- 26 acres of ground-mount solar constructed in 2021
- GZA’s geotechnical report, completed in December 2019, included 2 days of test pit explorations
- Test pit excavations (versus borings) allow full observation of soil types, layering and potential for obstructions, such as boulders and/or bedrock
- No tree cutting was allowed for GZA’s exploration program
- A mini-excavator was required to facilitate access through mature trees
Challenge
Preferred foundation systems for ground-mount solar projects are short driven or screw piles able to resist high lateral loads. The piles are typically designed by a design-build contractor based on geotechnical studies and multiple site-specific load tests. For bidding projects, designers need to know the soil type and potential for shallow obstructions, such as boulders and bedrock. ECA Solar and GZA needed a cost-effective approach gain site access and to characterize the site for pile foundations by addressing these design priorities.
Solution
GZA’s preferred approach to field subsurface investigation for ground-mount solar projects uses test pits that allow boulder counts, and observation of ease of excavation, soil types and layering. Many more test pits can be performed in a single day, compared to borings. Test pits also allow for collection of bulk samples for laboratory thermal resistivity and corrosivity testing.
Benefit
GZA completed its subsurface exploration program solely using test pits. Along with GZA’s geotechnical report, subsequent loads tests at the site helped the design-build pile contractor design a cost-efficient pile system for the project. GZA was a trusted partner on ECA Solar’s team that brought this project through to completion in 2021.