Group Interaction Effect of Helical Pile in Soft Clay under Uplift and Lateral Load-PPT Presentation

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The study examines how helical piles interact in groups when subjected to uplift and lateral loads in soft clay. Model tests and three-dimensional finite-element simulations in PLAXIS 3D were used to assess single helical piles (SHPs) and groups (GHPs) with different pile counts, spacings, and configurations. The clay had an undrained shear strength of approximately 7.5 kPa. Numerical models used a Hardening Soil model and were calibrated against laboratory results.<br /><br />The simulations reproduced measured load–displacement behavior reasonably well, with differences below 8% for uplift and 3% for lateral loading. Both uplift and lateral capacity generally increased as group size and pile spacing increased. Uplift capacity gains became small beyond a spacing of about four helix diameters (4D). Group efficiency was lowest at 2D spacing and increased as spacing widened, indicating reduced interaction between piles. The study identifies group effects as generally negligible at or above 4D, although lateral capacity continued to benefit from greater spacing. Pile configuration and spacing both influenced group performance.<br /><br />Displacement contours showed overlapping soil deformation around closely spaced piles, supporting the observed interaction effects. The study notes that its models do not account for soil disturbance during pile installation or pore-pressure dissipation, and that laboratory clay conditions differ from full-scale field conditions. Field verification is therefore needed before applying the results directly in practice.

Keywords

helical piles

group efficiency

uplift capacity

lateral loading

soft clay

PLAXIS 3D

finite-element simulation

pile spacing

soil-pile interaction

Hardening Soil model