Abstract This study evaluates the performance of instrumented helical piles subjected to quasi-static tensile cyclic loading in a sandy deposit. Instrumentation at three shaft sections enabled the monitoring of load transfer mechanisms and soil–pile interaction. Two cyclic tests were conducted to investigate the mechanical response across varying load stages. The results demonstrate that load increments promote localized soil densification while concurrently increasing cumulative displacements. Higher load amplitudes intensified the interaction between successive loading stages, thereby accelerating the rate of displacement accumulation. Residual cyclic stiffness (k rc ) decreased linearly with depth at rates ranging from − 20.1 to − 20.3 kN/mm per meter (Test A) and − 12.4 to − 16.2 kN/mm per meter (Test B), a phenomenon attributed to mechanical disturbance and density reduction during helix installation. Conversely, reloading cycles enhanced the overall system stiffness, leading to the mitigation of subsequent displacements. Stability analysis established that cyclic amplitudes below 13% of the static tensile capacity maintained stable conditions, with average displacement accumulation rates (v avg ) between 12.4 × 10 −3 and 25.2 × 10 −3 mm/cycle, whereas amplitudes exceeding 22% resulted in progressive instability (v avg ≈ 2140 × 10 −3 mm/cycle). Although loading and unloading phases followed similar behavioral trends, residual stiffness values were consistently 7–25% higher during unloading stages (k rc,un /k rc,load up to 1.25). This indicates a cyclic hardening effect that improves foundation performance over time. These findings provide critical quantitative benchmarks for refining design guidelines and evaluating the long-term stability of helical foundations under cyclic tensile loads in granular soils.
Farias et al. (Fri,) studied this question.