Study on mechanical properties and energy evolution of gas-bearing coal with different bedding angles under impact loads

To reveal the mechanical response and energy conversion mechanism of deep gas-bearing layered coal under impact loads, coal samples from a gas outburst mine in Gansu Province were taken as the research object. Based on a three-dimensional combined dynamic-static load testing system, impact tests were conducted on coal samples with different bedding angles β (0°, 30°, 45°, 60°, and 90°) under a gas pressure of 0.8 MPa. A preset axial static load of 2 MPa and confining pressure of 4 MPa were applied, followed by loading with an impact pressure of 0.6 MPa. The stress–strain curves, mechanical parameters, failure modes, and energy evolution laws were analyzed. The results show that the peak strength presents a U-shaped distribution with the change of bedding angle: it reaches the highest values at 0° (160.41 MPa) and 90° (164.66 MPa), and the lowest at 45° (124.96 MPa). This is because the shear stress concentration effect on the bedding plane is the strongest at 45°, making it easy for cracks to propagate along the bedding. The peak strain also shows a U-shaped trend, reaching 0.03 at 90°and stabilizing at 0.026 at 30°and 45°, which reflects the differences in the deformation mechanisms of coal samples under different angles. In terms of energy evolution, the total energy density ( U ) and dissipated energy density ( U d ) are higher and grow faster at 0°and 90°, while the elastic energy density ( U e ) shows obvious post-peak release only at 0°. In the range of 30°∼60°, the values of U and U d are low, and the release of U e is weak, which is consistent with the low energy consumption characteristics of shear failure along the bedding. The failure mode changes regularly with the bedding angle: multi-directional fragmentation at 0°, shear fragmentation along the bedding mainly at 30°∼45° (the most severe fragmentation at 45°), and cross-bedding splitting failure at 90°. The study confirms that bedding angle regulates the mechanical properties and energy distribution of coal by changing the stress distribution and crack propagation path. The research results can provide key quantitative parameter support for the assessment and prevention of dynamic disasters in deep gas-bearing coal.