How is helical pile capacity estimated from installation torque?

Qu = Kt × T, where Qu is ultimate capacity (kN), T is final installation torque (kN·m), and Kt is the empirical torque correlation factor (m⁻¹). Per ICC AC358 and Hoyt & Clemence (1989), Kt = 10 m⁻¹ for a single 3-inch shaft, Kt = 9 m⁻¹ for 3.5-inch shaft, and Kt = 7 m⁻¹ for 4.5-inch shaft. Manufacturer test data should be used when available.

What factor of safety is used for helical pile design?

Allowable capacity = Qu / FS where FS = 2.0 when verified by load test per ASTM D1143, or FS = 3.0 based on torque correlation alone without load testing. ICC AC358 requires the pile to be installed to a minimum torque of 27 kN·m and the last 3 ft of installation must achieve the design torque.

Helical Pile Torque-to-Capacity Ratio

Estimate ultimate capacity of helical screw piles from installation torque using the torque correlation factor Kt per ICC AC358 and Hoyt & Clemence (1989) method.

2D stress state at a point. All stresses in MPa.

σx — Normal Stress X (MPa)

σy — Normal Stress Y (MPa)

τxy — Shear Stress (MPa)

⚙ Mechanical Note: Results are based on standard textbook formulas and ISO/AASHTO references. Always verify critical designs with applicable codes (ISO 898, AASHTO 1993, AISC, Eurocode 3) and a qualified engineer.

How It Works

Estimate ultimate capacity of helical screw piles from installation torque using the torque correlation factor Kt per ICC AC358 and Hoyt & Clemence (1989) method

Each component has a specific meaning:

Installation torque — The installation torque recorded for the patient or scenario being assessed.

Note: Interpret the helical pile torque ratio result against the clinical thresholds and context described above.

How to Use

Enter the installation torque for the patient or scenario you are assessing. Estimate ultimate capacity of helical screw piles from installation torque using the torque correlation factor Kt per ICC AC358 and Hoyt & Clemence (1989) method. Use the helical pile torque ratio result to inform your clinical assessment.

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Frequently Asked Questions

How is helical pile capacity estimated from installation torque?

What factor of safety is used for helical pile design?