The applicability of a steel caisson with skirt, which takes a suction effect into the stability, was investigated by simulating the dynamic response of a caisson structure under wave attack. The dynamic response of caisson with suction acting between caisson base and seabed was numerically evaluated in the frequency domain by means of a caisson structure-seabed interaction analysis. In this paper the analytical model of a caisson structure was assumed to be a rigid rectangular prism with skirt, whose base has several square compartments, and the suction-was acting on each compartment. While the seabed was assumed to be a fluid-saturated poroelastic medium whose behavior is governed by Biot's theory of wave propagation. The effects of skirt length of caisson and suction acting on compartments on the dynamic response of a caisson was numerically investigated. This type of caisson is effective in soft seabed and has superiority in the case of low permeability of seabed, providing compartments.
It goes without saying that the design of appropriate foundation of an offshore structures plays a very important role for the stability of an offshore structures in great water depth. Severe sea conditions on site require the construction schedule to be shorten and easy. In addition, the construction of maritime structures has been developed from sites on rigid bed such as rock-base or sand layer in a shallow water to those on soft bed in a deep water. The demands mentioned above motivate to apply the suction effect to stabilize offshore structures. Actually it has been applied in the North Sea (Tsuzuki et aI., 1995). In practice, the suction is effective not only for the increase of the penetration force in the installation of an offshore structure but also for the resistance to a pullout force due to the interruption of atmospheric pressure after installation.