Evolution mechanism of deformation and failure energy in composite rock mass with structural planes of different inclinations

In order to investigate the mechanical properties and energy evolution patterns of composite rock masses with structural planes of different inclinations, this study selected composite rock samples made from coal and sandstone, with structural plane inclinations of 0°, 30°, 45°, 60°, and 90°. Uniaxial compression tests were conducted, and energy theory was applied to analyze the energy transformation characteristics during the deformation and failure process. The results show that the structural plane inclination significantly influences the compressive strength, peak strain, and elastic modulus of the composite rock masses. The compressive strength exhibits a "U-shaped" trend, first decreasing and then increasing, with the minimum at 45° and the maximum at 90°. The peak strain decreases monotonically as the angle increases, while the elastic modulus increases exponentially. The energy evolution process can be divided into four stages: compaction, elastic deformation, plastic deformation, and failure. The total peak strain energy and elastic energy percentages exhibit a pattern of first decreasing and then increasing with changes in the inclination angle. A piecewise damage constitutive model considering the compaction stage was established based on the experimental results. The model curve aligns well with the experimental data and can accurately characterize the stress-strain evolution characteristics of composite rock masses with structural planes of different inclinations. The findings of this study provide theoretical insights for disaster prevention and control in deep mines, as well as the stability analysis of composite rock masses.