Bearing Capacity of Breakwater Subjected to Tsunami-Induced Scour

Abstract

Physical models have suggested a large reduction in bearing capacity of simple foundations due to overtopping tsunami scour. We use the results of these tests to create scoured foundation geometries for simple breakwater-type structures and investigate the change in the system’s capacity due to scour through the use of simple two-dimensional (2D) numerical analysis using an advanced constitutive model. The particular aspects of the construction of such models and the general applicability of the method are also discussed. A simple method for estimating the reduction in capacity due to scour is proposed through the use of modified vertical, horizontal force, and moment (VHM) failure surfaces. The general method for creating such simplified scour-dependent failure surfaces is described thoroughly, such that the process can be replicated for other foundation configurations or scour problems. Results indicated that even a small amount of scouring can lead to a substantial reduction in the horizontal and moment capacity of a foundation, the effect of scour is shown to be a nonuniform contraction of the failure envelope, where both the ultimate vertical capacity V0 as well as the relative ratios between vertical, horizontal and moment capacity are strongly affected by the presence of scour. Such a conclusion demonstrates clearly how simply increasing the unscoured factor of safety of such structures is not sufficient to guarantee stability in the event of scouring. The presented methodology for determining the scoured failure surfaces provides a simple, logical means to estimate the performance of such systems undergoing scour.