Pile Testing: Investing a Little to Save a Lot
June 26, 2017
Investing in pile testing as part of a commercial or utility-scale solar project diligence phase is one of the smartest spends you can make. In fact, there are few other strategies that provide such an immediate return on the investment of time and money.
A thorough geotechnical assessment with on-site pile testing can reveal important truths about the project site that reduce steel costs, optimize system designs and improve installation times.
Relying on L-Pile or All Pile modeling exclusively without on-site pile testing translates into more conservative designs due to assumptions and higher safety factors. More conservative designs mean greater embedment depths and larger pile profiles.
It is widely recognized that reducing embedment depth requires less steel, but consider how dramatically those raw material savings can accrue. Using a W6x9 foundation, reducing each pile by only 1 ft. saves 9 lbs. of steel per pile, which translates into thousands of pounds of steel across a project site. In addition, pile testing sometimes reveals that a smaller post profile can be utilized, such as a W6x7. This amplifies the savings by reducing the amount of steel across the entire length of pile. For example, if a 14 ft total length W6x9 is reduced to a W6x7, this translates into 28 lbs. of steel savings per post.
Reducing embedment depth also reduces drive times and the potential to encounter obstructions at depth. For example, using on-site pile testing to reduce an embedment depth from 8 ft. to 6 ft. also reduces the drive time of each pile by up to 25%. This directly translates into reduced labor, machinery, and general operations costs. Limiting exposure to refusals also makes the installation budget and schedule more reliable.
To understand the impact load testing has on system size, it’s useful to think of each table as a sail. In layman’s terms, the larger the table, the bigger the sail, and the more the wind wants to grab the sail and pull the structure out of the ground.
Of course, larger tables are more desirable from both a material cost (more modules per support) and installation timelines (fewer posts to drive).
The ability to work with larger tables is made possible by a detailed understanding of the capacity of the soil. For example, if the soil is found to be very dense, it will have the capacity to resist higher loads acting on each foundation. Where modeling might have called for 2×6 tables, results from pile testing might indicate that 2x10s will work on the site.
The resulting savings from a project with optimized structural design compound by reducing total foundations, reducing total tables, and increasing table installation efficiency.
Taken together, the raw material savings and installation efficiencies made possible by the knowledge revealed by on-site pile testing yields lower-cost projects designed to perform optimally over the long-term within their environmental conditions. SunLink’s PowerCare team can help you explore your geotechnical options.