Numerical and theoretical analysis of vertical cyclic uplift of single-helix anchors in soft clay

Vertical cyclic uplift of single-helix anchors in soft clay can induce stiffness degradation, excess pore-pressure accumulation, and residual displacement. This study established an experimental–finite element–theoretical framework for preliminary assessment. A two-dimensional axisymmetric finite element model of the anchor–soil system was built from benchmark tests. An improved cyclic bounding-surface clay model included small-strain stiffness, cyclic hardening, plastic displacement accumulation, and pore-pressure generation.The finite element model was evaluated against the T1 cyclic uplift test with a 26 mm shaft. Numerical results reproduced displacement trends, captured the transition from shallow wedge uplift to deep local flow-around failure, and clarified excess pore-pressure development around the helix during cyclic uplift. A cyclic Q – z model combined a hyperbolic monotonic backbone, analytical ultimate-capacity bound, bounding-surface mapping, moving projection center, and cyclic degradation parameters. The model describes path dependence, stiffness degradation, and residual displacement accumulation at the anchor head. The calculations examined the effects of embedment depth, shaft diameter, mean load, and cyclic amplitude on peak and residual displacement. Cyclic interaction diagrams indicated rapid ratcheting when the maximum cyclic load approached 0.4–0.5 \(Q_u\) . The framework provides a practical method for preliminary cyclic uplift assessment of single-helix anchors in soft clay.