Toe structures of rubble mound breakwater

Abstract

This thesis is about the stability of toe material for rubble mound breakwaters in depth limited conditions. The present equation, Van der Meer 1998, gives results for depth limited conditions but is not validated. The empirical equation is based on physical model tests done by Gerding 1993. The Van der Meer equation implies deep water and breaking waves on the structure slope. For shallow water conditions this assumption is not valid. Waves start breaking at the fore shore slope and toe which results in a different hydrodynamical wave load at the toe. Toe material is exposed to waves and starts behaving as armour rock. The uncertainties, introduced by shallow water situation are investigated in this research. The objective for this thesis is finding a more reliable design equation in this situation. Fore shore slope and wave steepness are considered of influence. The research is done by performing scale model tests in a two dimensional wave flume. The observations from the experiments and the analysis of the performed dataset gave following conclusions: Fore shore slope is strongly influencing toe stability. This is not only valid in shallow water but also in deep water. In shallow water, wave steepness influences toe stability as well. This is not proven for deep water. Very shallow water shows different hydrodynamic behaviour. Wave breaking occurs at the fore shore. The toe structure is attacked by breaking or already broken waves. Although a reduced wave height reaches the toe, damage is larger because the toe is exposed to turbulent wave attack. A new design equation for very shallow water is suggested in which fore shore slope and wave steepness are included. This is an empirical relation, using dimensionless relations like the Hudson stability number and a new damage number in percentages.