A pragmatic approach to rock toe stability

• New approach to toe stability of rubble mound structures
• Semi-empirical approach for start of toe damage
• Empirical approach for toe damage progression
• Both approaches combined in a new design formula

A new stability formula is proposed for the toe protection of rubble mound structures. The new approach is based on a critical stability number that refers to the initial movement of armour stones on the toe berm. Damage progression is subsequently described by the ratio of actual and critical stability numbers. The ratio of toe berm submergence and incoming wave height has been identified as the governing parameter for the toe stability. Other parameters including sea bed gradient, wave steepness and toe berm geometry were found to be of minor importance. The new toe stability formula has been validated against model test results and has been compared with the widely used formula of van der Meer (1998). The new approach appears more accurate and more physically meaningful. The practical application of the new formula for toe berm design is briefly described.