Coal and gas outburst is a common dynamic disaster in underground coal mining activities，which seriously threatens the safety and green production of coal mines. In view of the uncertainty，suddenness and danger of coal and gas outburst，physical simulation test has become effective means to study the mechanism of coal and gas outburst. By consulting a large number of literatures，it is found that：(1) the outburst simulation experimental device was iteratively upgraded from uniaxial to biaxial，pseudo-triaxial and true triaxial. The size of the specimen was upgraded from small to large，and the data acquisition was changed from single to diversified. The successful development of various large-scale multi-functional true triaxial visualization and modular test systems provides an effective platform for quantitative research on the mechanism of coal and gas outburst. (2) A large number of physical simulation experiments on coal and gas outburst around the“three elements”were carried out，and the influence of in-situ stress，gas pressure and physical and mechanical properties of coal on the outburst was explored. Through the evolution of coal seam temperature and two-phase flow impact，the outburst intensity was inverted，the initiation conditions and disaster mechanism of outburst were basically mastered，and the theoretical system of coal and gas outburst with Chinese characteristics was formed. However，with increasing the depth of coal mining in China，the mechanism of deep coal and gas outburst becomes more complex. In view of the shortcomings of coal and gas outburst research under the new situation，the future research direction is prospected，aiming at improving the mechanism system of coal and gas outburst，breaking through the research stage of qualitative hypothesis，exploring the quantitative conditions of disaster preparation，occurrence and development stage，and providing a reliable theoretical basis for the prediction and prevention of coal and gas outburst on site.

Due to frequent stress disturbances caused by mining activities，the stability of surrounding rock in underground engineering is becoming increasingly prominent，which seriously restricts the safe and efficient mining of underground mineral resources. In order to explore the damage and fracture mechanism of rock mass in the process of stress disturbance under different buried depths，based on conventional triaxial tests，graded stress disturbance laboratory tests under four groups of confining pressures were carried out in this paper. Based on mechanical analysis，acoustic emission(AE) source phased location and evolution characteristics of damage evaluation indexes，the rock mechanics damage degradation law and meso-crack development characteristics under graded stress disturbance were determined，and the correlation among rock damage state，meso-crack development characteristics and the change of damage evaluation indexes was established. The results show that：(1) The peak strength and peak axial strain of rock increase with the increase of the confining pressure under the disturbance of graded stress. The axial strain increment of stress disturbance in each stage shows a slight fluctuation in the early stage，a slow increase in the middle stage，and a rapid increase in the late stage. The average elastic modulus increases slightly at the beginning and then decreases rapidly. (2) The confining pressure reduces rock damage accumulation rate by limiting crack propagation. The rock can withstand more stress disturbances under high confining pressure，and the creep characteristics of constant pressure stage are more obvious. (3) In the early stage of loading，the crack development in the rock is only the repeated compaction failure in the damaged area and the development of a few microcracks in adjacent areas. In the late stage of disturbance，with the increase of axial force，the limiting effect of confining pressure will be weakened，resulting in rapid crack propagation. (4) The changes of the number and scale of microcracks in rock at different loading stages can be effectively reflected in the AE b value and AE ΔF value，which are highly coupled with the rock damage degree and can be used to quantitatively evaluate the rock damage state. The research results can provide some guidance and reference for the stability and damage assessment of engineering rock mass.

The idea of intelligent tunnel support is an effective solution to the problem of low matching degree between tunnel support parameters and actual geological conditions. However，the research and implementation of tunnel intelligent support method are few，and the establishment and application of this method is in great demand. In this paper，by improving random forest algorithm and particle swarm optimization algorithm，an IPSO-MOC-RF intelligent decision algorithm adapted to multi-label and multi-output data types was proposed to analyze the complex and diverse support parameters of tunnels. The tunnel support parameter system was established according to three research scenarios of tunnel survey and design stage，construction stage and rock burst disaster，and 285，480 and 543 data samples were collected respectively for training models. According to the training results，the MR values were 0.886，0.917，0.897，and Hamming Loss values were 0.046–0.091，respectively，which verified that the model could effectively extract the complex nonlinear mapping characteristics between geological indicators and tunnel support parameters. In addition，a tunnel intelligent support platform was established by integrating BIM model and intelligent decision model with Cesium cloud platform，and applied to the Grand Canyon tunnel of the Ehan expressway in China. The validity of the intelligent tunnel support decision is verified by statistical analysis，theoretical analysis and field continuous monitoring. The results show that only 1 of the 7 samples in the survey and design stage failed；only 3 of the 47 samples in the construction stage failed，and the 3 selected test sections were all successful(the maximum displacement of the tunnel vault and side wall were 36.4 mm and 25.8 mm，respectively)；the three test sections of rockburst disasters were successful. The application effect of intelligent tunnel support model is remarkable，which verifies the feasibility of the practical application of this method，and provides a new idea for the research of intelligent tunnel construction.

In order to investigate the deformation and failure characteristics of coal around gas drainage boreholes under the influence of loading rates，uniaxial compression tests of coal samples with echelon crack and borehole composite defects under different loading rates were carried out. Combined with digital image correlation technology，the mechanical properties，failure modes and deformation field evolution of coal samples with composite defects under different loading rates were analyzed. Through computer vision technology，the characteristics of borehole failure and echelon crack propagation under the influence of the loading rate were further studied，and the loading rate effect of deformation and failure characteristics of coal samples with composite defects was revealed. The results show that：(1) The echelon crack and borehole composite defect samples have the characteristics of high strength at low loading rate and low strength at high loading rate under different loading rates. The critical loading rate of the sample is 0.2 mm/min，and the change trends of peak stress，peak strain and elastic modulus of the sample change at the critical loading rate. (2) The samples present progressive failure characteristics at different loading rates，and the failure mode is dominated by tensile shear mixed failure. With the increase of the loading rate，the tensile effect gradually dominates. Under the induction of echelon cracks，the sample shows shear dislocation failure along the penetration surface formed by new cracks and flying cracks at low loading rate，and shows tensile failure along the horizontal opening of new cracks at high loading rate. (3) The borehole shrinkage C is introduced to quantitatively characterize the degree of borehole deformation. The borehole is opened at low loading rate，and C is greater than 1. With the increase of loading rate，C gradually decreases. At high loading rate，the borehole first opens and then collapses rapidly，and finally C is less than 1. (4) Under the action of loading，the echelon cracks are staggered and opened in the counterclockwise direction，and the deformation is mainly concentrated in the unstable crack propagation stage. With the increase of loading rate，the dislocation momentum and opening amount increase significantly. With the increase of loading rate，the dislocation momentum and opening amount of the echelon crack increase significantly，and the tensile effect of the sample is enhanced，and the opening deformation ratio is gradually higher than the dislocation deformation ratio.

The poroelastic effect in micro/nano-pores of coal significantly affects gas production. However，it is currently rare for the poroelastic effect to be considered in gas apparent permeability model for micro/nano-pores. In order to investigate the influence of the poroelastic effect on gas flow mechanisms in micro/nano-pores，a gas apparent permeability model considering the dynamic evolution of pore size is constructed based on the poroelastic effect and multiple mechanism flow model in micro/nano-pores. The dominant flow mechanism of the dynamic apparent permeability model is determined and the contribution of slippage effect in micro/nano-pores to gas recovery production is evaluated. The results show that the poroelastic effect impacts the contribution of the slippage and the surface diffusion effects to the apparent permeability by influencing the evolution of pore size. As the pore pressure increases，the dynamic apparent permeability ratio(the ratio of the apparent permeability affected by the poroelastic effect to the initial apparent permeability) is controlled by the slippage effect and the poroelastic effect in turn. Additionally，the contribution of the slippage effect to the apparent permeability ratio decreases rapidly at lower pressure but decreases more gradually at higher pressure as the pressure increases. In the process of gas recovery from low-permeability coal seams，the contribution of the slippage effect to gas recovery production initially increases rapidly，then decreases gradually，and eventually reaches a slow increase. A smaller average pore size in micro/nano-pores leads to a greater contribution of the slippage effect to gas recovery production.

The combination of high ground stress in deep coal seams and high temperature thermal stress in underground gasification will cause rock damage and destroy the stability of the coal seam surrounding the rock. This research investigated the relationship between temperature(25 ℃，200 ℃，400 ℃，600 ℃，800 ℃，and 1 000 ℃) with the microstructure and mineral composition of sandstone through the application of scanning electron microscopy，X-ray diffraction，and CT scanning. The results suggests that the temperature has a significant impact on sandstone microstructure because an increase in the temperature can improve the total porosity. The porosity of sandstone at 1 000 ℃ is the maximum and the minimum at 25 ℃. The number of pores of different sizes decreases with the increase in the temperature. However，the number of tiny pores at 1 000 ℃ is the most，and the number of pores at other sizes at 25 ℃ is the most. After heating，the sandstone begins to produce microcracks. When the temperature exceeds 600 ℃，the number of microcracks increases significantly，and the length，width and density of microcracks further expand with the increase in the temperature. The diffraction intensity and mineral composition of the sandstone vary with the temperature. When the temperature is higher than 600 ℃，the diffraction intensity of various mineral compositions takes a turning point. When the temperature exceeds 400 ℃，a physical and chemical reaction occurs in the mineral composition of sandstone，and a transformation occurs between crystals. With the increase in temperature，the quartz mineral content gradually increases，and the feldspar mineral gradually decreases. The critical temperature of the specimen?s apparent morphology change was 400 ℃.

The mesoscopic heterogeneity of granite has an important influence on its damage and failure behavior. In this paper，an elastoplastic phase-field model is established based on the thermodynamic principle as well as the balance equations of forces and energy，and the non-associative plastic constitutive relationship suitable for rock-like materials within the framework of the classical phase field model is introduced. By comparing with the analytical solution and experimental data，the accuracy and reliability of the elastoplastic phase-field model are verified. Furthermore，a heterogeneous numerical model reflecting the real mesostructure of granite is established by digital image processing. The triaxial compression test of granite is numerically simulated，and the macroscopic mechanical behavior and the crack propagation mechanism of rock is analyzed at the mesoscale. The results show that compared with the experimental data and the traditional elastic-brittle phase-field methods，the elastoplastic phase-field model based on the real mesostructure of granite is capable of well capturing its macroscopic nonlinear mechanical behavior. The initiation and propagation of internal cracks in granite and the distribution of local stress field are affected by the mechanical properties，geometric shape and distribution of mineral particles. The research method of this paper provides a simple and effective way to study the multi-scale damage and failure of rock in the future，and it has important engineering practical significance for evaluating the mechanical properties of surrounding rock in underground engineering.

Grouting is one of the main technologies for controlling the stability of fractured rock masses，and different grouting materials have significant differences in their reinforcement effects on fractured rock masses. In this study，three grouting materials，sulfate-aluminate cement(SAC)，ordinary Portland cement(OPC)，and epoxy resin(EPR)，were selected to fill pre-existing parallel double-cracks rock samples，and uniaxial compression tests、AE and SEM tests were conducted on these samples. The results showed that epoxy resin filling had the highest strength for the fissured samples，followed by OPC cement，and SAC cement had the lowest strength. The failure mode of the samples was significantly influenced by the filling material，with EPR-filled samples not being controlled by pre-existing cracks，while SAC and OPC-filled samples mainly exhibited a tensile-shear mixed failure caused by crack extension and breakthrough. Electron microscopy scans indicated that the differences were primarily due to the bonding characteristics between the different grout types and the rock. The interfaces of SAC and OPC filling were of the cover type，while EPR filling belonged to the fusion type. Based on these experimental results，a numerical model representing different bonding patterns was established using the Particle Flow Code(PFC)，and the reinforcement mechanisms of different grouting materials were analyzed. The numerical simulation results showed that the proportion of tensile-shear microcracks，the distribution of microcrack inclination angles，and particle displacement vectors during the sample loading process were significantly influenced by the grouting material. Due to differences in the strength and bonding performance of the grout itself，the bonding pattern between the grout and the rock was altered，leading to changes in the movement of grout and rock particles and microcrack formation during the loading process，ultimately resulting in differences in macroscopic strength and failure modes.

The frequent water and sand inrush disasters in the sandy dolomite tunnels of the water diversion project in central Yunnan seriously restrict the progress of the project and threaten the construction safety. In this paper，the disaster conditions and characteristics of water and sand inrush in water-rich tunnel sections are summarized by means of construction tracking，case statistics and theoretical analysis of water and sand inrush in sandy dolomite tunnels. According to the typical disaster prototype of Xiaopu tunnel，the evolution of seepage field，stress field and displacement field in the process of water inrush and sand gushing is studied by FLAC3D numerical simulation. The critical criterion of safety thickness of rock plate for preventing water and sand inrush disaster is determined by theoretical analysis. In the other hand，systematic and feasible disaster prevention and control system is established. The results show that：(1) water and sand inrush disasters usually occur in the severely completely sandy and water-rich section of the fault development. (2) In the evolution process of water and sand inrush disaster，the pore water pressure of intense and severe sandy dolomite has funnel effect. There is a time lag in the change of seepage flow of severe sandy dolomite compared with that of strong sandy dolomite，the seepage flow of intensely sandy dolomite is obviously smaller than that of intensely sandy dolomite. (3) When the severely sandy dolomite tunnel is excavated to a distance of 4 m from the fault，the stress of the surrounding rock of the tunnel shows a sudden change. When the completely sandy dolomite tunnel is excavated to a distance of 8–9 m from the fault，it shows an obvious tensile stress area. (4) The maximum settlement of the vault of the severely sandy tunnel section occurs when the excavation is 1 m away from the fault，while the evolution of the displacement field of the completely sandy tunnel section has no obvious law. (5) The critical criterion of safe thickness of outburst prevention rock plate in water-rich sandy dolomite tunnel is determined. The minimum safe thickness calculated by engineering example is close to the reserved in practical engineering. On the basis of the above research results，combined with the comprehensive advanced geological prediction and the evolution process of water and sand inrush in water-rich sandy dolomite tunnel，the prevention and control system of water and sand inrush in tunnel can be established，which can provide theoretical basis for the prevention and control of water and sand inrush disasters that are prone to occur in water-rich sandy dolomite underground engineering.

Compared with the non-prestressed bolt，the prestressed bolt shows special supporting mechanical characteristics after being pulled out. In order to deeply investigate this characteristic of the prestressed bolt，the full-scale indoor experiments and theoretical analysis were used to study the mechanical response of the prestressed bolt after being loaded，and the supporting mechanical characteristics of the prestressed bolt and its mechanism were further understood，which further extended the active support theory of the prestressed bolt. Additionally，from the perspective of optimizing the support performance of the anchorage system，the numerical calculation method for the critical anchorage length of the prestressed resin bolt was proposed based on the secondary development mean. The results showed that：(1) After the prestress was applied，the shape of the load-displacement curve of the bolt changed obviously，the support stiffness increased in the early stage，and the load mutation point appeared at the same time. With the increase of prestress application value，the load value at the mutation point increased from 17.3 kN to 54.6 kN；(2) The prestressed bolt exhibited an initial increase in stiffness after being subjected to the tensile load，followed by an increase in strength in support mechanics，quickly providing the larger bearing capacity in the early stage of support and effectively improving the ability of the anchorage system to control the deformation of the surrounding rock；(3) The established numerical analysis model well reproduced the mechanical response of the anchorage system under the tensile load，based on which the peak bearing capacities of the anchorage system under different anchorage length conditions had been analyzed，and the critical anchorage length of the resin bolt under this experimental condition had been determined to be 44 cm. The relevant research results have guiding significance for understanding the support mechanical characteristics and parameter design of prestressed anchorage systems.

Taking the east area of Jinshandian iron mine of Wuhan Iron and Steel(Group) Company as a relying project，the engineering geological condition of the mine area and the mining process of the ore body were clarified. The spatial characteristics of surrounding rock failure in complex goaf were analyzed by ground pressure behavior investigation and microseismic fracture monitoring. Combining with the results of three-dimensional numerical simulation，surrounding rock fracture monitoring and roadway failure survey，the failure mechanisms of surrounding rocks in hanging wall and footwall of the mining area were elucidated，and the analysis index of discontinuous deformation of surrounding rock failure(i.e.，failure angle) was proposed based on the plastic failure of rock mass，which was verified by comparing it with the collapse angle index. Furthermore，the strata movement laws in both the plane and profile directions caused by the complex goaf in metal mine were revealed. The results show that the failure of surrounding rock and the ground pressure behavior of roadway are distributed around the goaf. On the plane，the convex shape of the half-moon goaf has a magnifying effect on the failure of the surrounding rocks of its two wings. On the profile，the failure of the haulage roadways in the sublevels has the characteristics of elevation lag. Initially，the failure of the surrounding rock in the goaf is mainly caused by the collapse and caving of the rock mass at its top position. As mining progressed，it develops into the fault-slip-controlled chimney caving failure，and finally expands into the through-slip failure controlled by the rock mass structure. The surrounding rock failure of hanging wall presents the characteristics of toppling-slip failure，while that failure of footwall presents the characteristics of the shear-slip failure tracking the faults and structural surfaces. Moreover，the values and variations of the failure and collapse angles of the surrounding rocks of the hanging wall and the footwall are relatively consistent for various exploration line profiles，and these two angles are approximate to show the first decrease after the tendency to stabilize with the mining process. In addition，the hanging wall goaf(FeI) spreads like a strip，and the failure angles that tends to be stable are approximately the same at different exploration lines，and the larger the inclination angle of the main dominant structural surface，the smaller the stable failure angle. Whereas，the footwall goaf(FeII) is distributed in a half-moon plane shape. The stable failure angle in the middle position of the half-moon is larger compared to its two wings，and this angle decreases with increasing the distance between its location and the middle position. The research results are of great significance for guiding the safety production of the mine and ensuring the normal life of the neighboring residents.

The hazard of a rockburst event is directly correlated with the scale of rock mass ejection in deep underground engineering. In order to further enhance the fine characterization and prediction level of rockburst hazards in deep underground engineering，a study was conducted on the classification and discrimination method of rockburst pit volume based on microseismic information. Firstly，a statistical analysis of one hundred and eleven rockburst cases from the deep tunnels of Jinping II hydropower station project was performed. It was found that six indicators，namely the cumulative number of microseismic events，cumulative microseismic energy release，cumulative microseismic volume，microseismic event rate，microseismic energy release rate and microseismic volume rate，showed a high correlation with the volume of rockburst pit. In other words，there was a significant hierarchical difference from low to high between the distribution of rockburst volumes and the values of microseismic parameters. Secondly，a hierarchical clustering analysis was employed to establish a classification scheme for rockburst volumes，taking into consideration engineering practicality and predictability. Taking the Jinping tunnel project as an example，the rockburst volume was divided into five levels，and the corresponding volume thresholds for each level were then determined. Finally，a decision tree based on the improved classification and regression tree(CART) algorithm was constructed to determine discrimination thresholds for various microseismic parameters under different rockburst volume levels，and six individual microseismic parameter criteria for rockburst volume classification were therefore developed. Furthermore，a spider web diagram method based on multiple microseismic parameters was developed for comprehensive discrimination of rockburst classification，and corresponding discrimination criteria were determined through case analysis. This method enables people to rapidly discriminate the potential level of rockburst volume during tunnel excavation. The results from retrospective verification of the collected rockburst cases showed an overall accuracy rate of 85.2% for rockburst volume discrimination，demonstrating a high accuracy and applicability of the proposed method. This research provides a new and effective approach to improve the fine prediction level of rockburst hazards in similar deep underground engineering projects.

The self-initiated static-dynamic state catastrophe behaviour is a key step in coal bursts. However，its dynamic processes and triggering mechanism to coal bursts have not been extensively explored and fully understood. Addressing this gap，our study modified the traditional coal-rock combined specimen and the corresponding indoor experimental method，and implemented physical experiments to simulate coal bursts and static brittle failure under quasi-static displacement loading conditions. Additionally，a novel multi-source information monitoring system was developed，enabling the capture of transient changes in both static and dynamic data on a millisecond time scale. With the new developed experimental method，a comprehensive investigation was conducted to explore the catastrophe process，formation mechanisms of the static-dynamic state catastrophe behaviour，as well as its role in triggering coal bursts. Then some novel insights into the mechanism of coal bursts were put forward. As a result，the elastic rebound dynamic behaviour of the surrounding rock during burst events was founded and identified as a key factor in controlling the self-initiated static-dynamic state catastrophic process. Mechanically，this behaviour exerts impact loads on the coal，directly initiating the dynamic process，and thus can be considered as the direct cause of coal burst. Energetically，through elastic rebound，the surrounding rock works on the coal instantaneously and promotes a large amount of elastic energy it stored to converge to the coal，and effectively reduces the time required for instability，and eventually leading to a large enough energy release rate，which is the inherent cause for coal burst.

Rockburst induced by the overall instability of fault coal pillar in the stope under thick overburden soil exhibits destructive characteristics such as high concealment，strong destructiveness，difficulty in protection，and long duration，which is challenging to predict and prevent effectively in the coal mine field. Taking the 2305S working face of a mine in the Juye coal field as the engineering background，this study adopts theoretical analysis，numerical simulation，and field measurement to investigate the mechanism of rockburst induced by the overall instability of fault coal pillar in the stope under thick overburden soil. The conclusions are as follows: the study discusses the spatial structure and mechanical characteristics of the initial and periodic interactions of rock-soil strata in the stope under thick overburden soil，designs a calculation method for the load-bearing strata to bear the transferred load，overlying self-weight load，and fault structural load，and proposes a mechanical criterion for the rockburst induced by the overall instability of the fault coal pillar in the stope under thick overburden soil. According to the evolution law of simulated stress growth rate，the mining process of fault coal pillars is divided into energy storage stage and critical stage，in which the overall instability shock hazard level rapidly increases during the critical phase. The mechanism of rockburst induced by the overall instability of fault coal pillar in the stope under thick overburden soil is revealed: the fault coal pillar，formed by the intersection of the fault and the goaf，carries a high level of base stress. When the working face advances to the initial interaction phase of the rock-soil strata，the transferred load from the trend strata increases the stress level of the fault coal pillar，while its bearing area decreases continuously under the conditions of continuous mining. When the load exceeds the instability threshold of the elastic bearing zone，a rockburst caused by overall instability occurs. A control plan for this type of rockburst is designed，including pre-mining overall impact risk assessment，well-ground joint regional monitoring-nuclear stress local early warning，and graded bearing multi-layer pressure relief design.

To investigate the interaction mechanisms and failure evolution processes of landslide-pipeline systems under different forms of micro-pile reinforcement，large-scale indoor model tests were conducted using grouting conventional piles and grouting flower tube piles for slope protection in the Southwest mountainous region，with a focus on the emergency rescue project of a natural gas pipeline landslide. Strain gauges，soil pressure sensors and dial gauges were used to monitor the corresponding indicators of the structural elements within the landslide system，and analysis was performed on the data of pile bending moments，soil pressures and pile head displacements. The results showed that the system consisting of piles，sliding masses and pipelines in the landslide exhibited coordinated changes during the development of the landslide，with deformation occurring in four stages：initial stage，uniform deformation stage，rapid deformation stage and failure stage. Micro-piles primarily experienced bending and shear failure near the sliding belt. Near the sliding belt，the soil pressure in front of the piles reached its maximum value，and the flower tube piles exhibited a rotational trend with the sliding belt as the axis，resulting in significant soil pressures at the pile base. The magnitude of bending moments exhibited an overall“S-shaped”curve distribution，and due to the interaction with the pile cap，larger bending moments were generated in the upper part of the piles. The pile-soil composite structure formed by grouting on one side of the flower tube piles better resisted the landslide thrust. Even after the piles reached their ultimate strength and failed，the composite structure still provided a certain degree of resistance against sliding. Through multidimensional integrated data analysis，it was observed that the deformation of the pipeline occurred later，providing a time window for emergency rescue work. The pipeline mainly experienced bending failure and compression failure，with the interface position being the weak point in pipeline protection. Micro-piles have significant potential for applications in the protection of oil and gas pipelines in mountainous regions，and further research and improvement play a positive role in the application of micro-piles in landslide control.

Seepage and heat transfer experiments of contact-type granite fractures were conducted to realize the efficient utilization and accurate productivity evaluation of geothermal resources in the surrounding rock of deep high-temperature mines. The contact rate of natural fractures under different normal stresses was measured，and the core fracture specimens with contact asperities were prepared. The evolution of permeability and convection heat transfer properties of contact fractures under different temperature-pressure conditions were studied，and the traditional evaluation model of the convective heat transfer coefficient was improved by introducing an effective heat transfer area. Results show that the attenuation degree of the equivalent hydraulic aperture of the contact fracture with the confining pressure is controlled by the contact rate，which reflects the uneven response process of the permeability of heterogeneous fracture to the confining pressure. The closure deformation of contact fractures has different degrees of response to confining pressure，resulting in an increase followed by a decrease in equivalent permeability with increasing contact rate under high confining pressure，while it shows a monotonic decrease under low confining pressure. Under the same pressure gradient，the cumulative heat production of high-temperature fractures first increases and then decreases with the increase in contact rate. The improved convective heat transfer coefficient model indicates a positive correlation between the convective heat transfer coefficient and the contact rate，which cannot be characterized by traditional theoretical models. Neglecting the natural contact characteristics will lead to the underestimated convection heat transfer coefficient of high-temperature fractures，and the underestimated degree will increase with the increase in contact rate. In addition，the convection heat transfer coefficient obtained based on the improved model does not strictly follow the power law correlation relationship with the volume flow rate，and the estimation effect of the fracture heat transfer coefficient depending on the flow rate needs to be further improved.

The deformation and failure characteristics of complex jointed rock mass has important theoretical and practical significance for the stability control of rock engineering. In order to overcome the difficulties of casting method in generating rock-like specimens with complex joints，and to investigate the effect of joint density on the deformation and failure characteristics of rock mass，sand-powder 3D printing is employed to generate rock-like specimens with complex joints based on Monte-Carlo method. By conducting uniaxial compression test with digital image correlation(DIC)，the effect of joint density on the mechanical behaviors，fracturing evolutions and failure patterns of rock mass has been investigated. The results show that：with the increase of the joint density，the peak strength and peak strain decrease exponentially，and the elastic modulus decreases linearly. Meanwhile，the pre-peak energy，elastic strain energy，dissipative energy and post-peak surplus energy decrease exponentially，while the post-peak release energy decreases linearly. Both the location and dip angle of joints affect the initiation and propagation of cracks；with the increase of joint density，the initiated cracks are more tend to propagate along a specific path，and the control effect of joint on crack propagation becomes more significant. The results provide a new method for the experimental test of complex jointed rock mass，and provide theoretical reference for the deformation failure mechanism and stability analysis of complex jointed rock mass.

Aiming at the plane strain problem in freezing method construction，the plane strain tests were carried out by using the improved true triaxial apparatus of frozen soil in Anhui University of Science and Technology. Subsequently，the strength and deformation of frozen silty clay were analyzed under different principal stresses and temperatures. Based on Weibull distribution and Drucker-Prager strength criterion，a damage constitutive model was established for frozen silty clay. The theoretical and experimental results demonstrate that the stress-strain curves under different minor principal stress exhibit different degrees of hardening characteristics at the same negative temperature. The failure strength increases first and then decreases with the increase of the minor principal stress，while it increases linearly with decreasing temperature. The established nonlinear Mohr-Coulomb strength criterion can describe the nonlinear correlation between the strength of frozen silty clay and the minor principal stress. Under different test conditions，the strain along the minor principal stress is expansion deformation，and the volume strain exhibits shear contraction. As the minor principal stress increases，the deformation modulus of the sample increases first and then decreases. For the same minor principal stress，the deformation modulus exhibits a negative correlation with temperature. Under the same temperature，the intermediate principal stress at failure also increases first and then decreases with increasing minor principal stress. The performed analysis revealed that the established damage constitutive model effectively considers the influence of minor principal stress and temperature on the strength and deformation of frozen silty clay under complex stresses.