Seismic Analysis of Delhi Metro Underground Tunnels

Abstract

Metro underground tunnels are strategic elements in transportation and utility networks in any metropolitan city and their importance makes their vulnerability to earthquakes a very sensitive issue. A large earthquake would not only cause loss of human lives but can also damage lot of other pertinent infrastructure. In order to reduce the potential loss of serviceability, it is essential to reduce the possible risk associated and the effects of damage. Underground structures cannot be treated as completely exempt to the effects of ground shaking, as demonstrated by the recent Kobe earthquake of 1995, Chi–Chi earthquake of 1999, and Niigata earthquake of 2004, where several underground structures suffered severe damage. Earlier work in this area suggests that various authors have presented explicit expressions for axial force, shear force and bending moment developed in the RC liners of tunnels. Some numerical studies were also undertaken. In this paper, an attempt has been made to simulate the case of Delhi metro underground tunnels through PLAXIS 2D and study their response to 1991 Uttarkashi earthquake of lower Himalaya and then conduct some parametric study. The response so obtained has been compared with the available closed form solutions. Damping plays a significant role in seismic analysis. Analysis shows that forces in RC liners reduce with increase in damping. Similarly, displacements, both in soil and RC liners, decrease with increase in damping. Amplification in horizontal acceleration occurs due to reduction in damping ratio. The effect of horizontal component of 1991 Uttarkashi earthquake was found to be more critical than the vertical component, though of course the influence of vertical component was also found to be significant. It has therefore been realized that seismic response of metro underground tunnels to the both horizontal as well as vertical component of earthquake should be considered in design. © 2016, Indian Geotechnical Society.