Three-dimensional non-linear seismic response of bored tunnels in port-Said clay

Abstract

This paper investigates the seismic response of one of the bored tunnels constructed underneath the Suez Canal in the very soft to firm Port-Said Clay deposit. A three-dimensional finite element model is developed to simulate the seismic interaction between one of the Port-Said Tunnels and Port-Said Clay, taking into consideration the nonlinear behavior of the Port-Said Clay under static and seismic conditions. The effects of the geological setting, the face/grouting pressure, and the peak ground acceleration on the acceleration response at the tunnel and the ground surface, the straining actions in the tunnel lining, the lining deformations, and the shear strains around the tunnel are investigated. The amplification factor is affected by the peak ground acceleration and the soft clay thickness, and is not affected by the face/grouting pressure. The study has enabled developing a correlation lumping the effects of the soft clay thickness and the PGA at bedrock on the free-field acceleration response. The study fills in a prominent gap in the current state of practice with respect to the amplification effects in soft clays and provides important recommendations to the design codes. The developed correlation and the study recommendations are of importance to research and applications on soft clays deposited in the Nile Deep Sea Fan in the Nile Delta Basin Province in the Eastern Mediterranean Area and other soft clay deposits with similar characteristics. The results also indicate that the structural design of the tunnel lining in the area under study is mostly governed by seismic, rather than static, loading conditions.