Back Analysis of Driving Resistance and Induced Driving Stresses in Vibratory Driven XL Monopiles: Case Study of Kaskasi Wind Park

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4. Back Analysis of Driving Resistance and Induced Driving Stresses in Vibratory Driven XL Monopiles: Case Study of Kaskasi Wind Park

The application of vibratory hammers for installing monopiles in offshore environments has received significant interest in recent years. The amount of reduction in soil resistance resulting from vibratory driving is a key factor influencing the accuracy of vibro-driveability prediction. This paper presents back-analyses of soil resistance during the vibratory driving of 6.50-meter-diameter monopiles at the Kaskasi Wind Park. An in-house one-dimensional wave equation program was developed and combined with an optimization algorithm to facilitate the derivation of soil resistance reduction factors due to vibratory installation. Driving logs, pile geometries, and CPT profiles were utilized to determine input parameters. An optimization algorithm was used to match the predicted penetration speed with the recorded one in the field to find the soil resistance reduction factors to reduce shaft and toe soil resistance. Subsequently, induced driving stresses predicted by the wave equation analysis were compared with stresses recorded by sensors mounted on the monopile during the installation. The compressional and tensile stresses are key inputs for the estimation of the pile integrity and the driving induced fatigue. A detailed analysis based on signal processing was carried out on the data of the strain sensors, and a clear understanding of induced stresses during the installation was obtained. It was observed that the explicit solvers of wave equation analysis may induce unrealistic noise in the calculated stresses, which leads to an unrealistic high fatigue estimation.

5th International Symposium on Frontiers in Offshore Geotechnics (ISFOG2025)

6 - Pile Installation Challenges and Decommissioning in sands and clays: monopiles, anchor piles, pin piles