ABSTRACT
Nozzle tunnels are enlarged mined sections that connect TBM running tunnels to stations, commonly used in Sydney Metro projects. This paper presents an assessment of the impact of TBM breakthrough on the loads imposed on rock bolts installed at nozzle headwalls for various Sydney rock conditions. The nozzle ground support consists of shotcrete and a pattern of rock bolts and is analyzed using both 3D continuum finite element and discontinuum finite difference models. Three types of ground conditions —Sandstone III, Sandstone IV, and Shale III—are considered. Results indicate that while continuum models show slight increases in axial loads post-breakthrough, discontinuum models reveal a more significant load increase. This research emphasizes the importance of incorporating defect modeling in tunnel design when a more accurate assessments of rock bolt loads is required, such as in the case of the present study.
