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How is the Soil Bearing Capacity Determined for Helical Pier Installation?

To ensure long-term structural stability, we determine soil bearing capacity through a combination of upfront geotechnical investigations and real-time field verification during installation.

Geotechnical Investigation

Before installation begins, we recommend a site-specific geotechnical report to map the soil profile. This process typically includes:

  • Standard Penetration Tests (SPT): These assess soil density and relative strength at regular intervals.
  • Soil Sampling: Disturbed and undisturbed samples are collected to evaluate cohesive strength in clays or friction angles in granular soils like sand and gravel.
  • Strata Identification: Identifying the depth of competent bearing strata and groundwater levels ensures the piers are sized to bypass weak surface soils.

Field Verification: The Torque Factor Method

During installation, we use the Torque Factor Method (Qult = Kt × T) to correlate installation torque with ultimate capacity. Because rotational resistance reflects the soil’s shear strength, the torque required to advance the pier serves as a real-time indicator of the ground’s bearing capacity. We utilize torque factors (Kt) derived from industry standards such as ICC-ES AC358 and ADSC guidelines, which vary by soil type:

  • Soft Clay: Typical Kt range of 3–5 ft⁻¹
  • Loose Sand: Typical Kt range of 6–10 ft⁻¹
  • Gravel: Typical Kt range of 10–15 ft⁻¹

Verification and Compliance

To maintain our commitment to Engineering Excellence and Design Support, we utilize proprietary design software to model these parameters. For critical applications, we may also perform Static Load Tests or Proof Testing to validate that the torque-capacity correlation matches actual performance.

Note: You must consult a structural engineer or our manufacturer’s engineering team for project-specific guidance. All installations must comply with applicable building codes and ICC-ES acceptance criteria.

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