Liquefaction analysis of metro underground tunnels

Tunnels located below ground water table in liquefiable soils can experience increase in lateral pressure, reduction in lateral passive resistance, sinking or flotation in liquefied soil, lateral displacements, permanent settlements, and tension and compression failure. In India, Delhi region being quite sensitive to earthquake, an attempt has been made here to investigate the possible response of Delhi Metro tunnels to liquefaction. Three dimensional finite element analyses were carried out, using Plaxis 3D software, for all the three components of 1999 Chamoli earthquake (M=6.5) of lower Himalaya. The study suggests that significant displacements in the soil-tunnel system can occur due to transverse component of earthquake. Liquefaction can occur when seismic waves travel in a direction parallel or nearly parallel to the alignment of tunnels, provided the ground water table exists above the tunnel crown. Influence of seismic directions, water table depth, boundary representation, and peak ground acceleration has also been investigated.