Effects of bedding angles on rockburst proneness of layered anisotropic phyllites

To examine the effect of bedding angle upon burst proneness in terms of energy, phyllites with seven various bedding angles are selected for conventional uniaxial compression and single-cyclic loading–unloading uniaxial compression tests. The ejection and failure during compression process of phyllites are monitored in real-time by high-speed camera system. The results demonstrate that the phyllites with different bedding angles all consistently follow the linear energy storage and dissipation (LESD) law during compression. The ultimate energy storage of phyllites with varying bedding angles can be calculated precisely via using the LESD law. Based on this, four kinds of energy-based rockburst indices are applied to quantitatively assess the burst proneness for phyllites. Combined with the recorded images of high-speed camera system, ejection distance, and mass of rock fragments and powder, the burst proneness for phyllites with various bedding angles is qualitatively evaluated adopting the far-field ejection mass ratio. Next, burst proneness of anisotropic phyllites is assessed quantitatively and qualitatively. It is found that phyllites with bedding angles of 0°, 15°, and 90° have a high burst proneness, and that with bedding angle of 30° has a medium burst proneness, whereas the ones with bedding angles of 45°, 60°, and 75° have a low burst proneness. Finally, the published experimental data of shale and sandstone specimens with different bedding angles are extracted, and it is preliminarily verified that the bedding angle does not change the LESD law of rocks.