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Seismic design of the foundation of an immersed tube tunnel in liquefiable soil

Autori: 
Vrettos C., Savidis S.
Numero: 
4
Anno: 
2004
Pagina: 
41

The road fixed-link crossing between Preveza and Aktio on the north-western coast of Greece that has recently been completed consists of an immersed single-tube tunnel under the strait and two cut-and-cover tunnels at the ends of the immersed part. The site is characterized by high seismicity. Foundation soil consists of marine sediments comprising irregular layers of sands, silts and clays that extend to great depth in the central part of the strait. Along the entire tunnel axis silty sands and sandy silts of the top layers are classified as potentially liquefiable. Soil improvement in the form of stone columns has been carried out below the tunnel foundation for reducing risk from liquefaction. The soil conditions and the seismic input parameters are presented and an overview of the extensive dynamic laboratory testing program conducted is given. The seismic site response analyses performed for determining the depth of ground improvement are summarized. The design of the stone columns is presented and the method for determining values for the spring coefficients of soil stiffness accounting for the effects of tunnel-ground interaction is described.

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