Performance of Square Shaft Helical Pier Foundations in Swelling Soils

The use of square shaft helical pier foundations in swelling soils is a standard of practice in Colorado. Since 1986 it is estimated approximately 130,000 square shaft helical piers of the type described herein have been installed for both remedial repair and foundations for new construction in swelling soils, including the highly expansive steeply dipping bedrock areas of the Front Range. There are no documented failures or adverse performance of correctly specified and installed square shaft helical piers. The underlying principles for this performance are: 1) Installing square shaft helical piers to a minimum of 4,000 ft-lbs (5.4 kN-m) of installation torque, or refusal, ensures that the helical bearing plate (helix) is embedded below the active zone (depth of seasonal moisture change), 2) The use of only a single helix lead section ensures that no helical bearing plates embed within the active zone, 3) The small surface area of the square shaft reduces uplift forces on the pier to levels that eliminate heave, even where there is no dead load, 4) The smooth steel shaft surface may reduce uplift forces on the pier, 5) The square shaft shape may reduce uplift forces on the pier, 6) Water does not migrate along the sides of the shaft down to the soil in which the helix is embedded, 7) Specifying IBC and ISO 9001 listed square shaft helical piers ensures the correct material is furnished and installed for swelling soil conditions and 8) The use of trained and experienced installing contractors ensures that square shaft helical piers are correctly installed in swelling soils.