Challenges on Large Diameter Driven Piles for Major Topside Loading: Road Map of Success from FEED to Installation

Abstract Foundation system of heavily loaded offshore platforms requires a careful design and installation planning considering type of foundation selected due to soil conditions encountered on site. Unique challenges were encountered on Marjan GOSP-4 where mega-topsides, up to 23,000 MT, were installed. The foundation system of these platforms comprises driven piles which require heavy hammers and large installation vessel. Conventional single main pile solution one under each jacket leg would require large size piles with associated very heavy pile driving hammers with a high risk of premature refusal. In case of refusal, several mitigation measures would be required including the use of drilled and grouted insert piles which can have significant cost and schedule impact. The design of driven piles on GOSP-4 was optimized using main pile in conjunction with skirt pile under each jacket leg to distribute the load thus reducing piles penetration depths and diameters. The optimized piles were successfully driven to target penetration with the selected hammer spread. During installation, site specific setup factors were measured from re-strike tests to establish aging effects in the site soils and hence increased pile capacity which formed basis of acceptance of pile foundations installed offshore. Back-SRD assessment was carried out using dynamic monitoring data records to compare predicted driving with actual driving behavior observed on site.