Safety and design of vertical breakwaters

Abstract

The design of the breakwaters based on the current design manual in Hong Kong uses the overall safety factor approach. This approach, in general, does not provide a safety consistent design, and lacks the invariant property by using different definitions for load effects and resistance identified through the rewriting of equilibrium equations. This study is focused on the selection of the design format to be used for designing vertical breakwaters subjected to wave loading. The required caisson width of a vertical breakwater is evaluated using Goda's formulas and different definitions of the overall safety factor. Also simple probabilistic analysis is carried out. The numerical results show that one should treat the wave induced load effects consistently in order to provide a more safety consistent design. Further, it is indicated that the overall safety factor format in the current design manual for designing breakwaters can be modified into the so-called partial safety factor format. This modification does not change the current design practice for designing breakwaters in Hong Kong, and the new format avoids the problem associated with how to take into account and interpret the uplifting wave pressure in design.