Helical piles: both failure modes, plus the torque check.
Individual-bearing and cylindrical-shear capacity computed and compared, per-helix bearing reported, and the AC358 torque correlation with your product's Kt — the full design loop in one tool.
Helical pile capacity has two mechanisms: individual bearing, where each helix mobilizes bearing independently, and cylindrical shear, where closely spaced helices fail as a soil cylinder between the top and bottom plates plus bearing on the lead helix. Which governs depends on helix spacing and soil — so PileCalc computes both, per Perko (2009) and the Chance Technical Design Manual, and reports the governing value with each helix's contribution visible.
The torque correlation Qult = Kt·T is evaluated with the Kt you supply in your unit system — Kt is product-specific, so PileCalc uses your product's value rather than inferring one from nominal shaft diameter.
Both mechanisms, governing reported
Individual bearing and cylindrical shear computed side by side per Perko and the Chance TDM — the governing mode is shown, not assumed.
Per-helix breakdown
Bearing at each helix plate reported individually, in compression and tension, with shaft friction where it applies.
Explicit torque correlation
Qult = Kt·T with your product's Kt supplied explicitly — no hidden shaft-size lookup.
Layered profiles
Multi-layer clay and sand profiles with the water table handled, the same soil definition as every other PileCalc tool.
Validated against published benchmarks
Every figure below is produced by the engine on the cited published problem — closed-form solutions, design-manual tables, or independent codes — and reproduced by the test suite on every release.
Individual bearing & cylindrical shear (Perko 2009; Chance TDM); ICC-ES AC358 torque
| Quantity | PileCalc | Reference | Agreement |
|---|---|---|---|
| Deep single helix in clay: Q = 9·cu·A (cu 50 kPa, D 0.30 m)Perko (2009) eq. 5.5 / Chance TDM individual bearing | 31.81 kN | 31.81 kN | exact |
| Single helix in sand: Q = σ′v·Nq·A (φ 32°, 5 m deep, D 0.35 m)NAVFAC DM-7.02 Nq (non-displacement) hand calculation | 129.8 kN | 129.8 kN | exact |
| AC358 torque correlation T = Q/Kt (Kt = 33 m⁻¹ ≈ 10 ft⁻¹)ICC-ES AC358 / Hoyt & Clemence (1989) | 0.964 kN·m | 0.964 kN·m | exact |
The numbers, published
PileCalc's engine is checked term-by-term against the reference codes. A representative sample of the benchmarks — every intermediate value is visible in the app so you can reproduce them yourself.
Helical piles: common questions
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