Field study on the load transfer mechanics associated with longwall coal retreat mining

Abstract

The two-entry longwall panel system is frequently used in underground coal mines in China. One of these entries serves only the current longwall panel while the other serves both current and subsequent longwall panels. The latter entry is built to survive the continuously high mining-induced stress generated by mining the current panel throughout the longwall mining process. The failure of the entry is controlled by the load transfer mechanics associated with the advancement of the longwall face. This paper presents a field study of the response of the entry during driving and longwall retreat phases. Extensive field data including entry convergence and changes in principal stresses are obtained for the Pingshu coal mine, China. A careful analysis of these data shows that the influence zone of the front abutment load on the trail entry can reach as far as 120 m outby the longwall face during panel mining. Bed separation can occur in competent fine-grained sandstone, which is 7.4 m deep into the trail entry roof. It is also found that the periodic collapse of the main roof above the mined-out area can continue when the longwall face has advanced 120 m away.