Commercial Helical Piles Near Ruston, Shreveport, Monroe
Micropile, Screw Piles, and Helical Piers
Helical piles are a factory-manufactured steel foundation system consisting of a central shaft with one or more helix-shaped bearing plates, commonly referred to as blades or flights, welded to the lead section. Extension shafts, with or without additional helix blades, are used to extend the pile to competent load-bearing soils and to achieve design depth and capacity. Brackets are used at the tops of the piles for attachment to structures, either for new construction or retrofit applications. Helical piles are advanced (screwed) into the ground with the application of torque.
The terms helical piles, screw piles, helical piers, helical anchors, helix piers, and helix anchors are often used interchangeably by specifiers. However, the term ‘pier’ more often refers to a helical pile loaded in axial compression, while the term ‘anchor’ more often refers to a helical pile loaded in axial tension.
Helical piles are designed such that most of the axial capacity of the pile is generated through bearing of the helix blades against the soil. The helix blades are typically spaced three diameters apart along the pile shaft to prevent one blade from contributing significant stress to the bearing soil of the adjacent blade. Significant stress influence is limited to a ‘bulb’ of soil within about two helix diameters from the bearing surface in the axial direction and one helix diameter from the center of the pile shaft in the lateral direction. Each helix blade therefore acts independently in bearing along the pile shaft.
Multiple piles shall have a center to center spacing at the helix depth of at least four (4) times the diameter of the largest helix blade (ICC-ES AC358). The tops of the piles may be closer at the ground surface but installed at a batter away from each other in order to meet the spacing criteria at the helix depth. For tension applications, the uppermost helix blade shall be installed to a depth of at least twelve (12) diameters below the ground surface (ICC-ES AC358).
Determination of Capacity
Like other deep foundation alternatives, there are many factors to be considered in designing a helical pile foundation. Supportworks recommends that helical pile design be completed by an experienced geotechnical engineer or other qualified professional.