Helical Pile Acceptance Torque for a Target Capacity
The inverse of the helical-pile tile: the installation torque a pile must reach to confirm a target capacity, torque = (allowable × 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 5) needs 9,000 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 and source
Installation torque = ultimate / Kt = (allowable × factor_of_safety) / Kt (lb-ft). Kt by shaft type: 1.5 in solid 10, 1.75 in solid 9, 2.875 in pipe 7, 3.5 in pipe 5.
ICC-ES Acceptance Criteria AC358 (helical foundation systems) by name; manufacturer technical bulletins (CHANCE, Magnum, Ram Jack, AB Chance) by name.
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