Failure mechanism and synergistic control of gob-side entry under thick hard roof conditions

To address the problem of large-scale deformation failure caused by stress concentration in gob-side entry retainment under thick and hard roof conditions, this study takes the return airway of the 9303 working face at Hengsheng Coal Mine as the engineering background. Through field measurements, theoretical calculations, and numerical simulations, the asymmetric instability mechanism of the gob-side entry under a thick and hard roof was determined. Based on theoretical calculations and numerical simulation results, a comprehensive “support-grouting” zoned asymmetric synergistic control technical scheme combining anchor cable clusters with deep and shallow hole grouting was proposed. Engineering practice verified that after implementing this technology, roof and sidewall stabilized at 58–61 mm and 144–157 mm, with rates of 0.11–0.12 and 0.14–0.16 mm/month, respectively. Consequently, the “support-grouting” synergistic control technology effectively maintained the surrounding rock of the gob-side entry under a thick, hard roof in a stable state. No abnormal mining pressure phenomena, such as support failure, rib spalling, or crack propagation, occurred, thereby validating the rationality of the “support-grouting” zonal asymmetric synergistic control technology.