In this paper，the size effect of basalt samples and green sandstone samples in a small size range of 20–50 mm in diameter was studied. The compositions of mineral particles inside the samples were observed by a high-precision 3D profilometer，and  the size，shape and distribution of the pores inside the samples were obtained by a CT scanner. The influence of the sample size on the uniaxial compressive strength，the elastic modulus and the failure mode was analyzed. It is found that，within the small size range，the size，shape and distribution of the pores in different rock samples have an influence on the size effect. The size effect curves of green sandstone and basalt samples conform to exponential and logarithmic distributions respectively. Combining the existing conclusions on larger size rock samples，it is pointed out that the segmental fitting method can better reflect the size effect of rocks. It is also shown that，with increasing the sample diameter，the modulus of elasticity of the samples tends to gradually increase and the overall failure mode of the samples changes from splitting failure to monoclinic shear failure and then to X-shaped conjugate oblique shear failure.

Seismic source location plays a key role in microseismic/acoustic emission data processing. The accuracy and timeliness are important for the analysis of rock fracture mechanism as well as rockmass dynamic disaster prediction and early warning. Based on a large number of study cases and literatures related to geotechnical engineering microseismic/acoustic emission monitoring source location，the domestic and foreign studies related to the practices and theories of microseismic/acoustic emission monitoring are summarized. Starting from the principle of seismic source location，the main research directions of influencing factors and related issues of seismic source location accuracy are discussed. The source location problem is considered to be a complex nonlinear inversion process interfered by multiple factors，and its location accuracy is affected by the following factors：seismic waveform denoising and first arrival time picking，the precision of the velocity model，the accuracy of the travel time algorithm with respect of the velocity model，the inversion performance of the seismic source location method，and the instrument performance and the design of the monitoring system. Based on the requirements of the massive data processing in microseismic/acoustic emission monitoring technology，the future applications and development directions of intelligent methods such as deep learning for improving source location accuracy are proposed.

In order to study the evolution of the permeability characteristics of oil shale under in-situ exploitation，permeability tests on the oil shale from Fushun west open pit mine were performed by high temperature triaxial permeability testing machine，and the pore microstructure of the oil shale was characterized by the mercury injection apparatus. The evolution mechanism of the permeability was discussed. The results show that the porosity and the permeability of the oil shale have a good correlation with each other. With increasing the temperature，the oil shale specimens evolve from the dense state to the porous medium，and both the porosity and the permeability increase. The pore pressure fluid has multiple physical effects on the variation of the pore structure，especially at the stage of oil and gas production due to pyrolysis of the organic matter. The pore characteristic parameters of the oil shale after high temperature permeability tests are significantly improved compared with those heated in muffle furnace. The porosities of the oil shale samples at the temperature of 300 ℃，400 ℃，500 ℃ and 600 ℃ increase by 0.6%，8.62%，1.82% and 7.83%，respectively. At 600 ℃，the macropore and mesopore volumes increase by about 1.3 and 2.4 times，respectively. Before 300 ℃，the permeability of the oil shale samples is mainly affected by the thermal stress caused by uneven thermal expansion of mineral particles and water precipitation. At 300 ℃﹣400 ℃，the complex reaction inside the oil shale occurs and many impermeable pores form，resulting in an uncoordinated change between the porosity and the permeability. 400 ℃﹣600 ℃ is the main pyrolysis stage of the oil shale. In this stage，the pyrolysis pores in the oil shale are continuously generated and connected，forming the flow channel of oil and gas products and increasing the porosity by 25.77%，and the permeability increases by about 9.06 times when the pore pressure is 1.0 MPa.

The structural response of underwater shield tunnels during operation is the basis of structural safety evaluation and abnormality early warning. The structural health monitoring(SHM) system is already a key technology for structural response monitoring and safety evaluation. The segment strains and joint openings of typical sections of the Wuhan Yangtze River tunnel during operation period (2013.09–2020.06) are obtained by the SHM system. Both a multiple linear regression model and a distributed lag model are established and their applicability in structural abnormality warning is evaluated. Effects of three factors，including the environmental temperature，the water level of Yangtze River and the time (considered irreversible structure change)，on segment strain，longitudinal joint opening and circumferential joint opening are studied by the distributed lag model. Study results show that the distributions of both the segment strain increment and the joint opening increment do not obey the normal distribution but have a fat-tail than the normal distribution，and hence，the normal values should not be eliminated as outliers in the analysis. The regression and prediction accuracies of the distributed lag model are better than those of the multiple linear regression model，and the distributed lag model is more sensitive to structural abnormalities when used for early warning. As environmental temperature decreases，the joint opening increases and the increment of the circumferential joint is much larger than that of the longitudinal joint，explaining the phenomenon that the water seepage of segment joints is more serious in winter than in summer and the water seepage of the circumferential joints is more serious than that of the longitudinal joints.

In order to explore the regular relationship between the imminent stress change of seismogenic faults and their instability process，this paper conducts a study on the phenomenon and mechanism of the stress drop of cross-scale rock mass samples before earthquakes. Through calculation，analysis and re-interpretation of typical seismic experimental data and field stress monitoring data，the pre-earthquake stress and strain changes of different scales are studied. The results show that the experimental data from rock blocks，boreholes to crustal scales all reveal that there is a sudden decrease in the stress(stress drop) before the fault fails. The pre-earthquake stress drop phenomenon spans 3 to 6 orders of magnitude in space，and the early response time of the stress drop covers 1 to 6 orders of magnitude，indicating that the larger the scale and quality of the media involved in the earthquake，the longer the precursor response time. Field borehole stress monitoring data show that there is a linear positive correlation between the stress drop and the early response time with natural earthquakes. The inherent plastic properties of the seismogenic fault rock mass make the overall collapse of the fault later than its mechanical imbalance. In addition，the fault slip needs to overcome the irregular asperities on its surface，and the differential stress-strain loading rate of the process leads to different stress-strain reply on the time scale. This research explains may be the underlying mechanism that stress drop can precede earthquakes.

Taking granite in Beishan of Gansu province as the research object，triaxial cyclic loading and unloading tests were carried out. The evolution characteristics of energy dissipation，friction energy dissipation and breakage energy dissipation of rock under cyclic loading and unloading were explored，and a rock damage variable based on breakage energy dissipation was proposed. The results show that，based on the characteristics of the energy dissipation ratio curve and the stress-strain curve，the cyclic loading and unloading process can be divided into five stages such as the compaction and elastic stage，the stable crack development stage，the unstable crack development stage，the post-peak unstable fracture stage and the residual strength stage. Correspondingly，the energy dissipation ratio shows a “spoon” shape evolution of slight decline，stable development，slow increase，significant increase and a stable trend. Meanwhile，the friction energy dissipation ratio decreases slightly in the compaction and elastic stage，remains at a low level in the stable crack development stage and the unstable crack development stage，increases significantly in the post-peak unstable fracture stage and stabilizes in the residual strength stage. Furthermore，the breakage energy dissipation ratio increases slightly before the peak， increases abruptly at the initial part of the post-peak unstable fracture stage and then rapidly declines，and finally stabilizes at a lower level. The damage variable defined in terms of breakage energy dissipation can reasonably describe the damage evolution of granite under cyclic loading and unloading.

The presence of rock joints significantly affects not only the propagation of stress waves but also the safety of underground engineering. The purpose of this study is to non-destructively observe the stress concentration around the joints and the characteristics of stress wave propagation. The test on specimens consisting of two contacted polycarbonate plates with an artificial joint was carried out using a modified Split Hopkinson Pressure Bar(SHPB) and a photoelastic equipment. In order to reduce the wave impedance of loading bars，the input and output bars of SHPB equipment were made of polycarbonate materials. The dynamic photoelastic experiment figures and propagation characteristics of the stress wave were studied according to the theory of viscoelastic wave propagation and the concept of energy flow density. Then，the relationship between the energy flow density of the transmission wave and the stress concentration near the joints with different contact area ratios and joint distribution forms was analyzed. The test results show that with decreasing the contact area ratio，the stress wave transmission coefficient decreases while the energy flow density of the transmission wave as well as the stress concentration near the joints increases. When the contact area ratio remains constant，the more dispersed the joints，the greater the stress wave transmission coefficient. In this case，the energy flow density of the transmitted wave increases while the stress concentration near the joints attenuates. Under a dynamic load，the stress concentration phenomenon appears near the joints，and the energy flow density of the transmission wave is closely related to the stress concentration near the joints.

In order to study the mechanical properties of sandstone in ultra-deep reservoirs and their difference from those of sandstone in shallow reservoirs，research of deformation and failure mechanism of sandstone under ultra-deep in-situ conditions was conducted to obtain influence rules of the burial depth on the mechanical parameters of sandstone. Laboratory rock mechanical experiments including uniaxial compression，triaxial compression，Brazil and shear tests were conducted，and variation laws of uniaxial and triaxial compressive strengths，tensile strength，shear strength，internal friction angle，cohesion，elastic modulus，Poisson¢s ratio，brittleness index，fracture amount and failure modes with depth were systematically analyzed. Effects of formation temperature on sandstone strengths and mechanical behaviors were also studied. The results show that there are significant differences of mechanical strength，anti-deformation failure and failure mode between ultra-deep and shallow sandstones. Ultra-deep sandstones have higher strength and lower brittleness index and hence，are notably difficult in shear compression failure. Increasing of the confining pressure strengthen major rock mechanical parameters of sandstone. With increasing the temperature，the strength and the brittleness index decrease while the ductility rises. The confining pressure，temperature，physical properties and diagenesis are critical factors affecting the mechanical properties of ultra-deep sandstone.

The interlayer shear weakness zone(ISWZ) is a typical weak structural plane which controls the safety and stability of the dam foundation and underground caverns in Baihetan Hydropower Station. It is very important for the long-term stability of engineering surrounding rock mass to study the time-dependent mechanical effects. However，from the existing research results，there is little research on the creep characteristics of ISWZs in Baihetan. In this paper，the creep characteristics of undisturbed ISWZs¢ specimens in the Baihetan engineering area are studied through direct shear creep tests. The experimental results show that the undisturbed specimens of ISWZs present typical creep characteristics. The long-term shear strength of the ISWZs under various normal stresses is determined by isochronous curve cluster method. Finally，based on the element method and the yield surface creep model，a non-stationary viscoelastic-plastic creep model which can describe the instantaneous elasticity，stable creep and accelerated creep characteristics of ISWZs is established. The fitting results show that this creep model can well reflect the creep characteristics of ISWZs. The research results can provide a reference for further revealing the time-dependent law of ISWZs.

The 1933 Dexi Mw 7.5 earthquake triggered numerous rock slides within Songpinggou meizoseismal area. To systematically describe the topographic and geological controls on these landslides，208 landslides including 48 large landslides(≥0.1 km2) are recorded by remote sensing，LiDAR，unmanned aerial vehicle(UAV) and field investigations. A series of indicators containing landslide type，frequency and ratio of frequency，area and ratio of area，non-weighted landslide kernel density and area-weighted landslide kernel density are selected to analyze the topographic(slope aspect，elevation，local relief and slope gradient) and geological(slope structure and lithological combination) characteristics of the landslide location. Results show that landslides are concentrated in the terrain with slope gradient of 50°–60°，local relief exceeding 370 m and elevation of 2 000–3 000 m. Notable differences of slope structure exist between left bank(reverse slope：3%) and right bank (reverse slope：41%) in the river valley(Waerbao-Jiaochang section). The proportion of landslides in the left bank is 85%，higher than 15% in the right bank. In the left bank，the proportion of planar and wedge landslides reaches 81% and no topple-type landslides are found，while the proportion of topple-type landslides in the right bank arrives at 38%. Rockfalls and debris slides have the same proportion in the left and right banks，9% and 12% respectively. More than 60% of plane and wedge landslides mainly occur in thick-megathick layered sandstone interlayered with thin layered phyllite such as Zagunao Formation，Zhuwo Formation and C+P (Carboniferous - Permian strata)，while more than 70% of rockfalls and debris slides are mainly distributed in Xinduqiao Formation and Bocigou Formation with geological characteristics of thin slate interlayered phyllite. The largest landslide area in thick-layer lithology is 7.89 km2，and the average area value of this lithological combination is 7 times more than the thin-layer type. It is pointed out that the slope structure and the lithological combination have mainly influences on landslide frequency，type and size. The topography of Songpinggou valley formed by rapid crustal uplift and river erosion，with significant elevation difference，high local relief and steep gradient，provides favorable topographic conditions for landslide distribution extent and concentration. The findings provide a basis for landslide identification and prediction from topographic and geological conditions.

For revealing the microscopic influence mechanisms of pore distribution on gas diffusion， a mass transfer model for multiscale porous media was established considering coal gas state and diffusion form diversity. Based on pore size distribution determinations，the roulette algorithm was used to generate random numbers in accordance with pore spatial distribution probability，and then a pore spatial structure model was inversed  approximately through the interpolation of these numbers. On the basis of the geometric model，numerical software Comsol was utilized to solve the equations of the new diffusion model，and the results were compared with the gas desorption experimental results of coal particles. Results show that the diffusivity of the coal is worse and the tortuosity of coal is much larger than other porous materials, and that the simulation and experimental results are approximately consistent with each other while the index in the exponential relationship between the tortuosity and the porosity reaching about 5.5. With various pore sizes，Knudsen coefficient and the diffusion coefficient are different in coal. The diffusion coefficient of coal particles calculated through the analytical solution of the uni-pore model has the same order of magnitude with the internal diffusion coefficient obtained through the model，about 10－9 cm2/s，but they have different variation trends as gas desorption.

In order to study the impact stress distribution law of ground reinforced embankments under falling rock impact，the model tests of ground reinforced embankments and pile-plate retaining walls under the impact of a rock block were designed. The comparison tests reveal the change law of the peak impact stress of ground reinforced embankments under the impact of rockfall. The test results show that the impact stress distributions of the ground reinforced embankment and the pile-plate retaining wall change in stages，while the impact force of ground reinforced embankment when cracks appear is about twice that of the pile-plate retaining wall. Compared with the obvious stress concentration near the impact point of the pile-plate retaining wall，the stress distribution of the ground reinforced embankment is uniform，the deformation of the wall is small，and the stress dissipation rate is about 50% smaller. Combined with the modified Hertz contact impact force calculation formula and Boussinesq equation，an internal impact stress calculation method of ground reinforced embankments is obtained. Through experimental and theoretical comparisons，it is found that the stress distribution and the impact resistance of the ground reinforced embankment under rockfall impact are better than those of the pile-plate retaining wall. The research results can provide theoretical basis for the performance research and engineering application of reinforced soil structures under impact loads.

In order to study distribution rules and formational reasons of loads on composite linings in deep-buried tunnels，firstly，the contact loads between the surrounding rock and the primary support as well as between the primary support and the secondary lining，monitored in 52 tunnels，were counted，and the load distribution range of each monitoring point and the load sharing ratio of the secondary lining were analyzed. Secondly，by equating BQ to GSI，a theoretical method for calculating the support load was developed based on the Hoek-Brown strength criterion. Finally，the theoretical method was compared with the monitoring data to verify its feasibility，and the important factors affecting the support load and the main load-bearing structure were analyzed. The analysis results show that there is a certain difference in the tunnel support loads for different surrounding rock grades，and that the lower the surrounding rock grade，the greater load sharing ratio of the secondary lining will be. The corresponding intervals of the GSI for classes I，II，III，IV，and V of the surrounding rock are 100–78，77–62，61–48，47–36 and 35–10，respectively. The theoretical calculation is more suitable for the burial depth greater than 100 m，and for the burial depth less than 100 m，some of soft surrounding rock section loads are reflected as loose loads. The load sharing ratio of the secondary lining of classes III，IV and V surrounding rock ranges from 17.43% to 37.96%，from 27.42% to 51.89% and from 37.52% to 66.6%，respectively. The installation time of the secondary lining，the support thickness and the surrounding rock conditions have great influence on the support loads，and the combination of these factors can change the main load-bearing structure. The research results provide some reference for the design of deep-buried tunnel support in mountains.

In order to explore the probabilistic distribution model of non-deterministic parameters of soils and its effect on random vibration of the site，the dispersion image of the site soil is obtained by multi-channel analysis of surface wave(MASW)testing combined with frequency-wavenumber method，and a prior probability model of the shear modulus of the soil varying with depth is established. Based on Bayesian theory and Monte Carlo Markov Chain-Metropolis-Hastings algorithm，a posterior probability model of non-deterministic parameters of the soil is achieved and its convergence and independence are validated respectively. Finally，a new method for predicting the vibration transfer function by means of the confidence interval with certain confidence level is proposed，in which the validated posterior probability model is combined with the kernel density estimation of the random response of the ground vibration. The proposed non-deterministic prediction method is also compared with the experiment results and the traditional deterministic vibration prediction methods. The results show that the posterior shear modulus has obvious randomness in spatial depth，and the non-deterministic shear modulus distribution has a greater impact on the prediction and evaluation of environmental vibration. The vibration interval estimation obtained from the probability model of the non-deterministic parameters of soils has great engineering application value.

Understanding the bearing behavior of geothermal energy piles in natural service will help researches in theory and design method，and provide evidence for safety assessment. A pile-loading field test for static drill rooted geothermal energy piles(SDRGEP) was undertaken to investigate the working mechanism of the piles in service under temperature cycles. In a SDRGEP of 52 m depth，the fiber bragg grating(FBG) sensors(including strain，stress and temperature) were buried to measure the temperatures of the pile and the surrounding soil，the mobilized axial and radial stresses and strains of the pile，the shaft resistance，etc. Test results show that，after heating of 14 d，the heat exchanging system reaches a stable state and the average temperature of the pile is raised by 15.8 ℃ with a distribution of low in middle and high at both ends and an influence range of 2 to 4 times of the pile radius. It is also found that the relationships of both the mobilized radial stress and the mobilized axial stress with the temperature are linear，with maximum fitting gradients of 0.014 MPa/℃ at 0.86 times of the pile length and 0.3 MPa/℃ at 3.05 m depth respectively. The mobilized shaft resistance first increases and then decreases with the depth，reaching the maximum value at 0.649–0.861 times of the pile length. Whilst the pile head is fully constrained，the null point locates at the pile top and there is no negative side shear stress along the pile，showing that the bearing capacity of the pile is closely related to the constraint of the pile head. The maximum axial force at the pile head is 1 954 kN under the mechanical and thermal loads，which is only 42.5% of the ultimate bearing capacity of the pile，indicating that the pile is safe.

A series of drying-wetting tests，constant suction isotropic consolidation tests and constant suction true triaxial shear tests were carried out on intact expansive soils subjected to different drying and wetting cycles to investigate the mechanical properties of intact expansive by using unsaturated true triaxial apparatus. The effects of drying and wetting cycles on the soil-water curves，expansion and contraction characteristics，compression characteristics and strength characteristics were studied. The results show that as the number of drying and wetting cycles increases，the hysteresis loop of the drying curve and the wetting curve is smaller and smaller，even reverse hysteresis，but the drying rate and the wetting rate increase. The volumetric strains in the process of drying and wetting show obvious yield characteristics，which verifies the existence of the SI and SD yield envelopes in the expansive soil constitutive model. The drying yield suction is larger than the wetting yield suction，and both of them decrease with increasing the number of cycles. Drying and wetting cycles have a great influence on the compression characteristics under low confining pressure and low suction while have little effect on the compression characteristics under high confining pressure and high suction. The cohesion and the internal friction angle of expansive soils will be reduced by drying and wetting cycles. After drying and wetting cycles, the cohesion of expansive soils increases with increasing the suction and the intermediate principal stress，but the internal friction angle decreases with increasing the intermediate principal stress. In the range of low suction (s≤200 kPa)，the suction friction angle jb of expansive soils after drying and wetting cycles is a variable. After three drying and wetting cycles，the strength of expansive soils tends to be stable，and the suction friction angle increasing nonlinearly with b value can be regarded as a constant.

Due to that domestic subway stations are generally constructed with columns，there are rarely studies on the seismic performance of column-free stations under bidirectional earthquake actions. Taking a column-free subway station as the objective，large-scale simulation shaking table test of a long-span column-free subway station under different loading conditions was carried out considering soil-structure interaction and bidirectional earthquake actions to investigate dynamic responses of the station structure and the surrounding soil. The results show that the acceleration response of the model foundation increases with increasing the magnitude of the ground motion, and that the acceleration components in vertical and horizontal directions respectively play a leading role in the depth of the foundation and on the surface of the soil layer. As the magnitude of the ground motion increases，the fundamental frequency of the structure gradually decreases. Under the action of the horizontal ground motion，the 20﹣40 Hz high-frequency component of the Fourier spectrum of the acceleration response in the horizontal direction at the measuring points gradually increases and the low-frequency component is gradually filtered. The deformation of the middle plate of the model structure is large under the vertical earthquake action. The peak acceleration of the model structure under the bidirectional earthquake actions is greater than that under the unidirectional earthquake action. When the earthquake action is large，the soil and the structure interact violently，the bottom plate and the soil are separated and the earth pressure at the bottom of the model structure decreases. Under the action of earthquakes，the damage of the model structure is mainly concentrated at the junction of the roof and the side wall where slight cracks occur along the loading direction, indicating that the connection between the roof and the side wall of the column-free subway station and the middle plate are structurally weak locations and should be strengthened. Under the action of EL Centro wave with a peak acceleration of 0.484 g，the peak stress and the peak acceleration at the middle plate are respectively about 2.5 and 1.4–1.5 times of those under the unidirectional seismic action，so the influence of bidirectional seismic actions on the column-free subway station cannot be ignored.

The determination method of unfrozen water content and ice content in frozen soils is one of the critical issues in cold region geotechnical engineering. This study performs a series of laboratory tests to investigate the electrical conductivity of frozen soils. The relationships among the electrical conductivity of frozen soils，the unfrozen water content and the temperature are revealed. The testing results show that the relationship between the conductivity and the temperature at positive temperature cannot be directly applied to negative temperature，and that the traditional simple methods which do not distinguish the electrical conductivity at positive and negative temperature zones will result in a considerable error. Based on the soil conductivity theory，an electrical conductivity model which can be applied at both positive and negative temperature zones is established to predict the unfrozen water content. Based on the analysis of the changing law of the bulk conductivity and the surface conductivity，it is found that the bulk conductivity can be ignored for the frozen soil. The developed simplified conductivity model is then validated by the tested results and the existing method in the literature，showing that the new model has a good agreement with the measured data.