Dynamic Behavior of Helical Piles in Dry and Liquefiable Soils using Scaled Shake Table Tests-Article

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The study used five scaled 1g shake-table tests, involving 36 shaking events, to compare a slender shaft with helical piles containing one, two, or three helices. Tests covered dense dry sand and layered ground with a loose, liquefiable sand layer over dense sand. Researchers varied shaking intensity, superstructure weight, and the number of shaking events, measuring pile bending, displacement, acceleration, pore pressure, and settlement.<br /><br />Across pile types, bending moments followed a similar pattern, with the maximum consistently occurring at the boundary between the loose and dense soil layers. Stronger shaking and heavier superstructure weights increased bending moments. Repeated shaking densified the liquefiable layer, reducing pile bending moments as the soil’s relative density increased.<br /><br />More helices generally improved dynamic performance compared with the slender shaft. The triple-helix pile showed up to a 60% reduction in residual horizontal displacement; maximum bending moment and peak pile-head displacement decreased by roughly 35–40%, while peak acceleration fell by about 20%. Ground settlement occurred mainly during early shakings and diminished with subsequent densification. No measurable settlement of the piles was observed, although ground settlement reached approximately 2 cm.<br /><br />The results indicate that helical piles—particularly those with more helices—can reduce dynamic displacements and improve performance in liquefiable soils. However, the authors caution that these scaled tests do not capture all field conditions; design should account for soil profile, liquefiable-layer depth, earthquake motions, superstructure properties, and soil–pile–structure interaction.

Keywords

helical piles

shake-table tests

liquefiable soil

pile bending moment

dynamic performance

residual displacement

soil-pile interaction

dense sand

pore pressure

ground settlement