Numerical simulation study on optimization of technical parameters of pier column backfilling mining in Wangzhuang Coal Mine

In view of mining method of pier column backfilling of No.4 thin coal seam in the seventh mining area of Wangzhuang Coal Mine, key technical parameters of the pier column backfilling mining were researched with FLAC3D numerical simulation method, influences of the technical parameters of interval, cover depth and mining height on long-term stability of the pier column backfilling body were analyzed, and conclusions were obtained that stability of the pier column backfilling are decreased with increasing of all the three influence factors. Combining with test condition of working face of the seventh mining area in Wangzhuang Coal Mine, a backfilling mining scheme was determined with elastic nuclear area proportion to define critical safe value and through interior vertical stress change to test it, namely the pier column backfilling size is 6 m×6 m and column interval is 4 m. The practical application result shows that the scheme of pier column backfilling makes goaf filling rate reduce to 30%, and the maximum surface subsidence is only 48 mm, which can effectively control surface subsidence and realize safe mining.