Implications of volume loss on the seismic response of tunnels in coarse-grained soils

This paper examines the seismic response of a “horseshoe–shaped” tunnel, inspired by a recently constructed Metro tunnel in Santiago, Chile. A FE analysis has been conducted, investigating the effect of soil density, apparent cohesion, the interface between the tunnel and the surrounding soil, the intensity of the seismic excitation and the effect of volume loss due to tunnel construction on the seismic behaviour of tunnels. The presence of apparent cohesion leads to a reduction of tunnel distress and to smaller post-earthquake ground settlements over a reduced distance from the tunnel. The consideration of volume loss does not significantly affect the acceleration field around the tunnel, but does beneficially decrease the lining forces. Furthermore, although it leads to an increase of the pre-earthquake settlements, it is found to decrease the co-seismic settlements. Finally, it was found that the most conservative model regarding the design detailing of the tunnel lining would be considering a rough interface, zero cohesion, and negligible volume loss (i.e., an ideally-excavated tunnel).