Case Study of Small-Diameter Continuous Flight Auger Piles Tested By Bidirectional Static Load Tests in Tropical Soil-Paper

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The study examines five 0.50 m-diameter continuous flight auger piles tested using bidirectional static load tests in lateritic tropical soil in Brasília, Brazil. The piles were 14–19 m long, with expanding-cell assemblies installed 2–4 m above their tips. The soil profile was mainly clay, becoming denser with depth; gravel appeared below about 11 m, and groundwater was encountered at 11.5 m.<br /><br />The tests separated shaft and base resistance and measured their load–displacement behavior. Most pile segments reached displacements equivalent to 10% of the pile diameter, allowing capacity to be assessed directly. For segments that did not, four extrapolation methods were applied. An abrupt displacement increase followed by recovery of stiffness in one test may indicate loose material along the shaft rather than immediate pile failure.<br /><br />Using the 10%-of-diameter criterion, measured total capacities ranged from 1,940 to 2,770 kN. The Brazilian standard’s failure criterion generally produced lower values, consistent with failure occurring at relatively small displacements. Comparisons with nine SPT-based semi-empirical methods found that Teixeira, Lobo, and Décourt–Quaresma generally agreed best with measured capacities. Aoki–Velloso, Meyerhof, Milititsky–Alves, and Robert tended to underestimate capacity, while Karez–Rocha and Shioi–Fukui often overestimated it.<br /><br />The authors conclude that bidirectional testing can effectively characterize small-diameter piles in lateritic soils, but load–displacement anomalies and the suitability of capacity-estimation methods require careful interpretation and regional calibration.

Keywords

bidirectional static load test

continuous flight auger piles

lateritic tropical soil

Brazilian standard

shaft resistance

base resistance

load-displacement behavior

SPT-based methods

pile capacity

Brasília Brazil