An investigation on the influences of initial confining pressure on coal mechanical properties and energy evolution law

Despite that new energy sources have been developing for years, coal still serves as a key resource in the energy structure in China, resulting in the deep mining as one of preferred method. In order to further explore the causes of frequent occurrence of dynamic disasters during the deep mining, the stress path of unloading confining pressure and axial pressure is designed based on the stress adjustment characteristics of the surrounding rock in the excavation roadway. The mechanical properties and energy evolution law of coal body under different initial confining pressures are studied through experiments. With the increase of initial confining pressure, the mechanical parameters of the coal body at the failure point reveals that the peak strength, confining pressure and axial strain increase nonlinearly, while the evolution law of the lateral strain and volumetric strain is not obvious. In addition, the failure mode develops into the brittle failure. In terms of the energy, the original rock energy storage, each energy (U1, U3, U, we, and wd) and elastic strain energy conversion rate increase nonlinearly, indicating that high initial confining pressure (large burial depth) significantly aggravates the risk and strength of coal dynamic failure. According to the experiments, the combined pressure relief measures should be taken in the actual production process to release energy and lower the risks of failures, contributing to a safe and efficient production. It is expected that the research results can provide some insights to the deep resource development and dynamic disaster prevention and control