An evaluation of using piezocone data to identify organic rich soils

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Organic rich soils characteristically have a thermal resistivity that can result in a more expensive subsea cable design or poorer power transmission during the operation of offshore wind farms. Thermal resistivity is sensitive to relatively small changes in loss on ignition (~10%), a parameter commonly used to assess the nature of organic rich soils. It is therefore important to identify their nature and presence spatially to minimise design uncertainty and for mitigating risk of poor cable performance or failure. Industry acknowledged methods and standards for classifying organic rich soils utilise soil logging, which is dependent on the opinion and experience of the practitioner, and geotechnical index testing, which only provide discrete data points and typically do not have a high degree of precision. Literature has shown potential in using derived parameters from piezocone penetration testing (CPTU) to differentiate organic rich soils from mineral soils. This could overcome these limitations of traditional laboratory-based approaches. Furthermore, the availability of CPTU data earlier in the design process than index testing would enable more effective risk management. A dataset has been collated from non-fibrous organic rich soils across several offshore wind farm sites pairing CPTU parameters to loss of ignition. A framework is then suggested on how CPTU parameters could be used to identify organic soils of differing thermal resistivity that could have a notable impact on cable design or performance.

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

2 - Site characterization, in-situ and laboratory testing, measurement