Response of caisson breakwater subjected to repeated impulsive loading

Abstract

An examination is made of the cyclic behaviour of a caisson breakwater in sand under repeated loads that can be divided into two categories: loads that are only applied in the landward direction and those applied in both landward and seaward directions. Wave loading on the model caisson was simulated on the centrifuge using an in-flight wave actuator system. The results show that regular non-reversal loading leads to a rapid stabilisation of movements with low excess pore pressure. On the other hand, much larger excess pore pressure and caisson movement were induced within much fewer cycles under reversal loading. For loose sand beds subjected to large reversal loadings, liquefaction was observed especially beneath the heel of the caisson. The difference in caisson response to non-reversal and reversal loading may be largely attributed to differences in sand behaviour under non-reversal and reversal cyclic shearing. As very different responses are produced by the two types of loading, it is suggested that, instead of non-reversal loading, caisson model tests should be conducted using reversal loading, which is more representative of actual wave loadings.