Stability mechanism and control of the pumpable supports in longwall recovery room

The load-bearing performance (LBP) of pumpable supports (PPS) is crucial for the stability of longwall pre-driven recovery room (PRR) surrounding rock. However, the unbalanced bearing coefficient (UBC)of the PPS (undertaking unequal load along the mining direction) has not been investigated. A mechanical model of the PRR was established, considering the main roof cantilever beam structure, to derive an assessment formula for the load, the failure criteria, and the UBC of the PPS. Subsequently, the generation mechanisms, and influencing factors of the UBC were revealed. Global sensitivity analysis shows that the main roof hanging length (l₂) and the spacing between the PPS (r) significantly impact the UBC. A novel design of the PPS and the coupling control technology were proposed and applied to reduce the UBC of the PPS in the adjacent longwall PRR. Monitor results showed no failure of the PPS at the test site, with the UBC (ζ) reduced to 1.1 consistent with the design value (1.15) basically, fully utilizing the collaborative LBP of the PPS. Finally, the maximum roof-to-floor convergence of the PRR was 234 mm, effectively controlling the stability of the surrounding rock of the PRR and ensuring the mining equipment recovery.