A successful solar project needs the sun, but nearly half of solar installation construction happens underground. This makes what happens under the surface critical to a project’s success. On a job with thousands of foundations, every foot of embedment affects the project cost and schedule. Without investing in proper geotechnical evaluations early in a project, owners could be left with unwanted surprises buried underground that could cost significant time and money.

Finding the most economical foundation design often depends on a project’s geographic location, soil type, local building code requirements, groundwater levels, corrosion potential and topography. While some sites may have clays that can swell or freeze to steel piles and jack them out of the ground, others can have loose granular soils with high ground water tables that need to be considered in the design plans. Cobbles, boulders, cemented soils and shallow bedrock on a site can also significantly affect construction plans. These early refusal conditions may require more expensive and time-consuming alternate foundation types and create the need for a change order or altered construction plans.

Those owners who spend a relatively small amount of money upfront to invest in proper geotechnical evaluation — and gain a more accurate sense of the conditions at a given site — will save money on the back end by reducing the number of project change orders and allowing for more accurate bidding from contractors.

Geotechnical investigations reduce an owner’s risk by getting data upfront to assist in design plans and identify potential performance issues before construction begins. For instance, a better understanding of site conditions can allow designers to divide a project into more efficient zones depending on the specific soil conditions and needs to account for the site variability, rather than adopting a one-size-fits-all foundation approach. Implementing a load testing program to install test piles and vet how foundations will perform in the site conditions allows for an even more accurate picture. 

The ideal investigation program and number of borings varies based on each site location, but owners and a knowledgeable geotechnical engineer can work collaboratively to create a cost-effective exploration plan that utilizes enough borings and test locations to give a better picture of the site without overextending the budget. 

Achieving this balance can be tricky and requires an experienced expert. If plans are too expansive, it can lead to unnecessary spending. However, if projects are bid based on incomplete data, it can give the owner a false sense of security and fail to identify and mitigate potential site risks.

While it’s not realistic to account for every square foot of the conditions underground, geotechnical studies provide owners with a more comprehensive look at the unknowns buried below that allow developers to adopt a proactive stance to project planning and risk management, saving both time and money.


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Josh Bergsten is a geotechnical engineer for Burns & McDonnell with more than 13 years of experience in foundation design, slope stability, retaining wall design, ground improvement, dynamic foundation analysis and construction oversight.