Failure analysis of flexible formwork concrete wall in gob-side entry and its control measures with roof cutting technology

Abstract Flexible formwork concrete wall (FFCW) is used as the roadside backfilling body in gob-side entry (GSE), which has the characteristics of quickly maintaining the roof and effectively isolating the gob. Its stability and deformation are essential for the success of GSE. The failure analyses of FFCW with and without roof cutting conditions were analyzed and compared through the theoretical model. The stress connection of the main roof can be broken through roof cutting technology to reduce the stress of FFCW and improve the supporting effect of the gob. Based on an GSE engineering case, the stress and deformation laws of FFCW during two stages of GSE retaining and reusing were analyzed by numerical simulation. The three stress periods were present during GSE retaining simulation and there were periods of rapid support, stress reduction, and stress stability. The peak and stable stresses were reduced by 5.4% and 10.5%, respectively, after roof cutting. During GSE reuse, the stress concentration appeared within 15 and 10 m ahead the longwall face without and with roof cutting conditions, respectively. The maximum deformation decreased by 50.3% after roof cutting. Finally, the stress and deformation of FFCW were measured in the field. After roof cutting, the measured peak stress was reduced by 87.5% and the deformation decreased by 41.6%. The stress changed from the three-period mode of rapid increase, slow increase, and stability to the three-period mode of rapid increase, gradual decrease, and stability. Thus, the deformation and stress measurement results of FFCW were reduced under roof cutting and stress relief during two stages, which improved stability.