GZA provided geotechnical and environmental services for this design-build project involving the construction of a new building for advanced fabrication and assembly of offshore wind turbine foundation platforms at Berth 6 at the Port of Providence. The building will be used by an offshore wind developer for the assembly and deployment of offshore wind turbine components for one of the large-scale offshore wind farms planned for construction in the mid-2020’s. The original design in the bridging documents included deep pile foundations due to the presence of undocumented fill and soft organic soils within the building footprint. The site is also located next to a former municipal solid waste landfill and methane is present in the soil gas. Methane can accumulate to unsafe levels in open excavations and within enclosed spaces, so mitigation procedures needed to be developed for construction and post-construction conditions.


GZA completed supplemental subsurface investigations and associated geotechnical and environmental testing. GZA developed an alternate foundation design that utilized rigid inclusion ground improvement in lieu of deep foundations which provided a much more cost-effective and efficient foundation system. The foundation and slab design needed to consider the relatively high floor loads due to the offshore wind components, as well as uplift from the relatively tall but lightweight building. GZA also designed and field-tested a sub-slab methane mitigation system that continuously extracts air from below the slab and monitors indoor air for methane. Construction is on-going and GZA is providing construction-phase inspection and environmental health and safety services for the project.


GZA’s local knowledge, geotechnical engineering experience with ground improvement and offshore wind, and environmental experience working with landfill gas were all integral to the successful design and construction of the project when completed in 2022.