Mine pressure behavior law and fault activation response of normal fault zones in thick coal seams under mining disturbance

The relationship between fault activation and ground pressure behavior, as well as the dominant stress-controlling mechanism, during the mining of thick coal seams across a normal fault requires systematic clarification. To this end, a 70° normal fault in a coal mine in the Ordos Basin was taken as the geological prototype, and a combined approach involving theoretical analysis and physical similar material simulation was adopted to analyze the evolutions of the fracture, displacement, and stress fields in the overburden as the working face advances toward the fault. The results showed that, as mining continued, the peak floor stress near the fault could reach 19.95 MPa. The subsidence profile of the coal seam exhibited an overall “U-shaped” form with local “M-shaped” characteristics. When the working face advanced to within 5 m of the fault, the peak stress in the immediate roof increased by 3.17 to 17.22 MPa, while the peak stress in the main roof increased by 4.55 MPa to 17.80 MPa, and the influence range of the advance abutment pressure extended. The average interval of periodic weighting shortened from 21.5 m in the footwall to 15 m near the fault on the hanging wall. Roof subsidence was greatest in the vicinity of the fault, with the maximum subsidence values along survey lines 1, 3, and 5 being 13.35, 12.02, and 11.45 m, respectively. Theoretical derivations indicated that fault activation was dominated by vertical stress loading and horizontal stress unloading. Instability occurred after the working face entered the influence zone of the elevated vertical stress and was mainly driven by the reduction in the horizontal stress. The risk level of ground pressure-related hazards at the working face increased significantly as it approached the fault; both support parameters and monitoring measures should be appropriately strengthened. These findings provide a theoretical basis for the safe extraction of thick coal seams in normal fault zones under mining-induced disturbance.