Instability criterion and integrated control technology for sector coal pillars based on a modified Drucker–Prager energy criterion

Narrowing sector coal pillars in thick coal seams can improve coal recovery but may intensify mining-induced stress concentration, plastic-zone expansion, and energy-driven instability. This study investigates a 12 m-wide sector coal pillar between the 15,104 working face and the 15,106 intake roadway in the No. 15 coal seam of Shangshe Coal Mine, China. A panel–roadway compound abutment-pressure model was established, and an approximate three-dimensional stress state was constructed using an elastic half-plane solution and the plane-strain assumption. A modified Drucker–Prager energy criterion was then developed using stored elastic energy density, ultimate elastic energy density, and stability margin. Theoretical calculation, FLAC3D simulation, and field monitoring were combined to evaluate stress redistribution, energy accumulation, and roadway deformation. As the roadway-side/goaf-side plastic-zone widths increased from 3/5 m to 4/7 m, the peak vertical stress increased from 24.973 to 28.757 MPa, and the peak ultimate elastic energy density increased from 0.10 to 0.14 MJ/m³. The 6–8 m region behind the working face was identified as the main energy-instability-sensitive zone. After integrated control, maximum roof subsidence, pillar-side rib convergence, solid-coal-side rib convergence, and floor heave were 218, 240, 228, and 208 mm, respectively.