Failure characteristics and support technology for a special-shaped roadway in an inclined coal seam under disturbance by roof stress waves

To analyze the dynamic response characteristics and failure behavior of the surrounding rock of a special-shaped roadway in an inclined coal seam, the special-shaped roadway of working face 21194 at Dabaoding Coal Mine of Sichuan Chuanmei Huarong Energy Co., Ltd. was taken as the engineering background. Numerical calculations and theoretical analysis were combined to investigate the factors influencing the failure and instability of roadway surrounding rock under disturbance by roof stress waves and to analyze the stress wave propagation process in a special-shaped roadway in an inclined coal seam and the vibration acceleration response characteristics of the surrounding rock. The results showed that: ① during mining of an inclined coal seam, the surrounding rock of a special-shaped roadway was subjected not only to mining disturbance but also to dynamic loads induced by stress waves generated by roof fracturing, thereby increasing roadway roof subsidence and shifting the peak subsidence toward the low sidewall. ② The propagation process of roof vibration acceleration waves comprised initial vibration, fluctuation, and residual stages. During the initial vibration stage, the vibration acceleration waves continued to spread. During the fluctuation stage, they reached the surface of the roadway surrounding rock, causing asymmetric vibration of the two sidewalls, and the peak vibration accelerations of the roadway surrounding rock decreased in the order of roof, low sidewall, high sidewall, and floor. During the residual stage, the intensity of the vibration acceleration waves continued to decay. ③ Under the influence of vibration acceleration wave propagation, the extent of failure in the roadway surrounding rock evolved through three stages: pre-steady-state, unsteady-state, and post-steady-state. In the pre-steady-state stage, the failure depths of the plastic zones in the two sidewalls exhibited an asymmetric distribution, with that in the high sidewall greater than that in the low sidewall. In the unsteady-state stage, the failure depths of the plastic zones in the roadway roof and the two sidewalls increased, and the asymmetric distribution in the two sidewalls changed to one in which the depth in the low sidewall was greater than that in the high sidewall. In the post-steady-state stage, the failure depth of the plastic zone in the roadway surrounding rock no longer increased. On this basis, a multilevel support system consisting of long and short anchor cables, rock bolts, and a shotcrete layer was proposed. Field monitoring results showed that after the multilevel support system was implemented, the deformations of the roof, floor, high sidewall, and low sidewall decreased by 85.7%, 74.8%, 70.1%, and 72.9%, respectively. The asymmetry of deformation between the two sidewalls was markedly reduced, and the stability of the surrounding rock of the special-shaped roadway was significantly improved.