Comparison of p-y Methods with Large-Scale Tests of Impact- and Vibratory-Driven Piles-Paper

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The TANDEM project investigated whether conventional p-y methods adequately predict the lateral behaviour of offshore wind monopiles, and whether installation method affects their performance. Researchers conducted large-scale tests on steel piles of three diameters in dense, water-saturated sand. Piles were installed by impact driving or vibration and tested under monotonic lateral loading. Cone penetration tests (CPTs) measured changes in the surrounding soil.<br /><br />The impact-driven pile tests showed similar load–displacement behaviour when results were expressed using dimensionless parameters, supporting the use of the test series to assess pile-size effects. Vibratory-driven piles were softer than comparable impact-driven piles, particularly at small displacements. Their lower lateral resistance corresponded with greater soil disturbance indicated by CPT measurements.<br /><br />The tests were compared with the API (2011) p-y method and the modified approach of Kallehave et al. (2012), using friction-angle profiles derived from laboratory tests and CPT interpretation methods. Predictions were highly sensitive to the selected friction-angle profile. Overall, the API method poorly represented the measured behaviour: it generally underestimated initial stiffness, while some parameter choices overestimated resistance at larger displacements. The Kallehave method improved estimates of initial stiffness for the tested piles when paired with a suitable friction-angle profile, but also overestimated the vibratory-driven pile’s resistance at larger deflections.<br /><br />The findings show that standard p-y methods may not reliably capture monopile behaviour and that pile installation technique influences lateral capacity. The authors recommend further assessment of alternative p-y approaches, scale effects, and extrapolation to full-scale projects. Future work under the Ho-Pile project will extend the research to cyclic loading.

Keywords

offshore wind monopiles

p-y methods

lateral behaviour

impact driving

vibratory driving

dense water-saturated sand

cone penetration tests

lateral resistance

API 2011

Kallehave method