The underground powerhouse caverns of hydropower station at Baihetan of Jinsha river is under construction currently and is large in size and complex in geological environment. Spalling failure of local surrounding rock occurred frequently in the excavation of the first layer of the left and right powerhouse. An overall summary and a deep analysis of the mechanism of rock spalling failure in basalts was made combined with the geological，construction，testing，experimental and numerical data. Firstly，the characteristics and laws of spalling failure，including the failure forms，the morphological characteristics，the spatial location，the scale of destruction，the lagging，the failure development process，the lithology and the support status were summarized. Secondly，the influence of the geo-stress，rock structure，lithology，construction factors on the surrounding rock failure were fully discussed. Finally，comprehensive analyses were made to reveal the mechanisms of spalling failure.

Due to the complexity of rock properties and the variability of environmental conditions，frost damage of rock can hardly be attributed to one single mechanism. Nonetheless，in most of the cases，one or more mechanisms dominate the process. We firstly reviewed the existing theories on frost damage and compare their applicable conditions. Afterwards the controlling role of the pore structure of sandstone(as an example of porous rock) in the frost damage process was discussed，and the “representative element of frost damage” was defined. The probable damage mechanisms and the predominant mechanism of sandstone under different freezing patterns were identified according to the thermodynamics. Under the low freezing rate，the capillary and crystallization pressure were found to play a key role in damaging sandstone，while the volumetric expansion process was restrained. While under the high freezing rate，the volumetric expansion process and hydraulic pressure process contributed predominately to the damage of sandstone rather than the capillary and crystallization pressure. To test the above findings，a series of experiments on frost damage of sandstone were conducted，including the direct observation of the microstructure of sandstone under environmental scanning electron microscope(ESEM) and monitoring of the frost deformation of sandstone using strain gages. The experimental results are consistent with the theoretical analysis.  

Accurate analysis and evaluation of the geometric features of joints around BS17，BS18 and BS19 boreholes are the major task of site selection and site suitability evaluation of Xinchang section at Beishan，a candidate area in China. Site investigation，mathematical statistics and probability analysis were applied to study the geometric features of joints. 4 joint sets were observed in three boreholes，and the dominant orientations for joints are NE and NW. Joints are mainly shearing and steep dip and obey the normal distribution function. The spacing of joints is a negative exponential function. Wide spacing，long trace length and small trace midpoint density are the main characteristics of Xinchang section. Considering the importance of joints in high-level radioactive repository， method was applied to evaluate the quality of rock mass. The results indicate that the joints of rock mass are little developed and that the differences between the regions are small. Hence，the integrity of rock mass is good. In addition，the existence of faults may promote the joints development along the two sides of the fault in rock mass. The research and evaluation of joints provided important data support for repository site selection and site suitability evaluation

Pressure relief blasting often leads to the damage of the surrounding rock and reduces the efficiency of rockburst controlling because of unreasonable design of the parameters of the blasting. The vibration and damage of surrounding rock of roadway with strong probability of rockburst under pressure relief blasting were studied quantitatively through the in-situ measurement with the portable microseismic detection system PASAT-M combined with the short pre-windowed Fourier transform technique. With increase of the distance between the source and sensor，the dominant frequencies in the mining wall and roof increase monotonically. The blasting dominant frequency in non-mining wall reduces firstly and then increases. The amplitude of blasting wall decays exponentially with the increase of the source distance，and the damage of the surrounding rock is very weak over 20 m range. Because of the different influence of surface wave and body wave，the differences of the vibration characteristics(type，dominant frequency and amplitude) of the surrounding rock are different. Vibration types, dominant frequency and amplitude of at different positions of the surrounding rock of the tunnel were not consistent with each other，so damage effect of the blasting vibration wave is very different from place to place. Based on different failure patterns，suggestions were proposed to prevent the roadway from damage by controlling amplitude，dominant frequency band and duration of vibration. In addition，the impact resistance performances of structure should be improved.

Under the engineering background of the Chongqing rail transit line No. 3，the geomechanical model test on the cross rock pillar concealed excavation method was carried out. The excavation process of the large cross section tunnel was optimized. Various similar materials of the surrounding rock were experimentally compared，the anchoring-grouting reinforcement was simulated and the deformation of cavern excavation was monitored and analyzed. The experimental results showed that the developed structural frame successfully simulated the cavern excavation under confining pressure and that the failure process of surrounding rock was directly observed during excavation. The sensors measured the displacements in real-time in the surrounding rocks during the excavation. The simultaneous excavation supporting and deformation recording were realized. The numerical analysis model was established and the calculated results were basically identical to the test results. The final displacement value met the test requirements，indicating that the expected effect was achieved with the model test.

In order to investigate the response of tectonic coal to cyclic loading-unloading of axial stresses，experimental study and analysis of dynamic model of permeability were carried out with experiment facility developed in-house for triaxial seepage test considering the fluid-solid-heat coupling in gas filled coal. The results show that the relation between the permeability of gas filled coal and the strain presents a trend of inclined letter ‘V’. The permeability of tectonic coal samples increases obviously after peak strength and the growth rate is greater than the reduction rate of permeability in the initial stage of compression. The permeability of coal samples and the axial stress presented a relation of negative exponential function during unloading. The permeability decreases under loading and recoveres a bit under unloading. The permeability and the effective stress does not form a closed curve. The reduction of permeability increases and the sensitivity of permeability to the effective stress decreases because that pores of coal sample are more compressed under cyclic loading- unloading. A factor in reduction of permeability sensitivity when loading and another factor in reduction of permeability when unloading were introduced，and then the dynamic evolution model of permeability and effective stress under cyclic loading-unloading was established. The comparison of experimental data with theoretical results verified the applicability of this model.

The squeezing deformation of soft rock is a problem in construction of the deep buried or high stress underground caverns in soft rock. The scientific evaluation of the squeezing degree is very important to the stability control of surrounding rock，but the existing methods of stress and deformation evaluation neglect the difference of rock deformability. After the basic concepts of the squeeze and its geological conditions were made clear，the test data of some types of rock was analyzed，which revealed the huge differences in the rock deformability. The potential squeezing ratio index based on the above understanding was put forward in the paper which was confirmed to be good to describe the individual differences. The definitions and criteria of the existing evaluation methods were summarized and analyzed. The obvious deviation of evaluation results based on the widely recognized Hoek?s method was due to the ignoring of rock?s individual differences. The Hoek?s method was thus modified based on the potential squeezing ratio and the evaluation method of squeezing degree based on the potential squeezing ratio was suggested.

In order to reduce the dependence of GSI system on the field geological observation，to reduce the difficulty of its application and to reflect more accurately the characterization of rock mass from the surface to a certain depth，a new GSI system in terms of the longitudinal wave velocity was built based on the correspondence of intactness and weathering between the results existing research and GSI systems. The geological strength indexes of rock mass from the region of Dagangshan dam were obtained from the new system. Its feasibility was confirmed through the analysis of the distributions and correlation between the results obtained from the new GSI system and empirical formula，and between the predicted deformation modulus of rock with GSI and the measured one. The squared ratio of the weathered rock to unweathered rock is a reasonable input parameter which represents the weathering degree. The input parameters of GSI system can be replaced with the intactness index and weathering index of rock.

Joints have significant influence on the dynamic properties of rock masses. Using the apparatus of modified split Hopkinson pressure bar(SHPB)，an experimental study was carried out on one dimensional stress wave propagating through the artificial granite joint. The interfaces of granite specimens were sawn to form the artificial joints with different joint match coefficients(JMCs). The incident wave across the joint and the reflected wave and transmitted wave induced by the joint were obtained with the method of two-points wave separation and then the transmission coefficients of the stress wave propagation through the joints were calculated. The relation between the pressure and closure of the joint was obtained according to the principles of SHPB test，thereby the specific stiffness of the joint was acquired. The effects of the joint match coefficients on wave propagation through the joint and on the dynamic mechanical behavior of the granite joint were discussed.

Resin anchor material has been widely used in underground engineering supporting. The pyrolysis characteristics of resin anchor material at high temperature directly affect its anchoring mechanical properties. The mechanical properties and variation characteristics of mesoscopic structures were analyzed using the pull-out tests and compression experiments and micro-CT scans undertaken at high temperatures. The high-temperature pull-out test results show that the anchoring force increases as the temperature increases from 20 ℃ to 250 ℃ and reaches the peak of 69.5 kN at 250 ℃ with an increase of 45.1% compared with the normal situation，which is due to the full solidification of the internal material. At the temperature of 250 ℃ to 350 ℃，the anchoring force is reduced to 47.2 kN，with a decrease of 29.2% compared with the peak value. At temperature of 350 ℃ to 400 ℃，the anchoring material in the simulated tube bursts and chars severely，with the average anchor force dropping to 15.2 kN. The anchoring force was completely lost from 500 ℃ to 600 ℃. In the high temperature compression experiments，the strength reaches the peak of 65.8 MPa at 200 ℃，with an increase of 31.3% compared with normal situation. At 350 ℃–400 ℃，the intensity reduces 95.2% compared with the normal value and at 600 ℃，the strength reduces 99.3%. CT analyses show that the average grey scale of the anchoring material reduces 22.6% at 350 ℃–500 ℃. The size of pore group increases 199.6%. Hence，the rapid pyrolysis and charring of resin anchoring material after 350℃ and the dramatic increase of internal pores are the fundamental causes of anchoring force attenuation.

The tests to study the development of internal micro-structure and the distribution of new surface fractures of coal samples under impact loads were performed with the drop hammer impact test equipment for coal and the ultrasonic detection device. The effect of dynamic loads on the development of internal structure of coal was analyzed. The results show that the development of the internal micro-structure of coal is related to the number of impacts，energy of a single impacting，sequence of impact energy，accumulative effect of impact energy，etc. Both the internal micro-structure and the newly developed surface fractures propagate anisotropically. The influence is larger along the impact direction than perpendicular to the direction. When the energy of a single impacting is constant，the total quantity of the internal micro-structure of coal has a trend of rapid increasing， gentle development and sharp increasing with increase of the impact number. The total quantity of internal micro-structure of coal increases exponentially as the energy of a single impacting increases，and the localized distribution of new developed surface fractures of coal is also more significant. The development of the internal micro-structure of coal is more sensitive under the decreasing cyclic loading than in increasing process. The accumulative effect of impact loads on the development of internal micro-structure is nonlinear，and shows a decreasing trend after the first increase. The accumulative effect of impact loads cannot be only simply considered due to the increasing of impact energy. The absorption rate of impact energy of coal decreases as the increase of the impact energy. The accumulative effect of the smaller single impact energy on internal micro-structure of coal is greater than the effect caused by the equivalent larger single impact energy.

To prevent the underneath collapse induced hazard in road transportation，the multi-layer geotextile reinforcement is a cost-effective and promising technology，although its bearing mechanism and design method remain to be further studied. The embankment models of 1∶5 in scaling，with the single-layer，three-layer and four-layer geotextile reinforcements installed respectively，were designed and tested in laboratory. In order to study the load distribution and displacement characteristics，the vertical pressure on each geotextile and the relevant displacement were measured with the load cells and deformeters installed in the model. The key issues in design and the relevant calculation theory were discussed based on the measured data. The test results revealed that，in multi-layered geotextile reinforcement，the foot of soil arch might rise to around the top-layer reinforcement，and the dual-soil-arch emerged. The upper load distributed non-uniformly among the reinforcements. The surface depression could be related to the bottom deflection with a simplified method ignoring the dilation effect. The bottom-layer reinforcement is the key to control the surface depression while the top-layer is of the most importance to control the limit state. Based on the measured data and further analysis，a flow chart of design was proposed for practical engineering application.

To avoid the weakness of the Winkler beam model on elastic foundation，a two-parameter foundation model of Pasternak reflecting the continuity of the foundation was applied in the analysis of the feet-lock pipe combined with steel arch. The formulae to calculate the deflection，shear force，bending moment and foundation reaction of feet-lock pipes were derived using the theory of structural analysis and beam on elastic foundation under the consideration of the compatibility of deformation and load transfer between the feet-lock pipe and steel arch. The influence of subgrade coefficient and shear stiffness of the foundation on the mechanical behaviors of feet-lock pipe was investigated through examples and comparison with the Winkler model. It was found that the smaller subgrade coefficient resulted in the larger difference of two models of feet-lock pipe regarding values shear force，bending moment and foundation reaction. The double parameter model produced a lager foundation reaction and smaller distribution range，and the foundation reaction mainly concentrated in the region near the near-end of the feet-lock pipe. The tunnel settlement was less than that calculated from the Winkler model. Finally，it was suggested that the designed length of the feet-lock pipe should be reduced and its diameter should be increased reasonably so as to obtain the desired supporting effect.

A theoretical model of the moving interface of grout was established on the basis of continuity equation of penetration，Darcy?s law and linear filtration law. The migration and plugging mechanism on the slurry interface was analyzed. The variation of designed spreading distance of grout and the permeability of the deposition layer were investigated using the model test system developed in-house. The experimental data were compared with the theoretical values. The results show that the designed spreading distance is dependent on the designed upper limit of coefficient of permeability and the grouting parameters. Influenced by the deep bed filtration effect，the coefficient of permeability of the deposition layer varies along the slurry interface migration.

The position and shape of failure zone are main factors affacting of the stability of tunnel faces. Therefore，the first problem in the stability analysis of tunnel faces is to reasonably determine the position and shape of the failure zone. The failure of tunnel faces is a nonlinear process of ‘stable equilibrium，unstable equilibrium to stable equilibrium’，so the stability of tunnel faces can be judged using the catastrophe theory. A method of predicting the potential failure zone ahead of the tunnel face based on the catastrophe theory is presented using the dichotomy and the curve fitting technique. Firstly，the model of catastrophe at cusp of the displacement of the center of the tunnel face is established to get the limit state of stresses. Then，the potential failure zone is obtained by the method of partition search. Finally，the position and shape of the failure zone are obtained using the curve fitting technique. The correctness of this method is verified by comparing with the results from the similar model test. This method can be adapted to the complicated conditions，especially for the deep buried and shallow buried conditions.

A staggered updated method for a phase field model was implemented in the commercial finite element software ABAQUS through UMAT and VUMAT subroutines. In order to verify the reliability of the algorithm，crack propagation in modes I and II under quasi-static and dynamic loads was calculated. All the results are generally consistent with the testing results in the existed references. In addition，simulations for wing cracks and curved surface cracks were also carried out. The results show that the main reason of dynamic crack branching is the high elastic strain energy stored in solids. The algorithm of phase field model is effective to simulate crack initiation，intersection，bifurcation and propagation in three-dimensional space，and can be executed conveniently in commercial FEM software.

A series of undrained tests were conducted with hollow cylinder apparatus for undisturbed saturated soft clay under coupled loading path of principal stress magnitude and principal stress rotation induced by traffic loading. The effects of principal stress rotation on pore pressure，deformation and stress-strain relationship were studied by comparing the results of cyclic triaxial tests and traffic loading path tests. The effects of the generalized shear stress level on the stiffness of stress-strain and non-coaxiality were also investigated. Test results show that compared to cyclic triaxial tests，the pore pressure and strain are significantly larger and the stiffness of stress-strain loops experiences a dramatic reduction under principal stress rotation induced by traffic loading. During cyclic coupling loading，two different cyclic responses，i.e.，the shear stress-strain relation and the normal differential stress-strain relation，were observed. The shear stiffness over stress-strain loops exhibited an anisotropic cyclic degradation and the strain increment vector displayed non-coaxility，which varied in different sections of the loop. In addition，in the lower shear stress level tests，the trajectory of strain paths tends to be stable，accompanied by the stiffness hardening and increase of non-coaxiality. In the higher shear stress level tests，the strain path envelopes tend to fail，accompanied by the stiffness degradation and reduction of non-coaxiality.

The frost heave and thaw subsidence of saline soil induced by freezing and thawing weaks the compressive property of saline soil in northern China. In order to study the effect of freezing-thawing cycles on the compressive properties of solidified saline soil，unconfined compressive tests(UCS) were conducted on the original saline soil，the lime-saline soil and the lime-SH agent-saline soil. The results indicate that the UCS values of the original saline soil，lime-saline soil and lime-SH agent-saline soil decrease as the freezing-thawing cycles increasing. The UCS value of lime-SH agent-saline soil is higher than that of other two types of soils after each freezing-thawing cycle. The lime-saline soil and lime-SH agent-saline soil are strain-softening after each cycle of freezing-thawing. The original saline soil without being frozen-thawed is strain-softening and after cycles of freezing-thawing is strain-hardening. Under the condition of same freeze-thaw cycles，the UCS values decrease with the increase of water contents of lime-SH agent-saline soil，meanwhile，the stress-strain curves tend to be flat gradually and the brittle behavior of specimen reduces. According to the results，the lime-SH agent-saline soil has a marked resistance against freezing-thawing，and the water content is the key factor to affect the compressive property of three soils after freeze-thaw cycles.

The mesoscopic damage development in soft soil was studied based on the triaxial test results measured with the CT in real-time. The relationships among the macroscopic and mesoscopic parameters and damage variable were investigated. The damage variable and its threshold value according to the mesoscopic parameters were determined. The close relationships were found among the average CT number，the shear stress ratio η and the damage evolution. The damage variable and parameters on the basis of average CT number were defined by the meso-parameters. A linear equation between the damage variable and shear stress ratio is presented，and an elastic damage model is established. The results calculated with the presented equation are in good agreement with the experimental data.

The Cam-clay model modified for the K0-consolidated anisotropic clay，which can properly describe the initial stress anisotropy and stress-induced anisotropy of the natural saturated clay，was used to derive a theoretical solution to the cavity expansion due to pile jacking-in. The method of calculating the resistance of pile sinking is presented. To verify the validity of the theoretical solution，a centrifuge test of pile jacking-in was carried out in K0 consolidated clay. The soil stress，pore water pressure and pile-sinking resistance were studied in detail by comparing the measured data with the predicted data. The results show that the proposed mechanical model reflects the pile jacking-in effects properly due to the intrinsic properties of the natural clay being sufficiently considered. The proposed solution provides a theoretical base for pile construction and bearing capacity determination.

In order to study the variation of vertical earth pressure and soil settlement of the open cut tunnel in high filled loess trench under different unloading measures，the unloading effect in different schemes were analyzed and compared through the indoor model test. The results show that increasing the angle of the filling slope，setting the low compacted soil on the top of the open cut tunnel，laying the geogrid and improving the compression modulus of filling on both sides of the open cut tunnel reduce the earth pressure on the top of open cut tunnel. The increase of slope angle has the best effect. The vertical earth pressure on the top of the open cut tunnel is reduced 20.6% in comparison with the one without the slope. The soil arch effect of low compacted soil and the effect of geogrid reduce further the vertical earth pressure on the top of the open cut tunnel. The vertical earth pressure is almost uniformly distributed when the height of earth filling is low. The vertical earth pressure decreases at first and then becomes stable as the increase of the filling height. The setting of low compacted soil resultes in a jump of the vertical earth pressure near the interface of virtual and compacted soil.

The soil elements within a slope or behind a retaining wall are subjected to the initial static shear stress prior to cyclic loading，and there exists an angle between the directions of initial static shear stress and cyclic loading under earthquake or wave loading. In order to investigate the effects of the angle between the directions of the initial static stress and cyclic loading on the softening index of soil，a series of tests were carried out using dynamic simple shear apparatus. The test results indicate that the softening index ? decreases with the increasing of cyclic shear stress ratio rc with a certain angle θ between the directions of cyclic loading and initial static shear stress. The difference of the loading cycles obtained from a certain value of δ corresponding to the two neighboring rc decreases. The softening index increases as the angle grows from 0° to 90°with a certain rc . An opposite evolution of softening index was observed for 90°＜θ≤180°. At the initial stage of cyclic loading，the softening index for θ = 120°，150°，180° is larger than that for θ = 60°，30°，0° when rc = 0.15，respectively. The softening index model and the model of pore pressure ratio versus softening were established through analysis of data regression.