Corrosion effects on axial pile capacity

Increase in surface roughness by corrosion processes has long been neglected as potential factor influencing pile setup. However, recently there has been an increasing number of studies who referred pile setups largely or solely to corrosion and sand incrustation. Only limited research has been conducted to assess the potential impacts of corrosion directly on pile capacity development. Therefore, we sampled steel and crust surfaces from a steel monopile having been aged for ∼four years in sand. Surface roughness measurements and interface direct shear testing were performed to quantify changes for friction angles. The impact of friction angle changes on pile capacity were calculated using ICP-05 and UWA-05 for a large- and small-diameter geometry and referenced by field data. We can show that corrosion can significantly contribute to temporal pile capacity gains. Evidence have been found that the maximum and critical interface friction angles evolve differently considering the same changes in roughness. Also, differences in shearing behavior to literature were observed, being potentially a result of the naturally corroded surfaces sheared in our study. A strong, maybe exaggerated sensitivity of the capacity prediction approaches to pile diameter was observed. Effects causing an increase in surface roughness, should be reconsidered as an important factor influencing pile setup. •The surface roughness of steel piles increased with progressive stages of corrosion (i.e., preserved surfaces, air-corroded surfaces, sand crusts).•The interface friction angles of corroded surfaces strongly correlated with surface roughness.•None of the considered corrosion scenarios proved to be suitable for accurately representing the End-of-Driving (EoD) capacity as all modelled capacities consistently overestimated the actual measured pile capacities in the field.•A strongly varying sensitivity of the modeled pile capacity to corrosion-related changes in surface roughness and shearing behavior was recognized.•For large-diameter piles the prediction models were just able to explain max. 5% of the setup observed in the field. For small-diameter piles instead, the models overestimated by far the capacities measured in the field.