Field and Numerical Investigations on Pumpable Standing Supports Failure Analysis in the Longwall Pre-driven Recovery Room

Pumpable standing supports without sufficient loading-bearing capacity (LBC) will result in the deformation failure of the pre-driven recovery room (PRR). A combined method of numerical simulation and field investigation is adopted to analyze the failure mechanism of the high-water cementitious material (HWCM) pier cribs and the PRR. The influence of main roof hanging length (MRHL), height-to-diameter ratio, and external constraint strength on the LBC of the HWCM pier cribs are analyzed accordingly. It indicates that when the MHHL increases, the bending deformation of the roof increases (eccentric load and eccentricity increase), the pier cribs gradually change from axial compression to shear sliding failure, the limit LBC of the inby pier crib is reduced from 13.5 to 8.6 MPa, and the maximum roof subsidence of the PRR is increased from 267 to 595 mm. The height-to-diameter ratio is negatively correlated with the LBC of the HWCM pier cribs, but the external constraint strength is positive. A corresponding optimization scheme is proposed and applied to engineering practice. The monitoring results exhibit that the maximum stress on the pier cribs was 18.5 MPa (without failure), and the maximum roof-to-floor convergence of the PRR is 220 mm, ensuring the safe and efficient recovery of mining equipment. Establishing a UDEC model to analyze the failure mechanism of the pier cribs under the eccentric load induced by advanced abutment pressure and roof rotation sinking.The contribution indicators of MRHL, height-to-diameter ratio, and external constraint strength to the load-bearing capacity of pier cribs were analyzed.A collaborative support method for pier cribs in PRR was proposed and applied to engineering practice, ensuring the recovery of mining equipment.