Mechanical response characteristics and destruction process simulation of aerodynamic cavitation in soft and brittle coal seams

As a local outburst control method for soft crushed coal seam, aerodynamic cavitation has been applied in Huainan Mining Area of China and achieved good results. However, the mechanism of aerodynamic cavitation is not clear, and the key parameters such as gas injection pressure and pressure holding time cannot be optimized. Based on the actual conditions of aerodynamic cavitation, the confining pressure triaxial compression test of rapid unloading was carried out to test the mechanical characteristics of coal mass during rapid unloading. Then, a numerical simulation test of aerodynamic cavitation was carried out, and the pore pressure and the time of holding pressure were selected as variables to study the variation rule of pore pressure and the damage depth of coal body in single gas injection and blowout (rapid pressure relief) during the process of gas injection and pressurization. The results show that with the increase of confining pressure unloading rate, the compressive strength, tensile strength, cohesion and other parameters of coal in the test decrease, the internal friction angle increases, and the coal is more easily destroyed under the rapidly changing stress environment. When the gas injection and pressure holding time is less than 60 min, the pore pressure is proportional to the pressure holding time. The damage depth of coal body in the process of single gas injection and blowout is about 65 mm, and the gas injection pressure is proportional to the damage depth of coal body. Aerodynamic cavitation coal body failure mechanism: after injecting high pressure gas into the coal seam cave, the coal pore pressure is greater than the coal seam cave pressure in a short time, so that the effective tensile stress of the coal skeleton is greater than the tensile strength of the coal body, so as to peel the coal body.