Stability of immersed tunnel in liquefiable seabed under wave loadings

Abstract

This paper presents a robust modeling method for fully coupled effective stress analyses of wave–induced liquefaction scenarios around immersed tunnels. The method is based on the Biot consolidation theory, and special emphasis is placed on modeling the high–strain behavior of the liquefiable seabed and the evolving boundary conditions at the tunnel–seabed interface. Motivated by the experimental results, the existing Masing model is extended to the high–strain regime in the cyclic plasticity framework to capture the liquefaction–induced nonlinear behavior of the sand. In particular, a newly–observed shear–volume coupling model is implemented into plastic flow rule to realize volumetric compaction by cyclic shearing and exercise as the source term for residual excess pore pressure accumulation in the Biot’s equation. Subsequently, the proposed cyclic plasticity model is implanted into an explicit time matching finite difference analysis platform, permitting a comprehensive simulation of the intensive response of the immersed tunnel in the seabed experiencing the excess pore pressure accumulation and residual liquefaction. Moreover, a model calibration procedure is presented based on the cyclic laboratory sample test data and prescribed loading paths. Finally, the liquefaction–induced uplift of an immersed tunnel under progressive wave action is studied numerically. The obtained results provide the cause of liquefaction and the resulting consequences for tunnel uplift in ocean wave environments.