Research on instability characteristics and precursory effect of coal-rock parting-coal structures.

The slip and instability mechanisms of coal-rock parting-coal structures under uniaxial loading conditions were investigated using experiments and case verification. The slip and the corresponding precursors were described by monitoring the displacement, strain, and acoustic emissions (AEs) of coal and rock parting blocks during testing, and the experimental results were verified by analyzing the microseismic (MS) effects during the working face advancing in a coal seam bifurcation area. The main conclusions were as follows: (1) each slip of the discontinuities sandwiched between coal and rock parting produced shear and tensile cracks, but the shear cracks was dominant; (2) for the instability mode that was characterized by low peak stress, high energy release, and a stable b value of AE, each slip corresponds to a peak frequency of AE, which can reveal the final instability mode; (3) the sudden drop in the fault total area of AE can be regarded as a precursor for the warning fracture or slip instability of a discontinuity; and (4) the MS events in the coal seam bifurcation area were mainly characterized by a wide frequency and high amplitude, especially near the coal bifurcation line, where there were obvious characteristics of low-frequency shear fracture for the MS events. This study is relevant for the early warning of coal-rock dynamic disasters triggered by the slip, fracture, and instability of coal-rock parting compound structures in coal mines.