COMPARATIVE ANALYSIS OF PRECAST SEGMENTAL LINING FOR METRO TUNNELS

Abstract

This thesis covers the analysis of precast tunnel segments for the Metro tunnels. Maximum overburden cases have been considered for analysis in this study. Precast concrete segments are permanent structural lining of a circular tunnel ring formed by TBM. They resist permanent structural loads from the surrounding soil, rock, and groundwater pressure. The segments function as a reaction frame for advancing the TBM by pushing its hydraulic thrust jacks directly against the front face of the most recently installed segmental ring. There are various technical papers and literature available pertaining precast segmental lining of tunnels. Some of the most relevant literatures are reviewed during this project work. The principal objective is to verify one single precast segmental lining ring for circular tunnel. The segmental lining is verified for the maximum overburden height and with a uniformly distributed surcharge load of 50 kPa applied at the ground level. Tunnel case considered for this study is 5.8 m internal diameter circular tunnel and this is to be constructed using precast segmental lining. The results obtained in this analysis can only be used for the segment lining design. No conclusions can be drawn regarding the ground surface settlements. The model indicated can be used to obtain normal effective stresses around the tunnel lining to define ground loads acting on the segmental lining of tunnel. The bending moments obtained from FEM analysis are higher than those from Analytical calculations using Muir-Wood and Curtis approach, except for the Case-4 (i.e. without Surcharge). Shear forces in FEM analysis are generally on higher in all four cases. The axial forces in FEM analysis are also higher than those from Analytical calculations, except for Case-4 as presented in this thesis. It can be concluded that the values obtained from FEM analysis are generally on conservative side, however, it is recommended that these values should be verified through independent analytical calculations to arrive at maximum governing forces to be used for design. The higher one obtained from FEM analysis and Analytical calculations shall be used judiciously for the structural design of precast segmental lining to ensure safe and optimum design of Metro tunnels. Despite the recent advances in structural designs of tunnels, more research is necessary for analysis of precast segmental lining for metro tunnels due to its complex behavior.