Cyclic load-displacement behavior of piles via Frustum Confining Vessel

The load-displacement behavior of piles under cyclic and static loading is largely influenced by geometry. This study evaluates various pile types with differing geometries and installation methods using the Frustum Confining Vessel (FCV). Twenty-one tests were conducted with cyclic amplitudes of 10 % and 30 % of the ultimate bearing capacity. For conventional piles, the 10 % diameter and offset limit methods yielded comparable results, while Brinch Hansen 80 % and Chin-Kondner methods overestimated capacities. For helical piles, the 10 % method was most accurate, with the offset limit method underestimating capacity. Helical piles initially experienced higher settlement under low-amplitude cyclic loading due to soil disturbance but stabilized over time. Under high-amplitude loading, they surpassed conventional piles, showing reduced settlement and greater stability. Conventional piles displayed higher initial stiffness, whereas helical piles exhibited greater post-cyclic stiffness improvements. Helical piles with spacing ratios of 1.5 and 3 achieved stiffness ratios of 2.7 and 2.8, respectively, compared to 2.0 for narrow cylindrical piles. When assessed from geotechnical and practical perspectives (including cost, manufacturability, and cyclic behavior), helical piles demonstrated better performance. The study validated the FCV results through scaling with similarity theory and field comparisons, ensuring the reliability of the experimental findings.