Martin Young, John Hayman-Joyce, Seok Hyeon Kim


Detailing and optimization of the toe reinforcement is presented as a case study from the construction of the 5.2km long main breakwater for the new Colombo South Harbour in 18m water depth. During the breakwater design the environmental constraints on supply of large rock armour were recognized, and CORE-LOC™ single layer concrete armour units were selected for the primary armour protection. During construction, supply of relatively small quantities of 8-12t rock for use in the toe reinforcement became an issue, and use of CORE-LOC™ units placed on the flat rock armour apron as an alternative to rock armour toe reinforcement was investigated and implemented. This use is unusual as there is no in-plane compression between units as found when they are placed on the slope. A site based prototype scale trial was conducted to evaluate placing method and criteria, and an “alternate opposing cannon” pattern placement, in rows going seaward from the primary armour, was successful. Packing density and unit spacing is the same as for the primary armour. Hydraulic stability of this alternative toe reinforcement was verified in 2D physical hydraulic model testing.


rubble-mound breakwater; toe reinforcement; single layer concrete armour units; physical model testing


Kyle, J. 1886. Paper 2164 Colombo Harbour Works, Ceylon, Concrete as applied in the Construction of Harbours, Proceedings of the Institution of Civil Engineers Vol. lxxxvii. Session 1886-87 Part I (Forrest J. (ed))

Van der Meer(103), d'Angremond and Gerding 1995. Coastal Engineering Manual, EM 1110-2-1100 Part VI, 2003, Table VI-5-46, p. VI-5-107

Baart, S., Ebbens, R., Nammuni-Krohn, J., and Verhagen, H.J. 2011. Toe rock stability for rubble mound breakwaters, Proceedings of the 32nd International Conference on Coastal Engineering, ASCE

Full Text: PDF

Creative Commons License
This work is licensed under a Creative Commons Attribution 3.0 License.