Offshore Geotechnics - The Challenges of Deepwater Soft Sediments

In principle, design 'practice' is represented by gradually evolving national and international design guidelines. In reality, most designs rely on more sophisticated analysis techniques and principles, informed by recent research publications that may take several years to be reflected in industry guidelines. This may be considered as 'art'. The more rapidly a sector of industry is developing, the wider will be the gap between practice (as represented by design guidelines) and art. In the offshore industry, the most rapidly changing sector is the move to increasingly deep water, with new developments now in water depths exceeding 2 km. In those conditions, the seabed typically comprises relatively soft fine-grained material, with very slow sedimentation rates. The challenges to be discussed in this state-of-the-art paper include characterizing the shear strength and other engineering properties of the sediments, and design approaches for a range of deepwater infrastructure including different forms of anchoring systems, shallow mat foundations, pipelines, flowlines and riser systems. Particular focus in the paper is on secondary characteristics of the seabed sediments that reflect effects of loading (or strain) rate and disturbance (or remolding) on the response of the infrastructure in question.