Suction caissons are a type of foundation which are penetrated into the seabed using net external water pressure, rather than more conventional techniques. The geometry of these foundations is such that, structurally, they fall into the category of shell structures. Due to the type of loading experienced by these foundations, which is predominantly hydrostatic, buckling of the caisson shell during suction installation becomes a consideration. This paper examines the factors influencing the buckling load of the caisson, including the boundary conditions of the shell, geometric imperfections, material plasticity, embedment ratio and the amount of lateral restraint offered by the surrounding soil Results are obtained from three dimensional finite dement analyses.
Suction caissons are a foundation system for offshore petroleum production facilities, which are finding increased use (Tjelta, 1995). Some of the earlier uses of these foundations are described by Wang (1978). These foundations consist of a thin-walled cylindrical shell with a top cap of varying rigidity, embedded in the sea bed material. Of concern in the Structural design is the possibility of buckling occurring during installation, which is performed by first an initial self weight penetration, and then completed by reducing the internal pressure of the caisson and allowing the pressure differential to force the caisson into place. This paper explores the factors which influence the buckling load of such structures, including what additional restraint, if any, may result from the soil surrounding the caisson during various stages of embedment. Only the pressure loading portion of the installation procedure, which generally covers the majority of the process, is considered here. The geometry of suction caissons is such that, with relatively large p/t ratios, they fall into the category of shell structures.
