Modified Mohr–Coulomb criterion and risk coefficient for mining-induced fault slip

Abstract Fault slip is a critical factor triggering coal burst accidents and poses serious threats to mining safety. In this study, the Mohr-Coulomb criterion is modified by considering mining effects. A mechanical model of fault slip under mining disturbance is established. Physical simulation test is conducted based on the Qianqiu Coal Mine to reveal the overlying strata movement and fault stress evolution. Furthermore, FLAC 3D is employed to systematically investigate how lateral pressure coefficient and fault dip angle affect stress distribution on the fault. The results indicate that a steeper dip leads to higher residual normal stress, whereas the shear stress exhibits nonlinear characteristics with abrupt transitions from minimum to maximum values. High-dip faults are more prone to appear stress concentration. The increase of the lateral pressure coefficient leads to an overall rise in shear stress, while the zone of normal stress release shifts from the upper part of the fault to the lower part. On this basis, a fault slip risk coefficient R f is proposed for real-time assessment of slip hazard during the mining activities. The study shows that R f dynamically increases as the mining face advances. Faults dipping at 45° exhibit the highest risk coefficient in the early stage of mining. The most prominent risk occurs under the combined influence of large lateral pressure coefficient and high dip angle when the mining face approaches the fault. This study can provide a scientific basis for stability evaluation of mining-affected faults.