Improving the gate road development rate and reducing outburst occurrences using the waterjet technique in high gas content outburst-prone soft coal seam

Most of the coal seams currently mined in the Southwest part of China have high gas content, are soft and prone to outbursts, which significantly influences the rate of gate road development and mining safety. It is believed that an outburst is mainly due to the internal energy stored in the coal seam, so it is necessary to release the energy to prevent the occurrences of coal and gas outbursts, which in turn improves the rate of gate road development. This paper presented herein discusses the usage of the waterjet slotting technique to prevent the occurrence of outbursts during gate road development, on the basis of the laboratory tests, numerical modeling and field work. The numerical modeling indicated that the internal effective stress levels can be reduced up to 70% and 45% for the vertical and horizontal stresses, respectively, when waterjet slotting is applied, and the field monitoring results showed that the gas concentration released from the face of excavation can be increased up to five times compared with the traditional borehole drainage method. As a result, the values Smix and K1, which are determined by drill cuttings to describe the possibility of outburst occurrences, have been kept below the critical limits 70% of the excavation time and the rate of gate road development increases from 30 m to 70 m per month.