Session B.18: Breakwaters (II)

Chris Jones, Marine and Coastal Solutions

For the issue of wave focussing caused by the extended toe blanket at the round-head did you consider localised lowering of the top level of the toe blanket to pre-existing levels (effectively replacing part of sand replacement with rock)

Reply by C Frith

Substituting rock for marine dredged sand was considered as an option. Replacing the sand with rock would have improved the Factor of Safety against rotational failure, but not sufficiently to provide an acceptable value under design conditions. The apron is essential to provide weight to the toe to stop potential failure slip circles. The cost, and practicality, also pointed towards the use of sand replacement and a separate rock apron placed later.