GZA was the geotechnical engineer for the Block Island Wind Farm, which was the first offshore U.S. wind farm. The project consisted of 5 wind turbines located within Rhode Island state waters approximately 3 miles southeast of Block Island, Rhode Island. The wind turbines will be constructed upon a jacket foundation anchored with steel pipe piles. In the Fall of 2008, GZA was contracted by Deepwater Wind to provide geotechnical engineering services for the offshore wind farm.
A geological desktop study was prepared by GZA providing a review of available geological information near the proposed wind farm site, and geotechnical implications on wind turbine foundation design and installation. Based upon existing geological information, preliminary pile capacity estimates were performed to identify the approximate foundation length and depth of the geotechnical explorations.
GZA managed and observed the 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 under the direction of GZA using a vessel mounted drill rig. A total of 8 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 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.