- Geotechnical services for export cable landings, onshore cable routes, and onshore electrical substations associated with 3 offshore wind developments in the Northeast U.S.
- Planning the explorations programs, permitting, subcontractor management, and geotechnical reporting in support of design of horizontal directional drilling, underground duct banks, and substation equipment foundations
- Geotechnical field and lab testing, thermal resistivity sampling, 4-point Wenner field resistivity testing, and environmental characterization of soil and groundwater, including for PFAS
- Unexploded ordinance (UXO) survey and UXO Avoidance Plan
- Construction over landfill and liquefiable soils
Challenge
The projects involved the design of three onshore interconnection substations, three export cable landings, and over 20 miles of underground transmission cable tasked with bringing power generated from three offshore wind farms to land and connecting to the onshore grid. GZA was the geotechnical engineer responsible for collecting subsurface information along the cable routes and at the substations and providing engineering recommendations for the project. Challenges included permitting though local, state, and federal agencies, and working on state and local public roads, private property, railroad rights-of-way, and beaches.
Solution
GZA worked with the project design team to plan and execute the subsurface exploration programs. GZA’s methods balanced the technical needs of the project with the budget and schedule, while minimizing the disturbance to abutting properties and other stakeholders. GZA coordinated all geotechnical laboratory testing, including thermal resistivity of soils for each site that was utilized in the development of ground models by the underground cable designers. GZA also provided recommendations for site development and foundation design for substation equipment. One of the substations is located on a closed landfill with development issued related to future settlement of the landfill material and organic soils below the landfill layer. Furthermore, GZA evaluated the soils below the landfill and organics for liquefaction potential and found that the soils were susceptible to seismic liquefaction. GZA recommended low-capacity piles and provided pile design criteria to address these issues.
Benefit
Resources from multiple GZA offices local to each project site were utilized for each project. That local knowledge, GZA’s geotechnical engineering experience, and extensive work within the offshore wind industry, were all integral to the successful execution of the subsurface exploration programs.