Study on Roof Support Technology of the Upward Two-Step Staggered-Drift Cut-and-Fill Mining Method Under Fractured Ore-Rock Conditions

To address the challenging stope roof support problem associated with the the Upward Two-Step Staggered-Drift Cut-and-Fill Mining Method (UTSCF method) under fractured surrounding rock conditions, this study establishes an elasto-plastic zoning model for drift roof surrounding rock to calculate the thicknesses of the loose zone and plastic hardening zone, proposes a combined support scheme comprising split-set (SS) bolts, metal mesh and cross-timber (CT) caulking for the working condition where backfill on both side walls fails to achieve full roof contact, and analyzes the support performance of this method via FLAC3D numerical simulation. The results indicate that the total thickness of the loose zone (LZ) and plastic zone (PZ) in the roofs of 6 m and 8 m drifts reaches 2.02 m and 2.15 m, respectively; after support application, the maximum principal stress (MPS) of the roof decreases by 49%, the plastic zone volume is reduced by 35.5–47.2%, and the average roof displacement drops by approximately 29%. Field industrial tests have preliminarily verified the engineering adaptability and stability control performance of the proposed support method. The mechanical mechanism of secondary roof contact by wedged cross timbers, as well as the quantitative relationship between theoretical zoning and support adequacy, still requires further verification.