Stability of berm breakwaters

Breakwaters which are used over years protect ports and also beaches from erosion and then wave attacks provide safe area for sea structues. There are five types of breakwaters such as rubble mound breakwater, vertical breakwater, floating breakwater, submerged breakwater and berm breakwater. Berm breakwaters decrease wave overtopping and rock size they are thus more economical compare to traditional breakwaters. Furthermore, berm influences on stability. Because of using rock in berm and all slopes of berm breakwater will be very expensive, using concrete armour units may be more effecient and preferable. Core-loc, dolos, accropod, tetrapod and cube are some of the examples of concrete elements. In this research cube blocks were used in berm and lower slope of the berm breakwater models. There are two types of breakwater models used in experiments. Firstly, traditional cube with straight slope was considered with different packing density (67% and 59%) in order to understand effect on stability. The second breakwater models were designed with berm, using cube in berm and lower slope. Damage in upper slope were not considered and was fixed with steel wire so as not to effect the model. These berm breakwaters were set up with different transition between lower slope and berm intersection. At transition one of them is untouched and the other one is touched. Both models have 59% packing density. There are four types of breakwater model and three different water depth were considered for the experiments. All of experiments were performed in Hydraulic and Coastal Engineering Laboratory, Civil Engineering Department at Yildiz Technical University. The wave flume that used for research is about 26 m in length, 1 m in width and depth. Irregular waves were produced. There is also wave compensation system that absorbs reflected waves. Six wave probes were used measuring wave parameters. Four of them were placed close to wave generator so that reflections were predicted. Other two wave probes were located in front of the toe and above the toe. Cubes were placed with double pyramid placement method in lower slope and berm. Rocks were used in upper slope of the berm breakwaters have 34 mm. There are 11 different irregular waves which were produced with JONSWAP spectrum. Each wave series consist of 1000 waves. After each test series cumulative damage were considered. In order to calculate damage overlay technique was used by taking photo of the model from opposite view. Then same photos were compared in digital media. Moved and displaced rocks were assessed separately. Finally, according to laboratory experiments with different packing density, using berm with touch and untouched transition have particular influence on stability and also wave run up.