Deformation Mechanism and Control Strategies of Gob-Side Entry Retaining by Roof Cutting in Ultra-Deep Coal Mines

Gob-side entry retaining by roof cutting and pressure relief (CRRE) eliminates coal pillar waste and mitigates mining-induced stress concentration. Although widely applied in mines shallower than 1000 m, systematic research on asymmetric deformation mechanisms and matched control technologies under ultra-deep conditions (>1000 m, σH > 60 MPa) remains limited. This study investigates the 5307 working face of Anju Coal Mine (burial depth: 1127–1195 m) using theoretical analysis, FLAC3D numerical simulation, and 480 m of field monitoring. The stress evolution, deviatoric stress field response, and asymmetric deformation mechanisms of the surrounding rock under ultra-deep mining conditions are systematically analyzed, based on which a targeted collaborative control technology is proposed. The key findings indicate that (1) CRRE significantly attenuates advanced abutment pressure compared with conventional pillar retention, with an average stress reduction of 20.1 ± 1.2% (95% CI: 17.8–22.4%, p < 0.01). (2) During the advanced mining stage, the second invariant of deviatoric stress exhibits a saddle-shaped distribution with a pronounced concentration at the mid-rib, identifying this as the dominant zone for rib bulging failure. (3) In the post-mining entry-forming stage, the roof deviatoric stress field demonstrates marked asymmetric evolution, with the distortion energy on the solid-coal side substantially exceeding that on the gob side; moreover, the low-position roof strata exhibit high distortion and poor stability, rendering them prone to bending fractures. Grounded in these mechanisms, a full-cycle differentiated surrounding rock control technology is developed, integrating pre-mining directional roof pre-splitting, active tough support reinforcement, post-mining temporary roof control and pressure relief, and gangue retaining with rib collaborative protection. The key parameters include a roof cutting height of 7 m, a cutting angle of 15°, NPR constant-resistance anchor cables with W-steel belts, and temporary support extending 300 m behind the working face. Field monitoring reveals staged deformation evolution, with stabilization achieved 250 m behind the working face. Maximum roof subsidence, floor heave, and total roof-floor convergence were 180 mm, 329 mm, and 422 mm, respectively, below the 500 mm allowable threshold for ultra-deep retained entries.