Load Transfer Curve of Piles in Sands under Uplift Forces-Paper

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The paper presents a method for predicting the load–displacement response of piles under axial uplift in sandy soils, including nonlinear shaft load-transfer (t–z) curves and pile-head response. Unlike methods focused mainly on ultimate tensile capacity or empirical t–z relationships, the approach models soil–pile interaction using a nonlinear soil stress–strain relationship.<br /><br />The pile is divided into segments supported by nonlinear springs representing shaft resistance. As the pile moves upward, the method calculates soil strains and mobilized shear stresses around the pile, accounting for changes in effective and confining stress under tension. It also considers soil layering, pile and soil properties, interface friction, and pile slenderness. The resulting local load-transfer curves are combined with pile elasticity to predict pile-head load–displacement behavior.<br /><br />The model’s predictions were compared with measured pile-head responses and back-calculated t–z curves from full-scale uplift tests in Louisiana and Brazil. Comparisons showed generally reasonable agreement, supporting the method’s ability to represent mobilized pile behavior.<br /><br />The analysis indicates that pile dimensions influence both the shape and development of the t–z curve. Larger-diameter piles mobilize shear stresses more gradually and tend to have softer curves, while slenderness affects the stress state and predicted resistance. Overall, the method offers a way to estimate nonlinear uplift response across layered sandy profiles using soil–pile interaction rather than relying solely on empirical curves.

Keywords

pile uplift

axial uplift

load-displacement response

sandy soils

nonlinear t-z curves

soil-pile interaction

shaft resistance

effective stress

pile-head response

full-scale uplift tests