Numerical investigation of load shedding and rockburst reduction effects of top-coal caving mining in thick coal seams

By comparing the overburden structure characteristics and the distribution of stresses around roadways and coalfaces in slice mining and top-coal caving mining in thick coal seams, this study analysed the effects of the two mining methods on rockburst prevention. Furthermore, by using FLAC3D numerical simulation, this research studied the distribution of surrounding rock stress in the first mining panels, subsequent panels, solid coal roadways, and gob-side roadways and the influence of parameters including mining height, bottom coal, and coal seam thickness on stresses in the surrounding rocks. On this basis, the effects of load shedding and rockburst reduction of top-coal caving mining of thick coal seams were summarised and verified through field investigation. The results show that compared with slice mining, overburden structures in top-coal caving mining of thick coal seams weakened the stress concentration in surrounding rocks, resulting in lower peak values but wider ranges of advanced abutment stress and side abutment stress in panels. The point of peak stress was observed deeper into the coal masses. With the increase of mining height and the decrease of bottom coal thickness, the stress concentration around roadways and coalfaces decreased rapidly and then tended to be stable. Therefore, top-coal caving mining can reduce the stress concentration around roadways and coalfaces to decrease rockburst risk. While mining thick coal seams, top-coal caving mining needs to be conducted preferentially over a reasonable range of mining heights. Field practice in Xing'an and Junde mines revealed that the top-coal caving mining induced a lower rockburst frequency, over a smaller range and with lower intensity, which validated the effects of load-shedding and rockburst reduction of the proposed mining method.