Research on Mechanisms and Precursors of Slip and Fracture of Coal-Rock Parting-Coal Structure

The bifurcation of coal seams is a universal geological structure in coal mines, and the special structure of rock parting intruded into coal can lead to a slip of discontinuities and shear failure, and even rockbursts due to the existence of discontinuities. Lateral confining stress unloading with axial loading tests was conducted on a coal-rock parting-coal structure (CRCS) to reproduce and simulate the stress conditions of increasing vertical stress and decreasing horizontal stress, similar to mining destressed effects. The stress and deformation of CRCS were comprehensively analyzed during slip and fracture. The precursors of shear slip and macrofracture were proposed based on the variations in the spectral distribution, cumulative apparent volume (CAV), and the energy index of acoustic emission (AE). Before and after advancing through the bifurcation area of the 5310 working face of the Zhaolou coal mine, the Microseismic (MS) observations were analyzed, confirming the experimental results. It was observed that a sharp decline in the energy index, a sharp rise in the CAV, and an increase in MS at a low frequency and high amplitude are the portents of rockbursts induced by slip and fracture of CRCS. Through field investigations of the 5310 working face, three stages was observed before and after the slip of the discontinuities, namely, stress accumulation (July-September), stress release (September-November), and stress redistribution and equilibrium (November-December). This study is relevant for understanding the mechanisms and precursors of rockbursts caused by the dynamic instability of the CRCS in coal mines.