Mechanisms Underlying the Slip and Failure of Coal-Rock Parting-Coal Structures Under Unloading Conditions

Herein, the mechanisms underlying the slip and failure of a coal-rock parting-coal structure (CRCS) under biaxial compression with horizontal unloading were investigated using numerical simulations and field observations. The failure and instability characteristics were studied, including fracture, slip, and energy release characteristics, as well as the mechanisms whereby different factors influence the failure and instability characteristics of the structure. Based on a rockburst triggered by rock-parting slip in the field, the results obtained from the numerical simulations were verified. In particular, the microseismic (MS) effects of rock-bursts were revealed in detail. The following four points were addressed: (1) a linear positive correlation between the peak value of axial stress and the actual value of the horizontal stress was found under biaxial compression; (2) shear stress of the discontinuities and local stress concentration were the leading factors for the failure and instability of the CRCS under both biaxial compressional stress and horizontal stress unloading conditions; 3) higher horizontal stress or higher unloading speed easily induced instability (fracture or slip) of the CRCS, while the fracture and slip degree weakened with the increasing unloading speed; and 4) the MS signals of the rockburst were characterized by a wide range of frequencies and high amplitudes, in which the low-frequency part was related to the slip of the rock parting and the high-frequency part reflected fractures of the coal-rock mass. This work is relevant for understanding the mechanism underlying coal-rock dynamic disasters triggered by the slip and instability of CRCS in coal mines.