Numerical simulation of roof movement and fill strength of coal deep mining

This paper explores the safety of surface structures over a deep coal seam (12#) in a coalmine of northern China’s Hebei Province. If 12# coal seam is mined by block caving, the surface might collapse and the surface structure could be damaged. First, FLAC3D simulation was conducted to simulate the influence of block caving in 12# coal seam and the shallower 9# coal seam on roof movement. The results show that the mining of 9# coal seam does not affect surface safety; but the mining of 12# coal seam would cause the surface deformation to exceed the requirements of the current regulation, posing a threat to the safety of surface structures. Hence, the excavation method for the coal seam was replaced with cut-and-fill mining. Further simulation on this coal seam indicates that the safety of surface structures could be guaranteed, when the equivalent mining thickness (EMT) was 0.2m. Under EMT=0.2m, the fill strength that best protects the surface structures and controls the surface deformation was found to be 0.5 times of coal strength. Finally, the EMT and fill strength for the cut-and-fill mining of 12# coal seam were optimized as 0.2m and 0.5 times of coal strength, respectively, laying a scientific basis for fill preparation.