There are three types of contact states between the primary linings and the secondary linings for the railway tunnels. Those are tight contact state，loose contact state and voids. Both the loose contact state and the voids behind the linings can be regarded as poor contact，which are deemed as typical tunnel quality defects. The research results show that the poor contact states have great influence on tunnel structure safety. General law of contact states behind railway tunnel linings in China is obtained according to the lining nondestructive test data of more than 100 railway tunnels. The research results show that：(1) Poor contact states behind linings are more incidental and serious in single shell lining than in the composite lining under the same conditions. (2) The occurrence proportion and severity of poor contact conditions behind linings have a close relationship with the surrounding rock classification；and they are more disadvantageous in the poorer surrounding rock. (3) The occurrence proportion and severity of poor contact states behind linings are affected by the positions of the poor contact states around the tunnel cross-section. The negative effects of the contact states decrease from the tunnel crowns to tunnel feet. (4) The appearance of the voids is affected by tunnel design principle，construction quality control，operational maintenance efficiency，etc. The prompt contact grouting between the primary lining and surrounding ground is the key to control this undesired phenomenon. The results obtained in this study can provide useful reference for studying the contact states between the primary linings and the secondary linings. It will also be helpful to study the development of the defects in the tunnel structure system.

Based on self-developed triaxial servo-controlled seepage equipment for hot-fluid-solid coupling of coal containing methane，permeability of coal sample after injected of CH4 or CO2 under different effective confining pressures and pore pressures is determined，in order to research the response law of the permeability to pore pressure. The results show as follows：(1) At the low pore pressure，the permeability decreases when the pore pressure increases；and its evolution can be divided into accelerating change stage and stable change stage；(2) The permeability of coal when filling CO2 is lower than that when filling CH4 at the same effective confining pressure and pore pressure. (3) Using the parameters，change rate of permeability Dp and the sensitiveness coefficient of pore pressure Cp to evaluate the pore pressure-sensitive，which indicates that the responsiveness of permeability to pore pressure is significant when the pore pressure is less than 1.0 MPa. Then based on the Cp，the functional relationship between permeability of coal and pore pressure is derived.

The visco-elastoplastic rheological failure model for rock block and joint is studied. A new concept of rheological instantaneous strength is firstly proposed；and on the basis，the nonlinear visco-plastic rheological failure model for rock and joint is established. Taking the uniaxial compression creep test for example，the visco-plastic deformation characteristics described by the new model is discussed. Then，the complete visco- elastoplastic rheological failure model for rock is established；and the creep as well as the relaxation characters of rock described by the model are analyzed. The influence of the parameter on rheological deformation and failure pattern is studied showing that the model can well reflect the brittle-ductile failure pattern of rock. By comparison with the uniaxial creep test of marble，it is found that the test and calculation by the model are coincident well，especially in the failure stage. Furthermore，the complete visco-elastoplastic rheological failure model for joint is also discussed. The calculation of creep failure process for a grouted joint is demonstrated to be well coincident with the test results. Finally，the new model is applied to the rheological failure analysis of the access tunnel of the Dagangshan hydropower station. The failure process is well modeled and the failure time is successfully forecasted，which can be the basis for further design of bolt and shotcrete support. The proposed visco-elasto- plastic rheological failure model for rock and joint is not only clear in concept，well simulating the rheological failure process and determining the failure time，but also the parameters can be easily measured by conventional tests showing the good application perspective in practical engineering.

The frost heave of surrounding rock in cold regions tunnel involves the complicated interaction of temperature field，seepage field，stress field and freeze-thaw damage. Starting with the thermo-hydro-mechnical- damage(THMD) coupling mechanism analysis，based on the continuum mechanics，thermodynamics，the percolation mechanics，damage mechanics and points of segregation potential theory，a THMD coupled model under the condition of freeze-thaw cycles was established. The model not only considered the influence of volumetric strain on temperature field and seepage field，temperature gradient and seepage pressure on rock mass stress，but also，according to actual engineering，considered the influence of frost heave pressure and freeze-thaw cycles on the damage of rock mass. This model was applied to simulate the temperature and deformation of a pipeline engineering in cold region. By comparing with the in-situ monitoring data，it is found that the proposed model can reflect the frost heave phenomenon exactly. After that，a forecast about frost heave pressure of Galongla tunnel under extreme weather conditions was given，and the stress and deformation law after freeze-thaw cycles are obtained. From the calculation results，it is concluded that the maximum frost heave pressure can reach up to 1.6 MPa and the stress is increased greatly after freeze-thaw cycles.

The dimensions of underground main and auxiliary powerhouse for the Xiaowan hydropower station is 79.18 m in height，28.0 m in width (the largest width is 30.6 m)，and 298.1 m in length. Two bridge cranes of 26 m in span and 800/160/10 tonnage in capacity are installed in the main powerhouse. The corresponding maximum design vertical wheel load acting on the girder is 840 kN per meter. The scale and capacity of the rock-bolt crane girder ranks the first class in the practices of domestic underground powerhouse construction，which is 3.63 m in height，2.8 m in width，and 271 m in single side length. Although rock-bolt crane girders have been widely applied to the underground powerhouse operation，yet nowadays there are still no specified design methods customized in the hydropower industry. According to the practices carried out in the Xiaowan project，the calculation results and monitoring data are systematically analyzed；the structural designs and support measures are discussed for the rock-bolt crane girder of the underground powerhouse. Several concerns in the designs for the rock-bolt crane girder are enlightened，which are managed and solved successfully in the engineering practice.

The twin-shear theory with a series of equations has not been compared directly with other true triaxial strength criteria on misfits for test data，although it has been studied thoroughly and applied widely in engineering. Linear and nonlinear unified strength theories are constructed with principal stresses. Parameters in various strength criteria are determined using true triaxial strengths，conventional compression and extension strengths as well. The theories present high mean misfits for test data，and cannot describe nonlinear increasing of conventional compression and extension strength with the minor principal stress，and the effect of the intermediate principal stress on strength. The nonlinear theory with two implicit equations of principal stresses is not friendly in calculation. The unified strength theories are not available in determining geostresses from borehole collapses and wellbore stability，as strength of rocks are extremely over-estimated at low minor principal stress.

Taking the metro station in Beijing as the project background，the study of stratum displacement has been performed based on the deflection distribution control method. The effective control measures are proposed to reduce the impact on the surrounding environment. The results show：(1) Mechanical response of the pile-beam- arch(PBA) method between strata and station structure can be divided into four processes of unloading-loading，the pilot excavation and support and supporting arch are the key points which caused surface subsidence. (2) Before pilot excavation，the surrounding strata is reinforced timely by advanced grouting. The measures are performed such as malposition excavation，short footage and tough supporting to reduce the adverse impact on the surrounding environment. (3) The stress adjustment is performed between formation and station structure in the supporting arch stage. The structure would produce a certain coordination deformation and long stress adjustment process. Due to larger settlement rate，the measures are suggested such as setting the horizontal steel support，short footage and reinforcement strata. (4) The range of plastic zone around station increases gradually with the construction development，especially pilot excavation and supporting arch stage. (5) Comparison of surface settlement rate of four construction stages，the numerical calculation rate is 4.5∶1∶6∶1 and the in-situ monitoring rate is 4.3∶1.6∶5∶1，the results show they are consistent.

Impact mechanical performance experiments are carried out for marble after different high temperatures under dynamic loading by using split Hopkinson pressure bar(SHPB) equipment. The stress-strain curves of specimens under impact loading are obtained. The temperature effects on the longitudinal wave velocity，as well as the peak stress，peak strain and elastic modulus of marble under impact loading are analyzed. It is demonstrated that the longitudinal wave velocity declines linearly with the increase of temperature. When the temperature is below 800 ℃，it does not remarkably affect the peak stress. When the temperature is above 800 ℃，the peak stress decreases obviously with temperature increasing. Meanwhile，the peak strain increases slightly with temperature increasing when the temperature is below 600 ℃，but the peak strain increases linearly with temperature increasing when the temperature is above 600 ℃. The elastic modulus under different impact velocities present the same change rule with temperature variation，decreasing approximately linearly with temperature increasing. The experiment results can be analyzed from the aspect of the changes in microstructural characteristics of marble after different temperatures.

The swell-shrink properties of argillaceous rock under varying aqueous environmental chemistry were studied by free swell test. Influence of the orientation of bedding，the same kind and different concentration aqueous solution，the same concentration and different valences of cation aqueous solution，the different chemical paths on the free swelling of argillaceous rock were analyzed. The essential mechanism of swelling and shrinkage variant of argillaceous rock were discussed by using SEM-EDS. Following results have been gotten：(1) The swelling of argillaceous rock decreases with the increases of angle between the horizontal plane of the device and the bedding plane of rock sample. (2) The concentration and cation valences of aqueous solution strongly influence the swelling and shrinkage of argillaceous rock under saturated conditions. The more concentrated the solution is，the weaker the swelling is under same kind aqueous solution. The more valence the cation is，the weaker the swelling is under same concentration and same negative ions kinds aqueous solution. The swelling and shrinkage of argillaceous rock connected with its go through chemical path under different kinds and different concentrations. (3) Argillaceous rock shrank when the low-concentration and low-valence cations aqueous solutions were displaced by the high-valence cations. (4) The swelling of argillaceous rock is connected with the proportions of low-valence and high-valence cations in the sample；the bigger the proportion is，the stronger the swelling is.

Based on the mechanical investigation，a coupled elastoplastic damage model is proposed to simulate the mechanical behaviour and damage evolution process of the intact deep granite in Beishan area. The experimental results revealed that Beishan granite exhibits typical brittle failure mode under low confining pressure. With the increase of confining pressure，the brittle-ductile transition of the mechanical behaviour took place；and significant plastic deformation and volumetric dilatation are noticed. The damage evolution process is also analyzed according to the initiation and propagation characteristics of the stress-induced microcracks. It is indicated that the failure and nonlinear mechanical behaviour of Beishan granite are essentially related to the coupling effect between the damage and plastic deformation. Based on this acknowledgement，a coupled elastoplastic damage model is proposed. In the model，a non-associated plastic flow rule is used to describe the compression-dilatation transition of the volumetric deformation. The coupling between the damage and plastic deformation is realised by introducing the independent damage variable in the plastic yield surface. The comparison between the predictive result and experimental data suggests that the proposed model is capable to reproduce the main mechanical performances of Beishan granite under compressive stress condition，especially the brittle-ductile transition of mechanical behaviour with the increase of confining pressure.

The largest cross-sectional area of Hongqihegou Station in Chongqing Metro third line has reached 760 m2. The shallow station tunnel is located in urban area，the engineering condition is very complex. The tunnel is shallow buried and the ratio of depth to span is small(only 0.4). By comparing different methods，a new excavation method named reserved cross rock beam-pillar is proposed；and the parameters are optimized with numerical analysis. The rock pillar is 8 m of width and the rock pillars excavation is 1 m of length. The surface subsidence and section convergence are monitored which are caused by the tunnel construction. The surrounding rock is stable during excavation，which proves that the proposed method is feasible in practice. Through the monitoring，the displacements law caused by construction process is researched. The result can provide experience to similar projects.

In view of the characteristics of B10 coal layers with significant horizontal bedding in Huainan mining area，tensile and compressive mechanical properties in the directions of vertical and parallel to the coal bedding plane are researched by the Brazilian splitting and uniaxial compression tests. The results show that：(1) Tensile strength in the directions of vertical and parallel to the coal bedding plane are discrete，but the former discrete level is much more. Comparing the mean values in both directions，the former is obviously less than the latter，tensile strength has obvious anisotropy. (2) The random distribution of macroscopic coal composition and its differences on physico-mechanical properties are the important conditions which lead to the discreteness of tensile strength. Moreover，banding distribution characteristics of macroscopic coal components and directivity of coal cleat system are the internal causes to decide the anisotropy of coal mechanical properties. (3) Comparing the axial stress-strain curves in the directions of vertical and parallel to the coal bedding plane under uniaxial compression，the former pre-peak deformation characteristics are similar；the mechanical properties are stable；the post-peak stress drops quickly and the brittle feature is apparent. However，the latter pre-peak and post-peak deformation characteristics of each curve are different；and mechanical properties are unstable. Meanwhile，the axial peak strains of all coal samples are less than 1%. Thus，the deformation features are in a brittle failure state. (4) Fracture failure patterns of coal samples in the directions of vertical and parallel to the bedding plane are respectively given priority to shear and fracturing failure under uniaxial compression；and the uniaxial compression strength and deformation parameters in both directions are obviously different. In other words，the anisotropy is apparent. (5) The uniaxial compression characteristics in the direction of vertical and parallel to the coal bedding plane are discrete；but the latter discreteness is much more obvious. (6) The uniaxial compressive strength is much greater than the tensile strength，uniaxial compression strength in the directions of vertical and parallel to bedding plane are respectively 40.1 and 14.7 times of tensile strength.

In order to test adaptability and directed blasting parameters of slotted cartridge in rock driving，firstly， design of blasting parameters is optimized，and making the hole utilization rate reach more than 90%，the requirements of rapid driving and smooth blasting are reached. Secondly，after the success of blasting program，the both-sides comparison experiment of the surrounding holes and all surrounding holes comparison experiment are made，hole mark rate can reach 90%. At the same space，the best charge is 0.5 kg，and it can be less 16.7% and 37.5% than smooth blasting and ordinary blasting. At the same charge，blast-hole space can be extended from 450 mm to 550 mm，improvement rate is more than 22%. The experiment results show that control blasting using the simple slotted cartridge can be better for forming and taking more benefits for enterprise；it is suitable for spread in rock rapid driving.

Understanding the permeability stress-sensitivity characteristics is vital for effective development of oil and gas reservoirs and nuclear waste underground disposal. Different types of fluid media(nitrogen，brine and kerosene) permeability stress-sensitivity have been comparatively studied in ultra-low permeability reservoir and outcrop sandstone rock samples obtained from Daqing oilfield and Changqing outcrop reservoir，respectively. Those factors including rock permeability，pore throat deformation fluid compressibility and fluid-solid coupling were also analyzed on the effect of permeability stress-sensitivity. The experimental results indicate that the magnitude of permeability stress-sensitivity of different types of fluid media is significantly different. Gas permeability and oil effective permeability at irreducible water saturation dramatically declined during the early increase of effective stress. The comparative results also suggest that water permeability stress-sensitivity is stronger than that of gas permeability when the rock gas permeability is larger than 1×10－3 μm2. But the gas permeability stress-sensitivity is stronger than that of water permeability when the rock gas permeability is less than 1×10－3 μm2. That the larger pore throats were firstly compressively deformed is the main factor causing the permeability dramatically decreased during the early increase of effective stress. Fluid compressibility and fluid-solid coupling differences among different types of fluid media cause different magnitudes of gas，water and oil permeability reduction. Oil phase should be used as the flow media in oil reservoir permeability stress-sensitivity evaluation. A clear distinction between rock core and petroleum reservoir permeability stress-sensitivity experiment and evaluation method were also proposed. The permeability stress-sensitivity of ultra-low permeability reservoir is weaker when the reservoir effective stress range is considered.

There are more rock bursts happen when coal mining comes near to the fault area. To solve this severe problem，a research on the burst mechanism in fault area has done by means of theoretical analysis，laboratory experiment，numerical simulation，engineering practice，and other methods. The main research contents and conclusions are as follows：(1) The mechanical model of fault locking and unlocking is established；and by theoretical derivation，the judge formula for up unlocking and down unlocking is obtained. The formula indicates that the fault unlocking is decided by fault friction strength，fault dip angle and the ratio between horizontal stress and vertical stress. (2) The concept of fault-pillar induced rock burst is proposed，and it is classified into three kinds：rock burst induced by fault slide，rock burst induced by coal-pillar failure and rock burst induced by the interaction of fault and coal-pillar. Moreover，the burst mechanisms of the three kinds are explained. (3) The burst source distribution rule，burst influence factors and burst mechanism of the 20 times rock bursts at coalface 25110 in Yuejin coal mine are analyzed；and it is found that the majority of the rock bursts are fault-pillar induced rock burst resulting from fault slide，main roof failure and fault-pillar failure. (4) From the two aspects of weakening fault slide and coal-pillar burst，some control measures against fault-pillar induced rock burst at coalface 25110 are proposed. The engineering application presents that controlling mining speed can reduce fault slide induced rock burst and rock burst disasters can be reduced effectively by strengthening roadway supporting and releasing pressure through blasting and large diameter drilling.

Rockburst is a common engineering geological disaster in deep rock excavations. To evaluate the possibility of rockburst，a rockburst prediction method using the particle swarm optimization(PSO) algorithm and the general regression neural network(GRNN) model is proposed. This approach employs the technology of neural network to build up a regression model based on existing rockburst database，and takes advantage of PSO algorithm to optimize the parameters of the network which is believed to reduce the adverse influence of man-induced factors in model construction. Then，four major influence factors，including the maximum induced tangential stress on the boundaries of tunnels or caverns，the uniaxial compressive strength and the uniaxial tensile strength of the rock，and also the elastic energy index of the rock，are selected as the inputs for establishing the PSO-GRNN model based on the energy theory and the data obtained from 26 practical cases. The generated PSO-GRNN model is finally applied to predict the rockburst for the Cangling tunnel and Dongguashan copper mine，in which the feasibility and applicability of the proposed approach are illustrated. The methodology presented in the paper provides a reference for some similar engineering involving rockburst.

As a new cross-sectional shaped pile，the stress distribution in soil induced by the side friction(SF) and the end bearing(EB) of X-section cast-in-place concrete(XCC) pile has not been studied completely. Stress distribution in soil estimated by Geddes?s solution has obvious difference owing to independent of the influence of pile radius and pile shapes as the bases of St. Venant?s principle. Based on the Geddes?s solution，the soil stress can be obtained by application of the double integration. This method can be called as modified Geddes?s solution. The soil stress obtained by Geddes?s solution and modified Geddes?s solution are compared. The results indicate that the difference induced by Geddes?s solution increases with the increasing of pile radius because of the shaped effect. Besides，soil stresses induced by the SF and EB of XCC piles with different cross-sectional dimensions are analyzed through the modified Geddes?s solution. The results indicate that the stress in subsoil induced by XCC pile is about 1/3 times that induced by the circular pile with the same cross-sectional area；and the stress due to EB of XCC pile is 1 to 2 times that of circular pile. For large zone of subsoil (below the depth of 1.05 pile length)，the stress induced by SF on concave surface is larger than that induced by flat surface. The stress due to SF on the flat surface increases and that due to the concave surface decreases with the increasing of SF ratio of flat surface to concave surface. The stress induced by EB on concave zone is 1 time to 3 times that on the flat zone. The stress induced by XCC pile is always smaller than the circular pile. As the basis of the comparison analysis of the settlement of single pile，a conclusion can be drawn that the modified Geddes?s solution is more suitable for estimating the stress distribution and settlement of XCC pile than Geddes?s solution.

Low-plasticity silt widely spreads all over the world， and its liquefaction easily develops in earthquake events. Some failure of civil infrastructures happened not only during but also after earthquakes，indicating that it is necessary to study postcyclic behavior of low-plasticity silt. The Mississippi River Valley silt in central America was selected as testing material. Excess pore water pressure was produced by cyclic loading in cyclic triaxial testing system and then dissipated for reconsolidation. Monotonic and cyclic triaxial tests were respectively conducted on two series of specimens experiencing the previous dynamic shearing. The testing results show that the dynamic shearing with a liquefaction level larger than 0.70 produced significant increases in the volumetric strain due to reconsolidation and undrained shear strength. Compared to sand，the Mississippi River Valley silt has an obvious increase on undrained shear strength at lower liquefaction level. The previous dynamic shearing showed a different effect on liquefaction resistance with on undrained shear strength. With a liquefaction level of 0.35 or a cyclic axial strain of 0.2%，the liquefaction resistance reached the peak and then decreased with an increase in liquefaction level larger than 0.35. With a large compression strain due to previous dynamic loading，the excess pore pressure developed less in the compression than in the extension during the second cyclic loading after reconsolidation.

Mechanical and deformational characteristics of sands are significantly affected by density and effective confining pressure. In order to reflect the effect of the two factors，the nonlinear elastic model with three-parameters (compression modulus K0，Young?s modulus and coefficient of volumetric deformation)，which was proposed by SHEN Zhujiang based on the initial strain method was modified. Firstly，a description mode of K0 compression curve was established，which could describe the effect of initial state effectively. Then，the variable of virtual peak deviator stress was defined based on state parameter；and a new description mode of shear curve was proposed so as to reflect the effect of density and effective confining pressure. In addition，dilatancy equation was also introduced to describe deformational characteristics of sand. Mathematical description of the modified model is simple，and only ten parameters are involved and easy to identify. Finally，the modified model was used to simulate drained and undrained triaxial tests. A good agreement between computed results and measured results show that the modified model can describe the effect of variation of state parameter on the mechanical and deformation characteristics of sands accurately，so as to verify the rationality of the model primarily.

This paper carried out the in-situ tests and laboratory tests to study the reinforcement mechanism and construction technology of a high fill airport under dynamic consolidation. The dynamic response of broken stone fills，of which gradation can not meet the specifications for earthwork construction，has been studied by measuring the acceleration. Then the relationship between compact energy，compact momentum(the height of hammer raised)，the size of hammer and settlement，effective reinforced range were researched by numerical simulation. The results show that the acceleration of the range of sideways and downward of the broken stone fills is weaker than around. The plastic dissipation energy and volume of plastic zone of fills for every ramming are stable；while the settlement for each ramming is decreased because the plastic zone is increasing. The larger compact energy is，the larger settlement is；but the compact energy can not affect the ramming time for stable settlement. The settlement and plastic zone can be affected by the height of hammer raised and the size of hammer when the compact energy is constant. Construction technology indices were proposed by the research results.

The suction is closely related to the mechanical characteristics of unsaturated soil，to explore the suction law of unsaturated soil，the total suction and matric suction of Jingmen unsaturated expansive soil are measured under six levels of compactness and thirteen levels of gravitational water content by using the filter paper method. The test cases cover almost the entire range of moisture and dense state of the expansive soil. Test results show that both the moisture and dense state have significant effect on the suction. With one fixed density，the suction of soil can increase greatly with the decreasing degree of saturation. On the other hand，under one fixed degree of saturation，the suction increases with the increasing density. The suction varies within wide range for the samples at the lower degree of density，whereas the suction for the samples at the higher degree of density changes gradually. Based on the test results，the constitutive formula is presented for predicting the suction which is the function of the degree of saturation and the void ratio. The comparison between tested suction and predicted suction indicates that the proposed constitutive formula can describe the suction law of compacted expansive soil in the may range of dense state and water-holding state.

Aiming at the inability to obtain enough information to describe the random distribution of uncertain variables accurately，the Information-Gap theory which is abbreviated as Info-Gap theory is adopted. Firstly，a robust reliability model for uncertainty analysis of stability about karst roof under foundation pile is established based on the research about the method to measure the uncertainty degree of uncertain variables and to determine the allowable change range of these uncertain variables on the condition that the structural performance can satisfy the intended function. Secondly，according to the existing limit equilibrium analysis method on safety factor of karst roof under foundation pile under different failure modes，a response output model to the stabilization and security function of karst roof is set up；then the calculation method of the robust reliability index is brought forward by interval combination algorithm；so an uncertainty analysis method for the stability of karst roof under foundation pile based on Info-Gap theory is put forward. It not only has lower requirement for the message amount of engineering data but also can not know the random distribution shape of uncertain variables；and it is a supplement and improvement for the existing relative research. What?s more，because these uncertain variables are divided into design variables and design parameters in this method to achieve the dynamic analysis of allowable uncertain degree of design parameters under different design variables；thus，the method proposed has the function of not only passive reply but also active disposal. Finally，the rationality and feasibility of the method are verified by analysis of practical engineering example.

A shaking table model test of the earthquake performance of PHC pipe pile under seismic excitations considering soil-pile-structure interaction effect is presented. Features of the shaking table test include a variety of pile models，i.e. single pile，three piles，and six piles，and a shear soil box consisting of clay，silt，and sand layers. The various developed soil-pile-structure systems are then subjected to three sets of seismic ground motions. Each set of the earthquake events is composed of five input excitation scenarios with varying intensities. The evaluation results show that along with earthquake continues，each model system natural frequency decreases and damping increases. The earthquake intensity has a significant effect on the soil-pile-structure system. Specifically，the soil-pile-structure interaction and soil nonlinearity effects are observed to go up as the intensity increases. The nonlinearity effects of systems with fewer piles are stronger than those with more piles. Moreover，the number and arrangement pattern of the piles as well as the configuration of the upper structure can exert substantial impact on the strain and bending moment responses. It is shown that compared to the single-pile model，the maximum tensile strains of the three-pile model and six-pile model drop by 23 percent and 66 percent respectively，whereas the maximum bending moments decrease by 29 percent and 70 percent respectively. On the other hand，the soil-pile interface pressure reduces by 22 percent and 32 percent respectively. It is also found that the damage behaviors for systems with more piles are less severe than those with fewer piles. The results of this preliminary investigation further indicate the feasibility of exploiting PHC piles in high seismicity regions. Nonetheless，it is also suggested that more research efforts are required for extensive application of PHC piles in such areas.

A simulation system is developed to investigate the changes in skin friction of piles due to the triaxial loading and unloading of soil. The system consists of four subsystems：triaxial loading and unloading system，model piles，measuring system and automatic data acquisition system. The system can get higher pressure with the help of pneumatic loading method；so that the impact of soil compression and rebound on model piles under different soil properties and end restraint conditions is simulated. The validity of the apparatus is verified by elementary tests. The test results show that the system with high intelligence can achieve long-term constant load. The maximum value of positive and negative skin friction for the bottom free piles increased with the increase of applied triaxial load. The neutral point lies in the region from 0.5L to 0.6L. At the beginning period of unloading small rebound deformation of the soil happened；but the tension of the pile caused by the rebound has developed rapidly to a larger value. The system can be used to simulate the effect of the soil loading and unloading on piles under different strss paths.

A hollow cylinder apparatus(HCA) was used to study the deformation behaviour of sand under rotation of principal stress axes. A series of drained tests were carried out with two types of stress path. The first one was pure rotating stress axes without changing the deviator stress，while in the other one the deviator stress was increased with the rotation of principal stress axes. Various constant deviator stresses were used to study the effects of stress level on the deformation and non-coaxial behaviour of sand. Specimens with two relative densities were prepared to investigate the influence of density on non-coaxiality. Meanwhile，study was carried out to validate the previous viewpoint that non-coaxiality was induced by the initial fabric anisotropy of material by comparing results from two different materials，which were Portaway sand and Leighton Buzzard sand. The results show that the deformation would accumulate with the rotation of principal stress axes. And the non-coaxial behaviour of soil was found in the study. It was also indicated that the non-coaxiality would be affected by the stress level，density and the initial fabric anisotropy of material.

The purplish-red mudstone of the Badong group appears in large numbers in the highway from Yichang to Badong. When the weathering mudstone was used as the fillings of highway embankment，lots of engineering problems appeared，such as road bulges，shoulder of road gushing，the uneven settlement and the lower bearing capacity. In order to eliminate the undesirable properties of embankment soil，a modified experiment was conducted with lime，cement，fly ash. The compaction test，California bearing ratio(CBR) test，unconfined compression test，disintegration test by using self-made disintegration instrument and soil-water test were conducted to study the characteristics of improved soil. The microstructure of improved soil was scanned by environmental electron microscope. When the improvement effect was evaluated；the basic indices such as bearing ratio，unconfined compressive strength，expansion index were not only considered but the index of soil-water characteristics and resistance of disintegration were also tried to be analyzed. The results show that the expansion characteristics of purplish-red mudstone is eliminated by modified materials. The bearing capacity of the subgrade soil and unconfined compression strength are vastly improved. The characteristics of water stability and resistance of disintegration are also improved. The improvement effect of the improved soil mixed with cement is the best，the best cement proportioning is 5%. The improvement effect of improved soil mixed with lime is the better and the best mixing ratio of lime is 7%. The improvement effect of fly ash soil is the worst and the best mixing ratio of fly ash content is 11%. To increase the fly ash content may make the improved effect to be better.