Effect of Confining Pressure Unloading Rate on Mechanical and Energy Characteristics of Coal-Rock Combinations

Coal-rock combinations is a composite structure often encountered in mining engineering. At present, the research on coal-rock combinations mainly focuses on the loading mechanical properties. However, when mining engineering involves excavation, the mechanical characteristics of the coal-rock combination during unloading are very different from those during loading. In order to clarify the acoustic emission (AE) and energy evolution characteristics of unloading failure of coal-rock combinations, the numerical simulation of confining pressure unloading of coal-rock combinations under different unloading rates was carried out by using particle flow numerical simulation software. The mechanical characteristics of the failure process of the coal-rock combinations under different unloading rates were analyzed. The research results indicate that: With the increase of unloading rate, the number of AE events in coal-rock combination increases, the total number of cracks increases correspondingly, and the failure becomes more and more serious. The higher the unloading rate, the simpler the failure mode of the coal-rock combination, and the smaller the breaking angle. And the elastic strain energy, dissipation energy and total input energy of the coal-rock combination under different confining pressure unloading rates all increase with the increase of the unloading rate. However, the increases of the three are different, and the dissipation energy increases the most. The study can provide a reference for the unloading mechanical properties of the combination formed by coal and rock, and provides a reference for the excavation unloading speed when the half-coal and half-rock roadway is excavated.