Application of Reliability in Breakwater Design

Breakwater design methods have been improved over the past years, especially
the mathematical formulations of the failure mechanisms. In the case of rubble mound breakwaters, and vertical breakwaters, the last decade has been used to develop methods to evaluate e.g. the wave loads and hydraulic response, but in one area information has been lacking; bearing capacity has not been treated in depth in a probabilistic manner for breakwaters. Reliability analysis of conventional rubble mound breakwaters and conventional vertical breakwaters is exemplified for the purpose of establishing new ways of approaching design problems in an early stage of breakwater design. The deterministic design of rubble mound breakwaters with emphasis on the armour layer, toe berm and crown wall, and conventional vertical breakwaters is reviewed. Breakwater failure modes are reviewed with emphasis on establishing new methods to design certain types of breakwaters. Reliability analyses of the main armour and toe berm interaction is exemplified to show the effect of a multiple set of failure mechanisms. First the limit state equations of the main armour and toe interaction are derived from laboratory tests performed by Bologna University. Thereafter a multiple system of failure for the interaction is established. Relevant stochastic parameters are characterized prior to the reliability evaluation. Application of reliability in crown wall design is illustrated by deriving relevant single foundation failure modes in the rubble mound only. A crown wall with a plane base and with an extended leg on the seaward side is analysed. Relevant stochastic parameters are characterized prior to a reliability evaluation. The reliability is performed with real sea states to measure the influence of the chosen deterministic design. Reliability based design of conventional vertical breakwaters is considered. Probabilistic models of important failure modes such as sliding and rupture failure in the rubble mound and the sand or clay subsoil are described. Characterization of the relevant stochastic parameters are presented, and relevant design variables are identified. The long-term goal is to be able to determine an optimal based design of vertical breakwaters where all relevant failure modes are modelled as components in a series system.