On many construction projects, soil borings are not completed due to the property owner wanting to reduce costs or, quite simply, being unaware of the need to obtain soil strength data for foundation design. During the installation of CHANCE® Helical piles, monitoring torque can provide real time data defining underlying soil strength and its load capacity. As a helical pile is installed (screwed) into increasingly denser/harder soil, the resistance to installation (called installation energy or torque) will increase. The higher the torque, the higher the axial capacity. In most projects, the installation torque increases with depth, and the capacity of CHANCE helical piles can be determined at the time of installation. Regardless of whether the pile is being installed in clay or sand soil, the torque to correlation factor (Kt) for each shaft size, is multiplied by the effective installation torque (T), resulting in the ultimate capacity for each pile. The standard equation for ultimate capacity is Kt * T. The torque correlation factors for CHANCE helical piles can be found in the CHANCE Technical Design Manual-4th Edition. The effective torque is the average torque taken over the last 3 feet of installed depth, measured in 1 foot increments.
Helical piles are an established solution for foundation underpinning, but their applications are as far-reaching as the creativity of an engineer. Helical piles are typically associated with gravity load - force pushing down on the pile. In the project below, helical piles are utilized to support lateral loads, including wind and seismic loads.