Columnar jointed basalt is a typical jointed rock mass formed from the contraction of volcanic lava. The rock mass has “columnar mosaic structure” showing complex discontinuous，heterogeneous and anisotropic mechanical properties. The control of the unloading relaxation is thus a key problem to the construction of Baihetan hydropower station. Based on the research results in recent years，the geological origin and evolution of columnar jointed basalt are first described. The engineering classification of Baihetan columnar jointed basalt is then introduced. The discontinuity，the scale effect and the anisotropic mechanical property of the columnar jointed basalt are obtained through geological examinations，rock mechanics tests and numerical simulations. Based on the field monitoring and the numerical analysis on the relaxation deformation of the dam foundation and the underground cavern，the relaxation characteristics of the columnar jointed basalt are revealed. The anti-relaxation control measures of the dam foundation and the underground cavern in the optimization of structure shape and excavation support method are analyzed，and the supporting time and methods for relaxation control of the columnar jointed basalt are summarized. This study shows that the Baihetan columnar jointed basalt has significant unloading relaxation. Optimization of the structural shape can reduce the relaxation range. The anti-relaxation ability of rock mass can be improved by reinforcement measures before excavation. Support measures to alter the stress state immediately after excavation are effective to limit the spatial extension of relaxation.

After the excavation unloading of rock mass，the formed roadway structures are in a relatively stable state. Disturbed by engineering disturbance，strain energy is accumulated in the rock mass surrounding the roadway. The surrounding rock mass may fail catastrophically under such combined dynamic and static loads，which is defined as impact rockburst. In this paper，the rockburst experiment was carried out under different dynamic load frequencies. Using the image acquisition system，pictures of the whole process of destructive rockburst inside the sample cavern were captured to reveal the destructive characteristics of impact rockburst. Resutls show that the incubation and destruction process of the rockburst can be divided into the calm stage，the particle ejection stage，the local drum stage，the detrital exfoliation stage，the penetration failure stage and the rockburst stage. The cross-section of the blast crater of a rock burst is V-shaped. As the frequency of the dynamic load increases，the damage of the V-shaped blast crater becomes more concentrated，and the blast crater becomes narrower and deeper. The dynamic load frequency thus has a significant impact on the intensity of impact rockburst failure. With increasing the dynamic loading frequency，the acoustic emission increases in the rockburst stage，releasing more strain energy. In addition，the fragmentation degree and the intensity of rockburst also increase with the loading frequency.

This work aims to reveal the fracture evolution characteristics and the meso-mechanical mechanism of the pre-flawed hollow cylinder granite subjected to stress disturbance with a kind of medium-low strain rate，and to further investigate the fracture and instability process of the cavity-fissure composite rock mass commonly encountered in underground engineering. Typical four hollow cylinder specimens with different prefabricated flaw angles were tested using the CTS-RTR 2000 rock mechanics testing system，the real-time acoustic emission(AE) monitoring and the post-test computed tomography(CT) scanning technique. The experimental results show that：(1) The rock fatigue strength，the volume deformation and the fatigue life gradually increase with the flaw angle，and the growth rate of the volume deformation becomes faster. Using the irreversible axial strain，a two-stage damage evolution model was proposed to describe the fatigue damage of rock. (2) The AE count and energy in the process of rock fracture are affected by the angle of two fissures. The cumulative count and accumulated energy count increase with increasing the fissure angle. The cumulative damage of rock at the moment of the sudden increase of stress amplitude is greater than that at the fatigue loading stage. (3) Post-test CT scanning reveals different fracture modes formed from the rock bridge segment，which is greatly affected by the fissure angle. The complexity of the fracture network increases with the increase of the fissure angle，indicating that the rock is different to be fractured with a larger fissure angle. The experimental results are helpful in understanding the fatigue failure mechanism of pre-flawed hollow rock，and provide necessary theoretical supports for the tunnel excavation design，the stability control of surrounding rocks and the long-term stability of jointed rock mass exposed to stress disturbance.

Coalbed gas-water slug flow is an important factor limiting coalbed methane production，but there have been relatively few studies on the patterns of two-phase slug flow in microscale channels. In this study，an independently developed microfluid injection-microscopic observation-microscale modeling system was used to conduct gas-water slug flow experiments under different humidity and fluid velocity conditions. Slug flow patterns were determined using the pressure data and the gas-liquid interaction captured by high-speed cameras. The pressure distribution of three-dimensional slug units was analyzed using the phase-field method. The results shows：(1) “Step pressure” on the gas-liquid interface of slug flow leads to a significant decrease in gas flow capacity. Equal flow injection reduces the gas conductivity by about three orders of magnitude in comparison with single-phase flow. (2) In two-phase slug flow，the apparent length of the gas phase decreases exponentially as the water saturation increases，as does the relative permeability of the gas phase. (3) The additional pressure drop caused by the gas lock is the main restrictor of slug flow，and the pressure drop decreases as the hydrophilicity increases. The gas permeability is more sensitive to changes in wettability at low water saturation. High liquid velocity produces greater inertial force，which makes the relative permeability of the gas phase less sensitive to changes in water saturation. This study reveals the patterns of gas-water two-phase slug flow in microscale channels，and provides a theoretical basis for suppressing the occurrence of slug flow and promoting the efficient production of coalbed methane.

In order to study the relationship between the creep characteristics of fractured hard rock and intact rock，and considering the fact that the creep characteristics of hard rock are quite different under different critical stress intervals，creep tests were carried out on single-flawed sandstones with different crack angles. The test results show that when the loaded stress ?1 is less than the crack initiation stress ?ci，the specimens only show the characteristic of the decay creep stage，and that the difference in creep characteristics of each specimen is mainly due to the different initial damage caused by the crack angles. When ?1 is larger than ?ci，all specimens enter the accelerated creep stage and fail at a certain time，in which the difference in creep characteristics of each specimen is affected not only by the initial damage but also by the time-dependent damage. In view of this，a whole process damage creep model of fractured rock mass is established. When ?1 is less than ?ci，the switch in the model is closed，and the model is only affected by the initial damage. When ?1 is larger than ?ci，the switch is broken and the time-dependent damage body enters work. For the model，the initial damage and the time dependent damage can be calculated by the theory of strain energy and the Kachanov creep damage formula respectively. Both intact and fractured rock masses are applicable to the model with only differences in parameters. Therefore，by first deriving the critical stresses of fractured rock masses from that of intact rock，and then calculating the damage variables under critical stress intervals，the creep model of fractured rock masses can be derived from intact rock. This idea can provide some reference for the study of the damage creep model of fractured rock masses.

To investigate the effect of the roughness on the strength and deformation characteristics of the interface between siliceous slate and mudstone，the direct shear test of interface specimens was conducted using an interface shear apparatus. The shear failure mode，the shear deformation and the strength characteristics of interfaces were analyzed，and then the influence mechanism of roughness on the shear strength increase of the interfaces was discussed. The results indicate that：(1) The shear failure modes of the interfaces of siliceous slate and mudstone are divided into cutting off along the interfaces，cutting off in mudstone and mixed shear-off between the interface and the mudstone. (2) Roughness has a significant effect on the shear deformation characteristic of the siliceous slate-mudstone interface. With increasing the roughness，the deformation modulus of the samples decreases and the shear displacement corresponding to peak strength increases，indicating that the deformation of interface samples during shearing are larger. (3) The roughness significantly improves the shear strength of siliceous slate-mudstone interface. The greater the interface roughness，the greater the increment of the peak strength and the residual strength of the interface are. The cohesion of the interface samples increases greatly with the roughness，whereas the friction angle hardly increases. (4) The mudstone is continuously scraped and compacted by the rough interface of siliceous slate during shearing，forming a “hardening shear band”. The greater the roughness of siliceous slate，the thicker the hardening shear band，and the shear plane of samples tends to occur in mudstone. As the shear strength of mudstone is greater than that of interfaces，the shear strength of interface samples increases continuously with increasing roughness，and its increment is mainly controlled by the cohesive strength of mudstone.

To explore the acoustic emission characteristics of limestone with different rockburst tendencies and its damage model，the laboratory tests on the rockburst tendency of limestone with different burial depths were conducted. The rockburst tendency of limestone which was collected in the same borehole burial depth from 600 to 1 000m was identified by integrating the elastic energy index WET criterion，the deformation brittleness coefficient Kε criterion and the linear elastic energy We criterion. The relationship between the accumulated energy of acoustic emission and the axial strain was derived using time as an intermediate variable. Based on the basic principles of damage mechanics，a damage model was established by the accumulated energy of acoustic emission. The result is that the rockburst tendency of limestone increases step by step with increasing the buried depth gradient. Before the peak stress，the number of acoustic emission events and the cumulative energy of limestone increase sharply，and the cumulative energy of acoustic emission evolves in the form of a “step” pattern. Rockburst tendency shows from none to intense，the lower the frequency of the high number of acoustic emission events，the longer the quiet period experienced by the accumulated energy，and the narrower the width of the “step”. The dissipation mode of the energy stored in the limestone gradually shiftes from the phased dissipation to the instantaneous release. The cumulative energy of acoustic emission of limestone without rockburst tendency increases with a power function，and the cumulative energy of acoustic emission of limestone with rockburst tendency increases abruptly in stages. The resulting damage model can be divided into two different forms based on whether the lime stone has a rockburst tendency. The three parameters A，BT and C in the damage model represent the energy storage capacity，the time of the energy release and the rate of energy release，respectively. The research provides theoretical reference for the discrimination of rockburst tendency.

To reveal the layered rock mass under the action of stress wave disturbance，the rock type size of anomalously low friction mechanism of impact ground pressure influence，five blocks of Shenyang red Yang coal mine roof sandstone were stacked up and down in the loaded cavity of an anomalously low friction testing device. The middle of the block to block was always the working block. The Hs/Hw(0.8–2.0) of different working blocks was used to simulate rock masses of different structural levels or different degrees of fragmentation in the same structural level. The disturbance effects of blasting，roof fracture and concentrated mining were simulated by applying stress wave disturbance Pv(frequency 0–10 Hz，amplitude 0–1 MPa) to the block model system. Axial compression Fv and horizontal impact Fh were applied to simulate the impact of overburden pressure and roof fracture respectively，and the anomalously low friction tests of sandstone blocks with different height-width ratios were carried out under stress wave disturbance. With the height-width ratio as the representation index reflecting the size of the rock block，the disturbance frequency and amplitude of the stress wave as the representation index reflecting the disturbance effect，and the horizontal displacement of the working block as the representation index reflecting the intensity of anomalously low friction effect. The effects of height-width ratio and stress wave disturbance on anomalously low friction intensity and energy evolution characteristics of sandstone working block under the combined action of axial compression，stress wave disturbance and horizontal impact are analyzed. The results show that when the stress wave disturbance，the axial compression and the horizontal impact are constant，the horizontal displacement of the working block decreases with the increase of its height-width ratio，i.e.，the more fractured rock mass under the same stress environment，the greater the intensity of anomalously low friction effect. When the height-width ratio is constant，the horizontal displacement of the working block increases first and then decreases with the increase of stress wave disturbance frequency，and increases with the increase of stress wave disturbance amplitude. Under different test conditions，the maximum kinetic energy per unit mass and power spectral density of the working block increase gradually with the decrease of the height-width ratio. When the height-width ratio is 0.8，the kinetic energy carried by the working block is the maximum，and the intensity of the anomalously low friction effect is relatively large.

基于深部煤层注热、地下气化、煤层自燃等工程所处的高温、高静载、不均匀受热等环境，以深部硬煤为研究对象，采用自制加热设备加热煤样模拟深部的高温环境，施加轴向静载模拟煤层所受的高静载，开展不同加热长度的分段高温轴向静载声发射试验研究，分析煤体的变形破坏特征。研究结果表明：分段高温处理后的煤样应力–应变曲线可划分为压密、弹性、塑性和破坏4个阶段，且同一加热温度下，加热长度越长，煤样的压密过程越明显；煤样的抗压强度、弹性模量和泊松比随着加热长度的增加出现一定的波动，但整体上来说呈线性趋势减小；轴向压缩过程中没有始终伴随着声发射，且压密、弹性和塑性阶段，声发射的幅值、计数、能量的值较小，一旦进入破坏阶段，声发射参量便产生剧烈波动，且煤样发生宏观破坏时应力曲线跌落，声发射信号随之停止；轴向压缩过程中的声发射累计值从常温到100 ℃高温的变化非常明显，且累计值与常温状态下相比会有不同程度的降低，但在同一温度下，随着加热长度的增加声发射累计值与分段长度并没有明显的规律；对破碎后的煤块进行筛分试验及分形特征分析，发现煤样发生拉伸破坏的同时也伴随着剪切破坏，且分形维数的变化特征和煤样破坏块度的变化规律较一致，能较好的反映煤样破碎特征。

In order to solve problems of ground pressure，surface collapse and buildings and structures damage caused by underground mining in metal mines with steeply dipping discontinuities，the footwall of the Jinshandian east area was taken as the research case and the basic law of ground movement was obtained first based on the in-situ failure investigation and monitoring data of underground and surface. Combined with geological conditions and theoretical analysis，the mechanism of ground movement was studied. Ground pressure appears in the roadway near the underground goaf and the F1 fault，which is mainly due to the sliding of the F1 fault caused by mining activities. The surface deformation of the footwall has experienced three accelerated stages since mining，and the accelerated deformation point coincides with the time of mining activities，surface collapse and underground roadway failure caused by steeply dipping discontinuities. It is obtained that the deformation and failure of the steeply dipping discontinuities rock mass is gradually transferred from the deep to the ground surface，which caused the movement of the ground surface and crack of buildings and structures. A ground movement mechanism analysis model of the footwall rock mass around goaf is simplified to the cantilever beam model，in which the rock mass failure is mainly caused by the F1 fault slip induced by mining and in turn causes the flexure toppling failure of the steeply dipping rock column. The failure surfaces of each rock column are connected and slip along the failure plane. The steeply dipping discontinuities are the main reasons for the large-scale ground movement of the footwall，and the special ground movement mechanism causes the monitored movement angle to be significantly smaller than the designed movement angle.

For accurate characterization of the statistical properties of orientations(i.e.，dip angle and dip direction) of a rock mass discontinuity，a Copula method is proposed to model the discontinuity orientations accounting for the cross-correlation between the dip angle and the dip direction. Based on the optimal fittings of the marginal probability distributions and Copula functions(i.e.，correlation structures) of the discontinuity orientations from the measurement data，a two-dimensional joint probability density function of the dip angle and the dip direction can be constructed. In the meantime，a visual comparison between the results obtained from the proposed method with those obtained from the traditional Fisher distribution and bivariate empirical distribution methods is conducted. The measured and simulated discontinuity orientations are compared on stereographic projection maps by using the stereographic projection method. Finally，four examples are investigated to illustrate the effectiveness of the proposed method. The results indicate that the traditional Fisher distribution and the bivariate empirical distribution methods cannot effectively characterize the cross-correlation between the discontinuity orientations，while the proposed method can be in a more flexible way to construct the joint probability density function of the discontinuity orientations that follow arbitrary marginal distributions and correlation structures based on a small amount of measurement data. In short，the proposed approach can better depict the cross-correlation between the dip angle and the dip direction，and circumvent the limitations of treating the dip angle and the dip direction as two independent variables in constructing the probability distribution models of the discontinuity orientations.

The impact tendency of coal and rock is an important factor of rockburst. Aiming at the microfracture development characteristics and precursor identification problems of impact tendency coal，the uniaxial compression test was carried out by the MTS testing machine. The characteristics of stress change，energy dissipation and dynamic deformation failure of impact tendency coal were studied by means of acoustic emission and high-speed camera. According to the temporal and spatial strong development law of coal micro fracture event in high-stress stage，the impact risk index was defined and applied to precursory identification. The results show that there is stepped sub failure behind the peak of impact prone coal. The greater the stress drop value and the stress drop rate of sub failure，the more intense the post peak impact failure. The microfractures of coal samples intersect with each other，resulting in the overall impact failure. There are many fracture nucleation areas in the coal sample，and the large-scale cracks (large energy events) in the areas are periodically accumulated and bred by many small cracks(small energy events). The concentration area of large energy events before the peak is basically consistent with the impact failure position after the peak. Near the plastic stress drop of coal and before the peak stress drop，the micro fracture events show instantaneous and strong localization characteristics，and the corresponding impact risk index exceeds 1，which can be used as an effective precursor index for the imminent macroscopic fracture (stress drop) of coal. The research results can effectively identify the precursory information of coal and rock fracture，and provide reference for the monitoring and early warning of coal rock disasters and rockburst.

At present，the seismic response of the underground structure-soil system is mostly studied without considering the vertical seismic action and the influence of surrounding buildings. In this paper，the tunnel-soil system was taken as the objective by considering the influence of a 10-story ground building. The shaking table test under multi-dimensional seismic waves was carried out to study the dynamic response law of the tunnel and soil. The test results show that the seismic response of tunnel and soil under multi-dimensional ground motions is stronger than that under unidirectional ground motions. With the increase of the seismic input dimension，the spectrum of soil does not change. The response of the soil and tunnel under far-field earthquake is strong. Because the near-field earthquake has high-energy velocity pulse，the difference of acceleration response between soil and tunnel under two types of seismic waves gradually decreases with the increase of the input intensity. The existence of surface structure-pile foundation leads to the obvious difference in the strain between the middle section and the end section of the tunnel. Compared with the strain of the end section，the strain on the right side of the middle section increases and the strain on the left side decreases.

There are more and more diseases caused by the horizontal action of bridge foundation piles built by experience in high and steep slope areas. In this paper，a set of loading devices and test scheme were designed with the Hongding bridge as the prototype. Considering the position of the foundation piles in the slope and the stress form，the horizontal static loading and lateral-axial combined loading model tests were conducted on the horizontal bearing characteristics of the foundation piles，and the fitting relationships of the pile top displacement，the horizontal load，the relative position and the vertical load were obtained，respectively. The results show that under the horizontal cyclic load，the horizontal displacement of the pile top and the bending moment of the pile body increase with the increase of the load and the load cyclic action times. Under the horizontal load，the ultimate bearing capacity of the foundation pile is inversely proportional to the horizontal distance between its position and the slope toe. That is，the closer the foundation pile is to the slope toe，the greater the ultimate bearing capacity，while the horizontal displacement of the pile top and the bending moment of the pile are smaller. The influence of simultaneous horizontal and vertical loading on the horizontal ultimate bearing capacity of the pile foundation is related to whether the pre-added vertical load reaches the critical value of the stable vertical deformation load of the foundation piles. When the vertical load is less than the critical value，the horizontal ultimate bearing capacity of the foundation piles can be increased；When the vertical load is greater than the critical value，the horizontal ultimate bearing capacity of the foundation piles would be reduced.

There is a complex coupling effect among soil arching effect of the embankments，the tensile membrane effect of the geosynthetic reinforcement and the load bearing effect of the soft ground in geosynthetic-reinforced pile-supported(GRPS) embankments. Due to the evolution of soil arching with embankment loading and soil settlement between piles，the current calculation theories and methods are challenging to evaluate the whole process of load regulation and settlement stability of GRPS embankments. By introducing the technical idea of the hybrid test，a set of array multi trapdoor test devices and pile-soil foundation hybrid test methods were developed. The timely data exchange between the physical model of reinforced cushion embankment and the numerical model of pile-soil foundation was realized. Nine groups of hybrid tests with different embankment heights and tensile stiffness of reinforcement were carried out. The test results show that the established hybrid test method could well model the full component participation and full effect coupling working performance of GRPS embankments，greatly save the test cost and time，which provides an innovative evaluation method for the long-term bearing performance and settlement prediction of GRPS embankments. The concentric arch model can accurately evaluate the maximum soil arching effect of GRPS embankments. When the embankment height is low，the geosynthetic reinforcement with high tensile stiffness can improve the loading efficacy of piles. The geosynthetic reinforcement with high tensile stiffness can significantly reduce the settlement and the differential settlement between piles and soil under different embankment heights. With the increase of embankment height，the pile and soil efficacies with different reinforcement stiffness tend to be consistent，which reflects that the subgrade reaction coefficient method cannot reliably reflect the actual load-bearing mechanism of soil between piles.

The infiltration angle of the soil/filter interface is deflected with nonhomogeneous anisotropic seepage filed and fluid regime in dyke-dams so as to bring about the local hydraulic factors mutation when the interface infiltration angle is nonorthogonal. In this paper，a multi-function seepage piping instrument was developed to carry out contact erosion tests. The test samples of the fill and filter material were taken from the site of the earth dam construction，and they were prepared at the angles of 30°，45°，60° and 90° between the seepage flow and the interface. It was conducted to investigate the mechanism of contact erosion by measuring the hydraulic interface factors under different hydraulic gradients in the laboratory. At the same time，a PFC3D numerical model was established by using the CFD-DEM method. The micro properties of internal erosion at the contact interface of soil/filter were simulated and analyzed by comparing with the experimental data according to the experimental facility?s working conditions. The results show that the seepage infiltration angle at the soil/filter interface has a significant impact on the effect of filtration. The indicators of the filter are better when the infiltration flow is orthogonal to the interface. However，the hydraulic factors comprising the infiltration flow velocity，the local hydraulic gradient，the pore pressure and the soil pressure have obvious variations due to the seepage flow refraction when the interface infiltration angle decreases. The fast seepage velocity aggravates the internal contact erosion and causes an accumulation more in the number of fine particles from the protected soil at the local interface，which weakens the filter efficiency of the filtering layer. It should be pointed out that both the experiment and numerical simulation reveal that the filter specimens still keep the function under a high hydraulic gradient，indicating that the current filter criterion has enough safety reserve.

The capillary barrier cover is maturely used in arid and semi-arid areas，but its service performance and design criteria in humid areas are less studied. In order to clarify the service performance of the capillary barrier cover under continuous rainfall，the relationships between the water storage capacity and the breakthrough time of the capillary barrier cover with the rainfall intensity，the thickness and the initial moisture content of the fine-grained soil layer were studied through the soil column infiltration test. The test results show that：(1) Decreasing the initial water content and increasing the thickness of the fine-grained layer can increase the water storage capacity. (2) Within the range of test thickness and moisture content，the breakthrough time decreases linearly with decreasing the initial water content while with increasing the fine layer thickness，and has a negative power function relationship with the rainfall intensity. Near the saturated permeability coefficient，the breakthrough time changes from a rapid decrease to a slow decrease with increasing the rainfall intensity. (3) Under extreme continuous rainfall，the infiltration rate of the capillary barrier cover is first controlled by the rainfall intensity，and finally tends to saturated permeability coefficient. This process can be described by the equivalent infiltration rate，which is significantly affected by the rainfall intensity and the initial water content. Based on the test results，a practical water storage capacity model and a semi-empirical theoretical model of the breakthrough time were proposed. The calculation results of the models are consistent with the test results，which illustrates that the proposed models can be used as the basis for the design of the capillary barrier cover in continuous rainfall. The research results can provide references for the design and maintenance of capillary barrier cover in humid areas and extreme rainfall conditions.