Model predicts cyclic uplift failure in soft-clay helix anchors

Vertical cyclic loading can reduce the stiffness of a single-helix anchor in soft clay, build excess pore pressure and leave a permanently displaced anchor head, according to a numerical and theoretical study that combined benchmark testing with finite element simulation. The research examined how an installed helical anchor behaves when repeatedly pulled upward, a loading pattern that can shift the soil around the shaft from shallow failure toward deeper local flow around the helix.

The investigators built a two-dimensional axisymmetric finite element model of the anchor–soil system using data from a benchmark cyclic uplift test involving a 26 mm diameter shaft. Its clay formulation included small-strain stiffness, cyclic hardening, plastic displacement accumulation and pore-pressure generation. Against the benchmark test, the model reproduced the observed displacement trend and captured the transition from a shallow wedge of soil moving upward to deeper local flow around the helix. The simulations also showed how excess pore pressure developed in the soil surrounding the helix during repeated uplift.

The researchers also developed a cyclic Q–z model to represent the relationship between load and displacement at the anchor head. This model combined a hyperbolic monotonic backbone with an analytical ultimate-capacity bound, mapping between monotonic and cyclic behavior, a moving projection center and parameters describing cyclic degradation. Together, these components allowed the model to account for path-dependent response, declining stiffness and the accumulation of residual displacement rather than treating each loading cycle as independent.

Calculations with the model examined embedment depth, shaft diameter, mean load and cyclic amplitude. The resulting cyclic interaction diagrams indicated that rapid ratcheting occurred when the maximum cyclic load approached approximately 0.4–0.5 times the ultimate capacity, Qu. This is a modeled threshold, not a universal field limit: the study presents an experimental–finite element–theoretical framework for preliminary assessment of single-helix anchors in soft clay, and the reported behavior depends on the modeled anchor geometry, loading history and soil response.

Subject of Research: Finite element and theoretical modeling of cyclic uplift in single-helix anchors embedded in soft clay

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

Article References: Shiwei, W., Sihua, L., & Hang, C. (2026). Numerical and theoretical analysis of vertical cyclic uplift of single-helix anchors in soft clay. Scientific Reports. https://doi.org/10.1038/s41598-026-75211-x

Image Credits: AI Generated

DOI: 10.1038/s41598-026-75211-x

Keywords: single-helix anchors, soft clay, cyclic uplift, finite element modeling, pore pressure, residual displacement, stiffness degradation, soil mechanics, anchor ratcheting, Numerical, theoretical, analysis