Plug heave prediction for suction caissons in cohesionless soil

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ABSTRACT: Suction caissons have recently become a popular foundation type to support offshore Wind Turbine Generator (WTG) structures. Suction pumps are mounted on the lid of the foundation and apply flow rate which induces pressure inside the caisson, causing the skirts to penetrate the seabed. Seabed sediments under the skirt tip are displaced to the outside and the inside the caisson. Seepage flow due to applied suction may cause particle flow from the exterior to the interior of the caisson in cohesionless soils. Upon the completion of installation, grout is typically injected inside the void under the lid. Sufficient void space should be maintained to prevent potential refusals and ensure grouting operations. Therefore, a reliable plug heave prediction model is required. This paper presents a new method for predicting plug heave inside suction caissons during installation in cohesionless soils. This study is based on a dataset from 72 caisson installations in clean sand, totalling approximately 750 meters in depth for the Seagreen Offshore Wind Farm project in the North Sea, UK Sector. A predictive model is proposed to estimate plug heave which incorporates caisson geometry (diameter  and wall thickness ), penetration depth , and a soil plug heave factor . The soil plug heave factor is estimated using cone tip resistance  from Cone Penetration Test (CPT) and suction pressure  based on installation parameter. The model demonstrates reasonable predictive capability, achieving a coefficient of determination  of 0.599 and a Root Mean Square Error  of 0.070 m.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

11 - Suction installed foundations and anchors