Investigations on the advanced fracturing mechanism and control of the main roof in the pre-driven recovery room: a case study

Main roof advanced fracturing (AF) can induce significant deformation of the pre-driven recovery room (PRR), threatening safe and efficient equipment recovery. This paper investigates the influence of main roof fracture structures above the PRR through field measurements and numerical simulation. A validated UDEC model was established to clarify how the last fracture position (LFP) governs roof structural evolution and pumpable support (PPS) performance. As the LFP distance from the PRR increases, the main roof structure transforms from a cantilever beam to a voussoir beam structure (VBS), and the AF location shifts from above the solid coal rib (SCR) toward the gob. Under the VBS condition, the PPS tends to fail in advance due to insufficient load-bearing capacity. When LFP is 15 m from the PRR, the PPS exhibits the highest crack damage (outside PPS DO = 69.1%, inside PPS DI = 58.4%). When AF develops above the gob (LFP = 30 m), DO = 25.7%, and DI = 14.5%. The maximum principal stress propagates along fracture paths and compression-shear zones toward the PRR roof and SCR, contributing to PPS instability. Sensitivity analysis indicates that the AF step increases with increasing block elastic modulus and contact tensile strength, but decreases with increasing burial depth. A coupled active–passive control technology was applied in practice. Field monitoring shows roof cable load up to 334 kN, roof-floor convergence peaking at 388 mm, mining stress of 21.5 MPa, and PPS stress of 16.05 MPa. The HS resistance remained below the rated 6400 kN without periodic weighting, ensuring efficient equipment recovery.