Firstly，the significances of rock structure and stability are introduced. Then，the methods to calculate limit bearing capacity for structure stability are presented. Finally，the basic problems on geotechnical stability，the constitutive relations and their positive-definition relations are studied. So far，the finite element method(FEM) for geotechnical structure stability could not obtain its exact solutions. However，by means of energy criteria，surplus-force reinforcement method and potential energy criteria，the solutions for engineering stability can be reasonably achieved. The following items could be preceded by FEM：limit load analysis in terms of structure failure and material failure，limit analysis of upper bound load and lower bound load of structures，nonlinear analysis of structure behaviors. The FEM is emphasized on how to solve structure stability problems for engineering projects，and on how to use energy criteria to problems of stability study for large-scale dam projects，and they could be optimized，through the context，from theory to practice. The real engineering problems are illustrated that are encountered in dam constructions during the last 40 years，and factors of safety gained from geomechanical rupture tests and rupture processes are submitted. With the corresponding achieved numerical analytical results，their factors of safety are reasonably cited in related codes or specifications. The results from these studies show that the large-scale dams in China have undergone the above-mentioned simulations，and their results are primarily verified with practical cases. Almost all of the dams are now under control and they are safe and stable.

For high rock slopes，the mechanical parameters on the potential sliding surface，the reinforcement forces needed after slope excavation，and the correlation between the calculated factor of safety and actual safety margin will directly influence engineering safety and economy. Based on back analysis methods for determining mechanical parameters of potential sliding plane and their shortcomings，the minimum value criterion of mechanical parameter selection is proposed；and the maximum reinforcement force criterion is then proposed on the basis of the equivalence of the largest reinforcement force needed and the weight of excavated rock body. Finally，the upper and lower limit criteria of the numerical results used for stability analysis and assessment are put forward and applied to engineering design based on PAN Jiazheng¢s upper and lower limit theory. It will helpfully provide designers with criteria of slope stability analysis and assessment on reinforcement scheme selection of high rock slope.

The calculation method of slope rock-soil pressure is discussed. The calculation method of slope lateral pressure in the “Technical code for building slope engineering”(GB50330–2002) is not reasonable because it does not take into account the factor of safety of slope stability. The calculation factor of safety in the imbalance thrust force method is not the true stability factor of safety in reinforced slope. Thus，a new slope thrust calculation method based on the strength reduction is presented. The slope lateral pressure and imbalance thrust force can be carried out through strength reduction. In accordance with this method，the stability factor of safety of reinforced slope is equal to the factor of safety of slope thrust calculation. Analysis and comparison of the imbalance thrust force method and strength reduction method are also discussed. Through a series of case studies，the applicability of the proposed method is clearly exhibited.

The problem of time-dependent heat conduction for tunnel in cold region with nonhomogeneous outer boundary conduction is transformed into both transient heat conduction with convection boundary condition of air temperature changed with sinusoid and steady heat conduction. Using the separation of variables and Laplace transform technique can obtain analytical solution to temperature fields of tunnel with insulation layer in cold region. The analytical solutions of the annual mean temperature and temperature amplitude can be obtained by energy conservation and experiential method considering heat conduction/convection between the tunnel ground and the air flow in the tunnel. Temperature of lining varies with both tunnel depth and annual mean temperature linearly. When the annual mean temperature is below 0 ℃ and the tunnel depth is less than 80 m，5 cm thick insulation layer alone can not satisfy the anti-freezing requirements. As the increase in thickness of insulation layer，lining temperature presents an upward trend，but the growth rate has gradually decreased；when the thickness of insulation layer is more than 5 cm，the increase in the thickness of insulation to improve the lining temperature is not economical. The insulation thickness can be calculated by engineering analogy and analytical solution based on climate and terrain conditions with piecewise calculation. Accuracy of the analytical solution is examined by comparing the calculated results with measured results. It is found that the calculated values agree well with those measured in the field.

Introducing the existing empirical relationships into a coupled thermo-gas-mechanical model，the porosity and the permeability of rock mass are regarded as functions of mean effective stress and volumetric strain resulted from shear dilation；and a corresponding two-dimensional finite element code is developed. Taking an assumed geological storage system consisted of an under-part reservoir and an upper-part caprock as an analytic object，the numerical simulation of the coupled thermo-gas-mechanical process in the rock mass during CO2 injection is conducted under three cases of different porosities and permeabilities. The calculation results show that the distributions and changes in porosities，pore air pressures，displacements，stresses，zones of tensile and shear failure in the rock mass are obviously different in three cases. Therefore，it is more accurate to consider porosity and permeability of rock as functions of stress，especially reckoning in the effect of volumetric strain resulted from shear dilation than to consider them as constants.

It is difficult to describe the thickness of joint with a constant in practical engineering. In order to model the mechanical behaviors of joints conveniently，a non-thickness three-node joint element is proposed on the basis of the existed three-node joint element；and the stiffness matrix of non-thickness three-node element is deduced. For it shares the same nodes with original three-node triangle element，the non-thickness three-node joint element is adopted to model crack propagation without remeshing or adjustment of the original mesh. Another advantage is that the cracked body is meshed without considering its geometry integrity and the existence of joints or pre-existed crack in the procedure of mesh generation；and then the triangular element intersected by crack or joint is automatically transformed into the three-node joint element to represent pre-existed cracks. These make the numerical simulation of crack propagation highly convenient and efficient. After the maximum strain failure criterion is chosen to determine whether the element is intersected by the extended crack or not，the extended crack is located in the model based on hypothesis of the direction of crack propagation perpendicular to the direction of the extended crack passing through the centroid of the triangle element. By simulating the marble plates with double parallel cracks subjected to uniaxial compressive loads，it is shown that the simulated results are in good agreement with the experimental results，so as to show that the present method is valid and feasible in rock crack propagation simulation.

In order to understand exactly the influence of unloading rate on mechanical properties of rock，the unloading confining pressure tests under different unloading rates are carried out，which use new loading path and operation method. Thus the disadvantageous effect on test process of the results is reduced. And the deep-buried marble samples cored from Jinping II hydropower station are tested. Based on a new description variable presented as strain-pressure compliance，the influences of the unloading confining pressure path are analyzed on the axial and volume deformations and strengths. The results indicate that the unloading rates of the confining pressure have significant influence on the deformation of Jinping marble，and the initial confining pressure levels mainly control the corresponding influence rules. There are obvious differences in the dilatant processes between the unloading confining pressure tests and triaxial compression tests. In unloading confining pressure tests，the limited bearing loads under the range of unloading rates between 0.01 MPa/s and 1.0 MPa/s are higher than those in the conventional triaxial compression tests under the loading rate of 0.5 MPa/s. Limited bearing capacity increases along with the rise of unloading rates，and increases 10%–15% at the rate of 1.0 MPa/s.

In order to study the status of global stability of a slope，the decision-making model of multi-attribute and interval number is constructed to carry out global stability analysis of slope. With this method，the research process can be realized. According to the actual geological conditions and the situation of engineering sections of Guanjia slope，the set of influence factors and research objects are established，and the decision-making model of multi-attribute and interval number is adopted，and the safe and stable states of slope are back analyzed. Moreover，the macroscopic signs of slope failure are referenced to perform comparison and verification. The research results show that through the model solution，the interval of global stability factor which can characterize the changing situation of global stability of slope ranges from 0.927 to 1.032，and the probability of sliding instability or failure is up to 70%. The slope，which has poor global stability and low safety level，is in an unstable state，and the tread of deformation expansion and sliding instability is obvious. In addition，the current active state of slope indicates that it has high possibility of sliding instability or failure. In order to maintain safety，stability and reliability of slope，it is noted that comprehensive treatment should be carried out for the slope. Thus it is shown that the decision-making model of multi-attribute and interval number can provide a feasible technical platform for state feedback and prevention countermeasures of slope disaster，which has positive guiding significance.

The thrust-dextral slip motion of Longmenshan tectonic belt resulted in Wenchuan Ms8.0 earthquake occurred on May 12，2008. 133 groups of three-component acceleration records were collected by digital strong earthquake networks in Sichuan Province. By using these original records and some strong motion records from digital strong earthquake networks in Shaanxi and Gansu provinces，the contour lines of acceleration peak values were drawn；and they show that the anomalistic ellipse-shaped contour lines of acceleration peak values along the long axis in NE direction conform to the distribution of earthquake response intensity. The attenuation of the acceleration records shows obvious directivity effect and hanging wall effect；i.e. the peak acceleration decayed relatively slower in NE direction of the rupture propagation than in SW direction. The attenuation of peak acceleration also decayed slower on the fault hanging wall in NW direction than that in SE direction；the systemic relative higher phenomenon of the peak acceleration attenuation was more remarkable in Yingxiu—Beichuan section of the causative fault；and it can be relative to fracture pattern and progress of seismic source. Another phenomenon is that the ratio of vertical peak ground value to horizontal one near the causative fault is obviously higher than that in the seismic far-field；and the ratio is about 1.0 near the faults，which is great different with the 2/3 from Code for seismic design of buildings(GB50011–2001). Furthermore，with fault distance increasing，the peak acceleration gradually shifted to the long-period in the acceleration response spectrum，which is more obvious beyond a distance of 200 km to the causative faults；but in the near-fault distance of 100 km，there is a large velocity pulse.

Great changes in pore structure and quantity of coal may occur as the pyrolysis temperature rises. To study the change laws，a mercury intrusion method was adopted to measure and analyze the pore structure parameters of the solid products of flame coal pyrolysis，which were generated in vacuum system with temperatures from 300 ℃ to 600 ℃ and in high temperature steam state at 600 ℃；the pore fractal dimensions were calculated under different temperatures；and pore properties of solid products under two different pyrolysis ways were compared. The results indicate that：(1) Under conventional pyrolysis，the total pore volume and porosity of Heidaigou coal decreased from 300 ℃ to 400 ℃ and increased from 400 ℃ to 600 ℃；the increasing rate is the greatest from 500 ℃ to 600 ℃；the specific surface area increased progressively from 300 ℃ to 600 ℃. But for Zichang coal，the total pore volume and porosity increased from 300 ℃ to 400 ℃ and then decreased from 400 ℃ to 500 ℃ and increased from 500 ℃ to 600 ℃；the increasing rate is the greatest from 300 ℃ to 400 ℃；the specific surface area decreased progressively from 300℃ to 600 ℃. (2) Under conventional pyrolysis，large pores were the major parts of pore volume，micropore and transition pore were the major parts of the specific surface area. (3) Under high temperature steam pyrolysis，the large pores were the major parts of pore volume；the proportion of large pores of Zichang coal was 99.91%；micropores and transition pores were the major parts of the specific surface area of Heidaigou coal；the large pores were the major parts of specific surface area of Zichang coal. (4) Compared with conventional pyrolysis，the permeability of solid products of high temperature steam pyrolysis was greater；and compared with inert gas injection，it is the best method in the coal situ-pyrolysis application. These results can provide a scientific basis and theoretical guidance for the issue that coal pore structure changes with temperature during coal situ-pyrolysis.

The elastic layered soil model is adopted to consider the soil non-homogeneous characters. The oval- shaped soil deformation model is imposed to the tunnel opening boundaries，and the boundary element method based on displacement-controlled technique is presented to analyze the free soil displacement. The displacement- controlled method is put forward to predict the deformation of adjacent pipeline due to non-uniform convergence of shield tunnelling in multi-layered soils. The accuracy of the proposed method is demonstrated with the displacement-controlled finite element numerical analysis and existing centrifuge model tests. The results indicate that the solution of the free soil deformation is rather important to estimate the effects on adjacent pipeline. It is also shown that the soil non-homogeneity，neglected in previous methods，has a significant influence on the deformation behaviors of municipal pipelines induced by tunnelling in multi-layered soils. The proposed method may provide a theoretical basis for proposing correctly protective measurements of existing pipelines influenced by adjacent underground construction.

To study the relationship between shrub roots and slope stability in loess area of northeast Qinghai— Tibetan plateau，four shrubs Caragana korshinskii，Atriplex canescens，Zygophyllum xanthoxylon and Nitraria tangutorum were planted on the slopes of the test area in Xining basin. The mechanical strength tests of root-soil composite systems were carried out and the increasing effect of slope stability of four two-year growth shrubs were simulated with two-dimensional finite element method. The results show that the horizontal and vertical displacements of four shrubs root-soil composite systems are obviously smaller than those of soil without roots. The order of four two-year growth period shrubs in the course of deformation in magnitude is Caragana korshinskii，Atriplex canescens，Zygophyllum xanthoxylon and Nitraria tangutorum. Lateral roots and main roots of shrubs play a part in reinforcement and anchorage in the soil，which increase the shear strength and the cohesion of the soil，thus the plastic area and the shearing stress concentration area can be reduced. The results of factors of safety of the slope in the testing area show that，compared with the safety factor of soil without roots，the increments of the safety factor of the related slope of the four shrubs root-soil composite systems of the four shrubs are 80.5%(Atriplex canescens)，48.7%(Caragana korshinskii)，22.1%(Zygophyllum xanthoxylon) and 8.0%(Nitraria tangutorum)，respectively. The achievements can be taken as criteria for choosing shrubs for protecting slope and preventing shallow landslide，collapsing and debris flow in loess area of northeast Qinghai—Tibetan plateau.

With the method of macro-meso incorporation，a failure criterion of anisotropic sand is proposed. A new anisotropic state variable is properly defined by two invariables of a joint tensor combined by loading direction tensor and fabric tensor from the mesoscopic point of view；then a failure criterion of anisotropic sand is put forward by introducing the new anisotropy state variable into macroscopic equation. In view of the relationship between fabric and stress state，the proposed criterion not only can describe the effect of mesostructure on material anisotropy under conditions of non-rotating and rotating stresses，but also has the clear physical significance parameters. Verifying the proposed criterion with a series of experimental data，the results show that the effects of mesostructure on anisotropic strength and peak friction angle are well captured by the proposed criterion under three-dimensional condition；and the adaptability and validity of the method can be confirmed from the comparison and analysis of calculated results.

The mechanical behaviors of interface between coarse-grained soil and concrete were investigated by simple shear tests with both bentonite slurry and mixed soil slurry(bentonite mixed with cement grout). In addition，the mechanical behaviors of interface were analyzed with different slurries. The results show that the relation curves between shear stress and shear strain exist strain softening，and strain hardening appears with bentonite slurry or without slurry，when mixed soil slurry exists；and the position of peak strength is mainly related to normal stress and cement content. The more the cement content is，the larger the strength becomes. The value of friction angle with 40 percent cement grouts is 3.2 times higher than that with 10 percent cement grouts，the strength accounts for 84 percent of the interface strength without slurry. The shear displacement increases with increasing normal stress and cement content at the same height in shear failure state. Shear dilatation is significant when the surface without slurry in small normal stress state，while shear contraction is significant with the bentonite slurry and the mixted soil slurry. Compared the sample with height of 100 mm to that with height of 30 mm，the errors of friction angle and horizontal displacement are about 3% and 6%，respectively，when the maximum grain size is 20 mm，which shows that the height of sample affects the strength and deformation to some extent. In addition，the friction angle reduces by 4.8%，i.e. 1.9°，compared to the maximum grain size of 60 mm.

As an essential portion of basic framework of soil mechanics，strength theory of saturated soils has been well developed and widely used in geotechnical engineering. However，unsaturated soils have a wide distribution and display more complex behaviours compared with saturated soils in engineering practice. Until now the research activities in the field of unsaturated soils have been still in the academic stage because of the difficulty of suction measurement. To solve this problem，the equivalent suction has been proposed and validated recently. Based on the principle of equivalence of deformation and the stress-strain curves obtained from triaxial compression tests of intact saturated and unsaturated loess，a determination method of equivalent suction is proposed. The nonlinear relationship formula between equivalent suction and degree of saturation is proposed；and the correctness of this exponential function relationship is verified. Based on testing results，the influence of water content on shear strength is analyzed；and shear strength formula of unsaturated soils is established. It provides a new feasible method for application of unsaturated soil theory to engineering practice.

The coefficient of permeability of unsaturated soil is a key parameter in performing seepage analysis in saturated/unsaturated soils. However，both the degree of saturation and the dry density influence the coefficient of permeability of unsaturated soil. A series of experiments are performed by using the improved measurement apparatus under different infiltration steps and various initial dry densities of unsaturated remoulded loess specimens. According to the results，the relationships among degree of saturation，dry density，coefficients of air and water permeability are analyzed. A new density-saturation-dependent air-water permeability function is put forward based on the above relationships；and it can not only determine the coefficient of water permeability but also quantitatively describe the mutual influence of movement of both air and water in the void of unsaturated soil. Finally，the new experiment is provided to verify the proposed permeability function. It is shown that the predicted curves are in good accordance with the experimental data.

To understand the formation mechanism of longitudinal crack of Qinghai—Tibet highway in permafrost region，the mechanical model of longitudinal cracks in subgrade is constructed during freezing and thawing processes by numerical simulation，based on the in-situ observation of thick ice layer in the cross-section K3020+200 and the testing data of temperature field in the cross-section K3016+000. The formation process of thick pure ice layer under road shoulder and its effect on subgrade stability are analyzed. The observation in the cross-section K3020+200 shows that the thick pure ice layer exists under road shoulder and natural ground surface. The time-history curves of ground temperature at different depths in the cross-section K3016+000 show that the change in ground temperature is larger near the ground surface；the change in temperature in subgrade lags behind that at ground surface；the upper limits of permafrost at road shoulder and slope toe decrease by ground surface water infiltration from road shoulder，slope and slope toe，i.e. the distribution of upper limits presents arch shape. The results show that the infiltration of ground surface water leads directly to the formation of thick pure ice layer；the formation and thawing of thick pure ice layer are immediate causes of nonuniform deformation of subgrade and formation of longitudinal cracks.

An investigation is put into the vertical dynamic responses of a rigid circular foundation on the poroelastic soil excited by incident fast P1 waves and SV waves. The radiation field and rigid-body scattering field are introduced in order to consider the dynamic interaction between the foundation and the underlying soil，as well as the scattering phenomena caused by the existence of the foundation. The motion of the soil is supposed to be governed by Biot¢s dynamic poroelastic theory，while the boundary conditions along the contact surface between the soil and the bottom of the foundation are assumed to be perfectly bonded for the skeleton and hydraulically drained for the fluid. Combining with the mixed boundary-value condition and the dynamic equilibrium equation of the foundation，the expression of the vertical dynamic amplitude of the foundation，subjected to the incident plane waves，is obtained by solving the control equations using Hankel integral transforms. The influences of incident angle，the mass of the foundation and the permeability of the soil on the vertical vibrations of the foundation are thus determined through numerical simulations. Significant differences are found between the responses of the foundation，which is excited by fast P1 waves and SV waves，respectively.

To validate the working mechanism of reinforced embankment supported by cast-in-situ thin-wall tubular piles，field test has been performed in a highway section from Jiujiang to Xiaotang around Guangzhou City. Test results show that tubular pile has a large vertical bearing capacity，and punching failure happens to most piles in static tests. Moreover，the bearing capacity of single tubular pile composite foundation is also large with small settlements. Tests still suggest that soil arching effect and tension membrane effect are the two key factors influencing the load transfer mechanism. The pile-soil stress ratio varies with the embankment loads and differential settlements between piles and soil. The total settlement of tubular pile composite foundation under embankment load is small. Differential settlements are found between soil above pile cap and soil among piles，respectively，and increase of this difference can reflect the degree of soil arching effect. In addition，excess pore water pressure，which is induced by embankment loads，turns up slightly and decreases rapidly along depth. It is nearly zero at the depth of 6.0 m. The lateral deformation of embankment is small，and decreases rapidly along depth；and it reaches its peak value at the depths of 3.0 to 4.5 m.

In the unsaturated compacted soil triaxial tests under controlled suction conditions，the digital image measurement technique is used，with which the strength and deformation behaviours of unsaturated compacted soil can be studied by considering the influence of end effect. The comparison of test results of the overall specimen and 1/3 zone in the middle of specimen under controlled suction reflects that end effect has a little influence on 1/3 zone in the middle of specimen；the test result of this part can better stand for the actual deformation properties of unsaturated soil；and it provides credible test data for the study of unsaturated soil stress-strain relationship. The end effect has great influence on parameters of shear strength formula，when using the double-stress state variable method to analyze the shear strength. The elastoplastic model of Alonso for unsaturated soil is adopted to further analyze the influence of end effect on numerical calculation.