Systematic principles of surrounding rock control in longwall mining within thick coal seams

Effective surrounding rock control is a prerequisite for realizing safe mining in underground coal mines. In the past three decades, longwall top-coal caving mining (LTCC) and single pass large height longwall mining (SPLL) found expanded usage in extracting thick coal seams in China. The two mining methods lead to large void space left behind the working face, which increases the difficulty in ground control. Longwall face failure is a common problem in both LTCC and SPLL mining. Such failure is conventionally attributed to low strength and high fracture intensity of the coal seam. However, the stiffness of main components included in the surrounding rock system also greatly influences longwall face stability. Correspondingly, surrounding rock system is developed for LTCC and SPLL faces in this paper. The conditions for simultaneous balance of roof structure and longwall face are put forward by taking the stiffness of coal seam, roof strata and hydraulic support into account. The safety factor of the longwall face is defined as the ratio between the ultimate bearing capacity and actual load imposed on the coal wall. The influences provided by coal strength, coal stiffness, roof stiffness, and hydraulic support stiffness, as well as the movement of roof structure are analyzed. Finally, the key elements dominating longwall face stability are identified for improving surrounding rock control effectiveness in LTCC and SPLL faces. (C) 2018 Published by Elsevier B.V. on behalf of China University of Mining & Technology.