Seismic Response of Shallow Buried Box Tunnels with Geofoam Side Cushions

Seismic response of shallow buried box tunnels with geofoam side cushions was investigated through finite difference analyses with a numerical model that was validated against published experimental results from centrifuge tests. Analyses were carried out to investigate the effects of embedment depth, geofoam cushion properties and seismic excitation characteristics. Wall deformations as well as lateral dynamic earth pressures at various points on the embedded structures were monitored in the numerical analyses. Results were compared to those of a deformation based analytical approach. The study demonstrates that installation of EPS geofoam cushions may result in a reduction of the seismic earth force and sectional forces on the tunnel structure compared to the case of a structure without geofoam cushions. Structural rigidity of the embedded structure and embedment depth, as well as thickness ratio of the geofoam cushion, play an important role in the reduction of seismic earth forces and racking deformations.