FRONT SLOPE STABILITY OF THE ICELANDIC-TYPE BERM BREAKWATER

摘要

The front slope stability of the berm breakwater has often been assessed through the recession parameter, Rec. Icelandic-type berm breakwaters are designed with very large rock, where recession under design conditions is very limited and where the erosion is in the same order of magnitude as the rock damage parameter, S_d. Recent tests of front slope stability of the Icelandic-type berm breakwater became available with very accurate measurements of recession Rec as well as damage Sd. Damage values are compared with the Van der Meer formulae for rock slopes and appear to agree fairly well. A more refined definition of recession has been developed. Instead of measuring the recession on top of the berm it is proposed to measure it either as the mean or the maximum horizontal recession on the front slope of the berm. The initial recession values have been compared with earlier work on recession and a main conclusion is that the effect of the wave height is far more important than the wave period. Therefore it is proposed to consider only the stability number and a prediction formula has been given. Finally, the paper discusses two alternative designs which can lower the risk of not getting the predicted and expected armour stone yield in a breakwater project. These are a gentler seaward slope of 1:2.5 and replacement of large class I rock by cubes.