Drag anchor fluke–soil interaction in clays

Abstract

Finite element analysis has been used to investigate the interaction between anchor flukes and undrained soil at failure. The behaviour of a rectangular and a wedge-shaped anchor has been investigated when the anchors are subject to combined rotational and translational loadings similar to those experienced during anchor dragging. The results have been presented in terms of a plasticity framework to produce an associated plastic failure locus for combined loading conditions. It is seen that the wedge-shaped anchor has a different shaped failure locus and displacements at failure because of its asymmetrical shape, and this will affect drag anchor behaviour. A new design method is introduced that aims to predict drag anchor embedment trajectory and holding capacity through examination of the fluke–soil interaction. The yield loci and plastic potentials produced from consideration of fluke–soil interaction are used in the new design method to predict drag anchor kinematics. Results from the new analysis method are compared to empirically based methods, and it is seen that there is good agreement between results, even without further calibration from physical modelling. This suggests that the approach has promise, and with further refinement of the yield loci and better approximations to the complex anchor geometry, it may develop into a useful anchor design tool that allows for both the anchor geometry and the soil conditions explicitly.Key words: drag anchor capacity, undrained clays, numerical method.