Research on allowable deviations of the pilot hole based on TBM conical cutterhead muck discharging simulation in inclined openings

Due to its high tunneling efficiency under steep conditions, the directed pilot hole in conjunction with the Tunnel Boring Machine (TBM) conical cutterhead has been widely utilized in inclined openings. However, the key factor influencing TBM tunneling efficiency, the mucking efficiency of the conical cutterhead, is significantly affected by unavoidable pilot hole deviations. In this study, the muck flow characteristics of the conical cutterhead with a pilot hole under steep conditions were analyzed using a comprehensive Discrete Element Method simulation that encompassed the stages of falling, shoveling, and discharging. Then the muck discharge efficiency and residual muck efficiency were employed as quantitative indicators to evaluate the cutterhead’s mucking performance and secondary cutter wear. Furthermore, the interactive effects of deviation distance of the pilot hole (DD) and deviation angle of the pilot hole (DA) on mucking performance were investigated. Based on various engineering requirements, a weighted multi-factor analysis method is proposed for determining the allowable deviations of the pilot hole. For a specific inclined shaft with the following characteristics: a cutterhead with a diameter of 7690 mm, a conical angle of 15°, a 2500 mm pilot hole and a tunneling inclination of 55°, the results indicate that DD reaches a minimum value, when DA=112.5°. Specifically, the minimum DD=183 mm when minimizing secondary cutter wear, and 401 mm when enhancing mucking performance. These findings offer theoretical guidance for determining positional parameters of the pilot hole in inclined openings.