BEHAVIOUR OF SHALLOW TUNNELS UNDER SEISMIC CONDITION

Abstract

Many hydro power projects are presently being constructed in Northern and North-Eastern region in India which involve large underground tunnel networks. Some of these tunnels or parts of length of these tunnels have a low overburden and these tunnels are likely to be affected during severe earthquakes. This problem of shallow tunnels, in which the mobilisation of shear stresses can extend up to topographic surface, is therefore taken up for the investigation in the present study. Effect of seismic wave towards the tunnel as underground structure could cause unforeseeable damages during earthquake event. The waves that transmitted through the rock medium would affect the behaviour of the tunnel depending on the rock properties and support system. In the present study, a software package ABAQUS 6.9 has been used. Within the confines of this thesis, stress and displacement behaviour of two tunnel section has been done in 2-D finite element models. Transmitting boundary is also modelled using viscous dashpots in the study. Time history with peak ground acceleration of values 0.30g from the Uttarkashi earthquake record (1991) has been used in this study. From this study, it was revealed that due to applied dynamic loading displacement and stress behaviour of tunnel significantly changes. Nevertheless, both the sections were designed with concrete liner and found out to be capable to resist the earthquake loading compared with the design capacity of the tunnels.