Composite breakwater with circular caissons

Abstract

A new breakwater design, consisting of a high rubble foundation with concrete cylinders in two rows placed on tophas been proposed for an extensive port development project.In this report, different types of breakwaters and constructional considerations is gone through. The composite breakwater in question is described in detail, and pressure distribution due to waves and resulting forces are investigated.There has not been much research on this type of breakwater design with circular cylinders, but results from experiments done by Khaskhachikh and Vanchagov (1971) are used. In these experiments, model tests were performed to investigate the distribution of pressures around closely spaced cylinders. Results showed that the pressures were lower at the front part of the cylinders and higher at the inward corners. This was due to a higherwater level at these corners.Pressure distribution and force calculations for breakwater design are given by Goda (2000). These are corrected for the circular shape of the cylinders with the results from the previously mentioned experiments. The horizontal forces are found using these formulas.The geotechnical stability of the breakwater has been investigated with mainly finite element analysis. A seabed consisting of low strength clay was modelled and found to be both too weak and too soft to be used as part of thefoundation. Another soil was used instead, giving critical failure surfaces.Model tests were performed to investigate the pressure distribution on the composite breakwater, in addition to forces. Key results were:- Using Goda's formulas corrected for the non-uniform pressure distribution around the cylinder perimeter, is useful for calculating the total horizontal forces.- The predictability of the forces is increasing when the wave heights are decreasing.- Measured pressure distributions were found to use for comparison with theoretical results