Stability Investigation of a Deep Shaft Using Different Methods

Abstract

The New Zigana Tunnel is, at 14.5 km long, the longest highway tunnel project in Turkey. In this project, it is planned to construct two service shafts to provide access to outside the tunnel and temporary ventilation. Service Shaft 2 (Ø = 2.60 m), which is 220 m in depth, was opened by the raise boring machine (RBM) method. In this study, the wall stability of Service Shaft 2 was investigated using empirical analysis, analytical analysis, and numerical simulation methods. To define the rock masses on the shaft route, the rock mass rating (RMR), Q, and geological strength index (GSI) classification systems were utilized as an empirical approach. The rock-support interaction and convergence-confinement methods were applied in the analytical analysis of wall stability. To determine the plastic zones that occurred around the unsupported shaft walls, 2D and 3D numerical simulations (FEM-based) were used. According to the results of empirical analysis, there is no need for support to ensure the stability of shaft walls. Conversely, the analytical and numerical methods exhibited more conservative results than other methods and suggested support application for stability. According to the convergence-confinement method and 2D FEM simulation, the plastic zone around the shaft walls developed after depths of 105 and 81 m, respectively. Finally, the results obtained from these analyses were compared with actual field situations, and their compatibility was investigated. It was concluded that, of these analysis methods, 2D FEM simulation is most compatible with the actual field data.