ABSTRACT
Tension leg platform (TLP) foundation piles could experience excessive lateral deformation induced by extreme TLP offsets which might jeopardize the structural integrity. Provision of fins onto pile top is evolving as an alternative to improve pile lateral performance. This paper presents suites of three-dimensional (3D) finite element analyses of the laterally loaded top-finned TLP foundation pile to evaluate the lateral pile behavior and efficiency of fins in comparison with regular pile. Advantages of the top-finned pile in structural design are described. Additionally, loading directional effect on lateral response of the topfinned pile is discussed. The results indicate that usage of fins could significantly increase pile lateral resistance by 77%, and consequently could save pile material take-offs by 39%. The current study demonstrates that provision of top fins is a viable and promising alternative which can improve the lateral performance of TLP foundation piles and provide pile cost savings.
A tension leg platform (TLP) is a vertically moored floating facility typically used for deepwater oil and gas production. The buoyant hull is tethered to the seafloor foundation by vertically oriented tendon clusters at each corner of the structure. The tendon system with high axial stiffness rigorously restrains vertical motions of the TLP; however, it allows horizontal offsets to a small percentage of water depth.
The foundations for TLPs usually consist of large-diameter driven pipe piles that provide resistance to sustain tendon tensions. The TLP foundation piles are typically long flexible cylinders (i.e., with diameter of 2 m to 3 m and length of 80 m to 140 m), with slender ratio (L/D) greater than 30.
Fig. 1 presents the foundation pile make-up of Magnolia TLP introduced in Tang, et al. (2005), which was installed in Block 783 in the Gulf of Mexico with a water depth of approximately 1,425 m. It represents a typical configuration of TLP foundation piles, which are normally assembled by segments of drive head, tendon receptacle, conical transition, main sections and drive shoe. It has an outer diameter (OD) of 2.44 m and an overall length (L) of 103.1 m, with a stepped wall thickness (WT) profile.
