CPT-Based Geotechnical Characterization of Foundation Zone Sediments at Atlantic Shores Offshore Wind Farm Development

Abstract

This study presents site-specific CPT-based correlation relationships for preconsolidation pressure, undrained shear strength, relative density and effective friction angle, developed for geotechnical characterization of foundation zone sediments at the Atlantic Shores offshore wind farm development. Results of laboratory geotechnical tests on samples from 49 soil borings performed at the Lease Area were correlated with corresponding measured cone resistance values from companion seabed or downhole CPTs. Ranges of overconsolidation ratios estimated using CPT-derived preconsolidation pressures from site-specific correlation relationships are in good agreement with overconsolidation ratios derived from laboratory measured preconsolidation pressures for various cohesive soil units. Interpreted ranges of cone resistance factors (i.e., Nkt) required in CPT-based undrained shear strength evaluation for cohesive soil units are significantly wider compared to the typical range of 15 to 20 representative for Gulf of Mexico clay sediments, as a result of large variability in soil plasticity as well as intermixed nature of the soils. Representative ranges of relative density and effective friction angle obtained from CPT data using site-specific correlation relationships, developed for the cohesionless soils at the Lease Area, are consistent with ranges of laboratory measured values.