Some Aspects of Seismic Soil–Structure Interaction of Lifeline Structures

Abstract

Historically, underground structures were considered to be less vulnerable to earthquakes. However, some of the recent earthquakes have demonstrated that underground structures too can suffer severe damages, especially when these are located in the vicinity of causative faults. In case of a shallow underground tunnel excavated in an urban area, design and construction is demanding due to interaction between the tunnels and the overlying pre-existing structures. Selection of a realistic ground motion of an earthquake plays a crucial role in the seismic analysis and design of underground structures. In the absence of realistic earthquake data for the given area, it becomes essential to generate artificial or synthetic time history compatible with the largest earthquake expected in that area. Depending upon the situation, it may become necessary to consider three-dimensional aspects of the problem rather than depending on only a two-dimensional behavior. Strong ground shaking can as well cause loss of strength in saturated cohesion less soils resulting in liquefaction. Liquefaction can cause the ground surrounding the tunnels to shift, with potentially severe consequences. An attempt has been made in this paper to discuss various analysis and design considerations of underground lifeline structures and then look in to the aspects of stability of metro underground tunnels of Delhi city on basis of response spectra compatible time histories of 1999 Chamoli earthquake of Uttarakhand, actual three-dimensional analyses, and some liquefaction studies.