Boundary distribution of top-coal limit-equilibrium zone in fully mechanized caving in steeply dipping coal seams

In fully mechanized caving mining, the earlier the top coal enters the limit-equilibrium zone, the easier it is for leakage to be induced in front of the support. As the dip angle of the seam increases, the leakage of the top coal in front of the support drastically reduces the stability of the stope support-surrounding rock system. In this study, theoretical analysis, a physical simulation experiment, a numerical simulation, and field measurements were performed to consider the influence of the coal seam dip effect on the gradual deterioration of top coal for the first time, and quantitative characterization of the limit equilibrium boundary of top coal was realized based on analysis of the continuous damage medium mechanics. The results show that the two boundaries exhibit a consistent, asymmetric 'double arch' distribution along the incline. The top coal in the inclined upper-middle region of the working face is the first to enter the limit-equilibrium state, whereas the inclined upper and lower regions lag behind. The initial and final boundaries of the limit-equilibrium zone are distributed from 1.24 to 3.04 m and from 0.19 to -1.95 m in front of the coal wall, respectively. The distribution of the limit-equilibrium zone boundary was verified by the leakage times of the top coal in the working face. These results could provide reference information for evaluating stope support-surrounding rock systems in fully mechanized caving mining with steeply dipping coal seams.

Automated summary

This study focused on the impact of coal seam dip on the gradual deterioration of top coal, using theoretical analysis, physical simulation, numerical simulation, and field measurements to quantitatively characterize the limit equilibrium boundary of top coal. The results revealed a consistent, asymmetric 'double arch' distribution of the two boundaries along the incline, with specific boundaries determined for different regions of the working face.