A yield design approach to the stability analysis of A seabed subjected to wave loading and pseudo-static seismic forces

The stability analysis of a seabed under the combined action of wave and seismic loading is investigated in the light of limit analysis theory and related static and kinematic approaches. Effects of cyclic wave loading are addressed in the context of the first-order Stokes theory, whereas the pseudo-static method is adopted to account for inertial forces induced in the seabed soil mass by earthquake events. Compared to existing works, the key contribution of the paper is two-fold: (i) incorporation of the destabilizing effects induced by the passage of seismic waves, and (ii) poromechanics-based evaluation of the pore pressure generated by the cyclic wave in the finite thickness seabed layer. Resorting to a total stress analysis, the stability condition of a purely cohesive seabed is formulated based on lower bound static and upper bound kinematic approaches, leading to closed-form expressions for seabed stability in terms of loading parameters or in terms of wave characteristics. For granular seabed soil, the stability analysis is handled within the framework of effective stress limit analysis reasoning in which the seepage flow related to pore pressure gradient can be accounted for by means of driven body forces. In that respect, particular emphasis is given to the decisive role of seepage forces that are derived from the pore pressure distribution associated with soil densification under the cyclic wave loading. Formulation of a seabed stability condition is then achieved by implementing the kinematic approach through a class of failure mechanisms, thus providing preliminary elements for assessing the influence of each loading component. Numerical simulations notably emphasized the destabilizing effects induced by seismic loading.