In order to study the energy storage and sound emission characteristics of rocks under different water content, uniaxial compression test, cyclic loading, unloading test and sound emission test were carried out using RMT-150B rock mechanics test system and DS5 acoustic emission system. The results show that the total strain energy of saturated rock samples and the area of hysteresis loop are the largest in the same period number, which indicates that the presence of water can reduce the elastic limit of rock samples, making the rock very easy to deform and even damage. Acoustic emission tests show that the damage energy of water-bearing rocks is small. The higher the water content, the smaller the peak damage energy. The bending energy index $W_{ET}$ of the rock sample under saturated and natural state is smaller than that under dry state, which further indicates that the presence of water can reduce the elastic limit of the rock and soften it. The results can provide a basis for the prediction of underground engineering construction and rock failure instability.

The roof fracture is the main cause of coal mine roof accidents. To analyze the law of movement and caving of the roof rock stratum, the roof subsidence displacement, rock stratum stress, and the rock stratum movement law were analyzed by using the methods of the particle discrete element and similar material simulation test. The results show that (1) as the working face advances, regular movement and subsidence appears in the roof rock strata, and the roof subsidence curve forms a typical “U” shape. As the coal seam continues to advance, the maximum subsidence displacement remains basically constant, and the subsidence displacement curves present an asymmetric flat‐bottomed distribution. (2) After the coal seam is mined, the overburden forms an arched shape force chain, and the arched strong chain is the path of the overburden transmission force. The farther away from the coal seam, the smaller the stress concentration coefficient is, but it is still in a high stress area, and the stress concentration position moves toward the middle area of the goaf. The stress concentration in front of the coal wall is the source of force that forms the abutment pressure. (3) Above the coal wall towards the goaf, a stepped fracture was formed in the roof rock stratum. The periodic fracture of the rock stratum is the main cause of the periodic weighting of the working face. Understanding the laws of rock movement and stress distribution is of great significance for guiding engineering practice and preventing the roof accidents.

Rock burst is one of the disaster accidents that can easily happen in rock cavern engineering. At present, one of the most commonly used methods to control rock burst is borehole pressure relief technology. In this paper, the influence of drilling layout schemes on the pressure relief effect of surrounding rock mass is systematically studied. The research results show that the strength reduction degree, AE evolution characteristics, failure modes of rock samples with different borehole positions, boreholes spacing, boreholes dip angles, and boreholes layout forms are different. The strength reduction degree of rock sample with an inclined arrangement form is the largest, followed by the arrangement form being up three‐flower layout or down three‐flower layout. Using the inclined layout and three‐flower layout can achieve better pressure relief effect of the surrounding rock mass. The research results are beneficial to the rock burst of surrounding rock of the cavern. The acoustic emission can effectively monitor the stability of the surrounding rock of the cavern. However, the threshold value and the occurrence time of the acoustic emission of the cavern instability changed after the cavern surrounding rock is drilled holes. If the borehole is arranged at the surrounding rock mass, the occurrence time of the cavern instability may be advanced.

The cracks in underground rock mass have an important influence on the stability of rock mass. In order to explore the deformation and failure characteristics of rock samples with different fracture angles and fracture propagation rules, uniaxial compression test was conducted on rock samples with prefabricated fractures by using digital image correlation (DIC) method and PFC3D, and the stress–strain relationship, deformation field evolution law and failure characteristics of rock samples with different fracture angles were analyzed. The research results indicate the following: (1) When the fracture dip angle is larger and the fracture orientation is closer to the direction of the principal stress, the compressive strength of the rock specimen is greater; (2) the crack propagation process, crack patterns and stress concentration phenomena in rock specimens are all related to the fracture dip angle; (3) The DIC method can effectively capture the evolution of the strain field on the crack surface. The strain field reflects the whole evolution process of crack initiation, main crack formation, and main crack propagation to sample failure. In this paper, the failure law of fractured rock is studied from the perspective of macroscopic digital image processing and granular discrete elements, which provides a new idea and method for understanding rock failure.

Joints commonly exist in the surrounding rock of underground roadway and have an important impact on the mechanical properties of underground roadway. In order to study the mechanical characteristics of the failure of joints on surrounding rock, the compression indoor test and the discrete element PFC2D numerical simulation study of jointed sandstone roadway with different dip angles are carried out to analyze the influence of joints on the strength characteristics of surrounding rock and the evolution of crack propagation. The results show that the peak strength of surrounding rock decreases first and then increases with the increase in joint angle around the roadway, and the peak strength curve shows a similar "V" shape. Moreover, the strength of the samples in the roadway with joints is less than the peak strength in the roadway without joints. The joints reduce the bearing capacity of the surrounding rock. The peak strength is related to the angular distribution of joints. When there is no joint in the roadway, the cracks are mainly concentrated in the direction from the left side of the roadway to the upper left corner and from the right side of the roadway to the lower right corner. When there have joints in the roadway, the displacement field of the roadway and the propagation law of the crack are basically consistent. One end of the joint extends toward the shoulder of the roadway, and the other end extends to the upper right corner. At the same time, there is an obvious vertical crack at the bottom of the roadway. The expansion, convergence and coalescence of microcracks and the formation of macroscopic failure zone are the fundamental reasons for the ultimate failure of surrounding rock.