Effect of Earthquake on Underground Metro Tunnels—A Parametric Study

Abstract

Metro underground tunnels are life line in many major cities across the world. Therefore vulnerability of these structures against the earthquakes is very critical. In this chapter, Seismic analysis of Delhi metro underground tunnels have been performed by finite element method. Chamoli earthquake (1999) of lower Himalaya, India has been taken for the analysis. Parametric study was also conducted by considering the parameters like volume loss during construction, depth of overburden, interfacial characteristics between soil and the tunnel liner, thickness of RC liners, peak ground acceleration, and damping. Values of the vertical stress concentration were found to increase with increase in volume loss during the construction. This observation is true for both elastic and elasto-plastic behavior of soil. Maximum dynamic axial force in RC liners has been found to increase with the ratio of depth of overburden to the tunnel size, whereas both shear force and bending moment in lining of tunnel have been found to reduce as this ratio attains value of 2 and 2.5 respectively. Dynamic forces in RC liners tend to reduce as the value of interaction factor at the interface between the tunnel and RC liners reduces from 1 to 0.1. Increasing the thickness of RC liners causes the axial force in RC liners to reduce but bending moment has been found to increase. These points need to be borne in mind while designing the support systems for the tunnels.