The effect of discontinuity density on key strata threshold span in longwall panels

Roof collapses account for more than half of all accidents in Chinese coal mines and are involved in nearly 40% of fatalities in recent decades. The key strata threshold span, which is a fatal factor for roof strata structure stability in longwall mining panels, could be an important forewarning for initial loading. In this paper, we explore the effects of discontinuity density on key strata span. Based on a selected longwall panel, a case study is conducted. The discontinuity density is obtained by an YTJ20 mine electronic borehole observation instrument. Support resistance is monitored at a selected hydraulic support in the middle of the longwall panel. The key strata threshold estimation method is applied and turns out to be coincident with field monitoring data. Sensitivity analysis indicates that the discontinuity could arouse early breaking of key strata. Further study reveals that the effect of discontinuity on the key strata threshold span increases with a decrease in longwall panel width.