Application and optimization of filling coal mining technology in “three-under” overburden coal mining operations

Abstract

In response to the problems such as large surface subsidence, strong overburden damage, low resource recovery rate, and prominent environmental constraints in underground coal mining under buildings, railways, and water bodies, this paper takes the filling coal mining technology as the core and constructs an integrated research framework of “equivalent mining height theory-FLAC3D numerical simulation-multi-objective parameter optimization”. It analyzes the influence of filling rate, filling body elastic modulus, filling body compressive strength, and advancement step distance on surface movement, overburden damage height, and stress distribution in the mining area. The simulation results show that compared with the traditional caving method, when the filling rate increases from 70% to 95%, the maximum surface subsidence value decreases from 684 mm to 54 mm, the reduction rate increases from 45.1% to 95.7%; the height of the water-conducting fracture zone of the overburden decreases from 78.6 m to 21.8 m, a reduction of 72.3%; the stress concentration coefficient in front of the working face decreases from 2.31 to 1.43. Considering both comprehensive safety control and economic cost, it is recommended to adopt the optimized scheme of “filling rate 90%, filling body compressive strength 3.5 MPa after 28 days, advancement step distance 1.2 m, filling lag distance less than 6 m”. This scheme can control the maximum surface subsidence to 96 mm, increase the resource recovery rate to 87.5%, and reduce the unit coal mining comprehensive cost by 13.6% compared with the high-strength filling scheme of 95%. The research results show that the combination of filling coal mining and numerical simulation optimization can provide a quantifiable design basis for safe, efficient, and green mining of “three underground” coal.