Numerical Study on Uplift Capacity of Helical Pile Embedded in Clay-Paper Upload 2

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The study investigates how helix spacing, blade thickness, shaft thickness, and helix number affect the uplift capacity of helical piles embedded in clay. Laboratory pullout tests were conducted on a dual-helix steel model pile installed 400 mm into clay prepared at a consistency index of 0.4. The results were used to validate a Plaxis 3D finite-element model; the fine-mesh numerical predictions differed from the scaled experimental results by less than 10%.<br /><br />Parametric analyses examined helix spacings from 0.5 to 3 m and blade thicknesses from 4 to 10 mm. Uplift capacity increased with blade thickness. For all tested thicknesses, capacity rose as spacing increased to 1.5 m, then declined. For a 10 mm blade, the modeled capacity at 12 mm displacement peaked at 39.88 kN at 1.5 m spacing.<br /><br />The authors attribute the decline beyond the critical spacing to a change in soil-resistance mechanism: closely spaced helices act through cylindrical shear, while widely spaced helices increasingly behave as individual bearing plates. Comparisons at constant helix contact area indicated that two helices at the critical spacing provided capacity similar to a single helix, leading the authors to identify two as the critical helix number for this case.<br /><br />The findings demonstrate that pile geometry and soil properties influence uplift resistance and that critical spacing should be considered in design. The authors recommend further research on helical piles under combined axial and lateral loading and on pile groups in different soils.

Keywords

helical piles

uplift capacity

clay soil

helix spacing

blade thickness

shaft thickness

helix number

pullout tests

finite element model

Plaxis 3D