Helical Pile Acceptance Torque for a Target Capacity
The installation torque a helical pile must reach to confirm a target capacity.
Example
You enter
- Shaft type 1.5_inch_solid
- Target capacity (lb) 25000
- Capacity basis allowable
- Factor of safety 2
You get
- Required installation torque 5000
Checked against published worked examples from: Supportworks, Inc.
Details, formula, and sources
Scopetorque = (allowable x factor_of_safety) / Kt = ultimate / Kt. A 22,500 lb allowable at FS 2 on a 1.5 in solid shaft (Kt 10) needs 4,500 ft-lb; a lower-Kt 3.5 in pipe (Kt 7) needs about 6,430 ft-lb for the same capacity. This is the field-acceptance torque the crew watches on the drive-head gauge. An installation check, not a load test; the engineer of record governs.
Formula or tableInstallation torque = ultimate / Kt = (allowable × factor_of_safety) / Kt (lb-ft). Kt by shaft type (ICC-ES AC358 defaults): 1.5 in solid 10, 1.75 in solid 10, 2.875 in pipe 9, 3.5 in pipe 7.
Source and editionICC-ES Acceptance Criteria AC358 (helical foundation systems) by name; manufacturer technical bulletins (CHANCE, Magnum, Ram Jack, AB Chance) by name.
Free accessICC-ES AC358 free at icc-es.org. Manufacturer Kt values free in each manufacturer's published evaluation report.
What governsEstimate. Engineer of record governs the design and acceptance. Verify against the project structural drawings and the manufacturer's published capacity / chart.
API field namesshaft, target_capacity_lb, capacity_basis, factor_of_safety, torque_ft_lb
- Kt table data/construction/helical-pile-kt.json keyed to shaft typemanufacturer technical bulletins
- Acceptance check only the torque correlation is an installation acceptance check, not a substitute for a load testICC-ES AC358
- Default factor of safety 2.0 unless user supplies (engineering-practice default for axial helical piers)ICC-ES AC358 typical