Experimental study on the bump-inducing mechanism of slicing in thick coal seams with hard roofs

The bump-inducing mechanism of slicing in thick coal seams with hard roofs is still not completely understood. In this study, a similar material simulation experiment was designed to research the overlying strata behavior and the stress distribution characteristics in mining the lower slice of a thick coal seam with a hard roof. The results showed that the lower part of the main roof could form a relatively stable semi-arc rock-gangue structure during the mining of the lower slice, which could make the voussoir-beam structure develop into the higher strata above. The shock wave induced by the sudden rupture of the voussoir-beam could lead to the further collapse of the semi-arch rock-gangue. The stress monitoring revealed that the stress variation was not sharp in the top slice, whereas the situation of the lower slice was very different There were many intermittent peak points in the stress variation rate curve that had a certain time interval between each point. For the fracture, the rotary process of overlying strata in the bottom slice was more severe compared with the top slice, so the coal damage gradually accumulated under stress wave loading, and when the coal stress exceeded the limit load, rock burst occurred in the roadways and coal faces. In addition, control measures including the top-coal caving mining method, pressure relief technology and support technology were proposed. The microseismic monitoring indicated that the total number of tremors with energy of 10 kJ to 100 kJ was 354 in 2014, the total number of tremors with energies of more than 100 kJ was 7, and the maximum energy of a tremor was 3530 kJ when the 8937 coal face advanced 210 m from the setup entry. The findings from this study will serve to strengthen the engineers' confidence in thick coal seams with serious coal bumps.