Installation performance of structurally enhanced caissons in sand

Abstract

Suction caissons are attractive solutions to support offshore structures. Their capacity, both pull-out and bearing, grows with their embedment depth. However, higher embedment depths increase risks of installation failure due to uncertainty of seabed condition, increased chance of piping and structural buckling. For the first time, this paper investigates installation of structurally enhanced caissons (SECs), in the form of flanges attached to the caisson shaft, through developing a numerical procedure based on finite element analysis. The SEC has the potential to offer additional (over 20%) pull-out and bearing capacity compared with standard caisson and can have substantial positive impacts on torsional capacity. Using the proposed numerical procedure, the impact of adding the flanges on the installation resistance was studied and compared against a standard caisson. A piping criterion was defined which allows tracking the soil region where piping develops and evolves as the installation proceeds. The impacts of flange base sizes and sand compaction on the required suction for installation were studied. The results of this paper can be used as guidance to predict the required suction to install flanged caissons and can facilitate the uptake of the proposed SEC. The proposed numerical framework is applicable to other SEC geometries.