Coal Pillar Width Determination and Roof Full-Cable Support Technology for Gob-Side Entry Driving in Extra-Thick Coal Seams

To determine a reasonable coal pillar width for gob-side entry driving in extra-thick coal seams and improve roof control under thick top-coal conditions, the No. 50604 return airway of Ti’an Coal Mine was selected as the engineering case. A combined approach involving theoretical calculation, numerical simulation, and field monitoring was adopted. Based on limit equilibrium theory and a modified Kastner formula for rectangular roadways, the reasonable coal pillar width was determined to be 7.13~8.42 m. Sensitivity analysis showed that the calculated width was sensitive to the stress concentration and lateral pressure coefficients. FLAC3D simulations compared the plastic zone and deformation of the gob-side entry under different pillar widths, and 8 m was determined as the reasonable width. Mining-stage simulations indicated that the plastic failure range and deformation increased markedly within 5~10 m ahead of the working face. A roof full-cable deep–shallow collaborative support system was proposed, and reasonable roof support parameters were determined through orthogonal numerical simulation and multi-index evaluation. Field monitoring showed that roadway deformation remained controllable during excavation and mining, verifying the rationality of the 8 m narrow pillar and roof full-cable support parameters.