What are the two methods for calculating screw pile capacity?

(1) Individual Bearing Method: each helix is treated as a deep foundation, Qu = Σ(Ahelix × (cNc + q'Nq)) summed over all helices, where Nc and Nq are bearing capacity factors for deep foundations. (2) Cylindrical Shear Method (for S/D ≤ 3 closely spaced helices): treats the soil cylinder between uppermost and lowest helix as a block: Qu = π × D_cyl × L_cyl × Su + A_bottom × (cNc + qNq). Per Merifield (2011) and CFEM 4th edition.

When does the cylindrical shear method apply?

The cylindrical shear method applies when helix spacing S ≤ 3D (D = helix diameter) — helices are 'closely spaced' and act collectively. When S > 3D, the individual bearing method governs. The individual bearing method is generally more conservative for tension loading; the cylindrical shear can be critical in compression for multi-helix piles in soft clay. Both methods should be calculated and the lower capacity used per CFEM (2006).

Screw Pile Bearing Capacity Calculator

Calculate the bearing capacity of screw (helical) piles from individual helix bearing and cylindrical shear methods using soil strength parameters and helix geometry.

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

Calculate the bearing capacity of screw (helical) piles from individual helix bearing and cylindrical shear methods using soil strength parameters and helix geometry

Each component has a specific meaning:

Individual helix bearing — The individual helix bearing recorded for the patient or scenario being assessed.
Cylindrical shear methods — The cylindrical shear methods recorded for the patient or scenario being assessed.

Note: Interpret the screw pile bearing result against the clinical thresholds and context described above.

How to Use

Enter the individual helix bearing, cylindrical shear methods for the patient or scenario you are assessing. Calculate the bearing capacity of screw (helical) piles from individual helix bearing and cylindrical shear methods using soil strength parameters and helix geometry. Use the screw pile bearing result to inform your clinical assessment.

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Frequently Asked Questions

What are the two methods for calculating screw pile capacity?

When does the cylindrical shear method apply?