In order to clarify the failure mechanism of deep buried caverns under the action of ground impact disturbance and to establish the criterion of ground impact damage，phenomena and laws of ground impact damage in large equivalent underground explosion test and blasting at home and abroad are systematically summarized and analyzed. According to the distance to the center of explosion，the damage caused by explosive can be divided into ground impact damage and induced engineering earthquake damage. The boundary range and failure characteristics of each zone of ground impact failure are calculated and compared by using two methods of empirical estimation and stress discrimination. Based on the systematic summary and analysis of the existing researches，it is pointed out that the energy-bearing and structural characteristics of rock mass are the causes of induced engineering earthquake damage. Then，the basic concept and mechanical model of block medium deformation under explosion are summarized，and the relationship between the size of activated blocks and the proportional blast center distance is analyzed from the essence of block medium deformation. Finally，a failure effect analysis method taking the energy factor as a parameter is proposed based on the existing researches，and the boundary range of the displacement under different explosion equivalents is obtained. The unified characterization of the deformation in each failure zone from near zone to far zone and from closed explosion to ground touching explosion is achieved by using the energy factor as the index parameter. The research lays a theoretical foundation for the determination of the safety range and the establishment of related engineering protection technology under the condition of large equivalent underground explosion.

In order to study the mechanical properties and energy dissipation laws of coal samples with different length-to-diameter ratios under three-dimensional(3D) coupled static and dynamic loads，four groups of cylinder specimens with a diameter of 50 mm and length-to-diameter ratios of 0.5，0.6，0.8 and 1.0 were respectively used to carry out 3D coupled static and dynamic loading experiment by using the improved split Hopkinson pressure bar(SHPB). The mechanical properties of coal samples with different length-to-diameter ratios were studied from the aspects of dynamic stress and dynamic strain，and the energy of the coal samples after crushed was analyzed. The results show that the dynamic peak stress and the combined peak stress increase as a power function of the strain rate，and the specimens with large length-to-diameter ratio are more sensitive to the strain rate when the length-to-diameter ratio of the samples is in the range of 0.5–1.0. At the same strain rate，the dynamic peak stress and the combined peak stress increase with increasing the length-to-diameter ratio，and the greater the strain rate，the more significant the length-to-diameter ratio effect. The dynamic peak strain and the dynamic maximum strain increase linearly with increasing the strain rate. There is little difference between the strain rate sensitivities of the dynamic peak strain and the dynamic maximum strain with different length-to-diameter ratios. Under the same strain rate，the dynamic peak strain decreases with increasing the length-to-diameter ratio. The dynamic maximum strain, affected by the double factors of the preload and the maximum allowable deformation of the specimens， decreases first and then increases with increasing the length-to-diameter ratio. The larger the length-to-diameter ratio of the samples，the lower the dissipated energy density and the higher the degree of crushing. The failure mode changes from tensile failure to shear failure with increasing the length-to-diameter ratio. The research results are helpful to explore the failure mechanism under the coupled static and dynamic loads，and provide theoretical support for the prevention and control of rockburst.

Liquid nitrogen(LN2) fracturing is a method of stimulating reservoir with ultra-low temperature LN2. Different from the conventional fracturing methods，the ultra-low temperature impact of LN2 will sharply reduce the reservoir rock temperature，produce strong temperature stress and induce fractures in the reservoir rock. To explore the initiation and propagation mechanisms of rock fractures induced by LN2 ultra-low temperature，LN2 ultra-low temperature impact simulation experiments were carried out on open-hole wellbores，preset fractures and hydraulic fractures respectively. The distribution characteristics of induced fractures were obtained，and the changes of the temperature fields along the radial direction of the open-hole wellbores and the normal direction of the preset fractures during ultra-low temperature impact were measured. The applicability of the maximum tensile stress criterion and the stress intensity factor fracture criterion to determine the fracture propagation range induced by ultra-low temperature was studied. The results show that the initiation of the ultra-low temperature induced fractures are mainly perpendicular to the existing fracture surface such as the open-hole wellbore wall，the preset fracture and the hydraulic fracture，and the secondary induced fractures perpendicular to the induced fractures also appear on both sides of the induced fractures，forming a complex fracture network. According to the experimental results of fracture propagation scale，the maximum tensile stress criterion and the stress intensity factor fracture criterion are proposed to determine the lower and upper limits of the induced fracture propagation length respectively. In addition，the method of hydraulic fracturing combined with LN2 fracturing was proposed and verified by experiments. The research results provide a basis for the feasibility and design of LN2 fracturing.

In order to select the key joints from the complex joint network，to provide a scientific quantitative criteria for the selective measurement of structural planes and to simplify the joint network，the threshold value of key joint trace length was studied by taking the trace length as a variable. The random joint network models were prepared by 3D printing technology and based on Monte Carlo theory，and flat specimens of 100 mm ?20 mm ?100 mm were cast. The integrity coefficient，strength，deformation and energy properties of jointed rock mass were analyzed under uniaxial compression, and the threshold value of the key joint trace length was studied based on the mechanical equivalence principle of jointed rock mass. The results show that：(1) The joint trace length is one of the key factors affecting the mechanical properties of specimens. The strength，deformation and energy properties of the specimens do not change significantly when the joints smaller than a certain length are removed. (2) Based on the principal component analysis and Gaussian mixed model clustering algorithm，a mechanical equivalence analysis method of jointed rock masses was established to realize the classification of rock masses with various mechanical parameters，and the differences of the joint network of mechanically unequal samples were analyzed. A set of key joint trace length threshold research method was formed. (3) Considering 9 physical and mechanical parameters，19% of the specimen edge length is considered as the trace length threshold of key joints which significantly impacts the mechanical properties of the specimens. The research results provide a theoretical basis for future artificial intelligence analysis of how to scientifically select joints in jointed rock projects.

Brittle failure of rock masses occurs frequently during blasting excavation of large underground powerhouse of the Baihetan Hydropower Station. In-situ monitoring equipments，such as microseismic(MS) monitoring，multi-point extensometers and rockbolt(cable) dynamometers，are adopted to fully reveal the mechanical responses of basalt under blasting excavation of the large underground powerhouse. The comprehensive monitoring results show that the fracture，deformation and stress of the surrounding rock increase to a certain extent after blasting excavation. Further analysis confirms that the surrounding rock deformation is compatible with the internal micro-fracture. The rock mass of the powerhouse cracks gradually under blasting excavation. The rock mass undergoes continuous fracture stages such as crack compaction，micro-fracture initiation and fracture propagation，accompanied by the growth of surrounding rock deformation. The early warning method of MS parameters based on energy index(EI) and cumulative apparent volume(CAV) can effectively warn the risk of macro-damage of the surrounding rock. It is also shown that monitoring the evolution signals of “fracture-deformation-stress” induced by blasting excavation has an important guiding role in the optimization of construction schemes of underground engineering under high-stresses as well as in the early warning of geological disasters.

Because the unconsolidated cores drilled from some of the tight conglomerate reservoirs in southern slope of Mahu sag indicate a strong water sensitivity，it is difficult to accurately evaluate their rock mechanical properties by using conventional mechanical tests. In this study，a cross-scale evaluation method for the macroscopic rock mechanical properties of conglomerate was proposed. Specifically，the elastic modulus，indentation hardness and fracture toughness of gravel and matrix were characterized at meso-scale through nanoindentation experiments. Afterward，the macroscopic mechanical properties of conglomerate were obtained by applying the homogenization method. Results show that the mechanical responses of the located indentations into gravels indicate a feature of clustering，reflecting the mechanical properties of quartz and feldspar. Different from that，the grid indentation in matrix exhibits complex mechanical responses，which primarily represent the mechanical properties of quartz particles，clay matrix and composite phase. The four-component model of matrix is able to consider the effects of the interface phase，the mineral alteration phase and the substrate-effect phase，such that the simple mechanical responses of the quartz particle and the clay matrix and the complex mechanical responses of the composite phase can be unified. The predicted macroscopic elastic modulus of conglomerate by using the Mori-Tanaka homogenization method tends to be higher than the measured value of rock cores. However，the correction by the deviation factor can give more accurate prediction ranges of the elastic moduli for the conglomerates with variable mineral contents and litho-facies，providing a valuable guidance for the mechanical parameter characterization of tight conglomerate reservoirs in Mahu areas.

To investigate the action mechanism of anti-dislocation design parameters of a tunnel with flexible joint，the effects of the parameters of ‘articulated design’ on the damage pattern and anti-faulting mechanism of a tunnel are investigated by small-scale physical model tests，such as the lining segment length，the lining thickness，the tunnel diameter，the angle between the tunnel and the fault zone，and the lining cross-section type. The model test results are compared with the small-scale numerical analysis results to verify the correctness of the numerical simulations. The full-scale numerical model is applied to analyze the effects of the ‘articulated design’ parameters on the internal force response of a tunnel，such as the fault width，the flexible joint width and the stiffness of the flexible joint material. The results of the study show：(1) The damage characteristics of a tunnel with flexible joint are mainly exhibited with the failure of the flexible joints in the fault zone，the rotation between the lining segments under the dislocation of the strike-slip fault zone and S-shaped deformation of the tunnel in the longitudinal direction. In a few cases，the tunnel presents compression-shear damage of the lining segments. (2) The deformation of a tunnel with flexible joint is mainly concentrated in the fault zone. At the junction of the two walls and the fault zone，the left wall of the active plate is in tension and the right wall of the active plate is in compression；The left wall of the fixed plate is in compression and the right wall of the fixed is in tension. (3) The lining internal force in the fault zone appears sawtooth variation，while there is an obvious drop at the flexible joints. It can be concluded that the lining is in center-symmetric bending state，and that the position of the maximum moment is found at the boundary of the rock mass and the fault zone. while the maximum shear force occurs in the central of the fault zone. (4) In the aspect of the action mechanism of the design parameters of the tunnel with flexible joint，this paper concludes that increasing the tunnel thickness，decreasing the lining segment length or reducing the diameter of the tunnel can improve anti-faulting performance of a tunnel. The circular lining cross-section can improve the anti-faulting ability of a tunnel with flexible joint compared with the horseshoe lining cross-section，and the best angle of the tunnel through the fault zone is 90º. The wider fault zone，smaller deformation joint width，and less stiffness of flexible joint materials within a reasonable range make a tunnel with flexible joint safer under strike-slip fault dislocation.

In order to analyze the fracture characteristics and the movement process of goaf roofs under the condition of gangue backfilled mining，this study based on the engineering conditions of Tangshan Mine F5001 gangue backfilled working face，the inclined borehole detect method is adopted to carry out long-term and fixed point detection on the roof. The distribution characteristics of mining-induced cracks in the roof are described quantitatively by the crack density，and the development process of roof cracks during gangue backfilled mining is revealed by using the method of similar model test. The results show that under the condition of gangue backfilled mining，the structural cracks in the roof usually appear at the boundary of rock strata. The forms of cracks are related to the rock strata where they are located. The roof movement of the coal seam presents five stages including fracture incubation，crack extend in advance，dense fracture development，steady fracture expansion and roof stability. Separation is the main component of the roof subsidence，accounting for more than half of the subsidence value. The conclusions of this paper can provide theoretical basis for support design of backfilled mining and upgrading of hydraulic support in working face.

With the main traffic routes cross complex and dangerous mountainous areas，more and more tunnels face the problem of under-crossing a landslide. The tunnel deformation in a unstable slope body due to potential earthquake has become one of the major hidden dangers to the operation and maintenance of the traffic tunnel in this area. In this paper，a typical case of tunnel orthogonal under-crossing landslide was taken for the first time to carry out the shaking table test，and the multi-attribute seismic data information such as characteristic image，acceleration，dynamic soil pressure and dynamic strain under different probability level seismic action were obtained. Through the model deformation characteristics and the time-domain characteristics analysis of the acceleration，the dynamic soil pressure and the dynamic strain，the regional spatial dynamic response characteristics of the lining were revealed. Based on multi-attribute seismic data comprehensive analysis，the time-frequency relationships among multi-attribute seismic data were obtained and the correlation between orthogonal tunnel and landslide damage level characterized by spectrum characteristics of different probability levels was proposed. The results show that：(1) The sensitivities of multi-attribute data such as the acceleration，the dynamic soil pressure and the dynamic strain under earthquake action are greatly different. The time-history effect of the dynamic soil pressure is the most sensitive，and the time-history effect of the dynamic strain has obvious lag effect compared with acceleration time-history. (2) Due to the spatial position relationship of the tunnel under-crossing the landslide and the influence of seismic effect，the damage sites of the lining have regional differences，and the cracking inverted arch becomes the weak area. (3) The dynamic soil pressure presents two intermittent jumps. The deformation of the lining is mainly controlled by the first wave of the dynamic soil pressure. The plastic deformation of the lining is completed in the first wave，and the second wave peak causes the residual dynamic soil pressure of the tunnel lining. (4) The excellent frequencies in the frequency domain of the multi-attribute seismic data signal are mainly concentrated in 1‐10 Hz，but the respective dominant frequencies are significantly different. The singular size boundary between the low frequency band and the high frequency band is 10 Hz，and the frequency structure in the 15‐20 Hz band is safer. (5) There is a positive correlation between the multi-attribute seismic data response variables of the earthquake action. The acceleration and the dynamic soil pressure response have a high degree of correlation，and the correlation between the ground motion acceleration and the dynamic strain response is weak，showing a significant correlation. The research results can provide a theoretical reference for the prediction of deformation and failure modes of orthogonal tunnel-landslide in high seismic intensity areas and the evaluation of engineering safety.

A multi-functional test system for coal and gas outburst simulation，composed of specimen cavity，loading module，seepage module，outburst inducing module，roadway module and data acquisition module，was independently developed based on modular development idea. The size of specimen cavity is ? 200 mm×700 mm，and its sealing gas pressure and axial loading stress are respectively 10.0 MPa and 20.0 MPa. The size and light transmittance of the roadway are ? 200 mm×10 m and 94%，respectively. The diameter of the outburst mouth is optional with 25 mm，50 mm and 100 mm. The test system can realize the functions of one time forming of coal samples，permeability test of coal samples and visualization of coal-gas two-phase flow. Taking Longshan Coal Mine in Henan Province as the engineering background，the outburst simulation test was carried out，and the results show that：(1) the permeability of the coal specimen is 9.88×10－3 ?m2，and the outburst inducing process reaches the millisecond level. After the outburst is trigger，the pulverized coals entrained by high-pressure gas continue to be thrown into the roadway to form a coal-gas two-phase flow. The outburst pulverized coal is 9 540.0 g，and the relative outburst strength is 47.7%. (2) During the outburst process，the roadway air is compressed to produce multiple shock waves that gradually attenuate in the form of alternating positive pressure and negative pressure，and the peak value of the shock wave overpressure reaches a maximum of 15.41 kPa at 5.5 m in the middle of the roadway. At the same time，the backward moving rarefaction wave generates to make the coal seam pressure in the cavity increase by 21%. (3) The outburst pulverized coal flow has the multiple reacceleration processes due to the paroxysmal outburst characteristics and the gas desorption，reaching the peak velocity of 42.6 m/s after the second acceleration. The shock wave propagates in the roadway ahead of the coal-gas two-phase flow at supersonic speed，and the wave front velocity is as high as 361.76 m/s which is much higher than that of the pulverized coal flow. (4) The two-phase flow temperature is mainly controlled by the endothermic process of the gas desorption and the disturbance of the shock wave，showing an evolutionary trend of “short rise，rapid decline and slow recovery”. The closer to the outburst mouth，the greater the decline of the temperature，with a maximum decrease of 2.1 ℃. The farther away from the outburst mouth，the greater the rise，and the maximum rise is 0.6 ℃. It is shown that the test system is stable and reliable，and can accurately measure the permeability of the specimen，realistically simulate the whole process of outburst，which provides an effective means for in-depth study of outburst disaster causing mechanism and guiding outburst prevention and control in coal mines.

Flexible barriers are a kind of protective structure widely applied in granular flow control，but there is no a comprehensive mechanical model to evaluate the protective characteristics of flexible barriers considering the composition of granular flow impact loads and the mechanical characteristics of supporting ropes. In this paper，a calculation model of the impact load of granular flow was established based on two kinds of impact modes of granular flow impact retaining structure and considering the composition of static，dynamic and frictional impact loads. Finally，combined with cable structure mechanics，a simplified mechanics model of flexible barriers considering the force characteristics of the supporting ropes and the combination of granular flow loads was constructed considering different impact stages and impact modes of granular flow. The comparisons between the calculation results by the proposed model with indoor chute model test results of granular flow impacting flexible barriers show that the impact load calculation results of the bottom support rope are larger than the experimental values，the calculation results of the impact load and the flexible barrier force under the slope accumulation condition are in agreement with the experimental results，and the calculation results under the continuous impact condition are greater than the experimental results. In general，the mechanical theoretical model can effectively describe the nonlinear distribution characteristics of the loads on the remaining support lines，and the calculation results are conservative.

The water movement and the collapse deformation development in loess under one-dimensional loading-wetting condition influence each other. A model for predicting water movement and wetting-induced deformation considering their interactions was proposed and the corresponding method of determining the model parameters was given. In order to verify the reliability of the model，one-dimensional load-wetting tests on remolded Lanzhou loess soil were carried out by using a self-made one-dimensional soil column infiltration instrument，and the model parameters were obtained through the indoor element tests. The model was applied to predict the water movement process and the collapse deformation development in the loading-wetting tests. The predicted and measured values were compared，and the model parameters were analyzed and inversed. The results show that the established model can reasonably predict the decrease of the rate of wetting front advancing with  the applied vertical pressure and the relation between the collapse deformation and the depth of wetting front. Considering fully saturated zone at the end of soil column，flow in macropores and the assumption in the model，the saturated permeability coefficient of the equivalent saturated body and the effective suction head at wetting front were inversed. The laws of the two inversed parameters changing with the vertical pressure are the same as those determined by indoor element tests with close values respectively，which indicates that the model is reasonable. The inversed parameters provide reference for the application of the model.

Based on the Rayleigh-Love rod model and three-dimensional continuum theory and considering the transverse inertia effect of piles and the vertical wave effect of soil，an interaction analysis model for the longitudinal vibration of a large-diameter pipe pile in three-dimensional axisymmetric radial inhomogeneous viscous damping soil is established. By utilizing Laplace transforms and complex stiffness transfer method，the interaction expression at the interface of pile and soil is also derived. Under the assumption of perfectly coupled condition between the pile and the soil，the semi-analytical solution for the dynamic response at the large-diameter pipe pile head is obtained in time domain by using Fourier inversion and convolution theorem. Then，the present analytical solution is reduced to verify its validity by comparison with the existing solutions. Finally，an extensive parametric analysis is conducted to investigate the effects of the Poisson?s ratio and the wave velocity of the pile as well as the construction disturbance of the soil on the dynamic response of the large-diameter pipe pile. The results show that：(1) With increasing the Poisson's ratio of the pile shaft，both the amplitude and the resonance frequency of the velocity admittance curve at the pile head decrease and the reflected wave curve shows obvious oscillation phenomenon. (2) Both the velocity admittance curve at the pile head and the amplitude of reflected signals at the pile bottom increase with increasing the wave velocity of the pile shaft. (3) When the transverse inertia effect of the pile shaft is considered，the influence of the construction disturbance effect on the dynamic response at the pile head is more significant. (4) By degenerating the derived solution and comparing it with the existing solutions，the rationality and accuracy of the solution are verified. The research can provide a reference for the longitudinal vibration analysis and design of pile foundations.

Accurately determining the strength parameters of the sliding zone soil is of great value to the stability evaluation and the landslide treatment of a slope. In this paper，the Gelongbu landslide in the upper reaches of the Yellow River is taken as an example to evaluate the accurate strength parameters. The measures include the field survey，physical parameter test，consolidation test，shear test，numerical calculation and correlation analysis. The shear strength values of the sliding zone soils at different positions were obtained from the relationships between the normal pressure(p) and the void ratio(e)，between the void ratio(e) and the water content(w)，and between the water content(w) and the shear strength parameters(c， f ). The average values，overall values and standard values of the shear strengths were calculated，respectively. The results show that there are good correlations between P and e as well as w and(c，f )，and the correlation coefficients are larger than 0.9. In the sight of engineering safety，the recommended values of the shear strength parameters for engineering design and construction were obtained. The present method for determining the shear strength parameters of the sliding zone soil of a slope can reflect the in-suit environment effect and can avoid the dispersion of the shear strength parameters obtained by the traditional shear test.

The Loess reinforced with fiber yarn was prepared by adding a certain proportion and length of fiber yarn，originating from waste textile fabric through opening，combing and cutting，into loess，and one dimensional creep deformation characteristics of fiber reinforced loess under different vertical loads were studied by using one-dimensional creep apparatus. The test results show that，under different vertical loads，the creep strain of the fiber reinforced loess is smaller than that of the plain loess，indicating that fiber yarn reinforcement has a positive effect on restraining the creep deformation of loess. When the vertical load is greater than 400 kPa，the time for the fiber reinforced loess to reach stable creep is longer than that of the plain loess. With increasing the proportion and the length of fiber yarn，the creep strain of the loess reinforced by fiber yarn first decreases and then increases. The optimum blending ratio and the optimum blending length of fiber yarn are 0.3% and 30 mm respectively. The creep index expression was constructed to reflect the long-term strength stability of soil after entering the creep stage. When the vertical load is between 400 and 800 kPa，the creep index increases significantly. When the vertical load is greater than 800 kPa，the creep index tends to be stable. Based on the data of one-dimensional creep test，an empirical model of one-dimensional creep of loess reinforced with fiber yarn is established considering the influence of fiber yarn proportion and fiber yarn length.

This paper studies the dynamic response characteristics of shield tunnels in water-rich soft strata under train loads，aiming to provide a theoretical basis for vibration damping of shield tunnels and liquefaction evaluation of foundation soils. Adopting the method of combining model tests and numerical simulations  and taking the pore water pressure，the frequency response function and the peak acceleration as the evaluation indexes，the response laws of the excess pore water pressure and the excess pore water pressure ratio in water-rich soft strata，as well as the vertical acceleration response laws of the shield tunnel segment structure and the surrounding water-rich soft strata under train vibration loads were studied based on time domain and frequency domain analyses. The results show that with the measurement point moving away from the tunnel，the peak value of the excess pore water pressure in the water-rich soft stratum under the train load decreases rapidly. The main influence range of the train vibration load on the pore water pressure of the water-rich stratum around the tunnel is small，which is mainly observed in the range of about 2 m below the arch bottom of the tunnel. Through transforming the time-domain results into the frequency domain results by the frequency response function(FRF)，it is found that in the frequency domain of the train vibration load，the vertical vibration acceleration level of the tunnel structure and the surrounding water-rich soft strata is positively correlated with the load frequency. Overall，the vibration acceleration level increases more significantly in the low frequency zone(0‐80 Hz) than in the medium and high frequency zone (80‐250 Hz)，and the vibration wave attenuation is more significant in the medium and high frequency zone(80‐250 Hz) than in the low frequency zone(0‐80 Hz).