HIGH CAPACITY GROUTED HELICAL PILES-Paper

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The study evaluates a new method for increasing the capacity of helical piles by injecting pressurized grout into the surrounding soil during installation. Grouting may reduce the effects of installation-related soil disturbance while improving shaft resistance, buckling support, and load transfer.<br /><br />Two hollow-shaft, single-helix piles were installed to a depth of 0.8 m in laboratory-prepared loose sand. One was ungrouted; the other had two nozzles above its helix that injected cement grout at an average pressure of 0.41 MPa. After a week of curing, both piles were tested under axial compression. The grouted pile formed a cylindrical grout column approximately 13 cm in diameter and 75 cm long.<br /><br />The grouted pile substantially outperformed the conventional pile. Using the failure criteria considered most suitable by the authors, its ultimate capacity was 55 kN, compared with 10 kN for the ungrouted pile—a 550% increase. Strain measurements showed that the ungrouted pile’s capacity came almost entirely from its helix, with shaft resistance contributing less than 2.5%. In contrast, the grouted pile developed about 42 kN of shaft resistance and 13 kN of bearing resistance at failure. The improved performance was attributed mainly to the larger, stronger grout-ground interface, with additional benefit from improved helix stiffness and soil conditions beneath it.<br /><br />The findings suggest that grouted helical piles could support heavier structural loads, including when slender hollow shafts are used. However, the evidence comes from tests on only two piles in a controlled laboratory setting and loose sand; further testing is needed to establish performance across field conditions and pile configurations.

Keywords

helical piles

pressurized grout

shaft resistance

load transfer

axial compression

loose sand

grout column

ultimate capacity

installation disturbance

buckling support