Support of Structures in Expansive Shale Using Recycled Plastic Piles-Article

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The study evaluates recycled plastic piles as an economical foundation option for lightly loaded buildings on expansive shale. Swelling soils can lift foundations and damage structures; conventional mitigation, including soil replacement and drilled shafts, can be costly. The researchers hypothesized that plastic piles’ relatively smooth, low-friction surfaces would reduce the uplift transferred from soil to a structure.<br /><br />Six fiberglass-reinforced plastic piles were installed at a South Dakota test site with highly expansive Belle Fourche shale. Two piles underwent compression load tests, while four piles and a concrete anchor were monitored for vertical movement over one year. The team also developed a nonlinear soil–foundation model using field and laboratory data to compare plastic piles with drilled shafts.<br /><br />Load tests indicated that the piles could support typical residential design loads of 25–35 kips with about 0.25 inches of settlement. The tests also showed that removing loose material beneath the pile and applying a seating load during installation are important for reliable performance. Long-term monitoring and a site-flooding test recorded little apparent movement, although the survey equipment was not sensitive enough to measure the small displacements predicted by the model.<br /><br />Modeling suggested that drilled shafts could develop damaging tensile stresses under swelling forces, whereas stresses in plastic piles remained compressive. Both foundation types were predicted to experience upward movement under some conditions. A cost comparison estimated that plastic piles could reduce costs by 10–20% relative to conventional approaches.<br /><br />The findings support recycled plastic piles as a promising alternative for lightly loaded structures, but the authors emphasize that further research is needed to confirm performance and refine design methods.

Keywords

recycled plastic piles

expansive shale

foundation uplift

swelling soils

lightly loaded buildings

fiberglass-reinforced plastic

load testing

nonlinear soil-foundation model

drilled shafts

foundation cost reduction