FULL SCALE UPLIFT LOAD TESTING OF MICROPILES IN COHESSIONLESS SOIL-Paper

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The study investigates how the drill-bit-to-hollow-bar diameter ratio (Db/Dh) affects the uplift capacity of hollow-bar micropiles in sand. Two full-scale micropiles were installed in medium-dense to dense sand in Ayr, Ontario. Both were 6 m long, with 5.75 m embedded; their diameter ratios were 2.25 and 3. Grout was injected under pressure, and the piles were tested in tension using a quick-load procedure.<br /><br />The pile with a ratio of 3 had a stiffer load–displacement response and greater uplift capacity. Its observed failure load was approximately 638 kN, compared with 510 kN for the pile with a ratio of 2.25—an increase of about 19.5%. Fuller and Hoy’s interpretation method closely matched observed failure loads, while Davisson’s method gave more conservative estimates. Exhumed pile diameters exceeded the drill-bit diameters, and calculated bond strengths for both piles fell within the FHWA range for Type B micropiles in sand.<br /><br />The findings suggest that increasing the diameter ratio can improve uplift performance in sand. However, the study tested only two piles in one soil profile; further testing is needed to confirm the effect in other soils and conditions.

Keywords

micropile uplift capacity

drill-bit-to-hollow-bar diameter ratio

Db/Dh ratio

sand

full-scale testing

tension load test

grouted micropiles

load-displacement response

bond strength

Ayr Ontario