Steven Hutchinson, Martin Young, Alasdair Macleod


The offshore caisson breakwater at Costa Azul installed in 25m water depth is designed to withstand Pacific swell waves up to a PLS test case Hs 9.2m Tp 18.6s. Overall stability design is in accordance with the recommendations of PIANC WG 28. The critical failure mechanism is sliding, and the caisson base is cast with a deliberately roughened (serrated) profile to increase sliding resistance and optimize the caisson cross section. Site based testing at prototype scale was conducted to validate the coefficient of friction used for design between the caisson base and nominal 100mm single size granular bedding material. This testing confirms that the use of a suitably dimensioned serrated base profile allows the full internal angle of friction (with allowance for dilation) of the bedding material to develop at the base of the caisson, allowing the cross section design to be optimized.


Design & Performance Analysis; Coefficient of Friction; Caisson Breakwater Sliding Stability; PIANC WG28.; Validation Testing

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PIANC PTC II Working Group 28, Breakwaters with Vertical and Inclined Concrete Walls, Report, 2003

BS 6349 Part 2, Design of quay walls, jetties and dolphins, 1988

BS 6349 Part 7, Guide to the Design and Construction of Breakwaters, 1991

CIRIA Special Publication 83/ CUR Report 154, Manual on the use of rock in coastal and shoreline engineering, 1991