Case study on pressure-relief mining technology without advance tunneling and coal pillars in longwall mining

To decrease the waste of coal resources, reduce the drivage ratio, and improve the stability of roadways, a pressure-relief mining technology without advance tunneling and coal pillars (PRMT) for longwall mining has been proposed in China. In this paper, the basic principle and implementation process of four key technologies (the new matching technology of three machines, the liquid directional roof cutting technology, the constant-resistance and large-deformation (CRLD) anchor cable supporting technology, and the granular side supporting technology) of the new mining method are introduced in detail. For the case of the Ningtiaota coal mine, specific parameters of the above key technologies are designed and applied, including the roof cutting parameters, roof supporting parameters and granular side supporting parameters. The test results show that the targets of non-advance tunneling, non-coal pillars and pressure relief are proved to be smoothly realized by using PRMT. In addition, monitoring data of the roof deformation and stress characteristics of the formed roadway indicate that the formed roadway can maintain good stability and the deformation of the surrounding rock can be well controlled. Within the range of 0-400 m, from the initial formation to the final stability of the roadway, the maximum value of the accumulated roof-to-floor deformation was 149 mm, the average value was 102 mm, and the deformation was generally small. In conclusion, these results prove that the principle of PRMT is feasible and can achieve the goal of safe, economical and efficient mining. The research contents of this paper can provide important guidance and reference for the application of PRMT in mines under similar conditions.