Installation and Efficiency of Common Helical Pile Couplings-Paper

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The study compared the installation efficiency and axial tension performance of three helical-pile couplings: external sleeve, square-on-square, and flange-to-flange. The authors tested 24 piles—12 with 6.625-inch shafts and 12 with 8.625-inch shafts—in sandy soil near Caseyville, Illinois, and clay soil in Centralia, Missouri. At each site, two piles of each size and coupling type were installed and tension-tested. Measurements included rotations per foot, installation torque, applied load, and deflection.<br /><br />Couplings were assessed using torque-to-capacity ratio (Kt) and rotations per foot. Results varied by pile size and soil. Each coupling type performed best in at least one test group, and rankings were inconsistent across sites. Overall, the square-on-square coupling received the best weighted score, followed by flange-to-flange and external sleeve. Most piles met or exceeded the theoretical Kt recommendations cited in the study; one 6-inch square-coupled pile did not.<br /><br />The authors conclude that square-on-square couplings may provide the greatest axial-load efficiency among the designs tested. However, the conclusion is tentative: only two piles represented each configuration at each site, test results showed substantial variability, and the ranking method gave greater weight to Kt than to installation rotations. The flange coupling’s protrusion may also impede pile advancement and increase soil disturbance. Further testing at greater depths and higher torque levels is needed to establish clearer performance differences.

Keywords

helical pile couplings

axial tension performance

installation efficiency

external sleeve coupling

square-on-square coupling

flange-to-flange coupling

torque-to-capacity ratio

sandy soil

clay soil

pile testing