Plate anchors are commonly embedded deeply in the seabed to efficiently provide the pullout capacity. The ultimate pullout capacity (UPC) of the anchor is an important index in engineering. Reliable prediction of the UPC requires the failure mode of the anchor well understood. Large soil deformations will occur when the anchor is pulled out of the soil. It is difficult for the classical finite element method to simulate the pullout process due to a loss of accuracy and numerical divergence. In the present work, the coupled Eulerian-Lagrangian (CEL) approach, which is one of most serviceable large deformation finite element methods, is used to simulate the pullout process of plate anchors. Considering the computational time and relative simplicity compared to advanced constitutive models, the Mohr-Coulomb constitutive model is chosen but modified to describe the sand behavior. For loose and dense sand, different functions are employed to introduce evolutions of the friction angle and the dilation angle. The calculated results are compared to centrifuge tests and existed load-displacement curves. It is demonstrated that the CEL method combined with the modified Mohr-Coulomb constitutive model could successfully capture the uplift behavior of plate anchors in sand. The UPC of plate anchors is then determined by the maximum resistance criterion from the load-displacement curves. The failure mechanisms are also observed during the pullout process.
Effective utilization of ocean space and rational exploitation of marine resources have already become the strategic direction of great powers in the world. Whether in shallow or deep waters, the mooring system is the most commonly adopted positioning technique for floating oil and gas production platforms. It should be noted that, within a large mooring system consisting of the floater, mooring lines and anchors, anchors are the core and root of the system. Since anchors are usually deeply embedded in the seabed and cannot be visually observed, the role of anchors is often undervalued or even ignored. The ultimate pullout capacity (UPC) of the anchor is one of the main concerns in designing and analyzing plate anchors.
The UPC of plate anchors in sand has been investigated by numerous researchers. Elastoplastic finite element analysis and experimental studies have been done by Rowe and Davis (1982), which proposed the bearing capacity factor as a function of orientation, the friction angle, dilation angle, embedment ratio, initial stress state and anchor roughness. Design charts were also proposed by Rowe and Davis (1982) to conveniently estimate the bearing capacity factors of plate anchors. Pullout tests for rectangular anchors in dry sand were performed by Das and Seeley (1975). By analyzing experimental data, a simple theoretical expression was established by Frydman and Shaham (1989) to predict the pullout capacity of slab anchors in uniform sand. Merifield and Sloan (2006) estimated the uplift capacity of plate anchors based on the upper and lower bound limit analysis.
