Investigation of Overburden Movement and Ground Stress Behaviour in Multiseam Mining

Abstract

Abstract In multiple-seam mining, severe deformation of roadways and coal bursts caused by overlying coal pillars can occur in the lower seams. Overburden movement and ground pressure behaviour when mining thick seam below the strong roof and upper four extracted coal seams were investigated in the Tongxin coal mine, China. The numerical model indicated that the abutment stress in the lower seam is affected by overlying coal pillars as suggested by the bubble and the cantilever beam models. The microseismic monitoring indicated that high-energy seismic events caused by large overburden movement under the overlying pillars were the source of the dynamic loads. The influence of upper pillar on lower longwall mining conditions can be broken down into three cases: (a) under no pillar area, no excessive deformation or dynamic failure was observed in the tailgate with medium static loads and low dynamic loads; (b) under single pillars or two overlapping pillars, severe deformation occurred in the tailgate with low to medium static loads and medium dynamic loads; and (c) under the three to four overlapping pillars, extreme deformation was observed with the high static loads and high dynamic loads. These findings can provide guidance for the roadway layout in the multiple-seam operations.