Comparing theoretical predictions and guidelines against pile test data for CFA piles in glauconitic sands in Belgium-Paper

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This study evaluates how well Belgian pile-design guidelines and settlement models predict the axial performance of continuous flight auger (CFA) piles in glauconitic sands. These sands are difficult to design for because glauconite grains can crush during installation and loading, turning coarse, stiff material into finer, weaker, clay-like soil and complicating pile resistance and settlement predictions.<br /><br />The researchers compared Belgian CPT-based capacity calculations, the De Cock load–settlement method, and a nonlinear t–z approach against static load tests on four CFA piles in Belgium. The 0.6 m diameter piles were installed in soil containing glauconitic layers with approximately 30% glauconite. A parametric analysis examined how model factors affected predicted load–settlement curves.<br /><br />The standard Belgian capacity guidelines provided a basis for analysis, but their empirical parameters were developed largely from tests in non-glauconitic sands and are not specifically calibrated for glauconitic soils. Back-calculated shaft-resistance parameters showed reasonable consistency for three longer piles, while the shorter pile required different values.<br /><br />Settlement predictions were sensitive to parameter selection. The De Cock method combined with Belgian capacity estimates matched test behavior at moderate loads for some parameter choices, but tended to misrepresent settlements or capacity at higher loads. The t–z method showed promising agreement: with suitable flexibility and stiffness factors, it closely reproduced the response of one pile and gave reasonable predictions for the others. Lower flexibility values produced predictions that were too stiff.<br /><br />The authors conclude that existing methods can be useful but require glauconite-specific calibration. Because the study includes only four tests, it cannot establish definitive design parameters. Further testing across pile geometries and embedment depths, including separate assessment of shaft and base resistance and characterization of glauconite content, is needed to develop more reliable design guidance.

Keywords

Belgian pile-design guidelines

continuous flight auger piles

glauconitic sands

axial pile performance

CPT-based capacity calculations

De Cock load-settlement method

t-z approach

settlement prediction

static load tests

glauconite-specific calibration