Effect of bedding dip on energy evolution and rockburst tendency of loaded phyllite

During the mining of deeply metal ore bodies, the accumulation and release of the strain energy of the surrounding rock is one of the causes of catastrophes. However, there are a large number of random distribution joints and fractures in a rock mass, which makes the evolution of strain energy more complicated and the catastrophe more difficult to predict. Therefore, five phyllites with different bedding dip angles were selected for uniaxial loading and unloading tests to investigate the effects of bedding dips on energy evolution and rock burst tendency during deformation and failure of phyllites. The strain energy evolutions of each rock sample are similar, showing energy accumulation before the peak stress and energy release and dissipation after the peak stress. However, with the increase of the bedding dip angle, the energy storage limit, residual elastic energy, and maximum dissipation energy show U-shape, and the minimum value is obtained at 60° by fitting. With the increase of the bedding dip angle, the ratio of the elastic energy of rock samples changes in an inverted U-shape before the peak, and the maximum value is obtained at 60°, indicating that the minimum work is done for bedding dip angle at 60° before peak. Moreover, the maximum elastic energy efficiency changes slightly with the increase of the bedding dip, which shows that the influence of bedding dip angle on the energy storage efficiency is small before the peak. After the peak, the decrease range of the elastic energy ratio is 60°→45°→ 30°→ 90°→0°, indicating that the post-peak fracture of the rock sample with 90° is the least developed and shows the greatest lithologic brittleness. A new criterion modified impact energy index (W) was established by combining the advantages of elastic deformation energy index (W_et) and impact energy index (W_cf). The W value of rock samples is calculated as 60°→45°→30°→90°→0° from small to large.