Hanxiao Guo

A fault disrupts the continuity of the rock strata in a mining area. To study the law governing the fracture of overlying strata in mining areas under discontinuous boundary conditions, the overlying strata were redefined and grouped based on the activity characteristics of each rock layer during the overall movement of the overlying strata. The activity patterns of different layers of the fault were obtained through the movement and failure forms of each group of rock layers. The relationship among the size of the coal pillar at the boundary of the fault, the dip angle of the fault, and the movement angle of the rock strata was considered. A model of the spatial relationship between the overlying rock movement zone of the quarry and the fault surface was established. The limit equilibrium equations of the key layer in the fault zone before breaking were established based on the tensile strength of the rock layer. In addition, the mechanical slip instability criterion and the deflection instability criterion of the discontinuous-boundary rock mass are given herein. Based on a field case, a double criterion was used to determine the initiating activated rock layers of the fault in the cases where the fault dip was smaller than the rock movement angle. Rock movement during excavation was simulated by similar simulation tests, and different levels of rock movement patterns in the boundary fault zone were focused on monitoring and analyzing. The stress and displacement changes in different rock layers in the fault zone were analyzed with numerical simulation results. The results show the following: if the dip angle of the fault is smaller than the movement angle of the rock layer, the delamination space of the fault surface is mainly distributed in the bending and sinking zone of the overlying rock; with an increase in the working-face advancement distance, the vertical pressure of the upper part of the fault gradually decreases, and the stress-concentration area in the middle and lower part of the fault gradually increases; the rock layer of the upper part of the fault, which is mainly composed of the key stratum, is the main area of activation of the fault.

Taking the geological conditions of a coal mine in Liupanshui City, Guizhou Province, as the background. The fracture law of the roof in the coal face and the height of the “Two zones” were obtained through theoretical analysis and empirical formula calculation, and the results were verified using similar simulation experiments. Through numerical simulation were researched the stress distribution characteristics of the overlying strata on the working face under the influence of multiple faults. The results showed that in the early stage of mining, F1 undergoes activation under the influence of the main roof weighting, leading to an increase in the degree of plastic damage to the coal seam and strata behind the working face, causing a redistribution of the behind abutment pressure. Finally, under the influence of the F1 barrier effect, the vast majority of the behind abutment pressure is transferred to the lower strata of F1, leading to a continuous increase in stress concentration there. But as the working face continues to advance, the blocking effect of the roof plastic zone above the goaf on the transmission of the behind abutment pressure of the working face begins to appear and continues to increase, leading to a decrease in the peak stress at the lower strata of F1. The stress change process on the F2 side is similar to that on the F1 side, the front abutment pressure is initially distributed in the strata in front of the working face, but as the activation degree of F2 continues to intensify, it gradually shifts to the lower strata of F2, and ultimately the majority of the front abutment pressure is borne by the lower strata of F2.

The stability of damaged rock mass is a critical problem in the control of surrounding rock in underground engineering. As the main macroscopic defect of rock surrounding engineering, it is of great significance to study its propagation mechanism and the experimental characteristics of rock mechanics. Surface-fractured rock mass is a typical representative of three-dimensional fracture. To reveal the failure mechanism of surface-fractured rock mass, a three-dimensional mechanical failure model of a surface-fractured rock specimen was established, including the initiation, crack propagation, and cooperative deformation of the rock micro-element. Taking the depth of the surface horizontal fissure as a variable, standard rock specimens with surface horizontal fissures of different depths were prepared, and an experimental study of surface-fractured rock specimens was carried out. The RMT rock mechanics test system was used to perform uniaxial compression tests on standard specimens containing fractured rock specimens of different depths. The complete stress–strain curves of samples with different fracture depths were obtained, and the influence of different fracture depths on rock strength and deformation characteristics was analyzed. The crack initiation, propagation, and failure modes of the specimens under uniaxial compression were analyzed based on high-speed camera technology. Through the combination of 3D image processing and acoustic emission monitoring, differences between failure before and after the peak in both asymmetrically damaged rock specimens and symmetrically damaged rock specimens were found. The mechanism of weak strength and weak stability of asymmetrically damaged rock specimens after the peak was explained theoretically. The research results showed that the existence of the horizontal joint plane directly led to a significant reduction in the strength of the jointed rock sample, and the fracture depth played an important role in controlling the failure mode of the jointed rock specimens. The uniaxial compression of rock specimens with horizontal non-penetrating surface fissures produced three-dimensional failure modes, and the depth of surface fissures changed the failure mode of the specimens under uniaxial compression. As the crack depth increased, the failure mode of the specimen changed from tensile failure to shear failure. The surface crack sample showed regional asymmetric failure and poor structural stability.

Under the influence of tectonism in geological activities, most fault structures appear in groups. Multiple fault structures can induce a variety of mine dynamic disasters, which significantly affect the safety of mine production. To study the dynamic instability mechanism of the strata in the multifault structure zone of the stope when mining, a numerical model of multiple fracture structures was established. At the same time, the mechanism of the dynamic instability of the rock formation in the multifault structure zone of the stope has been studied through similar simulation experiments and on-site data analysis. The research results show that the stress-affected areas of the faults in the multiple-fault structure area overlap, and the stress evolution law of the fault will distinguish its independent dynamic evolution model. The multifault structure area has a multifault overall evolution law model. In this model, there is a synergy between the fault layers, and the maximum value of stress concentration is diagonally distributed. Under the influence of mining, the fault structure will be activated to change the stress field distribution form of the stope. The two faults in multiple structural areas have a joint mechanism, which plays a key role in controlling the dynamic instability process of the surrounding rock of the stope. The first activated faults in the multiple-fault structure area will undergo secondary activation under the influence of subsequent fault activities. The evolution law of cracks in the overburden of similar simulation experiments confirms that the early active F1 fault will be affected by the subsequent F2 fault activity. The mine pressure data measured on-site verifies the reliability of the numerical simulation experiment and the similar simulation experiment.