Seismic Behaviour of Tunnels of Different Shapes in Rocks

Abstract

Based on the different purposes and utilities, the tunnels are constructed of various shapes such as D-shape, Horse-shoe, and Circular. Most of the shapes of the tunnel are designed based on the overburden load in the static conditions, but their behaviour in seismic condition is very complex and not well explored yet. There are number of tunnel damages reported during the past seismic events worldwide. In this study tunnels of different shapes in the rock mass are analyzed using Finite Element Method for harmonic loadings of different frequencies. Effects of shapes are observed in terms of axial stress, shear stress and bending moment generated in the lining of each shape and critical locations are identified at which stress concentration takes place. The stresses induced in the lining are maximum when frequency of excitation is near to the fundamental frequency of the system. The most affected shape identified is D-shape in which stress concentration takes place at the corners in both static condition as well as in dynamic condition. However best shape identified is circular which is obvious but in most of the cases circular shape does not fulfil the purpose i.e. the movement of vehicles is difficult, so other shapes are compared with these results. It was found that the best shape other than circular is horse-shoe.