Displacement of Monolithic Rubble-Mound Breakwater Crown-Walls

This paper evaluates the validity of a simple one-dimensional dynamic analysis as well as a Finite-Element model to determine the sliding of a rubble-mound breakwater crown-wall. The evaluation is based on a case example with real wave load time-series and displacements measured from two-dimensional physical model tests. The outcome is a more reliable evaluation of the applicability of simple dynamic calculations for the estimation of displacement of rubble-mound superstructures. The case example clearly demonstrates that a simplified one-dimensional sliding model provides a safe estimate of the accumulated sliding distance of crown-wall superstructures, which is in contrast to findings from previous similar studies on caisson breakwaters. The calculated sliding distance is approximately three times larger than the measured one when using the original one-dimensional model suggested in previous studies on caisson breakwaters, but correction terms are suggested in the present paper to obtain almost equal measured and estimated displacements. This is of great practical importance since many existing rubble-mound crown-walls are subjected to increasing wave loads due to rising sea water level from climate changes. Reliable and safe estimates are needed to determine whether displacements of crown wall superstructures during extreme situations would be acceptable or whether they lead to total failure of the structures.