ABSTRACT:

A plane strain analysis based on the generalized Biot's equation is utilized to investigate the wave-induced responses of a poro-elastic seabed with shear modulus increasing according to a continuous, bounded function of soil depth. By employing integral transform and Frobenius methods, the transient and steady solutions for the waveinduced pore water pressure, effective stresses and displacements are analytically derived in this study. The numerical results indicate that the inclusion of a variable shear modulus significantly improves the predictions of seabed responses. Moreover, it's shown that the distinction between the transient and steady responses should be taken into account for design of marine structures. Under the transient condition, the seabed is apt to transient liquefaction.

INTRODUCTION

The wave-induced responses in seabed are particularly important for geotechnical engineers involved in the design of marine structures. Based on Biot's poro-elastic theory, numerous models for the waveinduced responses of seabed have been developed with various assumptions since 1940's, such as un-coupled model (or drained model), consolidation model (or quasi-static model), dynamic model, poro-elastoplastic model and so on. Some of the surveys were contributed by Foda (1995) and Jeng (2003). But there are few studies on the transient responses of seabed due to wave. Shear modulus of the soil is one of important parameters which significantly affect the wave-induced seabed response. In nature, since soil formation differs from site to site, the rigidity of soils are heterogeneous through the soil matrix. A linear variation with depth can be used to approximately describe water-saturated normally consolidation soils (Gibson, 1967). Badiey et al. (1990) reported that the shear modulus profile in seabed varies with depth in field and laboratory tests. Jeng and Lin (1999) have proposed a finite element model for the wave-induced seabed response around a buried pipeline in Gibson soil.

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