Movement Laws of the Overlying Strata at the Working Face Ends and Their Effects on the Surface Deformation

Abstract

Underground coal mining causes stress relief and strata/ground movement, threatening the safety of the surface structures. Investigating the movement laws of the strata above the working face ends is important because it determines the deformation level of the surface subsidence trough at the boundary, which is also the zone with the largest deformation degree. This paper presents a study on the movement laws of the overlying strata at the working face ends, and assesses their effects on the surface deformation using field monitoring as well as physical and numerical modelling. The results show that the surface deformation at the subsidence trough boundary is closely related to the movement and rotation of the broken blocks of the primary key stratum (PKS), which control the development of the bed separation and the degree of the surface deformation at the corresponding locations. The numerical modelling results suggest that, the larger the mining height, the greater the rotation angle of the broken blocks and the more severe the surface deformation above the ends of the working face. The results also highlight the role of the thickness of the topsoil. The implications of the results and the limitations of the research are also briefly discussed.

Keywords

• longwall mining
• overburden strata movement measurement
• surface subsidence
• bed separation
• broken blocks
• key strata