Impulsive seaward loads induced by wave overtopping on caisson breakwaters

An investigation of seaward impulse loads on caisson breakwaters caused by wave overtopping is described. Attention is focused on mechanisms that may cause such loads, and consideration given to implications for the design of vertical breakwaters. A review of literature shows that there have been several reported, cases of seaward tilting of breakwater caissons. A description of the seaward failure of a prototype structure, apparently resulting from overtopping, was also found. The measurements of seaward impulsive loads reported in the literature do not show any case in which they are higher than associated landward forces. Physical model tests that are described show overtopping of a low crest breakwater in which the maximum seaward force is greater than the maximum force acting towards the land. A theoretical model for the pressure impulse generated by the re-entry of the overtopping plume is given. Comparison with physical model data shows that, for these experiments, pressure in the air pocket trapped during overtopping contributes significantly to the impulse. When this effect is included, good agreement is obtained between experiment and theory. It is concluded that seaward overturning should be considered as a failure mode of caisson breakwater designs that allow overtopping, particularly for structures of relatively low mass. (C) 2001 Elsevier Science B.V. All rights reserved.