At present no methodology exists to evaluate the failure mode of a caisson breakwater subjected to a tsunami attack. The present paper investigates the sliding and tilting failure of a caisson breakwater subjected to a solitary wave attack, and establishes a relationship between the sliding and vertical movement. The vertical movement of the caisson is evaluated using the method of Esteban and Shibayama (2006), originally was developed for wind waves. The method was verified by carrying out laboratory experiments using solitary waves and comparing the results to those obtained using the new methodology. The sliding failure will be discussed and a general expression for an upper bound limit to the sliding will be proposed.


In order to correctly design structures to withstand tsunami attack it is necessary to evaluate how reliable they would be against a range of tsunami wave types and heights. The development of these countermeasures is of paramount importance in order to prevent the loss of life and property that might occur as a result of these waves. Researchers such as Shibayama et al, (2006), Sasaki (2006) and Jayaratne et al. (2006) have noted how various types of coastal terrain can attenuate or magnify the damage due to tsunami attack. However the degree of protection that the various natural or artificial coastal structures offer against tsunami attack is not yet properly understood. For the case of Japan, sea dikes have been built along the coast to protect against tsunamis, high waves and storm surges, and numerous studies (e.g. Naksuksakul 2006) can be found of the construction of such counter-measures. However, expected tsunami heights are often higher than the existing defences, and hence the potential damage due to a tsunami of a given height should be evaluated in order to formulate a correct disaster prevention policy.

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