Reliable drivability studies enable appropriate hammer selection, pile geometry optimization and safe, cost-effective pile installation. Friction Fatigue is a general term describing temporary changes in soil resistance around the pile shaft during pile installation. Friction Fatigue is affected by factors such as soil type, geotechnical properties and initial stress state. Impact hammer driving records for large diameter monopile foundations at a Southern North Sea offshore wind farm provide the link between dynamic soil resistance during driving and static soil resistance. The objective of this paper is to evaluate the influence of friction fatigue parameters for the glacial deposits of the Bolders Bank Formation which, in this area, comprised layered sequences of stiff, high strength, over-consolidated CLAY and dense to very dense SAND. The assessment utilizes and expands on the Alm and Hamre (2001) friction fatigue model in conjunction with the drivability software WEAP (2010). The results indicate that friction fatigue is a required component for drivability assessments in these soils and calibration can enable refinement of drivability predictions. Friction fatigue parameters can be modified to develop a drivability envelope for predictions. Different soil behaviour types defined through cone penetration testing, may also require different friction fatigue models to improve drivability predictions.
S. R. Davies, G. Giuliani and M. Vaziri
Keywords: Bolders Bank Formation, pile drivability, friction fatigue, monopile
Publisher: DFI