To investigate the impact feature and dynamic behavior of coal-gas two-phase flow in the process of coal and gas outburst，physical simulation test of coal-gas two-phase flow was carried out by multi-field coupling testing system for dynamic disasters in coal mine. The results show that the outburst pulverized coal is thrown from the working face in a jet shape due to the high-speed airflow. As the distance increases，the solid-phase diffuses and converts into the plug flow，and the deposition amount increases accordingly and concentrates at the end of the roadway. The relative intensity of the outburst is 10%，and pulverized coal with a diameter of less than 0.150 mm accounts for the main part of the outburst coal which indicates that the fragmentation degree of pulverized coal is high. While the outburst is triggered，a large amount of pulverized coal is ejected by the high-pressure airflow from the coal seam to create a large impact force. The impact force near the outburst orifice changes repeatedly，which indicates that the outburst process presents paroxysmal characteristics. In the motion process of two-phase flow，the gas expands completely to form a steeply increasing impact zone. The impact force reaches the largest at 4 944 mm from the outburst orifice and then attenuates along the roadway.

Taking the toppling deformation body in front of the dam of Gushui hydropower station as the research object，the physical model of the slope is established on the basis of geological cognitions and similarity theory，and the process of valley cutting is simulated by prefabricated modules and graded excavation. Five-stage centrifuge model test is carried out and the key hazard-inducing factors of deep toppling deformation and the disaster patterns of the counter-tilt layered rock slope under gravity are studied. The results show that the occurrence，development and failure of deep toppling deformation of counter-tilt layered rock slopes go through a long geological history time when energy and deformation accumulate，and that the sharp increase of rock deformation is closely related to external conditions such as excavation and earthquake，etc.. Lithological conditions(relatively weak rock mass)，structural conditions(appropriate layer thickness and dip angle) and external conditions(undercutting of river valleys or excavation of slopes) are key factors for deep toppling deformation，while free face condition is the key hazard factor for deep toppling damage. Repeated valley incisions or multi-level excavations result in several bending belts with different depths inside the slope，and development and penetration of the bending belt gradually from the foot to the top of the slope result in the overall shear failure of the slope along the bending belt.

Based on the results of uniaxial，triaxial and acoustic emission tests carried out on basalt at Baihetan hydropower station，the pre-peak characteristic strength and post-peak mechanical behavior of basalt are discussed. The crack initiation strength of basalt is about 0.5–0.6 times of the peak strength，while the damage strength is close to the peak strength. There are obvious brittle and dilatant behaviors during failure process，and post-peak mechanical behaviors are nearly uncorrelated with the confining pressure. The conversion relationship between the plastic flow coefficient ? in Hoek-Brown constitutive model and the rock dilatancy angle ? is established，and the applicability of Hoek-Brown model for describing post-peak brittleness and dilatancy of basalt is demonstrated. Engineering application shows that the influence of dilatancy characteristics of the surrounding rock on its stability is closely related to the stress path of excavation response. In the stress concentration area，the stronger the dilatancy is，the more unfavorable to the stability of the surrounding rock. Due to that the stress relaxation area lacks the level of concentration stress required for triggering dilatancy，dilatancy is not the critical factor of control stability. In the practice of deep-buried cavern in brittle rock mass in underground engineering，it is suggested that differential support design schemes should be formulated for side wall and vault according to mechanism of excavation response.

In order to research the mechanism of coal and gas outburst from boreholes induced by the water jet technique for enhancing coal permeability，theoretical analysis of coal mass instability conditions and single factor test in underground field were carried out，and coal rock electromagnetic radiations(EMR) and gas emissions from boreholes were monitored based on the hydraulic slotting technique in high-gas coal seams. The action mechanisms of in-situ stresses and gas pressure on coal mass instability with hydraulic slotting and their influence characteristics were demonstrated. The results show that slotting expansion can enhance the effect of in-situ stresses and gas gradient force around the borehole and that the minimum critical pressure value of the water jet with enough impacting time is needed for the coal body to outburst in the borehole. It is also shown that the flow pressure of water jet has a linear positive correlation with the weight of coal debris discharged from boreholes while a linear negative correlation with the time of initial outburst occurring. Decreasing of the gas pressure around the borehole would weak the effect of coal mass instability ejection. The phenomena that the coal and rock EMR signal fluctuates sharply during the unstable ejection and the EMR energy level decreases after slotting reflect the instability influenced by the in-situ stress，and the phenomenon that the instantaneous gas emission from the gas pre-discharge borehole decreases obviously after slotting reflects the instability influenced by the gas pressure. The research conclusions provide a reference for the prevention and control of borehole ejection in the application of hydraulic slotting technology.

Deep rock mass exists in high in-situ stress environment and is often disturbed by dynamic loads. In order to study the effect of in-situ stresses on the dynamic fracture behaviors of cracks，the initial stresses of rock were given by lateral pressure equipment to simulate in-situ stresses，and impact experiments were conducted with medium and low speed drop weight impact device. Crack initiation time and crack propagation velocity were obtained by using crack propagation gauge(CPG) in impact test，and numerical simulations were also carried out by using AUTODYN finite different code and ABAQUS finite element code. The experimental and numerical simulation results show that the in-situ stress perpendicular to the crack surface changes the initiation time，crack propagation speed and crack propagation length but has no effect on the critical dynamic stress intensity factor. The in-situ stress perpendicular to the crack surface delays the initiation time of the crack，and the larger the in-situ stress，the lower the crack propagation speed and the shorter the crack propagation length.

The seismogenic mechanisms of engineering rock mass are the basis for both research and application of monitoring and early warning of rock failure. In this paper，based on the locating data of the precursory microseismic sources from a project case of a large-scale failure of the overlying rock mass over the mining goaf induced by a large blast，a back analysis of the seismogenic mechanisms was carried out by applying the moment tensor method to the precursory microseismic location events，and the pure double-couple components   were obtained by calculating and decomposing the moment tensor of the monitored microseismic localization events. The value of the discriminant parameter R，was calculated by the Feigner and Young moment tensor fracture criterion and used to determine failure types of the rock mass with the precursory microseismic events. The volume parameters of unchangeable part T and changeable part k were calculated according to the moment tensor components，and the T-k chart of Hudson source type was plotted. It is shown that the main failure type of the precursory sources is shear failure. Furthermore，the fault parameters of the locating sources were calculated according to the pure double-couple components  . The shear failure type of the precursory microseismic events analyzed by the focal mechanism solution basically matches with that of the on-site macroscopic shear-slip failure of the large landslide over the mining goaf. The research results show that the precursory focal mechanism solution based on microseismic moment tensor theory can more accurately determine the failure type of meso-scale engineering rock mass. The results of this study can be the reference to further research on the failure mechanisms of rock mass as well as early warning of engineering rock mass disasters.

In order to investigate the mechanical and strength variation characteristics of coal specimens under dynamic and static combined loading conditions and to analyze the difference of dynamic strength performances between true triaxial and conventional triaxial conditions with static and dynamic combination loads. The natural and 7 d saturated coal specimens were compressed and impacted using the true triaxial Hopkinson bar systerm at Monash University. Experimental results show that, under the true triaxial dynamic and static combination loading，the dynamic strength of the saturated 7 d coal specimens in the X-axis direction is about 17.43% lower than that of the natural coal specimens，while the former is about 15.88% and 14.23% higher than the later respectively in Y- and Z-axis directions. With the variation of the intermediate principal stress，the dynamic triaxial strengths of two types of coal specimens show a initial increasing and then decreasing trend with a turning point corresponding to the intermediate principal stress of 6 MPa. The coal specimens exhibit a distinct confinement dependence，and the effect of water on the strength and deformation of coal is also significant. Besides，comparison between the test results of true triaxial and conventional triaxial static-dynamic combination loads indicates that the opposite trend of the coal strength is mainly attributed to the different propagation modes of the internal water bearing fractures.

To study the static fracturing characteristics of marble after cyclic impact damage，cyclic impact loading test under a fixed pressure of 0.10 MPa was carried out on notched semi-circular bend(NSCB) samples by using split Hopkinson pressure bar(SHPB) system for preparing the samples with different degrees of initial damage，and static three-point bending fracture test was performed on the damage samples. The results show that the sub-critical cracks in samples initiate and propagate continuously at a low speed with increasing cyclic impact number and the dynamic peak stress and elastic modulus decrease under equal energy impacts. In the three-point bending fracture test，the static fracturing mechanical properties of samples degrade with increasing the cumulative damage with a maximum decrease of 52.37% in fracture toughness and a maximum increase of 140.49% in failure displacement. There is a linear negative correlation between the fracture toughness and the dynamic cumulative damage with a coefficient of determination(R2) of 0.98. The time distribution of AE events tends to be uniform and the total cumulative number of events increases greatly with increasing sample damage. When the samples are damaged，the cracks begin at the tip of the prefabricated crack and then extend to the loading point. With increasing impact damage，the crack propagation path tends to be tortuous. The local strain concentration zone can well predict the final failure modes of samples.

In order to deeply understand the fracture propagation mechanisms and bedding directivity effect of shale under tension，three-point bending and Brazilian tests were performed on Longmaxi shale specimens in various bedding orientations with respect to the loading direction to study the fracture propagation patterns and then to explore the fracture propagation mechanisms and bedding directivity effect under tension. For three-point bending condition，It is shown that weak bedding cracks and fracture path deflects in the case of a fracture propagating in the Arrester orientation，producing a complex fracture pattern with fracture branching and deflection，that fracture path usually deflects for a fracture propagating in Divider orientation，which is resulted from shear fracture across bedding planes，and that the fracture path is the bedding plane without deflection for the case of a fracture propagating along a bedding plane. For Brazilian condition，the bedding orientation has a great impact on the initiation point，initiation mechanism，propagation path and propagation mechanism of fractures. When the compressive load is loaded in the direction normal or oblique to the bedding，the fracture is usually initiated from the loading jaws with an arc-shaped fracture path and frequently accompanied by shear fractures across or along bedding planes，and the fracture pathway is determined by tensile and shear fractures which shift during propagation. Only in the Short-Transverse configuration，fracture starts from the disc centre and extends along the bedding plane without deflection. When a tensile fracture propagates along a bedding plane，it can be deviated away from the bedding plane due to the local stress. Complex fracture behaviours such as fracture branching，deflection and weak bedding cracking easily occurs while a tensile fracture propagates in a direction normal or oblique to the bedding. These complicated propagation behaviours are directly related to the stress condition and the relative orientation between the fracture and the bedding plane，and both the bedding and stress state play a dominant role in fracture propagation of shale under tension.

Roadway safety is related to the high productivity and high efficiency of coal mining，and the stability control of roadways in deep coal mines is particularly important. Based on the engineering background of 3－1101 working face of Hongqinghe coal mine，the mechanism of surrounding rock deformation in high-stress roadways was analyzed，and a surrounding rock control technology for deep roadways by directional roof cutting and pressure release was then proposed. The applicability of the technology was studied using numerical modeling and field experiment. It was found that the directional roof cutting and pressure release technology can help to optimize the stress environment of the roadway by artificially controlling the overburden structure without destroying the stability of the roadway. For different roof cutting effects，however，the caving shape，stress distribution and deformation characteristics of the entry surrounding rock are different. Numerical simulations show that，within a certain range，increasing the roof cutting height is beneficial to promote the collapse of the gob roof strata，to reduce the suspended roof length and to diminish the overburden load which was transmitted from the gob roof to the solid coal. Enhancing the roof cutting effect can reduce the deformation of the roadway and accelerate the stability of the entry surrounding rock. Field experiments show that，with enhancing the roof cutting effect，the peak stress and stabilized stress in the coal body decrease，the distance to be stabilized behind the working face is shortened and the deformation and deformation rate of the surrounding rock are reduced. Application of the proposed technology in practice indicates that the large deformation problem of surrounding rock in deep high-stress roadway is effectively solved.

Aiming at rockburst monitoring and early-warning，laboratory loading and unloading tests on coal specimens with various loading rates were conducted，and the data of full-wave acoustic emission(AE) and electromagnetic emission(EME)，and the images showing the dynamic failure process of coal were respectively collected using an AE-EME synchronous collecting system with a sampling rate of 5 MHz and a high-speed camera with a sampling rate of 1 kHz. Combined with spectrum analysis，correlation analysis，AE velocity tomography analysis，energy analysis，etc，the response law of AE and EME to coal failure as well as the temporal and spatial evolution of coal bursting failure process was studied. The results show that both AE and EME have strong positive correlations with instantaneous stress drop，EME is synchronous with AE in the time serial and the spectrum distributions of EME and AE signals with a dominant low-frequency band are consistent with each other，which indicates that both AE and EME originate from crack-generating within the coal. It is also shown that the whole dynamic failure process of coal consists of several stages of bursting damage with violent ejection of broken coal material and that each stage is positively correlated with an instantaneous load drop. In the developing process of coal failure，there are good correlations among crack extension，stress distribution，energy release and AE location within the coal. Bursting failure is likely to occur in the area close to the free surface characterized by high stress concentration，dense cracks. This research provides a reference for the study of rockburst monitoring and early warning.

In order to explore the characteristics of energy dissipation and damage of mudstone specimens under cyclic loading，cyclic loading and unloading tests with incremental stress level and fatigue failure tests are carried out. The plastic strain and energy evolution under different load levels are analyzed. Depending on the fatigue tests，the damage variables are defined from the perspective of energy，and the fatigue life of the specimens under different maximums of the cyclic load is predicted. The results show that the plastic strain and dissipated energy in the initial cycle under the same load level are much larger than those of other cycles，and that the dissipated energy ratio in the initial cycle increases rapidly in the elastic segment and increases abruptly when the specimen approaches to failure. The definition of the damage variables from the perspective of energy can avoid the occurrence of negative damage，and a power function relationship between the fatigue life and the load level of specimens is gained.

Artificial freezing method is widely used in the construction of subway，and freezing-thawing action will results in changes of hysteretic curves and damping ratio of soil. Dynamic triaxial test was operated on frozen-thawed soil samples to obtain the developing patterns of hysteretic curves and damping ratio of soil samples under cyclic subway loading. The test results show that, under cyclic loading，hysteretic loops change from wide to thin and long，that the area and opening of hysteretic loops increase with decreasing the freezing temperature or the consolidation degree，and that the effect of the cyclic load cannot offset the effect of the freezing temperature and the consolidation degree. With increasing the number of loading cycle，the damping ratio in turn declines rapidly，keeps constant，increases slightly，decreases slowly and tends to be stable. Both the initial and final stable damping ratios increase markedly with decreasing the freezing temperature. Decreasing the consolidation degree makes the initial damping ratio decrease conspicuously while has no obvious influence on the final stable damping ratio. The relationship between the damping ratio and cyclic loading times boils down to the relationship between the damping ratio and the accumulated strain. Based on the experimental data, a function describing the relationship of the damping ratio and the accumulated axial strain was derived. The study can give a beneficial guidance on controlling the post-construction settlement of the area where artificial frozen method is applied.

Vacuum-surcharge combined preloading is a commonly used method for soft ground improvement. Aiming at developing a reasonable calculation method for evaluating foundation settlement process in engineering practice, a numerical model called VRCS1 to calculate the large-strain radial consolidation of saturated soft soils stabilized by the vacuum-surcharge combined preloading method was developed based on the piecewise-linear approach. The algorithms of VRCS1 model were deduced，and comparisons between the VRCS1 model with the existing small-strain analytical solution，large-strain numerical solution and large-scale laboratory experiments were conducted. It is shown that the VRCS1 model can accurately simulate the process of large-strain radial consolidation of saturated soft soils. Besides，compared with the existing large-strain solutions in the literature，VRCS1 model has a wider range of application due to considering a variety of complex factors involved in the radial consolidation process and adopting the piecewise-linear method to define the compressibility and permeability of soils. VRCS1 model was used to calculate the settlement of an embankment at Second Bangkok International Airport，Thailand，and good agreement between VRCS1 model calculations and field measurements was obtained.

Drainage plate clogging often results in poor reinforcement effect of the conventional vacuum preloading technology applied to hydraulic fill super soft soil grounds. To solve the problem，a new type of vacuum preloading method，namely alternating vacuum preloading method，for treating hydraulic fill super soft soils，was proposed，and the reinforcement mechanism and effect were investigated based on the indoor model test and numerical simulation of PFC2D. The study results show that the alternating movement of soil particles due to the alternating vacuum preloading can effectively prevent the formation of clogging mud layers and“soil columns”and hence，make the overall reinforcement more uniform and effective. It is also shown that，compared with the conventional vacuum preloading method，the water discharge and the settlement of the soil ground reinforced by the proposed method increase by 14.92% and 11.80% respectively，the vane shear strength of the reinforced soil rises by 21.65% and the water content reduces by 26.74%. The compaction degree of the clogging mud layer decreases while the porosity of the clogging mud layer increases by more than 30%，which indicates that the anti-clogging effect of the developed method is obvious.

In order to make clear microscopic characteristics and mechanical property of natural paleosol and dry-wet cyclical paleosol，to reveal the correlation between microstructure change and macro-mechanical property and to distinguish the difference between paleosol and loess，the microscopic characteristics and mechanical properties of paleosol samples taken from Zaosheng tunnel No.3 of Yinchuan-Xi?an high-speed railway were systematically investigated under different conditions from the aspects of mineral component，porosity characters，contact form and relaxation time，adopting X-ray diffraction，scanning electron microscope and nuclear magnetic resonance，and comparisons were made with the existing research results on loess. Paleosol mainly containing quartz，feldspar and calcite shows some microscopic characteristics including coagulum and graining developing，indirect contact and surface-surface contact，a large proportion of tiny holes，quasi-circular grains and relative concentration of distribution. On the mesoscopic scale，the results of MRI show that paleosol has a T2 spectral distribution form with good inversions as well as one primary and two secondary peaks. With the proceeding of dry-wet circulation，intergranular contact form is gradually transited from surface-surface to side-surface and finally side-side or spot-surface Meanwhile，the proportion of micro holes gradually reduces accompanying with medium and large holes gradually increasing，the granular abundance value constantly increases and fractal dimension gradually decreases. On the mesoscopic scale，the main peak of T2 spectrum still takes a large proportion，and with increasing cycle number，the peak value of the spectrogram roughly increases and constantly moves right accompanying with the spectrum area gradually increasing. Due to the interaction of micro，fine and macro levels，both the cohesion and internal friction angle have a negative correlation with the number of dry-wet circulation，while the non-loading expansion rate has certain positive respondence. compared with loess，the content of quartz in paleosol is less，followed by illite and calcite，and the proportions of micro，small，and     medium and large holes are respectively larger，smaller and same. The granular distribution of paleosol is relatively centralized and the shape tends to be round.

An early warning system of slope instability is one of optimal choices to decrease casualties and economic losses resulted from landslide disasters. A new technique for forecasting landslides by means of elastic wave propagation in soil was developed. To verify its applicability，a series of small scale fixed and varied slope model tests，as well as a large scale model test，were conducted. The test results show that the elastic wave velocity continuously decreases with increasing the moisture content or the deformation of the slope soil and sharply drops near slope failure，and that the soil deformation has more significant effect on the elastic wave velocity than the water content. It was proposed that a warning should be issued once the wave velocity decreases drastically. Based on these observations，a workflow of the elastic wave velocity monitoring system for landslide prediction in the field application was presented，and the problems for applying the monitoring system in practice were also analyzed.

Based on the equivalent assumption of elliptic cylindrical drain and the linear loss law of the vacuum degree in the prefabricated vertical drain(PVD)，a solution for calculating the radial consolidation of PVD combined with vacuum preloading was proposed. The shape effect of PVD was discussed and the influence of relevant parameters on the foundation consolidation was analyzed. Case study was performed to validate the rationality of the present solution by the comparison between the settlement curve calculated by the present solution and the measured settlement curve，and the consolidation behavior is detailed investigated on the basis of the present solutions. The results show that，when considering the shape effect of PVD，the elliptic cylinder equivalent method is the optimum choice and the result calculated by the perimeter equivalent method is closer to that by the elliptic cylinder equivalent method. Increasing the loss coefficient of the vacuum degree or the vacuum pressure on the top of PVD can accelerate the discharge of pore water in the foundations，speed up the descent rate of the water table and lower the final water table. As the parameter κ increases，the consolidation rate of the overall foundation slows down.