Porous rock armour or porous blocks have been generally used for toe protection to caisson breakwaters to date and smaller rock for caisson foundations. Recent developments have been made using impermeable toe protection of insitu concrete mattress to caisson breakwaters. Impermeable toe protection prevents flow and the transmission of wave pressures underneath caissons. The reduction in wave loading and uplift pressures to caissons will be described along with the prospect for more efficient breakwater structures.

Comparative stability guidance for concrete mattress thickness will be presented along with the need for further development by scale model testing under wave conditions. Initial comparisons with precast block and rock toe protection will be made particularly in terms of porosity, stability and flexibility.

Where bedrock is available, the use of in-situ concrete foundations can eliminate settlement allowing the prospect of interlocked caissons and more efficient breakwater structures to be considered.