Design and Installation of Dynamically Installed Piles for Deepwater Mooring

摘要

The quest for reliable and cost-effective solution of installing piles in deepwater led to the development of dynamically installed piles that embed themselves into the seabed through free-fall. Several variations of dynamically installed piles have been devised and successfully entered into service at deepwater offshore sites. The most notable one is the torpedo pile patented by Petrobras. To facilitate the design and installation of the dynamically installed piles, ABS has developed Guidance Notes to provide geotechnical design and structural assessment methods. This paper presents an overview of the guidance and details of the technical development that forms the basis of the recommended methods. In support of the development of the guidance, finite element analyses and centrifuge tests were conducted to study pile/soil interaction and to verify and further improve the prediction methods for pile pullout capacity. The pile inclination after installation, which has a significant effect on the pile pullout capacity and is of significant concern to the offshore industry, was thoroughly studied. Since the dynamic installation process results in lower short-term pullout capacity of the pile, it is recommended that the piles be installed for a sufficiently long period to allow the development of the pullout capacity. A prediction of the pile capacity restoration over time was developed based on the results of a series of centrifuge tests. A framework on the normalized vertical and horizontal component is proposed to predict the pile pullout capacities subjected to different loading angles.