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.
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.
Public acceptance of offshore wind development projects is critical to successfully advancing and accelerating the US energy transition. A newly developed geo-data engagement platform has been designed to help operators and regulators manage the rapidly growing volumes of complex geo-data needed to plan, design, and construct offshore wind farms; this same platform can also be used to build public consensus for mutually beneficial outcomes of the triple bottom line: people, planet, and profit. The web-based platform was developed through a pilot project to help project owners, operators, their contractors, and regulatory agencies increase collaboration and streamline decision-making. Providing a single source for information, the platform integrates public datasets and historical project data with real-time field data, making it possible to track the ongoing site characterization effort while continually evolving the ground model. The ability to access a singular, authoritative source for project geo-data successfully increased collaboration and efficiency among project owners and their teams. Specifically, it supported and tightened critical project timeline decisions, such as adjusting the survey approach during early acquisition, delivering preliminary access to acquired survey data and geotechnical parameters, and integrating final interpreted geophysical data and geotechnical parameters into a ground model. The platform was also used to support the operator’s Construction and Operations Plan (COP) submission to the Bureau of Ocean Energy Management (BOEM), enabling interactive geo-data engagement with government stakeholders, streamlining review, and encouraging feedback on future assessment approaches. There is significant potential to further improve project outcomes by expanding access to public stakeholder groups. From a public perspective, understanding the proposed outcomes and participating in qualifying discussions can be challenging, as access to information and opportunities to engage with decision-makers is limited. In addition, interdependencies and complex feedback loops influence perspectives that can’t be fully understood without a systems thinking approach. This approach involves introducing innovative technology in a larger interconnected organization to kickstart a pressing social challenge. In this case, unifying all stakeholders—including the public—across a collaborative geo-data engagement platform that provides users access to non-proprietary information from the earliest stages mutually benefits the triple bottom line of people, planet, and profit (Elkington):- Social value (People) – A shared geo-data platform can enable meaningful engagement by balancing effective advocacy and inquiry. Citizen perspective stimulates awareness, acceptance, and alternatives with a shared sense of direction.- Environmental value (Planet) – The geo-data acquired in support of a wind farm can also serve as a range of measures to aid habitat preservation, mitigation, and restoration activities. Digital information-sharing platforms enable citizen science approaches to the targeted protection of marine natural capital.- Economic value (Profit) – Transparent, efficient, and collaborative data sharing via the web-based geo-data platform enables collective decision-making, which expedites project milestones, reduces permitting risk and operational costs, and thus makes energy more affordable to consumers. As the global offshore wind market expands, solutions that support 1) the evolving project and geo-data life cycle, 2) multiple internal and external stakeholders, and 3) engagement towards mutually beneficial outcomes are vital to advancing the energy transition. This is one paper in a collaborative series that demonstrates the value of an integrated geoscience approach considering regulatory requirements and project design essentials.
The cyclic soil behavior of North Sea clays and silica sands have been well-documented (Andersen 2004, 2009, etc), and have been used globally to develop soil models and design foundations for structures subjected to cyclic wave loading. The recent development of offshore wind farms within the Atlantic Offshore Continental Shelf (OCS) in the U.S. have prompted the large-scale design of fixed-bottom foundations of offshore wind structures, which are designed to be highly dynamic. In contrast to North Sea soils, very few data have been published regarding the strength behavior of typical Atlantic OCS soils. This has prompted the need to review industry-accepted soil models and cyclic design procedures based on empirical data and model testing from the North Sea and whether these may be applicable to Atlantic OCS soils. This paper presents cyclic soil data from a series of triaxial and direct simple shear tests on clay, silt, and sand samples from the Atlantic Shores Offshore Wind Lease Area in offshore New Jersey. A comparison of the soil behavior is made to published North Sea soils data and recommendations are provided on soil parameters for application to foundation design procedures for offshore wind structures within the Atlantic OCS.
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