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

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The study investigates how helix spacing, blade and shaft thickness, and the number of helices affect the uplift capacity of helical piles embedded in clay. Laboratory pullout tests were conducted on a dual-helix steel 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; predictions from a fine mesh differed from the experimental results by less than 10%.<br /><br />Parametric analyses showed that increasing helix thickness from 4 to 10 mm increased uplift capacity. Capacity also rose as helix spacing increased from 0.5 to 1.5 m, then declined at larger spacings. The authors attribute this reduction to a change in resistance from cylindrical shear around the helices to individual bearing beneath each helix. Thus, the critical spacing—where this transition occurs—depends on pile geometry and soil properties.<br /><br />For the studied configuration, 1.5 m was the critical spacing, and two helices were identified as the critical number. At 12 mm displacement, the single-helix pile carried 41.3 kN, compared with 39.88 kN for the dual-helix pile at 1.5 m spacing; triple-helix arrangements had lower capacities. 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

dual-helix pile

Plaxis 3D

pullout tests

finite-element modeling