Suction caissons have emerged as an increasingly popular option for anchoring systems. To date, suction caissons have been limited to relatively low aspect ratios. However, as new offshore fields are developed in deeper water, higher aspect ratio caissons are needed in order to provide higher capacity, particularly in situations where a large upward component of load has to be withstood. Theory suggests that a limiting aspect ratio exists beyond which complete caisson installation cannot be achieved due to upheaval of the internal soil plug. This paper presents the data from a series of laboratory tests, aimed at establishing relationships between caisson penetration, installation pressures and volume of evacuated fluid and comparing results with the theoretical behaviour. Model caissons of various aspect ratios were installed in both normally consolidated and overconsolidated kaolin clay. The data exhibited excellent consistency but indicated limiting aspect ratios before plug failure that were somewhat lower than simple theory suggests.
The exploration and development of offshore hydrocarbon resources in fields of increasing water depths has encouraged the evolution of a range of novel structures and associated anchoring systems. The focus of offshore foundation design has recently shifted towards the use of suction caissons due to their diverse application potential. Suction caissons have proved reliable under compressive and moment loading as a foundation for fixed jacket structures (Europipe and Sleipner, North Sea (Tjelta, 1994)), in pure tension to moor tension leg platforms (Snorre and Heidrun, North Sea (Fines et al, 1991)), and under the quasi-horizontal loads exerted by catenary anchored floating structures (N'kossa, Gulf of Guinea (Colliat et al, 1995)). The installation of suction caissons may be limited by structural and/or geotechnical mechanisms, the critical ones being lack of verticality, buckling of the thin walled caisson, or upward failure of the internal soil plug.
