Alkateeb, DiaaDiaaAlkateebGrabe, JürgenJürgenGrabe2026-03-052026-03-052026-02-23Computers and Geotechnics (in Press): (2026)https://hdl.handle.net/11420/61878Conventional Coulomb friction models often fail to reproduce the complete non-linear load–displacement response of soil–pile interfaces, particularly during unloading–reloading sequences. Advanced hypoplastic contact formulations address these limitations by capturing pressure dependency (barotropy), density dependency (pyknotropy), and surface roughness effects using the same constitutive parameter set as the surrounding soil continuum. This study presents the first three-dimensional back-analysis of a hypoplastic contact model benchmarked against full-scale tensile load tests on steel H-piles in a complex, 23-layer stratified soil profile. The methodology establishes a physically consistent calibration framework where the interface roughness parameter is derived directly from torsional interface shear tests on pile-specific steel, rather than empirical estimation. These same contact formulations are subsequently applied to simulate the laboratory tests, ensuring consistency between calibration and field-scale prediction. The model accurately reproduces the field response and reduces the root mean square error (RMSE) by 71% relative to the Coulomb model, capturing hysteretic loops that simplified models miss. A parametric sensitivity analysis identifies interface roughness and pile circumference as the dominant capacity drivers, while relative density and in-situ earth pressure exert a moderate influence. The results demonstrate that physically based contact formulations are essential for accurate pile-soil interaction modelling in complex profiles, enabling more reliable and economical foundation design.en0266-352X2026Elsevierhttps://creativecommons.org/licenses/by/4.0/Finite-element analysisHypoplastic contact modelLayered soilsPile-soil interactionTensile capacityTorsional shear testTechnology::624: Civil Engineering, Environmental Engineering::624.1: Structural Engineering::624.15: Geotechnical EngineeringJournal Articlehttps://doi.org/10.15480/882.1681610.1016/j.compgeo.2026.10799710.15480/882.16816Journal Article