Identification of soil damping for stiff piles based on experiments: Methodology and results

Considering a critical gap in research regarding soil damping for monopile structures, this research, conducted at the SAGE laboratory of the University of Surrey, investigates the damping behaviour of stiff piles in sandy soil. Three monopile sizes with slenderness ratios between 3.75 and 10 were examined at forcing frequencies from 0.1 to 2 Hz, with results from a monopile with a ratio of 3.75 presented in this paper. Employing experimental methods, a novel approach for measuring soil damping is suggested, which effectively isolated soil material damping from other damping sources in contrast to the prevalent research practice of back-calculating soil damping from the overall system damping. In processing the experimental data, validations with research databases identified discrepancies, particularly at the pile toe, emphasising the superiority of the model test data for industry design guidance. The observations reveal that the soil damping around the stiff pile exhibited a non-linear fluctuating shape. This research introduces the "zonal method", which intends to reduce the design complexities surrounding soil damping ratios by linearasing its non-linear profile. Dynamic Simple Shear tests run simultaneously with experimental model tests, provided results for direct comparison, hinting at possible computation of soil damping ratio using element test apparatus only.