State of Knowledge in Seismic Behaviour of Helical Piles-Article

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This review assesses the limited evidence on helical-pile behaviour during earthquakes and the lack of consistent design guidance, particularly in the United States. Helical piles may offer seismic advantages because they are slender, ductile, provide strong anchorage against uplift, and are relatively easy to install for foundation retrofits. Reports from earthquakes in New Zealand, Japan, and the United States describe good performance, but these observations are largely anecdotal and do not establish why the piles performed well.<br /><br />Existing experiments mostly examine single piles under simplified cyclic or dynamic loads applied at the pile head. Tests generally indicate satisfactory axial cyclic performance, with capacity often maintained and sometimes increased. Lateral performance depends on soil conditions and pile configuration; grouted reinforcement can improve lateral resistance, though cyclic loading may cause gaps or grout separation. Comparisons with driven piles are few and yield soil-dependent results.<br /><br />In the United States, AC358 evaluates helical-pile products but limits its scope to Seismic Design Categories A–C; use in higher categories requires project-specific professional analysis. International guidance, particularly in New Zealand, addresses seismic issues more directly. Crucially, the review found no direct tests of helical piles in liquefiable soils, despite their use in earthquake-prone regions. Liquefaction and lateral spreading can impose severe bending and displacement demands on deep foundations.<br /><br />The authors recommend full- and small-scale tests using realistic earthquake motions, directly comparing helical piles with established foundation types in the same soils. Research should also examine pile groups, pile-cap connections, liquefaction conditions, and potential use of helical piles for ground improvement. Long-term monitoring and documented post-earthquake foundation inspections are needed to provide field evidence.<br /><br />Overall, helical piles appear promising for seismic applications, but reliable design standards require quantitative evidence defining their benefits, limitations, and behaviour under realistic earthquake and liquefaction conditions.
Keywords
helical piles
earthquake performance
seismic design
foundation retrofits
axial cyclic loading
lateral resistance
liquefaction
pile groups
AC358
New Zealand guidance