Working with Solar Pile International (SPI), the first key step is to determine which of their pile types will suit the project best. In the case of the Wapello Solar Farm, a vast number of pile locations featured extremely weak soils, representing complicated and expensive problems for traditional piling solutions.

SPI’s Solar X Wing Pile (SXWP) is an innovative approach to a standard product in the driven steel beam. The company’s proprietary cupping plate and bracing wing design allowed our engineers to achieve the required design load requirements for over 10,000 extremely weak soil locations, while maintaining a relatively short pile length.

This design resulted in a significant cost saving for the client and won SPI the contract to supply the project.

The bracing wings create a dramatic increase to the piles lateral load capacity by increasing the north-south face of the pile. In traditional foundation design, piles are typically designed to be deeper to achieve additional lateral loads, with the SXWP, the pile can maintain a shorter length and therefore a ligher, more affordable solution.

On a solar farm, the arrays of solar modules can create extreme uplift forces, especially during high wind events. The cupping plates of the SXWP trap and strengthen the soil surrounding the pile during installation, providing an anchor-like resistance to uplift forces. The combination of the cupping plates and bracing wings resulted in a remarkable solution for the weak soil locations on this project.

The soil at the Wapello Solar Farm ranged from soft to medium stiff low plasticity clay(0 to 3 feet below ground surface) to medium dense granular soils (18 to 20 feet).

The typical solution for this type of situation is a W-series section deep enough to where the piles are founded within decent material to generate enough skin friction and lateral resistance. Pier and Pile Consulting Engineers proposed to use SPI’s patented SXWP to provide a more affordable alternative, while reducing installation risk.

The pile required only a single cupping plate on each side of the web to meet the required uplift resistance, while the lateral bracing wings were designed to a length of 1600mm to provide the necessary support elsewhere. 

The final, certified design was manufactured and delivered to the project throughout July and August, 2020. SPI were extremely happy with the work completed by Pier and Pile Consulting Engineers on this project, bringing a concept to life and solving a complicated problem directly with their team and their client.

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