The Use of BDSLT for Design of Large Capacity Cast-In-Place Piles-Paper

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The paper reports a full-scale bi-directional static load test (BDSLT) on a 1.8 m diameter cast-in-place pile for the Garden City Skyway project in St. Catharines, Ontario. The 37 m deep test pile extended approximately 6 m into Queenston shale bedrock and passed through fill, silty clay, and till. The test aimed to measure shaft resistance and end-bearing behavior and validate geotechnical design assumptions.<br /><br />The pile was tested using a sacrificial hydraulic cell under ASTM D8169/D8169M-18’s quick-test procedure. Embedded strain gauges and displacement instruments tracked pile response. Because theoretical assumptions about concrete stiffness could distort load interpretation, the authors derived pile axial stiffness from measured strains, adopting approximately 88 GN.<br /><br />The maximum cell load was about 21,075 kN. At the end of loading, pile-head movement was about 9.2 mm and toe movement about 7.9 mm; residual upward movements after unloading were 6.05 mm at the head and 5.1 mm at the toe. Strain-based analysis indicated substantial resistance along the rock socket, with roughly 16.7 MN mobilized across the two principal socket segments. The authors also constructed an equivalent head-down load–displacement response from the BDSLT data.<br /><br />The study concludes that BDSLT can provide valuable, direct evidence of pile resistance and settlement behavior where conventional testing is impractical because of the very high loads involved. Measured resistance and displacement profiles can inform design, including unit resistance estimates, while accounting for pile-group effects. Load-test verification may also support use of higher resistance factors and associated design savings.

Keywords

bi-directional static load test

cast-in-place pile

shaft resistance

end-bearing behavior

Queenston shale

ASTM D8169

axial stiffness

load-displacement response

pile settlement

geotechnical design