Seismic behaviour of Delhi metro tunnels in liquefiable deposits

Construction of metro transport networks has been on the ascent in Indian cities like New Delhi, since early 2000s. Metro tunnels in New Delhi traverse through various geotechnical profiles of altering stiffness at different cover depths. High water tables (< 5 m) are encountered in New Delhi, especially in north and north-eastern parts. Another concern is the possibility of tectonic activities, as New Delhi is placed in a zone of high seismic intensity. These issues could ultimately result in tunnels being constructed in liquefiable deposits, especially at low cover depths. Therefore, a study was performed for New Delhi, using site-specific artificial ground motion at different cover depths to identify the significant concerns. Tunnel uplift and thrust increments on the tunnel liner have been identified as issues to be addressed. The study culminated with suitable design suggestions like grouting, which could avoid these detrimental effects.