Numerical and Experimental Study of Axially Loaded Non-Displacement Piles in Sand-Paper

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The study combines finite-element (FE) analyses and calibration-chamber experiments to investigate the axial response of non-displacement piles in sand. The FE models used an advanced two-surface plasticity model and a carefully refined mesh to capture shear localization along the pile shaft and near its base. Model piles were tested in medium-dense and dense sand under a 50 kPa surcharge; digital image correlation (DIC) measured soil displacement fields during loading.<br /><br />Results show that shaft resistance is mobilized rapidly, reaching its limit at pile-head settlements of roughly 1–2% of the pile diameter. The unit limit shaft resistance depends on lateral effective stress and interface friction; the interface friction angle can be approximated by the sand’s critical-state triaxial friction angle. Mobilized lateral earth pressure decreases with depth as confinement suppresses dilation. Model piles mobilize higher lateral pressures than field-scale piles because of scale effects, so the proposed shaft-resistance relationship is intended for field-size piles.<br /><br />Base resistance develops more gradually and reaches the study’s defined ultimate value at a settlement equal to 10% of the pile diameter. FE analyses closely reproduced the experimental loading response and DIC-observed displacement patterns. Ultimate unit base resistance was approximately proportional to the initial horizontal effective stress raised to the 0.4 power, increased with sand relative density, and was independent of pile diameter in the analyses. The proposed base-resistance equation applies to piles with slenderness ratios greater than 50; shorter piles may not mobilize sufficient base resistance because of pile compression.<br /><br />Overall, the combined numerical and experimental approach clarifies how shaft and base resistance develop and provides design relationships for both. The findings emphasize that reliable numerical predictions require constitutive models and mesh configurations capable of representing localized shearing.

Keywords

finite element analysis

calibration chamber

non-displacement piles

sand

shaft resistance

base resistance

digital image correlation

lateral earth pressure

pile-soil interaction

shear localization