This present report aims at discussing the applicability of reliability based design methods to the design of breakwaters in view of safety against foundation failure.
Safety indices against soil failure of breakwaters designed with the present design system have been calculated by the reliability based design method. The design way of breakwaters by using the reliability based design method has been established.
　The main conclusions drawn from the study are as follows:
1)The level 1 reliability based design method is less applicable compared to the level 2 method,especially for those breakwaters on thick rubble mounds. The level 2 method is much applicable with the small range of safety indices.
2)The mean value of apparent safety indices of breakwaters designed by the present design method has been calculated to be about 1.6. It shows that safety against foundation failure is lower than that against sliding failure, which doesn't coincide with failures observed in the field. The reason of the disagreement has been considered to be due to the evaluation of dynamic soil strength to alow level in the present design method. through discussions such as comparison of safety indices against soil failure to that against sliding failure, the mean value of safety indices has been considered to be about 3.0. Dynamic soil strength has been considered to be more than 20% larger than that assumed in the present design method on average.
3)Allowable safety factor is set to be 1.0 in the present design method, in which hidden safety margin has been considered to be included.