To study the coupling influences of bedding and pre-crack directions on the fracture characteristics of coal，quasi-static loading experiments on SCB coal specimens with pre-crack were conducted，and the acoustic emissions during deformation and failure process were monitored. Regarding coal as a transversely isotropic body，the dimensionless factor was calibrated by finite element code，and the fracture toughness more in line with the actual situation was obtained. The results indicate that different combinations of bedding and pre-crack direction lead to significant differences in the loading curves and the fracture loads of specimens. In addition，the fracture modes and the fracture toughness are jointly affected by the bedding and the pre-crack direction. Meanwhile，the fracture toughness declines with decreasing the angle between the bedding and the loading direction，and the inclined pre-crack further weakens the resistance ability of specimens against crack propagation. Tensile failure dominates the crack initiation and propagation，and the propagation path of specimens shows significant anisotropy. According to the final crack morphology，the macroscopic failure modes of specimens can be divided into 4 types. The number of acoustic emission hits corresponds to the loading history，and the average total hit number at post-fracture load(including fracture load) stage varies obviously with the change of the pre-crack direction due to the different structure failure. Under external loading，specimens are damaged with tensile and shear micro-cracks continuously generating inside the specimens. The damage evolution is tightly related to the bedding and pre-crack directions. At different loading levels，tensile micro-cracks play a domination role，while the proportion of the shear micro-cracks is relatively low. With increasing the loading level，the micro-cracks continue to develop and propagate，and the damage of the specimens accumulates continuously，resulting in the crack initiation and failure.

Underground rock structures are often subjected to dynamic disturbances caused by earthquakes，explosions，impact vibrations，etc. Using the advantages of 3D printing technology to study the dynamic mechanical properties of rock under impact loads is of great significance to realize the application of 3D printing technology in the engineering field. Dynamic uniaxial compression tests were carried out on 3D printed rock specimens with prefabricated cracks by using f 50 mm variable cross section Hopkinson pressure bar device. The results show that the dynamic compressive strength of the specimens decreases first and then increases with increasing the prefabricated crack inclination angle，and when the prefabricated crack inclination angle is 30° and 90°，the strength of the specimens is the smallest and the largest，respectively. Compared with the static uniaxial compressive strength of the 3D printed rock specimens，it is found that the 3D printed sandy material has an obvious rate effect. When the strain rate is 139.65 s－1，the dynamic compressive strength of the 3D printed rock specimens is 4.34 times higher than the static compressive strength. The prefabricated crack defects intensify the energy dissipation and crushing process of the specimens to a certain extent，and the prefabricated cracks with a 30°inclination angle have the greatest influence. At the same time，the energy dissipation process and fragmentation of 3D printed rock specimens show obvious autocorrelation，and the relationship between the macroscopic crushing results and the energy dissipation of 3D printed sandy materials is similar to that of natural rock materials. The research lays a foundation for the feasibility of 3D printed materials to simulate natural rock in dynamic mechanical tests in the future.

In the exploitation process of geothermal energy，the temperature has a significant impact on the physical properties of dry hot rock，especially the thermal conductivity of high-temperature granite after water cooling. In order to investigate the influence of the temperature and the cooling mode on the physical properties of high-temperature granite，the air-cooling and water-cooling experiments of high-temperature granite are carried out in this paper. Through investigating the conventional physical properties such as mass，volume，density and P-wave velocity as well as the thermal conductivity，the change rules of the parameters by the two cooling methods are compared and analyzed. The results show that the mass loss rate，volume increase rate，density change rate and P-wave velocity decay rate increase exponentially with the temperature. When T = 450 ℃，the change rate of granite physical properties increases significantly. Water-cooling increases the density of micro-cracks in granite，which causes further changes in the physical properties of granite. After thermal treatment，the thermal conductivity of granite decreases non-linearly by 72.85% from 3.41 W/(m·K) to 0.96 W/(m·K) with increasing the temperature from 25 ℃ to 1 050 ℃. The thermal conductivity of granite after thermal treatment is inversely related to the mass damage rate，volume increase rate and P-wave velocity decay rate in an exponential form. Comparing the physical parameters，it is found that P-wave velocity is most sensitive to the temperature，followed by the thermal conductivity and the density. Therefore，P-wave velocity can be used preferentially as an index parameter to measure the thermal damage of granite.

To investigate the dynamic tensile mechanical behaviors of granite at the grain scale，a novel three-dimensional grain-based model based on the three-dimensional particle flow code(PFC3D-GBM) was proposed，and a three-dimensional split Hopkinson pressure bar(SHPB) numerical model was constructed based on the modeling technology of coupled finite difference method(FDM) and discrete element method(DEM). The numerical dynamic semi-circular bending(SCB) test was conducted on the numerical samples using the coupled SHPB system to investigate the fracturing process of the samples，and the effect of the grain size-particle size ratio on the dynamic tensile mechanical properties was also discussed. The numerical results show that，under dynamic loading，the crack number evolution process of the samples can be divided into four stages of initiation，slow development，rapid increasing and stability，and that the samples mainly show tensile failure. As the grain size- particle size ratio increases，the proportion of the transgranular contact to the total contact increases gradually and tends to be stable，while the proportion of the intergranular contact decreases gradually. The proportion of the transgranular cracks to the total cracks increases gradually after sample failure，increasing the external load value required for the sample brittle macroscopic fracture and hence，increasing the dynamic tensile strength. PFC3D-GBM is feasible in the study of rock dynamics and is a powerful tool for rock mechanics investigations at the grain scale.

The buffer zone within 2 km away from the main stream of a certain river in the HD and DHQ reservoirs，is taken as the research region to study the regional-scale early warning of water-induced landslides in the reservoir area. The preliminary landslide susceptibility factors in the research region are analyzed and screened through the chi-square test and the multicollinearity analysis. A final index system of landslide susceptibility in the research region is obtained，and landslide susceptibility assessment models are constructed based on different machine learning algorithms. The results show that the model based on random forest has the best accuracy of 98.00%. This model is applied to the whole research region and the landslide susceptibility mapping is completed. Besides，the rainfall and the reservoir water level，two main hydrodynamic inducing factors，are considered as early warning indicators and analyzed based on historical landslide data and monitoring data，and five early warning levels are put forward. Then a comprehensive water-induced landslide early warning model based on landslide susceptibility is established. The early warning zoning map of the research region on December 23，2019 is obtained，and the early warning zoning map under the assumed most unfavorable conditions is also proposed based on the rainfall and the reservoir water level conditions of the research region in the past five years.

Coal microstructure has a significant impact on gas production. However，current coalbed methane (CBM) extraction models fail to consider this factor. In order to quantify the influence of the coal seam microstructure on macroscopic seepage processes，a fracture-matrix seepage model is developed based on the power-law fractal permeability theory，which is able to simultaneously analyze the interaction between the coal seam microstructure and multi-physical field factors. This model defines the multi-physical field effects(including gas adsorption- desorption effect，seepage-induced reservoir deformation，coal matrix deformation，fracture-matrix interactions，etc.) as functions of the effective stress in the reservoir，which in turn operate on the reservoir porosity and the microstructure. Furthermore，the influence of the main structural parameters of the coal seam on the macroscopic permeability，including general power law exponent a，extremum crack length ratio r and maximum fracture length l，is investigated，and the spatial and temporal evolutions of coal seam deformation and permeability are also analyzed. The simulation results show that the structural parameters of the coal seam have a significant influence on the permeability. The permeability of coal is proportional to the extremum fracture length ratio and the maximum fracture length while is inversely proportional to the general power law exponent. Moreover，the maximum fracture length of the coal seam has a more significant effect on the coal seam permeability than the general power law exponent and the extremum fracture length ratio.

During coalbed methane mining，the gas pressure interactions within the matrix- fracture cause damage effects in the coal seam，resulting in a reduction on the strength of the coal. To investigate the damage effect of the coal strength，a conceptual model of matrix and fracture geometry deformation was proposed，and then，a permeability model with coupled damage constitutive parameters was deduced. The strength post-processing calculations for the permeability model considering gas action were also carried out by the COMSOL live link with MATLAB program. The results show that the permeability model obtained from the pore fundamentals is suitable for different boundary conditions，and that the new model matches the experimental data well under uniaxial strain and constant stress conditions while the Palmer-Mansoori(P-M) model is only suitable for uniaxial strain boundary conditions. Compared to the control coal samples，the strengths of the samples with Young¢s modulus ratios of 1/3，1/5，1/7 and 1/10 decrease by 46.6%，32.0%，27.9% and 26.4% respectively after gas action. The damage effect of gas transport on the strength of the coal sample contributes to the porosity of the coal in the form of damage-induced strain，and pore development changes the extension trace of the main fracture after uniaxial loading. Post-processing calculations of the permeability model were programmed to realize the evaluation of the damage effect on the coal strength arising from coal bed methane transport.

The actual underground engineering of fractured rock mass，which is different from the structural engineering with relatively clear mathematical models，shows obvious uncertainty of rock mass structure as a heterogeneous and discontinuous medium. Especially for the tunneling projects closely related to the fractured   rock mass excavation process，the analysis results by the mathematical models are quite different from the actual ones. For this issue，taking the geometry and distribution characteristics of rock mass fractures into consideration，a rock mass intelligent analysis and multivariate interpretation system was adopted to realize the adaptive  extraction of rock mass structure information and further，by coupled the advanced geological prediction technology，the multi-scale fine construction of the tunnel fracture network model in fault-affected areas was achieved. Based on the 3DEC optimization model，the spatial distribution law of block collapse in the fault-affected areas of tunnels was studied，and systematical analysis and mathematical statistics of the shape，volume and quantity of collapse blocks in different excavation cycles were carried out. According to the sensitive geological parameters such as connectivity rate，DFN density and joint spacing，the spatial shape evolution law and response characteristics of dangerous tunnel rock groups under different rock mass and fracture combinations were revealed with 108 groups of simulations. The results provide a scientific basis for the prediction，identification，prevention and control of dangerous rock collapse in the process of tunnel and underground engineering construction in fractured rock mass areas and hence，are of great theoretical significance and engineering application value.

In this paper，the macro characteristics and micro scanning results of the discing cores from hot dry rock wells in Gonghe Basin，Qinghai Province were analyzed，and then，the fracture evolution in the process of core drilling under different types of stress states was analyzed to explore the underlying mechanism of core discing from the micro perspective using the hybrid DEM-continuum method. The following results can be drawn. Firstly，the observed shapes of discing cores can be divided into four types according to the thickness，i.e.，crushed discing，thin discing，discing and thick discing，and the fracture surfaces，most of which are rough and uneven，present saddle，flat，cup-shaped concave and ellipse shapes. Secondly，the rock core discing is attributed to the tensile failure. Thirdly，the high horizonal principal stress is the main factor inducing core discing and leads to the zonal distribution of fractures and the cup-shaped concave surface at the root of the cores. The vertical stress restrains the zonal distribution of fractures，and the high vertical stress could result in a flat-shaped section in the case of low horizonal stress. Fourthly，under the influence of the stress redistribution，a large amount of fractures generate at the root of the core and the existing fractures at the upper part of the core continue to develop，augmenting core discing. Fifthly，the horizontal stress difference affects both the distribution and the strike of the fractures. The strike of the fractures is mainly along the direction of the maximum horizontal stress，and the fractures gather near the core edge. Sixthly，the strike of the fractures is also affected by the three-dimensional stress level. The proportion of the fractures striking along the maximum horizontal stress increases with decreasing the minimum horizontal stress or increasing the vertical stress. However，the indication effect of the fracture strike on the stress direction is minimized under high maximum horizontal principal stress.

Simulation of seismic wave propagation generated by shear dislocation sources is a theoretical basis for near-fault ground motion researches. However，existing deterministic methods have certain shortcomings in high-frequency solutions and cross-scale calculations. This paper proposes a frequency-wavenumber method for multi-scale modelling of broadband seismic wave propagation in the stratified half-space due to dislocations，which can effectively solve the broadband seismic response problem(covering 0.1–10 Hz engineering structure sensitive frequencies) from high-velocity crustal scale(kilometre level) to low-velocity geotechnical scale(metre level). The Fourier-Hankel transformation is used to convert the 3D wave equations from time-space domain to frequency-wave number domain in the cylindrical coordinate system，and the dynamic response of a viscoelastic layered half-space due to a dislocation source is derived by the modified stiffness matrix method in conjunction with the displacement-stress discontinuity conditions. The correctness and accuracy of the proposed method are first verified by comparing with the classical Haskell method，and then a cross-scale site model embedded in the Tianjin crustal structure is established to focus on the effects of the source frequency and the near-surface soft interlayer on earthquake ground motions. The results show that the new method is very suitable for modelling broadband ground motions and low-velocity subdivided layers，and the complex propagation processes such as reflection，conversion and transmission of seismic waves at layer interfaces as well as the ground motion characteristics due to dislocation sources can be clearly observed. The ground motions of soft sites are significantly affected by the source frequency，and the high frequency excitation can increase the intensity and extent of the earthquake radiation energy，which may lead to more serious surface rupture and structural damage. The near-surface soft interlayers with different buried depths and thicknesses have important impact on the seismic responses of soft sites，and the superposition of the filtering and amplifying effects from site and the isolation effect from soft interlayers makes the surface response very complicated.

To study the failure mechanism of floor rock mass in deep rock mining working faces of Pingmei mining area，a mechanical model of plastic slip line field for three-layer composite structure floor was constructed，and the theoretical solution of the maximum failure depth of the floor under five working conditions was derived on the basis of the traditional plastic slip line field theory of single rock floor. The stress field distribution law and plastic deformation characteristics of floor rock mass under different advance degrees were simulated and analyzed. Finally，vibrating wire strain gauges were used to monitor the micro-strain of floor rock mass in No. 15–31040 rock mining working face of No.12 Mine in real time，and the deformation development pattern and failure domain of the floor before-during-after mining were obtained. The results show that the depth of the active failure zone of the floor of the working face is located between the middle and the lower structural strata，which belongs to the third working condition with the theoretical solution of the maximum failure depth of 17.08 m. According to the simulation experiment，the failure and damage of floor rock mass are mainly concentrated in the open-off cut and under the two lanes at the depth of 17.1–17.9 m，mainly in the form of plastic slip failure. The height of uplift of cold ash confined water is less than the thickness of bauxite mudstone at the bottom of carboniferous system，and the effective waterproof layer can resist the uplift of cold ash water. The measured data reveal that the initial position of floor failure is 7.9 m ahead of the mining face，mainly in the form of compression-shear failure，while that the rock mass near the mining face turns into tensile-shear failure after entering the goaf and the failure depth can reach 16.5–18 m. According to the temperature monitoring，the lower rock mass in the mining failure zone is still impermeable. The theoretical calculation is consistent with the simulation experiment and measured results. The research could provide theoretical guidance and practical reference for prevention and control of floor water disasters in coal and rock mining working faces under similar geological conditions.

In order to solve the problem of intersection support of expansive soft rock roadways，taking the intersection point of the main inclined shaft and #2 coal feeder maintenance connecting roadway of Qingshuiying coal mine as the engineering background，and based on the analysis of the geological characteristics and deformation causes of the intersection，the repairing support design based on rectangular concrete-filled steel tube composite support is proposed. Through the numerical simulation analysis of the support bearing capacity，it is found that the flexural bearing capacity of the straight beam section of the composite support is insufficient，which affects the overall support effect. The bending test of the concrete-filled steel tubular straight beam is carried out. The results show that the welding bending round steel in the tensile area of the straight beam can effectively improve the bearing capacity of the concrete-filled steel tubular straight beam. The structure of the rectangular composite support is optimized with f50 mm bending round steel. The simulation analysis shows that the overall
bearing capacity of the optimized composite support is increased by 36%. In engineering practice，the support scheme based on the rectangular concrete-filled steel tube composite support has no obvious deformation in three years of using，and the intersection point of the expansion soft rock roadway remains stable for a long time. The research has an important guiding significance for the intersection point support under similar conditions. 

The multi-field coupling effect of underground high-level waste repository is complicated. As the first choice of buffer materials，unsaturated compacted bentonite needs to be able to effectively discharge the gas generated on the surface of the metal tank to the outside to avoid pressure accumulation. The quasi-stationary flow method and strain gauges are employed in this paper to measure the volume deformation and the effective gas permeability of two sets of unsaturated compacted bentonite samples under real-time temperature and confining pressure cycle. The influences of real-time temperature and stress cycle on the gas permeability and deformation characteristics of the samples are analyzed. Results suggest that the temperature increment will increase the compression deformation of the samples during loading，but has little effect on the deformation recovery during unloading. And there is a good exponential relationship between the effective gas permeability and the connected porosity of the samples during entire stress cycle under the same temperature condition. Combined with the NMR scan results，the mechanism of decline in gas permeability caused by temperature increasing is explained as：(1) the temperature rise increases the compression deformation of the samples and reduces the connected porosity，(2) the increase in temperature enhances the slippage effect of gas molecules and increases the resistance of air flow through pore channels，and (3) thermal expansion of pore water changes its distribution in the samples and further compresses the effective throat diameter of the connected pores. The present work deepens the understanding of the multi-physics coupling mechanism of buffer materials and provides data support for engineering design and numerical simulation.

In order to solve a series of engineering problems encountered in the artificial freezing process in permeable strata with high seepage velocity，laboratory model test for studying the development law of the artificial freezing temperature field under different flow velocity conditions was performed based on a self-built large-scale water-heat coupled physical model test system. The test results show that，when the seepage velocity is equal to 0 and 3 m/d，the earliest closure position of the frozen wall locates at the intermediate point between two neighbor freezing pipes and the closure time is 740 and 840 min respectively. When the seepage velocity is equal to 6 and 9 m/d，the earliest closure position of the frozen wall moves from the intermediate point to the downstream by 50 mm，and the closure time increases to 1 770 and 4 250 min respectively. By fitting the test data，a prediction formula of the closure time of the frozen wall under the seepage field was obtained，and the limiting velocity for the closure of the frozen wall was predicted to be 12.73 m/d. The seepage field causes uneven development of the thickness of the frozen wall. Specifically，when the seepage velocity is equal to 3，6 and 9 m/d，the ratio of the downstream expansion radius to the upstream expansion radius of the frozen wall is 1.17，1.21 and 1.81，respectively. It is also found from analyzing the freezing process that，when the distance between adjacent freezing fronts is reduced to a critical value Lc，the “group-pipe-effect” will occur，which will accelerate the expansion speed of the freezing front and shorten the closure time of the frozen wall. Since the convective heat transfer effect of the water flow offsets part of the “group pipe effect”，Lc decreases as the seepage velocity increases. When the seepage velocity is less than 3 m/d，Lc is 400 mm，and when the flow velocity reaches 6 and 9 m/d，Lc is reduced to 154 and 130 mm，respectively. The results of this study can provide reference for the arrangement of artificial freezing holes in the permeable formations with large flow velocity，and also provide verification basis for the hydrothermal coupling numerical calculation model.

Unbound aggregate permeable base(UPAB)materials with load-transmitting skeleton and pore structure are increasingly used due to their desired drainage performance，while how to control and optimize bearing capacity and permanent deformation of such layers under repeated applications of traffic loads remains a critical challenge to be resolved. In this study，seven different UPAB gradations were designed using the gravel to sand ratio(G/S) concept along with the conventional dense gradation as the baseline. The laboratory compaction tests and monotonic triaxial compression tests were conducted to investigate the effect of the gradation on the shear strength behavior of UPAB materials，whereas the effects of the gradation on the resilient modulus，the damping ratio and accumulated plastic deformation were studied by repeated load triaxial tests with different combinations of deviator and confining stress levels controlled by the shear stress ratio(SSR). The testing results indicate that the peak deviator stresses of specimens are different with varying gradations，and such difference becomes more significant as the confining pressure increases. The internal friction angle governs the shear strength of UPAB materials. As the number of load applications increases，the resilient modulus increases while the damping ratio decreases rapidly，and both attenuates around the 1 000-th load application. The initial damping ratio，the resilient modulus and the axial accumulative plastic strain of specimens with varying gradations increase with increasing the shear stress ratio(SSR)，and the inter-specimen differences become increasingly significant at relatively high SSR(≥0.7) levels. There exists an optimum G/S value of 1.6–1.8 that could yield the best performance in terms of achieved dry density，shear strength，resilient modulus and accumulative plastic strain. The findings could provide technical guidance and reference for cost-effective and sustainable use of UPAB materials in permeable pavements.

Loose spoil slopes are naturally formed under gravity throwing(rolling) and prone to be instable for the loose structure of spoil under the circumstance of external environment. At present，there are few studies on the engineering characteristics of loose spoil. In this paper，a high loose spoil slope in a hydropower project was taken as the research object. Considering the distribution characteristics of particle configuration，four sampling lines along the vertical direction on the slope surface were arranged and a series of sampling，measurement and engineering characteristic tests of loose spoil were conducted. A new method for obtaining the natural density of loose rock and soil aggregates was proposed and verified by large-scale triaxial compression test. The research conclusions are as follows：(1) The field relative density of loose spoil is between 0.50 and 0.55，increasing along the vertical direction from top to downward. (2) Large deformation feature is the main engineering problem for loose spoil. During the process of large deformation，the spherical stress p well follows a linear relationship with the volume strain ev，whereas the bulk modulus B is linearly independent of the stress level s，only changing with the confining pressure s3. The Duncan-Zhang E-B model is more suitable for loose spoil. The failure stress ratio Rf of loose spoil is about 0.65，and loose spoil generally exhibits strain hardening characteristics. There¢s no peak deviator stress on stress-strain curves when the axial strain reaches 15%，and the mechanical mechanism of loose spoil can be summarized as large friction deformation of unstable granular materials. (3) The volume modulus B and the confining pressure s3 of loose spoil with different sampling heights have a good linear relationship，and the intercept of B on the stress coordinate axis is about equal to 0. The above conclusions are conducive to simplify calculation and to predict the deformation of loose spoil，also identifying the structure instability of loose spoil on the free surface.

Carbonate coarse-grained soils are widely distributed in South China Sea. Since it is difficult to obtain undisturbed samples of coarse-grained soils，the field tests are often used to evaluate the physical and mechanical properties of coarse-grained soils. Large-scale direct shear tests on the carbonate coarse-grained soil from South China Sea were performed，and the strength parameters of carbonate gravel were obtained. The results show that based onMohr-Coulomb failure criterion，both the internal friction angle and the apparent cohesion of the carbonate coarse-grained soil are high，and that poor grade will lead to the decrement of the internal friction angle and the increment of the apparent cohesion. Indoor light dynamic cone penetration tests on the same soil were carried out，and the influences of the relative density，the average particle size and the uniform coefficient on the penetration index(Pindex) were discussed. An index named initial penetration depth，for characterizing the apparent cohesion，was proposed to establish the relationships of the penetration index with the apparent cohesion and the internal friction angle of carbonate coarse-grained soils.