A Study of the Augmenting Effect of Equipping Piles with an Expander Body-Paper

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The study reports full-scale static load tests on four pairs of 9.5 m piles installed in silty to dense sand at the B.E.S.T. research site in Bolivia. The pile types were slurry-bored piles, continuous-flight-auger (CFA) piles, full-displacement (FDP) piles, and small-diameter micropiles. One pile in each pair was fitted near its toe with an Expander Body (EB), which was expanded by pressure grouting and followed by grouting beneath the toe.<br /><br />Comparisons of EB-equipped and conventional piles showed that the EB substantially increased stiffness and load resistance. Its effect was attributed not only to the larger toe area, but also to preloading the soil below the toe, improving resistance along the EB, and inducing axial residual force in the pile. At movements of approximately 5–10 mm, the EB-equipped bored pile and micropile were estimated to carry about three times the load of their unaugmented counterparts. The CFA pile carried about twice the load, while the FDP pile showed an approximately 30% improvement. The CFA and FDP piles already had relatively stiff shaft resistance, so the toe enhancement had a smaller relative effect.<br /><br />Some test measurements were incomplete or unreliable, particularly for strain gauges and certain bidirectional-test movements. The authors therefore used measured results and load-transfer simulations to make comparisons.<br /><br />Overall, the study concludes that toe expansion and post-installation grouting can markedly improve pile stiffness and capacity, with the greatest relative benefits observed for bored piles and micropiles. The authors suggest that, under similar ground conditions, this method may allow shorter piles, reduce the number of piles required, and provide useful quality control.

Keywords

pile load test

Expander Body

toe grouting

pile stiffness

load resistance

bored piles

micropiles

continuous-flight-auger piles

full-displacement piles

sand soil