The Influence of Friction Fatigue on Pile Drivability Predictions for Large Diameter Monopiles in the Bolders Bank Formation-Paper

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The study examines how friction fatigue—the temporary reduction in soil resistance along a pile shaft as surrounding soil is sheared and remoulded during driving—affects drivability predictions for large-diameter monopiles in the Bolders Bank Formation, offshore Yorkshire.<br /><br />The formation contains highly variable glacial deposits, including stiff, overconsolidated clays and dense to very dense sands. Researchers compared driving records from 73 monopiles, using 12 locations representing a range of ground conditions, with predictions from the WEAP drivability program. The analysis applied the Alm and Hamre CPT-based soil resistance model and tested different friction-fatigue parameters. Predicted and measured blow counts were compared.<br /><br />Predictions without friction fatigue generally overestimated driving resistance. The standard Alm and Hamre parameters improved estimates at some locations, but still did not consistently match the records. Reducing the degradation shape factor—so that shaft resistance fell more rapidly during driving—produced a better overall fit at eight of the 12 locations, while underpredicting resistance at the other four. Shape-factor values between 20 and 80 broadly captured the observed range of driving behaviour.<br /><br />The findings indicate that friction fatigue should be included in drivability assessments for these soils and that parameter calibration can improve predictions. A single degradation factor can provide an initial estimate of the drivability envelope, but different CPT soil-behaviour types may require different models to reduce over- and underprediction. The authors recommend further work on soil-type-specific fatigue parameters, as well as the effects of pile diameter, hammer energy and load cycles.

Keywords

friction fatigue

drivability predictions

monopiles

Bolders Bank Formation

WEAP

Alm and Hamre model

CPT-based soil resistance

pile driving records

glacial deposits

shape factor