The Impact of Installation Method on Monotonic Loading of Monopiles in Sand-Paper

Paper

Pdf Summary

The study examines how installation method affects the lateral stiffness and capacity of monopiles in sand. It compares full-scale piles installed by impact driving and vibration at the Cuxhaven site in Germany, where the piles were embedded in dense sand. Field lateral-load tests and post-installation cone penetration tests (CPTs) were used to assess pile response and changes in surrounding soil.<br /><br />Three-dimensional finite-element analyses in PLAXIS used the Hardening Soil Small-strain model. Soil parameters were derived in two ways: from correlations with sand relative density (Method 1) or primarily through direct correlations with CPT cone resistance, qc (Method 2). The analyses also represented installation-related soil disturbance.<br /><br />Field measurements showed that the vibrated pile had lower stiffness and lateral resistance than the driven pile. However, the numerical models predicted smaller differences between installation methods than were observed. Method 1 generally underestimated stiffness and capacity. Method 2 reproduced initial stiffness well for both piles, but overestimated resistance at larger displacements; Method 1 better matched some of the softer response of the vibrated pile but still underestimated its final capacity. Neither method captured the significant creep effects observed at higher loads, which the soil model did not represent.<br /><br />The findings indicate that installation effects, soil strength, and installation conditions influence monopile performance, but the available analyses do not fully explain the field differences. The authors recommend further research and, until more reliable models are available, periodic CPT testing to assess soil changes and ageing around piles, combined with soil parameters derived from direct CPT correlations.

Keywords

monopile

installation method

lateral stiffness

lateral capacity

impact driving

vibration installation

dense sand

cone penetration test

finite-element analysis

PLAXIS