Variability Assessment of Helical Piles Performance via Geometric Conical Enhancement-Paper

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The study evaluates whether conical helix geometry can improve helical pile performance by reducing installation-related soil disturbance and increasing axial capacity. Researchers conducted six full-scale compression and pullout tests on three pile configurations at a coastal site in Babolsar, Iran: a conventional two-helix pile and two conical piles, with helix spacing-to-diameter ratios (S/D) of 1.5 and 3.<br /><br />Conical piles showed greater initial stiffness and load capacity than the conventional pile in both loading modes. The conical pile with S/D = 1.5 performed best in pullout, while the S/D = 3 conical pile performed best in compression. Disturbance-factor results also indicated less installation-related disturbance for the conical configurations.<br /><br />To examine uncertainty from natural soil variability, the researchers used Monte Carlo simulations to generate 100,000 correlated combinations of cohesion and friction angle. They compared capacity predictions from individual-plate-bearing and cylindrical-shear methods against capacities interpreted using four load-test criteria. The reliability analysis generally favored the cylindrical-shear method, particularly when paired with lower-displacement criteria (5% or 10% of helix diameter), though the preferred criterion varied by pile configuration.<br /><br />Overall, the findings suggest that conical helix geometry can improve axial performance and reduce soil disturbance, making it a promising alternative for coastal and offshore foundations. The authors emphasize that design should account for soil variability and use suitable capacity-interpretation and reliability methods. These conclusions are based on a limited number of tests at one site and therefore require further validation across different soils and conditions.

Keywords

conical helix geometry

helical pile performance

axial capacity

soil disturbance

full-scale compression tests

pullout tests

Monte Carlo simulation

reliability analysis

cylindrical-shear method

coastal foundations