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Abstract Thorough investigation into the laws governing frozen rock damage in high-altitude and cold regions can offer valuable insights for advancing infrastructure construction, ecological environment protection, and sustainable development on the Qinghai-Xizang Plateau. This study combined with the seasonal variation patterns of frozen rocks in the Qinghai-Xizang Plateau, and processed the rock samples using a freeze–thaw interval of -20 °C~20 °C. Uniaxial compression test was conducted based on the MTS816 rock mechanics testing system. The porosity changes of rock samples with different freeze–thaw cycles were analyzed using the MesoMR12-060 H-I nuclear magnetic response analysis system. A rock freeze–thaw load coupled damage constitutive model was derived using the Lemaitre equivalent strain theory. Research has shown that during the freezing process, the pore water inside the rock sample is affected by the phase change of water-ice, resulting in frost heave force, which further promotes the expansion of the pore walls and the initiation of new cracks. When melted, pore water migrates towards newly formed micropores, thereby affecting the changes in the pores of rock samples. The increase in porosity at the micro level weakens the mechanical parameters of rocks at the macro level. The segmented freeze–thaw damage constitutive model based on Lemaitre equivalent strain theory can well fit the experimental results involved in this study, as well as the experimental results obtained by other researchers. The compaction stage can partially reflect the changes in sandstone pore structure under freeze–thaw cycles.

Coal mining can cause the deformation, fracture, and movement of overlying strata from bottom to top, leading to surface subsidence and other problems. This is a mechanical process, so it is urgent to develop a movement theoretical model based on the mechanical mechanism of rock fracture. Firstly, this paper reviews some theoretical models of rock movement worldwide, and then focuses on our research progress in the field of overall rock movement theoretical models in recent years. Based on the mechanical analysis of the fracture morphology of different layers of rock and the results of similar simulation tests, an “analogous hyperbola” model for the overall movement of mining induced overlying strata was proposed, the focus of the model was approximately located in the layer of the main key stratum of the overlying strata. Furthermore, the overall model of “analogous hyperbola” inside and outside the strata movement was established, and the expression and physical significance parameter system for the internal and external movement of mining overlying rocks were provided. The evolution law of the “hyperbolic like” model for the overall movement of rock layers was analyzed based on different occurrence conditions of overlying rocks and coal seams. On this basis, further extending the two-dimensional “analogous hyperbola” model to the three-dimensional “analogous hyperboloid” model, the three-dimensional movement model of “analogous hyperboloid” in the whole space of mining overburden was established, which includes “quasi-single-leaf” and “quasi-double-leaf” hyperboloids. This theoretical model is based on the research of many predecessors and scholars in China, from the perspective of systems science, it considers the overall movement law of rock layers. A preliminary theoretical model framework of the “analogous hyperbola (hyperboloid)” theory for the overall movement of mining overburden has been formed, hoping to provide a theoretical guidance for scientific coal mining in China.

The mechanical behavior of splitting tensile damage and the law of stress wave propagation of rock-like materials (RLM) are of great significance to further reveal the dynamic disaster mechanism of the deep rock mass. The meso-damage mechanical behavior and stress wave propagation characteristics of RLM disks under impact splitting were studied by using a large diameter split Hopkinson pressure bar (SHPB). In terms of dynamic damage, the splitting tensile stress-compression strain curves of RLM disks obviously showed three stages of mechanical behavior evolution: initial elastic-plastic deformation, pre-peak plastic damage, and post-peak brittle fracture failure. The macro-damage of RLM disks increased with the increase of strain rate. The meso-tensile fracture was the result of both the initial meso-damage and the impact splitting meso-damage. The dynamic splitting damage variable defined based on the damage fracture energy can accurately describe the damage evolution characteristics of impact splitting on RLM disks. In the aspect of stress wave propagation, the peak value of transmission stress showed an advanced effect with the increase of incident stress wave. In the early stage (0–50 μs), the transmission stress wave ratio (σT/σI) increased with the increase of strain rate, while in the later stage (82–200 μs), the transmission stress wave ratio (σT/σI) decreased with the increase of strain rate. The stress wave propagation law in the process of impact splitting on RLM disks was clearly revealed based on the stress wave propagation model established by the one-dimensional elastic stress wave theory. Finally, the dynamic mechanical mechanism of splitting damage and fracture of RLM disks under different strain rates was discussed deeply.

Abstract With depth increase of many mines, the damage of surrounding rock by high ground stress cannot be ignored under the blasting excavation method. In view of the strong disturbance of surrounding rock caused by dynamic excavation and unloading under high initial rock stress conditions, based on the elastic unloading theory, the analytical solution of dynamic excavation and unloading stress is given using the residue theorem and Laplace inverse transform. The stress field distribution under the coupling effect of blasting load and initial rock stress is described. By making a rock model and implementing biaxial loading using a drop hammer to simulate the impact load, radial cracks generated by the impact stress wave and circumferential cracks generated by unloading during excavation were captured, and the stress change curve during excavation was monitored. The monitoring curve and theoretical curve have consistency in trend. Under the coupling effect of blasting load and initial stress, surrounding rock will generate tensile stress and broken, and the unloading effect of initial stress occurs after the blasting load, which causes tensile damage to the surrounding rock. The stress field curve plotted by the theory explains well the crack propagation caused by the coupling effect of blasting load and initial stress.

The deformation, fracture, and movement mode of rock strata are greatly related to underground pressure, surface subsidence, etc. The fracture modes of the thin rock stratum and thick rock stratum are significantly different. How to uniformly describe the fracture modes of rock strata with different thicknesses and establish a mechanical model is a difficult theoretical problem in rock movement. In this paper, the fracture structures of mining strata in 23 typical working faces are investigated. In addition, the fracture mechanical factors and movement modes of the rock stratum are classified based on fracture mechanics, and the relationship between fracture structure and rock stratum thickness is analyzed. Based on the medium-thick plate theory, the fracture mechanical model of rock strata with different thicknesses is established. The fracture mechanical mechanism and fracture mode of rock strata with different thicknesses are revealed, and the corresponding criteria are given. The breakage and movement laws of rock strata with different thicknesses and fracture modes in the mining process are analyzed by numerical simulation. The research shows that when different mining conditions and different stress boundary conditions act on rock strata with different thicknesses, different fracture modes will occur. With the increase of the rock strata thickness, the shear stress of rock strata increases continuously, and the fracture mechanical mechanism of rock stratum presents the evolution law of tensile fracture, tensile shear fracture, and shear fracture. Also, the corresponding rock mass structures are masonry beam structure, layered fracture, and step voussoir beam respectively. Moreover, the statistical data show that the rock layers with a thickness span ratio greater than 0.5 are more prone to occur shear fractures and form step voussoir beams. Based on the above analysis, a mixed fracture model is proposed aiming at the possible tension shear failure of thick rock strata, and the rock fracture mechanical factors are further subdivided into three types: tensile fracture, tensile shear fracture, and shear fracture. There are seven types of fracture modes in rock strata in total. Tensile fracture often occurs in a thin layer, which will change to a shear fracture when the fault appears. Tensile fracture, tensile shear fracture, and shear fracture are typically fracture modes in a thick layer, in which tensile shear mixed fracture is divided into end tensile shear mixed fracture, layered linkage movement, and layered uncoordinated movement. Further research on the fracture modes of rock strata can provide valuable theoretical support for the control of ground pressure and the prevention of surface subsidence hazards in mining.

Dynamic disasters, such as rock burst due to the breaking of large area stiff roof strata, are known to occur in the hard rock strata of coal mines. In this paper, mechanical models of the fracturing processes of thick hard rock strata were established based on the thick plate theory and numerical simulations. The results demonstrated that, based on the fracture characteristics of the thick hard rock strata, four fracture models could be analyzed in detail, and the corresponding theoretical failure criteria were determined in detail. In addition, the influence of weak interlayer position on the fracture models and ground pressure of rock strata is deeply analyzed, and six numerical simulation schemes have been implemented. The results showed that the working face pressure caused by the independent movement of the lower layer is relatively low. The different fracture type of the thick hard rock strata had different demands on the working resistance of the hydraulic powered supports. The working resistance of the hydraulic powered supports required by the stratified movements was lower than that of the non-stratified movements.

The shape of the gasifier cavity and the high temperatures induced by underground coal gasification (UCG) have a significant influence on the failure characteristics of the surrounding rock. In this study, the variations in the mechanical properties of the surrounding rock in gasifier cavities subjected to different temperatures (20–700°C) were obtained experimentally, and the results were used to establish numerical models. FLAC3D was used to analyse the failure of the surrounding rock in drop-shaped and traditional rectangular gasifier cavities. The mechanical parameters of the surrounding rock in the numerical model were assigned a gradient distribution based on the temperature propagation law and the experimental results. The results revealed that the temperature of the surrounding rock has a significant influence on the coal pillar stability, and the surrounding rock primarily undergoes shear failure. As the temperature of the surrounding rock increases, the width of the stable coal pillar increases exponentially; the reasonable widths for coal pillars between adjacent drop-shaped gasifier cavities are 12 m (room temperature), 17 m (700°C and 850°C), 18 m (1000°C), 19 m (1150°C), and 20 m (1300°C). In contrast, the reasonable width of coal pillars in traditional rectangular gasifier cavities is approximately 21 m, which is significantly higher than that for drop-shaped gasifier cavities.

Due to the influences of various factors, such as temperature, stress, and composition, the research regarding rock permeability has been complicated. This study examined the variation laws of sandstone specimens under changing rates of confining and pore pressures after high-temperature heat treatments. The results showed that the free water in the rock volatilized during the low-temperature heat treatments in the range of 100°C to 300°C, with the increase of the heat-treatment temperature above 500°C; the crystal water in the rock is gradually separated out; and the particles in the samples had undergone phase transformations resulting in increased permeability. According to ultrasonic wave velocity test results, the internal cracks of the samples expanded with the increases in the heat-treatment temperatures. In addition, the high-temperature heat treatments were found to improve the accuracy of the direction of the Earth’s stress when using circumferential wave velocity anisotropy methods. Under the influence of slippage effects, as the pore pressure increased, the measured permeability of the samples decreased and the slippage effect occurs in the rock samples with the permeability of 10-3 μm2~10-6 μm2. The experimental results showed that the contribution rate of the slippage effect decreases with the increase of the heat-treatment temperature of the specimen, and the contribution rates of the sandstone slippage effect were generally higher than 5%. Therefore, the impact effects on the permeability of sandstone slippage should be considered in practical engineering processes.

Rock burst is one of the major dynamic disasters that directly threaten production safety in coal mines. According to the current research, the occurrence of rock burst can be described by the generalized Newton’s second law with three elements which are research object, force condition, and motion state. These three elements refer to the coal and rock mass in the mining area, concentrated static and dynamic loads, and dynamic instability of surrounding rock, respectively. On this basis, a comprehensive rock burst research method involving the three elements of Newton’s second law was proposed, which especially focuses on the investigation into geological conditions of mining areas. The research procedure of this method specifically includes the detailed exploration of engineering geological bodies, the classification and stability evaluation of surrounding rock, the measurement and inversion of in situ stress, the evolution analysis of mining-induced stress field, energy field, and fracture field, the study of multiscale failure mechanism of coal and rock mass, the establishment of theoretical failure model of coal and rock mass, the real-time monitoring and warning in potentially dangerous areas, and the reasonable prevention and control in key risk zones. As a preliminary discussion, the significant research progress in each aspect mentioned above has been reviewed and the feasible research directions of rock burst are presented in this paper.

With the effects of high geostress and intensive dynamic disturbances in deep mining, the stability and safety of tunnels are seriously affected. The optimization for U-shaped steel support is of vital significance and can solve the problems of cost reduction and tunnel instability. Based on the perturbation equation, a coupled formula for U-shaped steel and the surrounding rock mass was proposed to evaluate the practical stability of a U-shaped steel support. Through a numerical simulation method, the characteristics of U-shaped steel support can be obtained under coupled static-dynamic loading. Furthermore, the field test was carried out and compared with the numerical simulation, which was discussed. The results show that there will be a stress concentration when the contact area is small. In addition, the concentrated stress will release with the increase in contact area. With the increase in the lateral stress coefficient, the deformation exhibits a downward trend under static loading, indicating that the lateral stress is the dominant force driving the deep geostress activity. The support requirement of this section of surrounding rock can be satisfied by a U-shaped steel group with 1.5 m spacing under dynamic disturbance.

In view of the phenomena of coal and gas outburst induced by fault activation under dynamic disturbance, a mechanical model of faults and surrounding rock mechanics was established based on the theory of fold catastrophe. Moreover, the dynamic disturbance factors were introduced and analyzed to analyze the influencing factors of outburst coal rock outburst. Through theoretical analysis, it shows that the thinner the fault medium is, the more energy the external input is required for system instability, and the external energy can reflect the stability of the system. When the width of fault media is fixed, the stronger the mining disturbance, the less energy the external input is required for system instability; on the contrary, the weaker the mining disturbance is, the more energy the external input is required for system instability. In addition, through the equation of conservation of kinetic energy, it can be seen that the stronger the mining disturbance, the greater the critical value of the surrounding rock thickness. The paper introduces the dynamic disturbance parameters through the catastrophe theory and analyzes the influence of the existence of faults on coal and gas outburst in detail, which provides a new theoretical basis for the prediction and prevention of coal and gas outburst disasters.