In this paper, a modified PZIII model by considering the impact of principal stress rotation for the wave(current)-induced soil response in a sandy seabed is cited. Unlike the previous works, the proposed model considers the effect of PSR by treating it generating the plastic strain rate independently. Then, the proposed model was incorporated into the finite element analysis procedure DIANA-SWANDYNE II. Both wave and current loadings are considered in the present model. The proposed model was first validated through comparisons with the previous experimental data for the soil response under wave and current loading. Adapting the proposed model, effects of the PSR on the fluid-seabed interactions will be investigated.
Recently, the human exploration and development of ocean are more frequent due to the abundant marine resources and colossal development. However, in the complex marine environment, the constructions of offshore engineering projects have huge challenges in the present due to various uncertain factors. The cyclic dynamic load which is produced by wave and current propagation on the seabed surface will cause the fluctuation and accumulation of pore water pressure. When the pore pressure extreme growth, the effective stress will decrease, which will lead to instability of the soil as the consequence of the horizontal or vertical movement of the soil particles, resulting in instability of the soil (Sumer, 2014). Therefore, determining pore-water pressures within a porous seabed is particularly crucial for coastal geotechnical engineers involved in the design of the offshore infrastructures foundations. Numerous studies have been carried out to calculate the stability of the seabed in the past, including poro-elastic model and poro-elastoplastic model, but most of them did not consider the effects of PSR (Jeng, 2013).
The continuous rotation of the principal stresses in a seabed is an essential feature of the dynamic response of soil under cyclic wave loading. Unfortunately, due to the assumption of pure PSR, this process cannot be trapped by conventional elasto-plastic theory without changing the cyclic deviatoric stress amplitude of the plastic strain. However, several experimental results have confirmed that the plastic strains are generated merely through altering the principal stress orientation in both monotonic and cyclic rotational share tests (Ishihara and Towhata, 1983; Towhata and Ishihara. 1985; Sassa and Sekiguchi, 1999; Jafarian et al. 2012; Konstadinou and Georgiannou, 2013). However, the inhomogeneity materials determines the effect of PSR. If the seabed soil is always homogeneous, even if the wave loading is rotating, the principal stress axis may not produce a significant effect.