ABSTRACT

Floating facilities with mooring systems have been widely applied in the offshore oil and gas sector and are a viable solution for exploiting offshore wind and wave renewable energy. Plate anchors, an efficient foundation type embedded in the seabed and connected to mooring lines, provide high pullout capacity for floating structures. The evaluation of the undrained pullout capacity of plate anchors in clay is simplified into two extreme categories, namely, immediate breakaway and no breakaway, which correspond to zero and infinite tensile capacity at the anchor-soil interface. In reality, intermediate tension could be triggered at the base of the anchor between those two extremes. This study uses finite element (FE) analyses and a user-defined model of the anchor-soil interface to investigate the effect of tension on the uplift behaviour of plate anchors in undrained clay. The contribution of the interface tension on the pullout capacity is demonstrated, and soil failure mechanisms are investigated. The pullout capacity factors that are influenced by different interface tensile capacities are between the two breakaway conditions. A critical tension factor is defined beyond which no further capacity can be gained from the interface tension. The results allow for the evaluation of the actual pullout capacity of plate anchors with different magnitudes of tension beneath the anchor.

INTRODUCTION

Floating facilities with mooring systems have been widely applied in the offshore oil and gas sector and are a viable solution for exploiting offshore renewable energy, such as offshore wind in deep waters and wave energy. Plate anchors, which serve as an efficient and cost-effective hold for mooring systems, are installed in the seabed to provide high pullout resistance for floating structures (Randolph and Gourvenec, 2010). Plate anchors provide pullout resistance through their bearing area when subjected to vertical or inclined loading. Therefore, an accurate evaluation of the ultimate pullout capacity of plate anchors is critical for the integrity of the mooring of floating facilities.

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