Aiming at the problem of energy change and transmission under the influence of the mining depth in steeply inclined extra-thick coal seam，the physical simulation experiment method and microseismic monitoring equipment were used to analyze the energy distribution and its change characteristics. By cluster analysis of microseismic events，the energy migration path affected by the mining depth is clarified，and the influence law of the mining depth on the elastic energy and the horizontal stress of steeply inclined coal and rock mass is obtained by numerical simulation experiment. The dynamic response characteristics of energy induced by the deep mining are mastered，and the concept and strategy of power disaster prevention and control in steeply inclined extra-thick coal seam are formed. The results show that with the increase of the mining depth of steeply inclined extra-thick coal seam，the peak energy and concentration degree in concentrated areas obviously increase，and the number and proportion of microseismic energy，frequency and large energy events obviously increase. The bent loaded energy storage head of coal and rock is mainly located in the range of the clamping rock pillar in the mining level of fully mechanized top-coal caving face and the two mining stages above it. The energy is mainly conducted along the clamping rock pillar as the dominant path. And in the process of deep mining，the focal center gradually shifts from the middle of the rock pillar to both ends. The peak energy density of steep coal rock mass and the area of high energy accumulation area all increase with the increase of mining depth. When the mining face reaches +400 level，the peak stress increases by about 30.14% compared with +475 level，and the growth rate is about 0.11 MPa/m. With the increase of mining depth，the maximum horizontal stress variation of the single advance of the working face obviously increases，that is，the loading rate of the working face increases under the single advance. Through the comprehensive analysis of simulation experiment and field microseismic measurement，this paper reveals the mechanism of“Target source-predominant conduction path-release terminal”of dynamic disasters in deep mining of steeply inclined extra-thick coal seam，and puts forward the concept of dynamic disaster prevention and control of deep mining in steeply inclined extra-thick coal seam with“Weaken the source-transfer the path-and strengthen the terminal”. The research results provide a scientific basis for the safe mining of steeply inclined extra-thick coal seam.

To comprehensively demonstrate and scientifically prevent natural hazards，decades of studies at home and abroad are summarized，and four patterns of natural disasters are proposed and discussed systematically based on comprehensive induction and abstract analysis. Generally，main causing factors and occurring processes of disasters are considered in the classification of natural disasters such as meteorological disasters，drought and flood，earthquake，geological disasters，marine disasters，etc. With the deepening of recognition and the widening of application，the above descriptions cannot well reflect the characteristics of natural disasters，and it is necessary to consider basic patterns of natural disasters including distribution of space，intensity of destruction and their interrelation. In this paper，natural disasters are divided into isolated pattern，pattern in chain，pattern in group and pattern in wide field，which correspond to the spatial distribution of disasters in point，line，plane and volume respectively. Isolated pattern of disasters means that a natural disaster occurs at a single point，such as snow avalanche，rockfall and lightning stroke. The pattern in chain of disasters means that the natural disasters are composed of a chain action in spatial correlation，time continuity，dynamic conversion and disaster amplification，such as landslide-surging wave-dammed lake-burst flood. Pattern in group of disasters refers to the gathering distribution in group of many disaster events in a region，which is composed of several points or chains of disasters. Pattern in extensive area of disasters refers to appearance of disasters in wide space of three-dimension，which not only occurs in the points，chains and groups of disasters but also appears with many attacks from ground to aerial spaces，such as tornadoes，tsunamis or ash clouds of volcanoes. There are some combinational relationships among the four patterns of natural disasters，in which multi-points of disasters can be a chain，and points and chains can be a group of disasters. Furthermore，points，chains and groups of disasters may occur in a wide region. A class of natural disasters can transform from a pattern，and vice versa. Natural disasters can be classified by triggering factors or causes，and patterns of disasters can be determined from destructive characteristics or consequences. The causes of disasters and their patterns are inter-transformable. Based on the discussion on the causes and patterns of natural disasters，countermeasures are proposed to reduce the disaster risks and to set up more solid basis for theoretical research of disaster mitigation，action of prevention and emergency response.

The interface shear mechanical properties of soil-rock mixture and bedrock are complex，and the meso-morphology of the interface has an important influence on the shear mechanical properties and the deformation characteristics of the shear zone. Based on simple shear test and numerical simulation，the shear mechanical properties，shear zone characteristics and evolution law of the interface between soil-rock mixture and bedrock with different mesoscopic morphology were researched. The results show that the Roughness is the main controlling factor of cohesion. When roughness increases from 8.9 to 11.5，cohesion increases by 95.3%. Roughness has little effect on the interface friction angle，which fluctuates at 27°. The anchor effect can occur in the micro-groove structure at a certain inclination angle，and the soil and stone in the groove form anchor solid，which can increase the shear strength of the interface and control the development of shear band along its outer contour，namely so-called surrounding stone phenomenon. The block rock at the gentle interface has hysteresis effect，and is easy to form false anchor solid with the surrounding soil and stone，which is much less strong than the anchor solid，and controls the bifurcation development of the shear zone around its outer contour and the bedrock interface，resulting in the phenomenon that shear encloses the stone in the shear zone. Based on energy changes，the shear process can be divided into three stages: at the beginning of shear，the strain energy and friction energy increase rapidly，which is the shear densification stage. The proportion of strain energy and friction energy growth rate is approximately 9:1，which is a linear increase stage. At the end of shearing，the strain energy ratio continues to decrease，but still occupies a dominant position，which is the strain hardening stage.

The simulation of the transformation process of rock brittle-ductile property is one of the important contents of the existing statistical damage constitutive model theory. Firstly，based on the triaxial compression test data，the influence law of confining pressure level change on rock stress eigenvalue and its brittleness index is analyzed. In view of the fact that the M-C strength criterion can only predict stress eigenvalue at low confining pressure levels，a new rock strength criterion which can be applied to predict the large range variation of confining pressure level is proposed. Then，combined with the statistical damage theory，a statistical damage evolution model based on strength theory is established. On the basis of the damage model considering the residual strength characteristics，a statistical damage constitutive model of brittle-ductile transformation is established，and the determination methods of parameters are given. Finally，the analysis of marble test data shows that the strength criterion in this paper can well predict the change law of marble stress eigenvalue，and the model can well simulate the transformation process of marble brittle-ductile property. It is revealed that the key factor that the existing statistical damage model cannot simulate the transformation of brittle-ductile property is that it lacks the strength criterion applicable to the condition of large range changes in confining pressure level，and ignores the influence of the deviation degree of the predicted value of stress eigenvalue on the model curve，which widens the applicability range of the existing statistical damage constitutive model theory to the stress level.

Rockfall impact force is an important basis for the design of protection engineering. Therefore，based on the principle of energy conservation and the introduction of proportional coefficient of energy，the calculation method of the maximum impact force of rockfall impacting soil considering the impact angle was established. Through physical model tests，the effects of rockfall mass and size，impact velocity and angle，soil density and compressive strength on the proportional coefficient of energy were explored，and a dimensionless empirical formula for the proportion coefficient of energy was constructed. Furthermore，the calculation model of the rockfall impact force was established and its reliability was verified. The results show that the proportional coefficient of energy is negatively correlated with rockfall mass，impact velocity and impact angle，but positively correlated with rockfall size，soil density and compressive strength. The proposed method based on the proportional coefficient of energy can effectively predict the maximum impact force of rockfall，and is in good agreement with the results of large-scale model tests in literature. The research can provide theoretical basis and technical support for the prevention and control of rockfall disaster.

In order to explore the true triaxial compression under the energy and the damage evolution law of sandstone，with independent research and development of disturbance unloading rock true triaxial test system for a real triaxial unloading test and true triaxial compression test，the evolvement of true triaxial compression stress-strain are studied，and the influence of the principal stress on rock mass is discussed. The elastic energy density of true triaxial compression，dissipation energy density and input energy density are calculated by graphics area，and their variations with the unloading level of the maximum principal stress are analyzed. The damage evolution law of the rock mass during the true triaxial compression process，and the elastic energy index for determining the tendency of impact ground pressure is discussed. The results show that the increase of the maximum principal stress under true triaxial compression makes the internal stress of sandstone adjust，resulting in the change of strain in the direction of medium and small principal stress. This phenomenon is defined as“induced increase”of energy from the perspective of energy. The types of principal stress loading and unloading in three directions were divided into damage loading(maximum principal stress loading) and protection loading(medium and small principal stress loading). Unloading is divided into conventional unloading(maximum principal stress unloading) and damage unloading(medium and small principal stress unloading). Under true triaxial compression，the confining stress in the middle principal stress direction is larger，making the proportion of induced elastic energy density in this direction higher than that in the direction of minimum principal stress. The stress of maximum principal stress direction increases under true triaxial compression，and there is a linear function relationship between the elastic energy density，dissipated energy density and input energy density of sandstone. The energy analysis method of true triaxial compression is proposed，and the energy storage limit of sandstone is further obtained. Compared with uniaxial compression，its energy storage capacity is greatly improved. The damage variable of sandstone under true triaxial compression changes approximately linearly before the plastic stage，and presents a nonlinear evolution trend with the increase of maximum principal stress.

Engineering rock mass in cold regions is subjected to the combined effect of stress and freeze-thaw cycle. Under the long-term coupling action of stress and freeze-thaw，the mechanical properties of rock will be significantly weakened，which may result in engineering rock mass disasters. To investigate the deformation and damage characteristics in macro and micro view of sandstone under stress and freeze-thaw coupling，the freeze-thaw cycle test was carried out firstly on sandstone samples. The change in frost heaving deformation of sandstone during freeze-thaw cycle without stress was studied. Then，a numerical method for rock freeze-thaw cycle simulation based on particle flow and particle expansion was proposed. The method was used to carry out numerical simulations of rock freeze-thaw cycle under axial stress. The evolution of deformation and fracture in the process of freeze-thaw under axial stress is studied. Results show that without the action of axial stress，the axial and radial strains of sandstone first increase and then remain unchanged as the number of freeze-thaw cycles increases. There is a significant difference between axial strain and radial strain of sandstone samples during freeze-thaw cycle. The radial strain of sandstone samples is greater than the axial strain. The difference between axial strain and radial strain of sandstone samples first increases and then decreases with the increase of the number of freeze-thaw cycles. When the axial stress is greater than zero，the axial strain decreases with the increase of the number of freeze-thaw cycles，and the radial strain increases with the increase of the number of freeze-thaw cycles. Under the action of frost heaving force，the crack density near the sample surface is greater than that inside the sample. During the freeze-thaw cycle，the axial stress will inhibit the crack initiation and propagation along the direction with a large angle with the specimen axis. During the freeze-thaw cycle，the cracks formed inside the sample are mainly tensile crack. The numerical simulation method based on particle flow and particle expansion can better simulate the freeze-thaw deformation and fracture evolution of sandstone in the process of freeze-thaw cycle.

Aiming at the characteristics of rich cultural information，prominent deformation and high sensitivity to disturbance for grotto roof，the micro-sized flexible anchors with little disturbance and high concealment can meet the strong tensile resistance to flexible deformation and plastic state of anchorage system. In order to reveal the effectiveness and scientificity of micro-sized anchorage technology used in rock mass of flat roof of sandstone grottoes，as well as to evaluate the anchorage performance of different series of anchors under various operating conditions，GFRP and NPR anchors with a diameter of 8 mm were selected and implanted with different apertures，the strain gauge was laid at the rod body-paste interface，and then the field pull-out test was conducted in cyclic loading mode. The results show that micro-diameter GFRP and NPR anchors have good anchoring performance and interface deformation coordination，and GFRP anchors have better ductility and shear resistance. What?s more，the anchoring effect performs best when the ratio of the diameter of the anchor span to that of the anchor rod reaches 2–2.25 times. The research provides a basis and reference for the application of micro-sized flexible anchors in the reinforcement engineering of rock mass of sandstone grottoes roof.

The deformation and failure of fissured rock are the results of the initiation，growth and coalescence of cracks into macroscopic cracks. To simulate the complicated fracture failure process of fractured rock，a new phase-field model is proposed based on the conventional phase-field fracture model by means of decompositions of the strain energy density into tensile，tensile-shear and compressive-shear parts. According to the Mohr-Coulomb criterion，the shear stress and compression-shear strain energy are individually defined. The coupling governing equations of the displacement field and phase field are derived. And the finite element method(FEM) is used for spatial discretization and the staggered algorithm is used for the numerical solution of the phase-field theory. The accuracy of the phase-field finite element program is verified by comparing the simulation results and the analytical solution of benchmark example. Then，model parameters are determined based on test data of yellow sandstone. The program is used to simulate the uniaxial compression tests of the rock containing a single fissure( = 30°) and rock containing double fissures( = 30°， =30° and =30°， = 60°). And the growth and propagation modes of tensile，shear and mixed cracks produced by the fissured rock are replicated，which is well consistent with the test results. Therefore，the improved phase-field model can simulate the crack initiation and crack propagation of fissured rock.

The existence of the non-stationary trend of rock joint(the angle between the rock joint and the shear plane) directly affects the accuracy of the shear strength evaluation of the rock joint specimen. The existing shear strength calculation models do not consider the influence of the non-stationary trend of rock joint and are not suitable for the calculation of the shear strength of the rock joint with non-stationary trend. To do this，this paper quantitatively characterizes the trend directions and of the rock joint( and representing the inclination angle of the rock joint along the shearing direction and the deflection angle of the rock joint perpendicular to the shearing direction). The least square fitting plane of the rock joint is taken as the reference plane，the external normal and tangential stresses are decomposed into the normal and tangential stresses of the reference plane，a shear strength model of the rock joint considering the influence of non-stationary trend is established based on this. The numerical solution of the model is calculated by numerical analysis method，and the accuracy of the numerical solution is verified by direct shear test. The research results show that the shear strength of rock joint is mainly controlled by the trend ，while the influence of the trend on the shear strength is less than 1.5%，which can be ignored in the calculation；The upper and lower error limits between the improved value of shear strength and its prototype value increase with the increase of the normal stress and the three-dimensional roughness JRC3D of the rock joint；Compared with the shear strength model without considering the influence of non-stationary trend，the accuracy of the shear strength calculated by the improved model is increased by 24.45%，23.693%，25.37% and 14.504% respectively，the proposed shear strength model can effectively evaluate the shear strength of the rock joint specimen with non-stationary trend，which lays a theoretical foundation for the evaluation of shear strength of rock joint.

The mesoscopic heterogeneity of sandstone works as the fundamental cause of its stress-strain curve and variances in failure characteristics. In this paper，to investigate the macroscopic and mesoscopic failure characteristics of heterogenous sandstone，diffraction of x-rays(XRD) was employed for the precise characterization of mineral components and contents of sandstone，fish language was utilized to establish the UDEC-Tri heterogeneous normal distribution model of minerals and joint mechanical parameters. Indicators to identify damage of heterogenous rock samples were proposed，and the influence rules of heterogeneity in modulus of elasticity，spatial distribution of mineral particles and joint cohesion of minerals on the macroscopic failure and mesoscopic damage of rock samples were studied. The results show that with the increase of heterogeneous level( )，the nonlinear characteristics of stress-strain curves of rock samples are enhanced，the tangent modulus and compressive strength decreasing linearly，and macroscopic failure changes from the mode of shear failure to splitting failure. The increased value results in a non-synchronized yield of adjacent mineral particles，a higher proportion of tension crack，and decreased crack initiation stress and damage stress of rock samples；when embodying the identical value，the variance distribution in minerals of rock samples leads to the presence of “weak contact surfaces”，as measured by mechanic parameters，between adjacent particles，which shows good consistency with the extension path of macroscopic crack and serves as the basic cause of the discreteness of crack characteristics in low-strength rock samples. Compared with the mineral ，joint heterogeneity( )embodies a more conspicuous weakening effect on the mechanical properties of sandstone. As increases，the length of tension crack grows to more than that of shear crack，with an enlarged proportion of small-scale crack；and with the increase of joint cohesion ，the failure mode of rock changes from “shear failure on single slopes” to “X-shaped shear failure on conjugated slopes”. In general，the research findings explain the mechanism of variances in failure characteristics of sandstone samples collected of the identical origin and the same size，as references for building the mapping relation between heterogeneity and sample strength，and between heterogeneity and failure characteristics.

Abstract：The anisotropy of rock gradually weakens or even disappears with increasing the confining pressure. However，the critical condition for the transformation from anisotropic to isotropy is still lack of in-depth research. Taking foliated rocks as the object，the fabric characteristics of this kind of typical anisotropic rock were summarized and the empirical criterion for shear-slip failure along the weak plane of rock was constructed. Combined with the previous failure criterion created based on the concept of critical state and Mohr-Coulomb criterion，the critical confining pressure at the point where the anisotropy of foliated rock is transformed into isotropy was predicted theoretically. Then，the prediction result was verified by statistical analysis on previous experimental data. The results are as follows. Foliated rocks contain representative phyllosilicates，which constitute directional weak layers and are distributed in a quasi interbedded manner with the hard layers composed of granular minerals. Under a certain loading direction，foliated rocks suffer shear-slip failure along the weak plane. The empirical friction coefficients of rocks in this failure mode are 0.40 and 0.25 under the conditions of medium-low and high confining pressure respectively. The transformation confining pressure is dependent on the uniaxial compressive strength and internal friction angle of foliated rocks subjected to compressive loading perpendicular to weak planes. The transformation confining pressure of foliated rocks is generally greater than 1.5 and increases with the increase of and . For the foliated rocks with a high content of phyllosilicates，the transformation confining pressure coefficient is often between 1.9 and 3.6.

The dynamic response characteristic of rockfall impact cushion is the key basis of rock-shed design. As an important feature of cushion particle size distribution，gradation determines the distribution of particle size and affects the dynamic process of rockfall impact cushion. To study the influence of particle gradation on the dynamic response of rockfall impact cushion，the numerical simulation of the dynamic response of cushion with different gradations is carried out by using a discrete element-finite difference coupling algorithm. Under the condition that the average particle size is equal，through the analysis of impact force，central compressive stress，and impact depth of falling rock，the dynamic response mechanism of rockfall impact particle cushion is revealed. The results show that： the stability of the force chain between particles determines the dynamic response characteristics of the cushion after impact. The friction between particles is the main way of energy consumption，accounting for 70%–80% of the energy consumption. For single-peak grading，the smaller the particle size of the single peak is，the longer the force chain length is，and the weaker the stability is. When the peak particle size = 75 mm，the peak impact force is 1.9 times that of = 25 mm，and the peak compressive stress is 3.6 times. For bimodal gradation，the closer the distance between the two peaks is，the less the number of constraints around the particles is，and the worse the stability of the force chain is. When the heterogeneity coefficient = 0.65，the peak impact force is 40% larger than that when = 0.33，and the peak compressive stress is 30% larger. The uniformity of particle distribution determines the response characteristics of the cushion after impact.

Shear acoustic emission monitoring tests of granite were carried out，and S- and P-waves sensors were used to receive acoustic emission signals. The variation rules，and similarities and differences of S- and P-waves signals of acoustic emission are analyzed，and the difference between the two kinds of signals is discussed. The research results show that the variation trend of acoustic emission S-wave and P-wave event rates is inconsistent in the process of shear failure. The P-wave event rate decreases after reaching the maximum value in the elastic stage，there is a“quiet period”before the peak stress，and the cumulative count changes in an“S”shape. The S-wave event rate reaches its maximum value near the peak stress，and the cumulative count changes exponentially. The energy variation trend of S-wave and P-wave is consistent in shear failure process. During the failure process，the energy increases continuously，and the energy rate near the peak stress reaches the maximum value. The cumulative energy increases sharply. The frequency evolution and distribution of acoustic emission S-wave and P-wave signals are obviously different. The main frequency of the P-wave is at six fixed frequencies and approximately evolves in bands. S-wave frequency components are complex and the evolution of main frequency bands is not obvious. The dominant frequency of P-wave is concentrated in the range of 90–110 kHz，while that of S-wave is discrete in the range of 0–500 kHz. Due to the different types of S-wave and P-wave sensors，the response mechanism of different acoustic emission signals with different frequencies of rock failure process is different，which is the reason for the inconsistent variation trend of the number of acoustic emission events between the two sensors. The energy variation trend of S-wave and P-wave acoustic emission events is consistent，which may be related to the low-frequency characteristics of both high-energy signals. The research results further enrich and improve the understanding of acoustic emission signal characteristics of rock fracture process，which is helpful to reveal the mechanism of rock fracture catastrophes.

To solve the problem of querying the internal property information and spatial mechanics analysis of 3D geological model，a 3D complex geological modeling method based on generalized trigonal-tetrahedral voxel is proposed. The method is formulated as follows：firstly，the strata of the study area are divided according to the borehole data and profiles，combined with the geological evolution history of the strata and the theory of horizontal set theory，and then the Kriging interpolation method is used to introduce virtual boreholes into the borehole point cloud data. After that the irregular triangular network algorithm is applied to construct the stratigraphic model，and finally the 3D complex geological body model in the study area is established by the generalized trigonal-tetrahedral voxel algorithm. In addition，the local area property information extraction and encryption algorithm are preset in the strata-level construction algorithm to ensure the accuracy of computation and analysis when the model is applied later. This method enables the expression of special geological phenomena such as stratum unconformity，cusp extinction and lenticular body，as well as the extraction of internal attribute information of geological bodies and the construction of local refinement models，which provides a computational model that can be visualized simultaneously for subsequent engineering stability analysis. Taking the Hong?ao muck field in Guangming New District of Shenzhen as an example，a true 3D geological model was constructed by combining the borehole data and profile data of the muck field，which realized the spatial query and analysis of the internal property information of the spoil site and laid the foundation for the stability analysis of the muck field.

The landslide factors used in the existing landslide susceptibility evaluation methods are mostly static data(eg. topography，geology) and lack of dynamic data(eg. surface deformation)，which cannot fully extract the characteristics of deformation landslides，resulting in poor reliability of landslide susceptibility evaluation. Synthetic aperture radar interferometry(InSAR) data can reflect the deformation characteristics of landslides in both vertical and horizontal directions. In this study，two-dimensional InSAR deformation data are introduced as dynamic factors，topography，geology，hydrology and humanities are combined，and a convolutional neural network(CNN) model is constructed for dynamic evaluation of landslide susceptibility. Multiple evaluation metrics are used to evaluate the model accuracy，while landslide susceptibility evaluation results with and without taking into two-dimensional InSAR factors are compared. The proposed method is compared with support vector machines(SVM) method，in addition，the proposed method is applied in different cases. The results show that the overall accuracy of multiple evaluation indexes considering InSAR deformation dynamic factors has been improved，and the model has shown good results in identifying landslide susceptibility areas that are in slow deformation，and the recognition rate has been improved from 0.78 to 0.93 in the training data. In the validation data，the recognition rate is improved by 0.21，revealing that considering the 2D InSAR deformation factors can improve the accuracy of dynamic evaluation of landslide susceptibility. The CNN model constructed in this study has more reliable evaluation results compared with SVM method，and is more applicable and generalizable in different cases. The high susceptibility areas in the Liujiaxia Reservoir are mainly located in the northeast of Yangta Township，Hongquan Township and Sanluo Township of the mountainous areas，real-time monitoring should be strengthened. The dynamic evaluation model of landslide susceptibility using CNN considering 2D InSAR deformation factors proposed can provide the new ideas for landslide disaster prevention.

As one of the common forms of foundations for the wind turbine，monopile is often subjected to cyclic lateral loading，which can lead to changes in the dynamic response of the pile-soil system. In order to investigate the internal force variation and the cumulative deformation characteristics of the monopile，a series of model tests were carried out by varying two parameters：the relative density and the particle size of the soil. And the movement law of the soil around the pile under cyclic loading was analysed by the PIV technique and fractal theory. The test results showed that：(1) The influence of cyclic loading on the bending moment of the pile was relatively significant. With the increase of the number of cycles，the magnitude of the bending moment reduced，and the amplitude rose with the increase of the relative density of the soil. In addition，the smaller the particle size of the soil around the pile，the larger the bending moment. (2) The monopile rotated rigidly around a point. The amount of cumulative deformation of the pile decreased with the increase in the relative density. The interfacial friction angle of the sand-steel contact surface was affected by the particle size of the soil. The larger the particle size，the smaller the interfacial friction angle and the larger the lateral cumulative displacement of the pile. (3) The displacement range of the surface soil decreased with the increase in the relative density of the soil，and the particle size had less influence on the displacement field. As the loading progressed，the displacement range of the soil behind the pile increased，while the displacement range of the soil in front of the pile decreased，and convective movement occurred in part of the soil along the loading direction. (4) The displacement field of the soil around the pile exhibited fractal characteristics，and the fractal dimension value decreased with the increase in the relative density of the soil，varying between 1.18 and 1.42. The fractal dimension showed a positive linear relationship with the area of the soil displacement field and an exponential function with the number of cycles. Four sets of fitting formulas were proposed，and the results fit well with the existing data. The results of this research can provide an experimental basis for exploring the stability evaluation of the pile-soil system under lateral cyclic loading.

Hydraulic impermeability and homogeneity should be ensured before the newly built cutoff walls put into operation. The difficulties of the rapid evaluation of the cutoff walls lie in the high-quality sampling and time-consuming laboratory testing. In this study，piezocone penetration test(CPTU) is used to evaluate the barrier performance of a newly built cutoff wall. Based on the correlation analysis between excess pore water pressure and horizontal permeability coefficient，the random field theory is used for modeling，and the model parameters are defined to quantitatively describe the impermeability defects. Bayesian approach combined with particle swarm optimization is used to solve the model parameters，which realizes the rapid identification of impermeable defect layers and quantitative characterization. Comparing with the stratification results of traditional Robertson soil behavior type(SBT) method，the inapplicability of SBT method in evaluating the goodness of cutoff wall is pointed out. Finally，combined with the CPTU pore pressure dissipation test results，the continuous horizontal permeability coefficient profile of the cutoff wall is evaluated. Results show that the proposed CPTU in-situ evaluating method based on the excess pore water pressure can identify the impermeable defect layers and quantitively reflect its causes. The analysis results can be used as guiding information for making remediation plans.

Sand grains are under three-dimensional stress condition in natural state. Particle shape varies due to complex physical and sedimentation process，further affecting the contact mode under loading. The macroscopic mechanical properties of sand are influenced by microscopic particle shape. This study carries out true triaxial tests on mixture of silica sand and round(crushed) glass beads，examines the effect of particle shape on the mechanical properties of sand under three-dimensional stress condition. In combination of dynamic particle image analysis technique to quantitatively analyze the particle shape，the varying tendency of particle shape parameters with glass beads content is acquired. The coupled effect mechanisms between the intermediate principal stress and particle shape on the macroscopic mechanical response are investigated. The test results show that the glass beads-silica sand mixture with regular particle shape effectively suppresses the dilation characteristics of the mixture. For a given medium principal stress level，the peak friction angle of the glass beads-silica sand mixture increases with increasing particle shape irregularity，and the large principal strain corresponding to the peak strength decreases with increasing particle shape irregularity. In this experimental study，the varying tendency in peak strength of glass beads-silica sand mixture accompanied by the variation in the intermediate principal stress can be well predicted by the classical failure criterion.

The characteristics of dynamic strain，earth pressure and cumulative displacement of pile-soil system under multi-train operation mode were tested by laboratory model test of railway screw pile composite foundation under simulated train loads. The time-frequency characteristics of dynamic response of the screw pile-soil system under train load were analyzed，and the correlation of pile-soil deformation under different speeds was further discussed. Based on the linear fitting method，the empirical relationship between the pile-soil dynamic stress ratio and the train speed was established. Combined with the pile-soil load sharing relationship，the pile dynamic axial force and the pile side dynamic friction，the interaction relationship and loads transfer mechanism of screw pile-soil under train dynamic loads are revealed. The results show that：(1) under the train dynamic load，the deformation degree of a screw pile is greater than that of straight rod，especially at variable section. (2) Under the conditions of general speed，fast speed and high speed，the dominant frequencies are concentrated in 2–6 Hz，8–11 Hz and 14–16 Hz respectively. With the increase of train speed，the dominant frequency tends to the natural vibration frequency of the train，and the frequency band width decreases. (3) The dynamic characteristics of screw pile composite foundation are highly correlated with the speed of train operation. (4) Under the reinforcement of screw pile composite foundation，the critical velocity of railway foundation is about 280 km/h，which is 29.62% higher than that of ordinary pile foundation. (5) The faster the train speed is，the greater the effect of soil load on pile-soil composite foundation，while the less the effect of pile load on pile-soil composite foundation，resulting in the decrease of pile-soil synergistic effect. The research results have certain reference significance for the design optimization of railway screw pile composite foundation and the planning of train operation speed.