Strain-based performance of drilled displacement piles through load tests and CPT database

Drilled displacement (DD) piles have emerged as an efficient deep foundation solution, yet their axial behaviour, particularly under diverse loading regimes, remains insufficiently characterised due to limited high-quality, full-scale records. This study develops a comprehensive database of 60 static load tests, encompassing various DD pile types: Fundex, De Waal, Olivier, Berkel D, APGD, Omega, and Atlas. The database covers diameters from 356 to 720 mm and embedment depths from 6 to 21 m, installed in cohesive, granular, and mixed deposits, along with corresponding CPT data. Load-displacement responses are normalized into a unified pressure–relative displacement framework, analogous in form to stress–strain representations in solid mechanics but operating at the pile–soil system level rather than the material level. A hyperbolic transfer function is implemented to extract the initial tangent modulus, E i , critical for small-strain stiffness under transient loading, and the limit pressure, σ i , governing ultimate capacity under sustained static loads. The analysis delineates performance thresholds: the elastic serviceability range (0.5 – 1.0%), dominated by E i , and the ultimate limit state mobilised at strains of 5 – 10%. The derived strain-based characterization provides direct inputs for both static design and dynamic analyses, where accurate stiffness from small to large strains is paramount. The findings provide a potential link between static load-test data and the strain-dependent parameters required for design under transient loading.