Static and Dynamic Properties of US Atlantic Outer Continental Shelf Cohesionless Soils for Offshore Wind Farm Design

Abstract

Abstract Soil behavior assessment is an essential part for the design of offshore wind farm foundations, especially for those situated nearshore with layered soil profiles. This paper presents the key results and study findings of an offshore geotechnical site investigation campaign conducted for a large wind farm development project along the US Atlantic Outer Continental Shelf (OCS) offshore New Jersey, specifically focusing on the cohesionless soils encountered at the study site. As indicated by Andersen, et al., (2023), the static, cyclic, and dynamic soil parameters for offshore wind turbine foundation design include static and cyclic shear strength, deformation parameters, initial shear modulus, Gmax, consolidation and deformation characteristics, effective stress (drained) strength parameters, and damping. In this paper, the conventional index and physical properties for the cohesionless soils are discussed together with the stress history (overconsolidation ratio, OCR), deformation (static secant modulus, E50), and permeability characteristics and dynamic initial shear modulus (Gmax)evaluated from the in situ cone penetration tests (CPTs) and onshore laboratory testing. The undrained and drained shear strength parameters (effective peak friction angles, residual friction angles, and dilation angles) and strength anisotropy from direct shear (DS), direct simple shear (DSS), and triaxial tests of the cohesionless soils are addressed.Results of the soil/steel interface residual strength measured from a suite of ring shear tests on reconstituted cohesionless samples using a Bishop apparatus are detailed herein. Additionally, soil erosion function apparatus (EFA) tests were performed on selected cohesionless samples to investigate the threshold seabed stress (τcr) and scour rates for the use of sediment mobility potential assessment. The EFA test results are compared and discussed with empirical shields diagram and correlations.This paper provides a thorough overview of the static and dynamic soil properties of the US Atlantic OCS cohesionless soils for offshore wind farm foundation design. Comparisons of the soil properties with those published for the soils in other regions also are included.