The cohesion and internal friction angle were characterized as quadratic functions of strain and were assumed to follow the Mohr-Coulomb criterion after the yield of peak strength. These mechanical parameters and their variations in post-peak softening stage can be exactly ascertained through the simultaneous solution based on the data points of stress-strain curves of triaxial compression tests. Taking the influence of the fault into account, the variation of strata pressure and roadway convergence with coal advancement, the temporal and spatial distribution of axial bolt load were numerically simulated by FLAC3D (Fast Lagrangian Analysis of Continua) using the ascertained post-peak mechanical parameters according to the cohesion weakening and friction strengthening model. The change mechanism of axial load of single rock bolt as abutment pressure changes was analyzed, through the comparison analysis with the results of axial bolt load by field measurements at a coal mine face. The research results show that the simulated results such as the period of main roof weighting, temporal and spatial distribution of axial bolt load are in accordance with field measurement results, so the validity of the numerical model is testified. In front of the working face, the front abutment pressure increases first and then decreases, finally tends to be stable. A corresponding correlation exists between the variation of axial bolt load and rock deformation along the bolt body. When encountered by a fault, the maximum abutment pressure, the influential range of mining disturbance and the roadway convergence between roof and floor before the working face are all increased. In the roadways along the gob, axial bolt loads on the side of the working face decrease, while the other side one increases after the collapse of the roof. As superficial surrounding rock mass is damaged, the anchoring force of rock bolts will transfer to inner rock mass for balancing the tensile load of the bolts.

Rock masses, especially those with different pre-existing cracks, are prone to instability and failure under tensile loading, resulting in different degrees of engineering disasters. Therefore, to better understand the effect of pre-existing cracks with different dip angles on the tensile instability failure behaviour of rocks, the mechanism of crack initiation, propagation and coalescence in precracked sandstone under radial compression loading is investigated through numerical simulations. The temporal and spatial evolution of acoustic emission (AE) events is investigated by the moment tensor (MT), and the fracture mode of micro-cracks is determined. The results show that the pre-existing cracks weaken the specimens. The strength, crack initiation points and macro-failure modes of the specimens differ significantly depending on the dip angle of the pre-existing crack. For different dip angles of the pre-existing cracks, all the micro-cracks at the crack initiation point are tensile cracks, which are dominant during the whole loading process, and mixed cracks are mainly generated near the upper and lower loading ends after the peak stress. Of the total number of events, more than 75% are tensile cracks; approximately 15% are shear mode cracks; and the remainder consist of mixed mode cracks. The study reveals the instability and failure mechanism of pre-cracked rock, which is of great significance to ensure the long-term stability of rock mass engineering.