Uncertainty quantification of offshore anchoring systems in spatially variable soil using sparse polynomial chaos expansions

Abstract

SummaryThe trend toward deep water energy production has led to a growing use of plate anchors to moor floating production facilities. The effect on anchor uplift behaviour of the inherent spatial variability of soil deposits has so far been little considered, despite having important implications for anchor design. Spatial variability problems are commonly analysed by Monte Carlo simulation but it is difficult to establish the probabilities of failure that are of interest in practice. In this paper, sparse polynomial chaos expansions (SPCEs) are used for moment and reliability analysis of plate anchors in spatially variable undrained clay. A novel two‐stage methodology is proposed: in the first stage, an SPCE is constructed to meet a target global error, allowing statistical moments of the uplift capacity to be obtained; in the second stage, an active learning method is used to refine the SPCE for reliability analysis. Anchor uplift capacity is obtained by a finite element method, which is coupled with a random field representation of spatial variability. The effect of embedment depth and the soil‐anchor interface is investigated. The failure mechanism of the anchor is shown to have a significant effect on the statistical moments of the uplift capacity and the probability of failure in relation to current design guidelines. To inform future design, factors of safety are presented for a range of failure probabilities.