Seismic isolation of tunnels in blocky rock mass using expanded polystyrene (EPS) Geofoam

Abstract

Damages to mountain tunnels reported following recent seismic events have challenged the long-held belief of buried structures to have adequate earthquake-resistant features. Field observations also highlight that the geological joints play a dominating role in governing the seismic response. However, most investigations idealize the geological medium as a continuous domain, which has an inherent limitation in their inability to capture the wave–joint interaction. Given the above, the present study attempts to assess the seismic response of a circular lined tunnel in a distinct element-based framework, which can capture the interaction between the wave and joints. First, the seismic response of a circular lined tunnel under the action of a recorded earthquake time history is performed for two different depths. Subsequently, the feasibility of using Expanded Polystyrene (EPS) Geofoam as an effective buffer material for seismic isolation of tunnels is investigated. The evolution of variation of axial force and bending moment in the tunnel liners are highlighted for both the cases. A marked reduction in the seismic demand is observed when EPS Geofoam is utilized as a coating material around the liner. The results of the numerical simulation highlight the promising capabilities of using EPS Geofoam as a protective material for underground tunnels.