API: helical pile

Computes helical (screw) pile axial capacity by individual plate bearing and cylindrical shear, taking the lesser as governing, with the AC358 torque correlation. The methods and inputs are explained in Helical piles; the same analysis runs interactively at the helical tool.

Endpoint

The request takes the same soil object as /v1/axial, the shaft geometry, a helices array (1–8 plates, each with depth and diameter), loading mode, factor of safety, product structural limit, explicit cylinder and shaft interface factors, and numerical controls. torque is either a pre-install target or an installed-pile verification and always carries kt, its basis, and a traceable reference. The API never guesses a torque factor from shaft diameter.

Authentication, rate limits, and the error envelope are shared by every endpoint — see the API overview. Requests are unit-agnostic: any self-consistent unit system works, and results come back in the same units. The examples below use SI (m, kN, kPa, kN/m³).

Request fields

This table is generated from the same schema that validates the request, so it cannot drift. Where a field appears once per variant row, it belongs to that variant only.

Response fields

Code examples

A complete, runnable request. Replace YOUR_API_KEY (or set PILECALC_API_KEY in your environment).

curl https://api.pilecalc.com/v1/helical \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "unitSystem": "si",
  "method": "deep-individual-bearing-cylindrical-shear",
  "shaftShape": "round",
  "soil": {
    "layers": [
      {
        "type": "cohesive",
        "top": 0,
        "bottom": 3,
        "gamma": 17.5,
        "cohesion": 40,
        "ka": 0.9
      },
      {
        "type": "cohesionless",
        "top": 3,
        "bottom": 8,
        "gamma": 19,
        "phi": 32
      }
    ],
    "waterTableDepth": 2,
    "waterUnitWeight": 9.81
  },
  "shaftDiameter": 0.089,
  "shaftLength": 6,
  "helices": [
    {
      "depth": 4.5,
      "diameter": 0.2
    },
    {
      "depth": 5.25,
      "diameter": 0.25
    },
    {
      "depth": 6,
      "diameter": 0.3
    }
  ],
  "mode": "compression",
  "fs": 2,
  "structuralAxialCapacity": 800,
  "cylinderEarthPressureCoefficient": 1,
  "shaftInterface": {
    "mode": "included",
    "earthPressureCoefficient": 1,
    "sandInterfaceFrictionRatio": 0.67,
    "clayAdhesionFactor": 0.7
  },
  "torque": {
    "mode": "design-target",
    "kt": 33,
    "basis": "evaluation-report",
    "reference": "Project product evaluation report"
  },
  "segments": 240,
  "convergenceTolerance": 0.03
}'

The GET variant returns ultimate,allowable,requiredTorque as a plain-text CSV line — made for Excel's WEBSERVICE() and Sheets' IMPORTDATA() (see Use PileCalc in Excel). Omit fields to get the full JSON response.

Interpreting results

• governing tells you which mechanism limits the pile — closely spaced helices shear as a cylinder, widely spaced ones bear individually.
• requiredTorque is the torque implied by the declared kt. Treat it as a field criterion only when that factor and the evaluated product/install procedure are supported by the applicable AC358 evaluation report and project specification.
• mode: "tension" flips the cylindrical-shear leading helix to the top — use it for tie-downs and uplift anchors.
• Helix depths must lie on the embedded shaft (depth ≤ shaftLength); rock layers are rejected. The released deep domain also requires top H/D 5.1–134, adjacent spacing 1.55D–4.5D, a round shaft, and sand friction angle within the declared NAVFAC 26°–40° table.