This technical note is devoted to present the effect of a seismic isolation layer, which is a soft thin layer located in ground in order to isolate seismic waves. In this study, a series of shaking table tests was carried out on the model of a box caisson type quaywall with various seismic isolation layers. The following results were obtained.
1) In the case of the model with no isolation layer, maximum acceleration larger than about 350Gal was reduced at the boundary of the rubble mound and caisson. This result implies sliding of the caisson.
2) In the case of the model with the isolation layer between the caisson and the mound, the maximum acceleration was very small because of reduction of acceleration wave in the isolation layer.
3) The residual horizontal displacement of caisson was decreased to 50% by the seismic isolation layer.