Ultimate uplift resistance of circular plate anchors in undrained two-layer clays

The vertical uplift resistance of circular plate anchors buried in undrained two-layered clays was studied by means of finite element method. Anchors with immediate breakaway (vented) and no breakaway (bonded) are taken into account. The numerical results are given in the form of the breakout factors accounting for the anchor embedment depth, top layer thickness, clay strength ratio, and clay overburden (clay self-weight), which are compared with existing empirical and analytical solutions.It is found that the breakout factors for strong-over-soft clays are greater than those for soft-over-strong clays. Also, the breakout factors of bonded anchors are identical to those of vented anchors with large overburden pressure. Failure patterns are examined for the cases of soft-over-strong clay and strong-over-soft clay, depending on anchor embedment depth and top layer thickness.