• Comprehensive geotechnical and geophysical investigations for evaluating re-burial options for 34.5kV submarine transmission cables.
• Land-based and submarine geophysical survey utilizing an unmanned submarine rover, to assess sea bed and subsurface conditions, and identify cable alignment, and burial depths.
• Geotechnical test borings on the beach, in the surf zone, near shore, and off shore.
• Evaluated seasonal and long-term sediment transport, soil conditions, and submarine anomalies to assist with potential remedial alternatives analysis.
The 30 MW offshore Block Island Wind Farm consists of 5 wind turbines located approximately 3 miles southeast of Block Island, Rhode Island. Energy generated by the turbines is transmitted to a substation on Block Island via the Block Island Wind Farm (BIWF) 34.5 kV submarine cable. The 21.7-mile, 34.5 kV submarine, cable conducts energy to and from the eastern shore of Block Island, Rhode Island to Narragansett, Rhode Island.
Challenge
Since the initial burial of the cables in 2016, sediment transport caused the beach grading and seafloor bathymetry to change leading to a reduced cover depth over the cables.
Solution
GZA led the on-land and marine geophysical and geotechnical explorations using local on-island and international resources. The work entailed characterization of the subsurface conditions, cable locations and burial depths, and sea floor anomalies and obstructions in order to assess potential remedial alternatives. The work was completed during the winter months to achieve a compressed time schedule and coordinating around tide, wind, wave, and daylight constraints. Utmost attention was paid to the protection of natural resources, health and safety, and coordination with the public.
Benefit
The cables have regained cover depth, protecting them and preserving natural resources.