Experimental investigation for dynamic instability of coal-rock masses in horizontal section mining of steeply inclined coal seams

The rockburst in steeply inclined coal seams (SICSs) is a typical dynamic instability event in coal-rock masses under dynamic and static loads. Existing physical experimental studies mainly investigate the quasi-static failure characteristics of coal-rock masses and lack physical experimental data gathered under applied dynamic loads, thus failing to reveal the full nature of the mechanism driving such a rockburst. On this basis, the spatio-temporal evolutionary characteristics of dynamic instability in SICSs were explored by conducting similar simulation experiments under dynamic and static loads. The results show that, under the compound influence of increasing dynamic loading intensity and decreasing distance from the dynamic loading source to the stope, the extent and severity of dynamic damage were aggravated correspondingly, and the characteristic parameters of displacements and accelerations varied non-linearly. The peak values and scope of influences of mining-induced stresses, degree of dynamic damage, and dynamic deformation of coal masses at the roof side were all greater than those at the floor side for the same sub-level; meanwhile, the rockburst also occurred inside the coal masses at the roof side, which reflected the asymmetry of the stress state and dynamic instability in SICSs. The vibration displacements at the roof side instantaneously reached a peak and the accelerations rapidly declined only after a single fluctuation during the rockburst, which revealed the explosive nature of such rockbursts. By contrast, the significant growth in the characteristic parameters of displacements and accelerations could reflect the remarkable destructiveness of rockbursts. This study may eventually lead to an experimental methodology for researching rockburst mechanisms in horizontal section mining of SICSs.