STABILITY OF RESHAPING BREAKWATERS WITH SPECIAL REFERENCE TO STONE DURABILITY

Abstract

Traditionally, conventional rubble mound breakwaters are designed with stable armour units, and consequently, very large stones or even artificial armour units are required. Reshaping breakwater designs allow reshaping of the seward slope thus involving stone movements. Ultimately, dependent on the degree of safety in the design, this reshaping process might end up in a stable profile where no changes in the cross sections occur even though stone movements are allowed. Unfortunately, large movements of the protecting stones during the structural lifetime in combination with high stone velocities inherently cause some breakage and abrasion of the individual stones and thereby also reduced stability. In order to avoid excessive abrasion a high stone quality is demanded or larger stones must be applied when constructed. To allow the designer to account for abrasion and armour stone breakage due to the stone motion a description of the overall wave climate during the structural lifetime must be derived involving knowledge of transport rates, movement patterns, stone velocities and stone quality. The main objective of the paper is to describe a tool enabling calculation of the anticipated armour stone movements. Also tensile stresses occur, as a result of stone against stone impact are discussed in order to make a more close connection between wave climate, stone movements and abrasion/breakage. Finally, a comparison to selected prototype structures is made to compare the armour stone movement model with visual profile observations of existing breakwaters.