Mechanism and Control of Roadway Instability in Thick Oil Shale Roofs with “Weak Friction-Strong Cementation” Characteristics

Thick oil shale roofs in the Zichang mining area frequently suffer from delamination and sudden brittle fracture, compromising support stability. Using the 50117 return-air roadway as a case study, this paper integrates microstructural characterization (SEM-EDS/XRD), mechanical testing, theoretical interpretation, and FLAC3D simulation to elucidate the instability mechanism. Results indicate that the preferred orientation of clay minerals along bedding yields a “weak friction” signature, facilitating delamination. Simultaneously, the rigid quartz framework enables rapid energy storage, yet constrained bending dissipation triggers instantaneous fracture. This “weak friction-strong cementation” property drives the “delamination-brittle fracture” mechanism. Notably, the roof exhibits low principal stress concentration but extreme sensitivity to deviatoric stress, typifying a “low-stress environment and weak structural damage” behavior. Accordingly, a synergistic control technology featuring “high-prestress normal clamping and dowel shear resistance” was proposed. Field application confirmed its effectiveness in suppressing delamination and reducing rib convergence, thereby ensuring long-term roadway stability.