Field Test and Numerical Analysis of Monopiles for Offshore Wind Turbine Foundations

This paper describes field pile tests for offshore wind turbine foundations. Both vertical and horizontal pile load tests were carried out to investigate soil-pile interaction. Finite difference analyses, implementing a Mohr-Coulomb failure criteria with a non-linear elastic stiffness considering strain-compatible effects, were used to perform the back-analysis. The results from numerical modelling are compared with the measured data obtained from optical fiber sensors installed on the internal steel pile surface. It was found that the pile-soil interaction is sensitive to the non-linearity of the soil. The non-linear soil stiffness provides a close match to the pile displacement (and consequently stress-resultants). In addition, the p-y curve method recommended by API was also used for back-analysis. The results from the p-y curve method were found to overestimate the pile displacement and bending moment for large diameter piles in clay.