Research on shock mitigation on circular tunnels using expanded polystyrene

Earthquake-induced dynamic response effects of circular tunnels with and without a seismic isolation layer are studied using an infinite element dynamic boundary technique. The seismic isolation layers are made of Expanded Polystyrene (EPS) geofoam. Four EPS arrangements are proposed and analyzed numerically. The results are compared with the results of the same tunnel without an EPS layer. The numerical results show that there are great differences in shock mitigation between the different schemes. The largest shock reduction effects were achieved when the EPS layer is placed between the inner and outer concrete layers of the tunnel lining. When the EPS layers are placed as planar geofoam barriers beside and/or below the tunnel the seismic-induced tunnel forces are reduced but the mitigation effects are as not great as the first scheme. If an EPS layer is placed above the tunnel, the static load on the tunnel is reduced by soil arching, but shock mitigation is not obvious. Results of this research demonstrate that EPS geofoam holds promise as a method to provide seismic shock insulation to concrete tunnels.