Double-factor control method for calculating hydraulic support working resistance for longwall mining with large mining height

To control surrounding rock in longwall mining with large mining height, we consider the coal seam conditions in Jinjitan Coal Mine to analyze how roof failure and coal wall spalling affect the stress path. A simplified dynamics model of surrounding rock and hydraulic support is developed based on the mechanical model of roof stratum that involves the cantilever beam and the voussoir beam. The proposed criterion for the supporting force well fits with the roof stratum stability. The process of coal wall spalling is divided into two stages: First, the coal wall transitions from an elastic state to a plastic state, and then the plastic coal wall slides unstably. To analyze how the supporting force and guarding force affect the coal wall spalling in the two stages, we develop the tensile-cracking-sliding mechanical model of coal wall spalling, which allows us to calculate the critical guarding force. Through analyzing the relationship between the supporting force and guarding force, we propose the double-factor control method to calculate the working resistance of the hydraulic support and apply it to the working face with 8.0 m mining height in Jinjitan Coal Mine.