raft foundation with different pile spacings had been investigated. The results indicate that the effect of loading share ratio between pile and subsoil could be adjusted by different pile spacings. Then the mechanical properties of piled-raft foundation are regulated. The piles are mainly bearing body of piled-raft foundation being in conventional pile spacing，and the subsoil takes the second place. As the pile spacing is over 6 times of pile diameter，the shared-load effect of subsoil increases；piles go at plastically bearing capacity status earlier. Then the raft becomes the main bearing body of piled raft foundation as loading increases. With pile spacing increasing，the internal force distribution properties of raft transfer from wholly bending status to locally bending status. The uneven loading distribution regulation on pile-raft tops is affected by pile spacing. The maximal loading of pile under raft transfers from corner pile to middle pile with the pile spacing increasing. It is suggested that the effect of pile spacing on relative stiffness of raft-pile-soils and mechanical properties of piled raft foundation，such as raft bending moment and uneven distribution characteristics of piles loading，should be considered in design of piled-raft foundation.