Field and numerical investigations on linkage failure of the main roof and pumpable supports in the pre-excavation recovery room

In western China, longwall mining faces (LMFs) are usually equipped with a large cross-section pre-excavation recovery room (PRR). This type of entry is commonly reinforced with pumpable supports (PPS). This study investigates the stress and field failure behavior of the PPS, as well as the internal fracture mode of the roof above the PRR. A UDEC model has been developed and validated against field measurements for investigating the failure behavior of PPS and PRR under different main roof structures (MRSs). The linkage instability mechanism between the MRS and PPS has been elucidated. The rotation and misalignment of the fractured MRS triggered shear failure in the roof cables and rockbolts. The reduction in the intact width of the solid coal rib (SCR) increased the load borne by the PPS. The PPS failed prematurely, resulting in linkage instability with the unstable MRS, leading to a large deformation of the PRR. As the main roof fracture shifts from the gob to the SCR, the SCR changes from a tensile-shear failure to a tensile fracture. The PPS beneath the fractured roof primarily fails due to compression and shear failure caused by sliding. The crack damage degree (D) of the outby PPS reaches 85.58 % when the main roof fractures above the PRR(FP3#), while the D of the inby PPS is 71.24 % when the roof fractures above the SCR(FP4#). The proposed coupling control technology was implemented at the test site. Monitoring results show a maximum PPS stress of 19.3 MPa and a maximum PRR roof-to-floor convergence of 308 mm. As the LMF cuts into the PRR, the hydraulic support pressure drops significantly, reaching a peak of 5747 kN without periodic weighting. It effectively controls the large deformation of the PRR and provides a useful reference for PRR support under similar geological conditions.