The influence of toe geometry on toe armour stability for conventional rubble mound breakwaters

Rubble mound breakwaters have toe structures that provide support to the armour layer and prevent damage to the structure from scouring. In this way, toe failure may be regarded as one of the primary failure modes of rubble mound breakwaters. Several formulae have been proposed for toe stability with conflicting results owing to the neglect of factors such as storm duration and armour layer slope. In the present study, a statically stable rubble mound with rock armoured toe was tested under irregular waves. The effects of wave height, wave period, armour layer slope, water height in front of the structure, water height above the toe, and toe width on the hydraulic stability of a toe structure are investigated. Toe width was found to be ineffective on toe stability, while the relative depth was found as an effective parameter for the toe stability. Greater toe damage was observed by increasing wave height and storm duration. The results highlighted the necessity for a new stability number involving the type of wave breaker on the armour slope with a critical Iribarren value of 4.1. Based on the data from the present study and the findings of another study, new formulae have been developed for estimating toe damage in rubble mound breakwaters. Evaluating the proposed formula using other researchers' data and formulae highlighted its strengths.