In 2008, Deepwater Wind entered into an agreement with the State of Rhode Island to develop the first US offshore wind farm. The project consisted of 5 wind turbines located within Rhode Island state waters approximately 3 miles southeast of Block Island, Rhode Island. At this time, Europe had developed many offshore wind farms, predominantly using monopile foundations, which were not manufactured in the US. Given the failure of previous US offshore wind projects, European firms were waiting to see how and if the US offshore wind industry would develop before becoming engaged.
In 2008, GZA was contracted by Deepwater Wind to provide geotechnical engineering services for the offshore wind farm. The wind turbines were designed with a jacket foundation anchored with steel pipe piles. GZA prepared a geological desktop study and preliminary pile capacity estimates to estimate approximate foundation length and design the depth of the geotechnical explorations.
GZA managed and observed geophysical surveys conducted by Ocean Surveys Inc. (OSI) of Old Saybrook, CT. The geophysical survey consisted of a hydrographic survey, shallow subbottom profile survey, deep subbottom profile survey, side scan sonar survey, and a marine magnetic survey. A turbine layout plan was generated by Deepwater Wind based upon the results of the geophysical survey and recommendations by OSI and GZA.
GZA developed and implemented an offshore geotechnical investigation consisting of 8 borings. Geotechnical explorations were conducted from a lift boat in approximately 75 to 100 feet of water. Borings were drilled by DOSECC Exploration Services LLC using a vessel mounted drill rig, under the direction of GZA. A total of eight geotechnical borings were completed, each to a depth of 225 feet below the seafloor. In addition to coring and sampling, a downhole cone penetrometer (CPT) was pushed at discrete intervals and electronic logging was performed in the borehole to determine in situ properties of the soils.
Off-shore laboratory testing for index and strength properties were performed. On-shore laboratory testing was completed in GZA’s geotechnical laboratory in Hopkinton, Massachusetts consisting of index testing, triaxial strength testing, and consolidation testing.
A geotechnical evaluation and engineering report with interpreted soil profiles was completed. The report included recommended soil parameter values for each turbine location, pile capacity, pile axial and lateral deformation curves, and analysis of pile drivability and constructability issues.
Construction of the project started in 2015 and was completed in 2016. GZA supported the project during construction by providing geotechnical design of the port facility in Providence, Rhode Island which was used for staging and assembly of the wind turbine components. This included evaluation of the stability of the existing seawall, geotechnical investigation of the port facility, bearing capacity evaluation of the staging area, and design of temporary foundations for assembly and staging structures for the tower segments.
The success of the Block Island Wind Farm paved the way for additional development of offshore wind along the US Northeast and Mid-Atlantic coast. Projects are being pursued by global developers, engineering firms, manufacturing, and contractors.