Analysis of Suction Piles for Mooring Floating StructureFoundations in Clay Soil at Deepwater Levels

Abstract

Oil and gas exploration is increasingly moving to deepwater locations to meet the increasing energy demands. In this environment, floating structures with suction pile foundations are commonly used because their cost-effectiveness. Some studies have been conducted to examine the behavior of suction piles in clay soils, but the typical clay conditions considered are normally consolidated and lightly over-consolidated. In this paper, the behavior of suction piles in under-consolidated clays and under-consolidated, normally consolidated clays, as extracted from actual deepwater soil conditions. The evaluation was performed using geotechnical 3D finite element software Plaxis. Suction piles with two different aspect ratios (L/D = 2 and 6) were considered, and the focus was on the effect of load angles (0 to 90) and the effects of pad-eye positions (0.5 L to 0.9 L). For short piles, the load angles had a relatively insignificant effect on the overall ultimate resistance, while for long piles, the angles affected the overall resistance considerably with a decrease in resistance up to approximately 50 percent. This different behavior could be explained from the observed pile deformation patterns. The pad-eye positions affected the pile resistances significantly as well with a decrease in the resistance factor up to about 30 percent. Nevertheless, it can be concluded that the overall behavior of suction piles in combined clay conditions is practically similar to that of piles in normally consolidated and over-consolidated clays.