Breakwater Engineering

Abstract

Breakwaters have been built for thousands of years to protect harbours and coasts against the waves. Because of their very nature, breakwaters are exposed to strong wave attack. During recent years a number of newly constructed breakwaters have been severely damaged: Sines in Portugal in the winters of 1978 and 1979; Arzew-el-Djedid in Algeria in 1980; Tripoli, Libya, in beginning of 1981; Gioja Tauro in Italy in 1980; San Ciprian, Spain, during the winter of 1980. These recent examples of breakwater failure are not unique: there have frequently been reports of storm damage. One can even say that a rubble-mound breakwater is designed to absorb a certain amount of damage during its lifetime. What now alarmed the world of designers and builders of such structures, however, was the unprecedented increase in the number of failures, the fact that the breakwaters were either under construction or had been just completed and also the extent of damage in each of the above cases, the total damage being estimated as a thousand million US dollars.So far, no overall picture has been presented. All failures were individually investigated. The investigation reports left few issues unexamined, but remain confidential themselves. The Delft Hydraulics Laboratory participated in some of the damage investigations and was entrusted with the hydraulic investigations for the rehabilitation of all five breakwaters. A unique chance, therefore, existed for the development of an overall picture. Without affecting the confidentiality of the individual cases, the most important deficiencies in the design of rubble-mound breakwaters are treated in this paper. A plan is made for a design approach in which hydraulic, structural and geotechnical aspects are integrated. The state of the art of each of these different aspects is presented globally, emphasizing the interactions between them and the consequences of an integral approach for the design methods.