Effectiveness of mining-induced subsidence control and its suitability for farmland protection in the coal-grain overlapping area

Coal mining in the Huang-Huai-Hai Plain is associated with a high risk of mining-induced subsidence, extensive waterlogging, and severe ecological damage,taking the main coal and grain production compound area in Henan Chensilou as the research object. A representative coal-grain overlapping area was examined through theoretical analysis and numerical simulation to clarify the principle of active control of mining subsidence, evaluate its control effectiveness and engineering applicability, and reveal the load-bearing mechanism of the composite load-bearing structure. The results showed that active subsidence-control mining reduced the maximum farmland subsidence by 74.9% compared with conventional caving mining. Increasing the backfill ratio enhanced the load-bearing capacity of the composite structure and had the greatest influence on farmland subsidence control. Considering both subsidence-control performance and economic cost, a backfill ratio of 85% was selected. At this backfill ratio, the predicted maximum farmland subsidence was 880 mm, and the minimum depth to the phreatic water table was approximately 1.12 m, indicating good engineering applicability. The load-bearing stresses in the backfill body and coal pillars exhibited a nonuniform bimodal distribution, forming a synergistic load-bearing system based on skeleton support, spatial filling, and mutual confinement that effectively controlled surface subsidence.