Abstract

The Ichthys Riser Support Structure (RSS) is a large subsea structure in 250 m water depth, which comprises a 110 m tall tower with a 130 m wide arch for supporting up to 25 flexible risers and umbilical's as they transition from the seabed to the semi-submersible Central Processing Facility (CPF). The foundation for the RSS comprises a skirted raft approximately 69 m x 38 m in plan with a central cut-out and 6.8 m deep skirts installed in uncemented carbonate sediments through a combination of self penetration and suction assistance. A 40 year design life combined with the requirement for no loss of containment during a 1 in 10,000 year metocean or seismic event made the geotechnical and foundation engineering design a challenge.

This paper will describe the innovations adopted in assessing the RSS foundation capacity against the design in-place loads and the key results and observations with respect to the installation of the foundation.

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