- Provided geotechnical design recommendations for equipment pad support on shallow foundations
- Excavation during construction identified landfill waste outside the assumed landfill area
- Landfill waste would not provide suitable bearing conditions for the equipment pad, requiring GZA design helical piles to carry loads below the waste
- Designed new capping to seal the waste below the pile penetrations of the existing landfill cap
- Observed and documented pile installation
Borrego Solar Systems, Inc. is a solar development company that specializes in ground-mount solar farm and energy storage projects. The Chelmsford project consisted of the development of a solar farm over an existing landfill for the town of Chelmsford’s “Community Shared Solar Project” making solar energy available to residents unable to construct solar panels on their own property. GZA was contracted to provide geotechnical foundation recommendations for the battery storage and equipment pads, as well as landfill capping recommendations.
Challenge
The proposed equipment and battery storage pad was located adjacent to the landfill cap in an area supposedly outside the landfill area. After the contractor excavated for shallow pad foundations, landfill waste was observed below portions of the proposed pad area. Geotechnical borings then performed at the location of the pad indicated that landfill material extended up to 17 feet below ground surface. Landfill waste would not properly support the pad structures. The loads from the equipment and energy storage modules on the pads required an intermediate/deep foundation system be designed to transfer loads to competent soil below the waste. GZA selected helical pile foundations to support the loads. Once the helical piles were installed, the structural zone directly below the pads needed to be properly sealed and capped over the landfill waste.
Solution
GZA designed a helical pile foundation system to support the equipment and battery storage pads, working closely with the structural engineer. Geotechnical analyses, including the evaluation of pile group effects, were performed by GZA. The pile installation, performed by Conte, was observed by GZA to confirm and document that the installation procedure was in conformance with the contractor’s submittal previously reviewed and approved by GZA. GZA evaluated several capping alternatives and provided landfill capping design and construction sequencing for once the piles were installed.
Benefit
GZA provided services to help our client quickly change from a shallow foundation to a helical pile foundation to support the pad area.