Punch-Through Risk of Spudcans: A Comparison of Design Models and Field Measurements-Paper

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The paper evaluates methods for predicting spudcan punch-through in sand-over-clay soils, a brittle failure that can cause sudden leg penetration and threaten jack-up stability. Accurate predictions are especially important for offshore wind projects, where costly ground or foundation mitigation may not be feasible.<br /><br />The authors focus on the failure-stress-dependent model developed by Hu et al. (2014), which combines resistance from the sand, the underlying clay, and the weight of a sand cone displaced into the clay. They compare model predictions with measured peak punching pressures from 129 field datasets collected at two offshore wind farms, as well as results from laboratory and centrifuge tests.<br /><br />The Hu model agrees reasonably well with the laboratory data, generally within about 25%. However, field results—particularly from one site with strongly overconsolidated clay—show substantial overprediction. The discrepancy is linked to the undrained shear strength of the underlying clay: predictions become increasingly biased as clay strength rises. Other established methods also show bias, suggesting the issue is not unique to the Hu model. The authors consider uncertainties in soil characterization and strength assumptions but find these do not fully explain the difference.<br /><br />To reduce the bias, they develop an empirical model factor using regression analysis. Applying it improves the field predictions while leaving laboratory results largely unchanged. Across the combined dataset, the adjusted prediction-to-measurement ratio has a mean of 1 and a coefficient of variation of 0.183.<br /><br />The authors conclude that existing methods may produce either overly conservative or unsafe estimates depending on clay strength. Their correction is specific to the model and assumptions used, and further research is needed to explain the field–laboratory differences and develop a more physically representative prediction model.

Keywords

spudcan punch-through

sand-over-clay soils

jack-up stability

offshore wind farms

failure-stress-dependent model

undrained shear strength

peak punching pressure

field datasets

laboratory and centrifuge tests

empirical correction factor