Uplift forces on a ceiling slab of wave dissipating caisson with a permeable wall have been studied by model experiments and an analytical model is presented to estimate uplift forces in the prototype. Principal conclusions are as follows:
1) As high waves act on a slit caisson, an air layer is enclosed at the upper part of wave chamber. Uplift forces on the ceiling slab are caused through the compression of this enclosed air layer.
2) The uplift forces can be reduced by the air leakage through the air holes which are equipped in the ceiling slab. Too large air holes, however, cause larger uplift forces than those on a ceiling slab without the air hole, since direct impact of water mass becomes to predominate on the ceiling slab.
3) The uplift forces caused by the compression of enclosed air layer can be analyzed by the Bagnold-Mitsuyasu's model. In the present study, the effect of air leakage through the vertical slit wall as well as air holes in the ceiling slab is considered in the analytica model.
4) It should be noted that the pressures are imposed on the vertical walls and the bottom slab in the wave chamber at the same time when uplift force acts on the ceiling slab.