Helical Pile Capacity-Torque Correlation: A More Reliable Capacity Torque Factor Based on Full Scale Load Tests-PPT Presentation

PPT Presentation

Pdf Summary

The presentation examines whether helical-pile capacity can be predicted more reliably from installation torque. Researchers analyzed 799 full-scale load tests—440 compression and 359 tension tests—covering round and square shafts, multiple shaft sizes, and single- and multi-helix configurations.<br /><br />The study found that capacity-to-torque relationships vary with axial load direction, shaft geometry and diameter, helix configuration, and installation torque. Measured torque factors for typical shaft sizes were broadly close to industry values, but the traditional factors did not represent performance consistently across torque levels: they tended to be conservative at low torque and less conservative at high torque.<br /><br />Starting with an empirical power relationship between capacity and the diameter-to-torque ratio, the researchers developed a modified formula that applies adjustment factors for different pile configurations and loading conditions. Reliability comparisons across eight shaft, helix, and loading cases generally favored the modified method over the traditional AC358 torque factor, although results varied by case.<br /><br />The authors recommend using the new relationship only for shafts with sizes and product specifications similar to those in the test program. Its capacity criterion is based on net deflection of 10% of the average helix diameter, so it should not be applied when capacity is defined using other criteria. Further research is needed to assess soil type and condition and determine whether a soil-specific adjustment factor is required.

Keywords

helical pile

installation torque

load test

capacity prediction

torque factor

axial load

shaft geometry

helix configuration

empirical formula

reliability analysis