Effect of principal stress rotation on dynamic characteristics of a sandy seabed under a partially reflected standing wave

Principal stress rotation (PSR) is one of the main stress conditions for a soil element subject to cyclic waves. It is one of the main causes behind generation of excess pore water pressure and cumulative plastic strain in soil deposits when drainage conditions are impeded, and thus compromises the stability of any supported marine structures. This paper aims to investigate the influence of PSR on the cyclic characteristics of soil under standing waves that are partially reflected, in which a generalized plasticity model considering the effect of PSR was adopted to model the soil behavior. Comparisons between the present model, previous hollow cylinder apparatus tests, and geotechnical centrifugal wave tests all show good agreement. Numerical results indicate that ignoring the PSR involved in the standing-wave-seabed interactions will significantly underestimate the build-up of pore water pressure, particularly at the standing wave nodes. Furthermore, the exclusion of the effect of PSR may lead to contradictory results in terms of susceptibility to liquefaction between the antinode and the node, when compared to the wave flume test and geotechnical centrifuge test. Numerical simulation results also demonstrate that while considering the impact of PSR, a sandy seabed exhibits higher liquefaction resistance when subjected to standing waves compared to the case when subjected to progressive waves with an equivalent wave height. Parametric studies show that the coefficient of wave reflection, wave characteristics (wave height, period, and water depth), and soil properties (permeability and saturation) significantly affect the liquefaction characteristics of soil under partially reflected standing waves.