Stability control of roadway surrounding rocks under repeated mining: a case study

Repeated mining makes the deformation and failure of roadway surrounding rocks more complex than those under single-seam conditions. To address the large deformation and support failure in the 40,111 roadway of the Dafosi Coal Mine, this study combined theoretical calculations and numerical simulations to analyze the evolution of stress, displacement, and plastic failure under different seam spacings and mining stages. Failure depth h0 of floor was affected by the synergy of included angle θ, internal friction angle φ4, and elevation H. h0 decreased with increasing θ (0.35-0.45 m/°) but increased with higher φ4 (0.36 m/°) and H (1.6 m/m). The coupling effect significantly changed h0 within 14.76-36.37 m. Reduced interlayer spacing intensified roadway deformation, increasing roof displacement from 230 to 394 mm and peak horizontal stress from 25.7 to 29.3 MPa. Based on the simulation and field verification, an optimized support scheme using "5-4-5" roof and "3-4-3" side cables effectively limited roof-floor convergence to 165 mm and side displacement to 125 mm. Besides, the surrounding rocks became stable after approximately 90 m of excavation. The 41,213 return airway employed an asymmetric support system, using left-side anchor cables and right-side anchor bolts, which effectively limited surface displacement to 22 mm at the sides and 15 mm at the roof and floor. After compensating for a 17.9% pretension loss, the cables maintained stable anchorage. Field observations indicated that the mining influence extended from 10 m ahead to 60 m behind the working face, with dilatancy concentrated in the shallow strata and more pronounced deformation on the left side. The results provide theoretical guidance for the stability control and support optimization design of roadways with complex stress.