Improving safety by further increasing the permeability of coal seams using air cannons after hydraulic punching

As shallow coal resources deplete in industrialized nations, mining operations expand to the deeper resources to meet the requirements of the society. Deep coal seams in China have the characteristics of high gas pressure and high gas content. There is a persistent track record of gas-related accidents in Chinese coal mines. In an effort to eliminate gas explosions and gas outbursts, a new permeability improvement technology of “hydraulic punching plus air blasting” is developed for soft and low-permeability coal seams. To intensively enhance the permeability and achieve efficient extraction of gas from low-permeability coal seams, hydraulic punching is performed first, followed by air blasting. The LS-DYNA software was used to simulate the blasting process by the air cannons. Results were obtained from the Guhanshan mine. Comparisons were done for the stress field, deformation field of the coal body using the law of coal body deformation. Deformation at different blasting times was compared in combination with the field air blasting tests. With 40 times air blasting, the gas drainage increased by about two times compared to drainage without air blasting. The pure gas extraction volume was also observed to be about 2.2 times higher than that without air blasting. The results proved improvement of the coal permeability and gas drainage by this new technology.