Helical Piers, Piles & Anchors

The Round Shaft Helical Pier:  We Recommend Round Shaft In Compression

In applications where Compression is the primary consideration we recommend the Round Shaft Helical Pier – In Compression the round shaft helical has several advantages over the typical square shaft helical anchor.

Round Shaft Advantages:

  • Superior Lateral Stability
  • Greater Section Modulus Strength to resist Twisting and Deflection
  • Greater Load Capacities

The Helical Pier consists of:

  • A round hollow shaft 2 7/8” thru 12 ¾” O.D. typical.
  • Circular tapered plates (helices) are welded to the center of the shaft.
  • Helix diameters can range between 6” – 48” with a thickness of 3/8” – 1”.
  • Helix pitch will range from 3” – 6”.

The Square Shaft Helical Anchor: We Recommend Square Shaft In Tension

In applications where tension is the primary consideration we recommend the Pier Tech Square Shaft Helical Anchor. The Pier Tech Square Shaft Helical Anchor has several advantages over the typical square shaft helical anchor.

Square Shaft Advantages:

  • Greater Yield and Tensile Strength
  • Increased Safety Factor
  • Higher Torque Capacity

The Helical Anchor consists of:

  • A square solid shaft 1 ¼” thru 2” O.D typical.
  • Circular tapered plates (helices) are welded to the center of the shaft.
  • Helix diameters can range between 6” – 48” with a thickness of 3/8” – 1”.
  • Helix pitch will range from 3” – 6”

Helical Foundation Systems – General Information

Design Information

Helical piles are designed such that most of the axial capacity of the pile is generated through bearing of the helix plates against the soil.  The helix plates are typically spaced three diameters apart along the pile shaft to prevent one plate from contributing significant stress to the bearing soil of the adjacent plate.  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 plate 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 plate (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.

Helix Plate Geometry
For tension applications, the uppermost helix plate shall be installed to a depth at least twelve (12) diameters below the ground surface (ICC-ES AC358).  The actual depth will vary depending upon soil conditions and capacity requirements, but should not be less than 12 diameters.
The uppermost helix plate shall be embedded in the ground to a depth of at least five (5) diameters to create a deep foundation bearing condition.
The upper helix plate shall also be located below the depth of seasonal frost penetration and below the “active zone”; i.e., the depth of soil that undergoes seasonal volume changes with changes in moisture content.  The depth of the helix plates should therefore be determined from the greatest of these values.

Helical Foundation Systems – Components

Helix Plates

Standard and V-style cut plates
The initial installation of a helical pile is performed by applying a downward force (crowd) and rotating the pile into the earth via the helix plates.  Once the helix plates penetrate to a depth of about 2 to 3 feet, the piles generally require less crowd and installation is accomplished mostly by the downward force generated from the helix plates, similar to the effect of turning a screw into a block of wood.  Therefore, the helix plate performs a vital role in providing the downward force or thrust needed to advance the pile to the bearing depth.  The helix plate geometry further affects the rate of penetration, soil disturbance and torque to capacity correlation.
The consequences of a poorly-formed helix are twofold; (1) the helix plate severely disturbs the soil with an augering effect which (2) directly results in more movement upon loading than a pile with well-formed helices.  The differences between a well-formed helix and poorly-formed helix are visually obvious and are shown in the figure above.
ICC-ES AC358 establishes design and testing criteria for helical piles evaluated in accordance with the International Building Code.  AC358 further provides criteria for helix plates in order to be considered as a “conforming system”.  Foundation Supportworks helical piles feature plates manufactured with a helix shape conforming to the geometry criteria of ICC-ES AC358. Conversely, blades that are not a helix shape are often formed to a “duckbill” appearance.  These plates create a great deal of soil disturbance, do not conform to the helix geometry requirements of ICC-ES AC358, and their torque to capacity relationships are not well documented.