Comparison of pile driveability methods based on a case study from an offshore wind farm in North Sea
Significant research effort has been put into pile driveability analyses with the aim of determining a successful, safe and cost efficient installation. Driveability analysis involves selection of appropriate hammer, determination of pile makeup details and careful review of soil profile to reach desired penetration or capacity with reasonable number of blows without overstressing the pile. In this paper, pile driving records from the installation of 6.5 m diameter monopiles at a wind farm in southern North Sea are considered. The ground conditions at the site generally consist of between 10 50 m thickness of over consolidated clay with some layers of sand overlying chalk bedrock. The most important of the variables to establish is the Static Resistance to Driving (SRD) There are proposed procedures for evaluating SRD in sands and clays; however, the knowledge about pile driveability in the chalk at the site is very limited. This makes prediction of the soil response after driving the pile into the chalk layers unreliable. The piling records are used to test how well the existing driveability suit the conditions at this site by comparing the predicted blow counts with results from back analyses of as measured pile driving records.