A case study on the stability of three-layered rock armour in breakwater roundheads

For the design of the breakwater for the protection of Barra do Dande Ocean Terminal in Angola, a rock armour rubble mound structure was the obvious solution due to the proximity of a suitable quarry. For this type of breakwater exists a close relationship between damage resistance in terms of armour unit size and the required maintenance. Designing for small probability of damage generally infer high construction costs but lower maintenance costs. Breakwater roundheads are generally the most critical part of rubble mound breakwaters. In search for minimum lifetime costs, a stable low-cost solution for the breakwater head was investigated in terms of a three-layer rock armour solution applied in the most critical sectors of the roundhead. The aim was to avoid the production wise and construction wise costly large rock sizes while still maintaining a low probability of repairs. The three-layer rock armour solution applied in the critical roundhead sectors was studied in physical model tests at the Aalborg University Ocean and Coastal Engineering Laboratory, Denmark. This solution means that smaller rocks can be applied as failure occurs at significantly higher damage levels. The three-layer solution was a viable technical and economical solution for the port construction and operation.