Submission Category: Case History, Lessons Learned, and General Practice Scope Suction pile is a robust foundation system that offers significant lateral and axial capacities with minimal displacement. While scour around suction pile is generally not a concern in deepwater; scouring becomes a considerable risk in shallower water caused significant current and wave actions in cohesionless sediments. A case history is presented where significant scour of a suction pile supporting a SPM (Single Point Mooring) PLEM has been observed in a relatively short span of time, which considerably exceeded predicted scour, requiring emergency mitigation. Methodology During detailed design, a considerable scour was predicted using conventional analytical methods using site-specific geotechnical data and nearby metocean data. It was decided by the project team not to install scour mitigation measure during construction. As part of scour mitigation plan, post installation periodic surveys were conducted for the subsea infrastructures including the PLEM. These surveys reveal progression of scour around suction pile supporting the PLEM. Several widely used analytical approaches were used to back calculate the observed scour. Observations The observed scour exceeded the predicted scour depth considerably nearly reaching full depth. The back-analysis of the observed scour revealed applicability of available analytical solutions for complex structures such as suction pile supported PLEM structure. Proper assessment and use of input parameters are essential for reasonable prediction of scour around complex subsea structures. Novel Information The case study presents the measured progression of scour around suction pile supporting PLEM in shallow water which are scarce in the public domain. The applicability of the available semi empirical and analytical solutions for prediction of scour around complex structures are presented. Lessons learned from this study should be beneficial for the design and project team involved in similar projects.

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