Abstract:
In practice, the torque exerted on the shaft of a helical pile throughout its installation is measured to determine a stopping point for the installation of the element. This is based on the required load resistance by the anticipated structure, and the shaft-specific torque correlation factor for the shaft being installed. The underlying principle that is established by this methodology is bearing capacity. Helical piles are used to provide a sufficiently dispersed area via the helical flights into the soils below as to not overcome the soils bearing capacity. In a sense, the soils bearing capacity with depth is measured by the installation of a helical anchor through it—the measured torque, however, will be based on the total surface area of the flights on the lead section (due to drag on the soils). A less-flighted lead section will likely have more penetration ability, and therefore less torque observed in the same soils as a more-flighted lead.
The intent of my presentation will be to install a number of helical anchors having a different lead flight configurations (with 3- to 4-helical flights each) to establish the predictive behavior of the torque vs. depth between multiple elements in the same soil profile, and present the general steps to creating this model within HeliCAP. With an installed element we should be able to use the installation torque data from one element to accurately model the shear strength parameters of a soil profile, and roughly predict and anticipate the torque with depth data for another element having a different lead section configuration.