Stability Control of Underground Roadways Subjected to Stresses Caused by Extraction of a 10-m-Thick Coal Seam: A Case Study

Extraction of a 10-m-thick coal seam in one single lift using the longwall top coal caving method caused severe deformations in underground roadways in Majialiang coal mine in Shanxi Province, China. Field monitoring of stress changes in the roof and in the coal pillar, and deformation of the 14202 tailgate, were carried out. The deformation monitoring found that the maximum floor heave of the 14202 tailgate was 1.85 m when the monitoring point was 250 m behind the longwall working face, while the maximum roof subsidence and the maximum rib-rib convergence was 0.93 and 1.14 m, respectively. The deformation rate of the 14202 tailgate increased dramatically when the monitoring point was at distances of 100-150 m behind the longwall working face, which reflected the fact that the tailgate underwent sharply increased loads within this range. Field monitoring of stress changes and the displacement of the 14202 tailgate revealed that the impact range of the mining-induced stresses in longitudinal direction (the same as the mining direction) was from 60 m ahead of the longwall face to 250 m behind the longwall face. Additionally, the mining impact range in transverse direction was more than 45 m, indicating that the coal pillar width should be larger than 45 m to avoid significant influences of mining-induced stresses. This finding was applied to the 14103 tailgate, which was subjected to similar mining and geological conditions as the 14202 tailgate. A coal pillar with width of 56 m was adopted in the 14103 tailgate, and displacement monitoring showed that large deformation was successfully controlled. The field investigations in this study provide a basis for design of a proper coal pillar width of underground roadways when subjected to large stresses induced by mining of thick coal seams in a single lift.