Geotechnical Characterization of the US Atlantic Outer Continental Shelf Fine-Grained Cohesive Sediments

Abstract

An offshore geotechnical site investigation campaign was completed for a large wind farm development project along the US Atlantic Outer Continental Shelf (OCS) offshore New Jersey, a frontier location with few published data on soil characterization. Field exploration and a comprehensive onshore geotechnical laboratory testing program have been performed to understand the site-specific soil behavior. This paper describes the geotechnical properties of the fine-grained cohesive sediments encountered at the study site interpreted based on a consistent framework leveraging the sitewide soil data. Discussions of sample quality, soil stress history, soil compressibility and permeability, peak and critical state shear strength, strength anisotropy, and shearing rate effect for the Atlantic OCS fine-grained cohesive soils are presented from oedometer consolidation, permeability, direct simple shear, ring shear, and K0-consolidated triaxial compression and extension tests along with other conventional index and property tests. Furthermore, the Stress History and Normalized Soil Engineering Properties (SHANSEP) parameters, namely S and m, for the cohesive soils, are developed based on the specific monotonic constant volume direct simple shear (CVDSS) tests. The undrained shear strength Su profiles within the specific geotechnical cohesive soil unit developed from the SHANSEP and SP-SPW methods (Quiros, 2000) is compared to the site-specific PCPT data and laboratory undrained shear strength measurements. Comparisons of the discussed engineering properties of the Atlantic OCS fine-grained soils with other published databases for soils of the Gulf of Mexico (GOM), Offshore Trinidad, and Offshore Mozambique also are included. This paper is in a collaborative series that demonstrates the value of an integrated geoscience approach considering regulatory requirements and project design essentials. It provides a comprehensive overview of the engineering characteristics of the Atlantic OCS fine-grained soils and can assist engineers with the assignation of rate-dependant undrained shear strength parameters developed specifically for wind farm foundation design with applicability in a regional setting.