On Seismic Behavior of Marmara Submerged Tunnel: Ssi, Irregular Topography and Input Wave Angle of Incidence Effects

Abstract eng:
The Marmaray submerged tunnel is about 1400 m in length, running under the Bosporus strait in Istanbul, Turkey. Since 2014 this tunnel has been monitored for seismic activities. Due to the complicated geological characteristics where the tunnel is located and large scale of analysis domain, considering the soil structure interaction (SSI) effects becomes important. This paper discusses the characteristics of earthquake wave propagation in the tunnel. The local site effects have been investigated analytically using the SuperFLUSH/2D program [1]. This program can perform a pseudo-three-dimensional analyses considering equivalent stiffness for the in-plane and out-ofplane directions. Due to large-scale of the tunnel, a domain of around 5km length is considered for the FEM model.The tunnel and soil are modelled by beam and plane strain elements respectively. Input seismic waves in the in-plane and out-ofplane directions are considered. The previous studies [2], [3] clarified the importance of SSI effects using two-dimensional (in-plane direction) model. In this study, apseudo-three-dimensional analysis is performed, by considering the soil stiffness and the input motion angle of incidence as study parameters. Good correlation between the analysis results and observed data at the sedimentary layer, but there were results deviated near the bedrock. This can be attributed to the presence of irregular topography in orthogonal NS direction, which cannot be considered in the out-of-plane direction of pseudo-three-dimensional analysis model.

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