Evaluation of Driven and Helical Pile Options for Solar Power Plant Site Constructed on Poor Near-Surface Soils

Renewable energy, such as solar, is rapidly advancing and developing into a reliable source of energy in modern society. A solid, economic, easy-to-install foundation is a major component of the solar power plant. Several foundation types are utilized in the solar industry such as driven piles, ballast foundations, cast in place piles, or any specialty foundation types. In this case study, W-shaped driven piles and helical piles were evaluated to select the most feasible foundation type for a proposed 100-MW solar power plant located in Calhoun County, Michigan. The subsoil condition of the site encounters some deposits of weak and compressible soils at depths of 5 ft or deeper, which are not generally favorable to cost-effective and commonly used driven piles. As such, additional spatial and vertical delineation of these poor soil deposits was performed to refine the buildable area utilizing geophysical survey technique in combination with soil borings. Based on the geotechnical and geophysical investigation, an extensive pile load test (PLT) program was performed to develop preliminary pile capacities data. Fifteen (15) locations within the proposed photovoltaic (PV) solar array areas were selected to conduct PLTs. At each PLT location, two driven piles (short and long) and one helical pile, with different embedment depths that correspond to the poor/soft soil layer depths, were installed. A total of 30 axial compression, 45 tension, and 45 lateral PLTs were performed. Finally, the PLT results are used to select the most feasible foundation option for the lightly loaded PV panels and racking system with the consideration of the poor soils (peat/marl) extent in the project site.