It is well accepted that faults have significant impacts on the safe production of underground coal mines; however, the fault-slip mechanism during longwall mining through a fault still needs to be investigated. In this study, the distribution of microseismicity events during panel mining through a fault is analyzed, and 3-dimensional fast Lagrangian analysis of continua was used to study the mining stress distribution and fault-slip behavior under the two different mining directions, i.e., mining the panel through the fault from the footwall, or mining the panel through the fault from the hanging wall. The research shows that when the panel is mined through the fault from the footwall, the shear displacement of the fault is significantly greater than those created by mining the panel through the fault from the hanging wall. Under the two mining directions, the variation behaviors of the normal stress and shear stress on the fault are quite different, and fault-slips mainly occur in fault areas where the normal stress decreases. When mining the panel through the fault from the footwall, the slip mainly occurs in the coal-seam roof fault, and when mining the panel through the fault from the hanging wall, the slip mainly occurs in the coal-seam floor fault. According to the variations in the normal stress and shear stress of the fault during the period of mining the panel through the fault, the mechanism of the fault slip can be divided into three categories. 1: Normal stress and shear stress decrease abruptly, but the reduction of the normal stress is greater than that of the shear stress. 2: The normal stress is continuously reduced, the shear strength of the fault is decreased, and the shear stress is suddenly increased. 3: Both the normal stress and the shear stress increase, but the increase in the shear stress is greater than that of the normal stress. These research results can provide a reference for the layout of panels and for fault-slip-induced disaster prevention under similar conditions.

Microseismic events commonly occur during the excavation of long wall panels and often cause rock-burst accidents when the roadway is influenced by dynamic loads. In this paper, the Fast Lagrangian Analysis of Continua in 3-Dimensions (FLAC3D) software is used to study the deformation and rock-burst potential of roadways under different dynamic and static loads. The results show that the larger the dynamic load is, the greater the increase in the deformation of the roadway under the same static loading conditions. A roadway under a high static load is more susceptible to deformation and instability when affected by dynamic loads. Under different static loading conditions, the dynamic responses of the roadway abutment stress distribution are different. When the roadway is shallow buried and the dynamic load is small, the stress and elastic energy density of the coal body in the area of the peak abutment stress after the dynamic load are greater than the static calculations. The dynamic load provides energy storage for the coal body in the area of the peak abutment stress. When the roadway is deep, a small dynamic load can still cause the stress in the coal body and the elastic energy density to decrease in the area of the peak abutment stress, and a rock-burst is more likely to occur in a deep mine roadway with a combination of a high static load and a weak dynamic load. When the dynamic load is large, the peak abutment stress decreases greatly after the dynamic loading, and under the same dynamic loading conditions, the greater the depth the roadway is, the greater the elastic energy released by the dynamic load. Control measures are discussed for different dynamic and static load sources of rock-burst accidents. The results provide a reference for the control of rock-burst disasters under dynamic loads.

In a complex stress field of underground mining or geotechnical practice, tension damage/failure in rock masses is easily triggered and dominant. Unlike metals, rocks are generally bi-modularity materials with different mechanical properties (Young’s modulus, etc.) in compression and tension. It is well established that the Young’s modulus of a rock mass is directly related to the presence of the fracture or joint, and the Young’s modulus estimation for jointed rocks and rock masses is essential for stability analysis. In this paper, the tensile properties in joint rocks were investigated by using numerical simulations based on the discrete element method. Four influencing parameters relating to the tensile properties (joint dip angle, joint spacing, joint intersection angle, and joint density) were studied. The numerical results show that there is an approximately linear relationship between the joint dip angle (α) and the joint intersection angle (β) with the tensile strength (σ_t), however, the changes in α and β have less influence on the Young’s modulus in tension (E_t). With respect to joint spacing, the simulations show that the effects of joint spacing on σ_t and E_t are negligible. In relation to the joint density, the numerical results reveal that the joint intensity of rock mass has great effect on E_t but insignificant effect on σ_t.

By employing the longwall mining method, a series of intensive strata structure responses and activities will be induced including stress redistribution, fracture extension and strata movement. Due to the geological stratification feature of coal mine strata, tensile failure and tension-induced fracturing play dominant roles in the strata of the fractured zone. These responses induced in the strata require the consideration of the weakening effect on the rock mass behavior due to failure and fracturing in tension. In this study, a numerical modeling approach on mining-induced strata structural behaviors was proposed by considering the mechanical behaviors of the caved zone consolidation and tension-induced weakening in the fractured zone. Based on a numerical model built according to a study site, a parametric study with respect to different fracturing intensity parameters was performed to investigate the fracturing weakening effect on the mining-induced stress redistribution and strata movement. The numerical results showed that the tensile fracture intensity had a notable effect on the mining-induced stress distribution in two aspects: (1) Increase in peak and area of the front abutment stress; (2) variation in the patterns of stress recovery in the goaf. The stress data obtained from numerical simulation represent and help to back-analyze the structural behaviors (failure, movement) of the overlying strata. The high stress on the coal seam indicated that the strata lay on and transferred loads to the seam, while the low stress indicated the detachment between the seam and the suspending strata. With the increase in fracture intensity, the roof strata were more prone to breaking and caving, and the suspending length of the roof beam decreased, which made the strata sufficiently break, cave and transfer the overburden load to loose rock in the goaf; caving along the strike direction of the panel became the dominant overlying strata structure movement, while the dominant movement caved along the dip direction in the case of strong and intact overlying strata with few tensile fractures. Thus, the tensile fracturing intensity should not be ignored in studies related to the behaviors of the overlying strata. Validated by analytical studies, this study presents a novel numerical modeling approach for this topic and can be utilized for multiple studies based on proper roof fracturing estimation or back analysis.

The seismic source release by fault slip under the influence of mining is an important factor to induce rock burst. In this study, the normal fault and reverse fault with different horizontal stress are constructed by numerical simulation and the fault slip law and stope dynamic response characteristics when mining the panel through the faults are compared and analyzed. Studies show that compared with mining the panel through the normal fault, the normal stress level of the reverse fault is higher, so the shear strength of the reverse fault is greater. When the fault coal pillar is small and the mining disturbance to the reverse fault is severe, the slip displacement of fault increases significantly, the shear stress drops suddenly, and the fault slip seismic source is greater. Under the influence of reverse fault slip dynamic load, the vibration velocity of coal and rock mass near the mining space, the reduction value of advanced abutment pressure and the affected range are larger, and fault slip rock burst is more likely to occur. The on-site statistical of fault slip rock burst cases are consistent with the numerical simulation results, verifying the reliability of the numerical simulation methods and conclusions.