API: drilled shaft

Computes the axial capacity of a drilled shaft (bored pile / caisson) with the FHWA method of O'Neill & Reese (FHWA-IF-99-025, 1999): α-method side resistance in clay, β-method (SPT-based) in sand, rock-socket resistance in rock, base bearing, belled-base uplift, and optional service-load settlement. The method and every input are explained in Drilled shafts; the same analysis runs interactively at the drilled-shaft tool.

Endpoint

The request mirrors the axial endpoint — a pile and a layered soil profile — and requires an explicitmethod, constructionMethod, and analysisMode. The released slice is fhwa-if-99-025 for a dry-stable-open-hole shaft. Cohesionless layers require sptN (the SPT blow count that drives the β correlation), not phi. Cohesive layers need cohesion (or qu); rock needs qu. Add bellDiameter and bellHeight together for a belled base. Rock layers require an explicit rockJointCondition; jointed layers also requirerqd from 20 through 100, and jointed rock at the base is rejected. Service mode also requires an explicit service load and numerical controls.

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/drilled-shaft \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "unitSystem": "si",
  "method": "fhwa-if-99-025",
  "constructionMethod": "dry-stable-open-hole",
  "analysisMode": "capacity-and-service",
  "pile": {
    "kind": "uniform",
    "length": 22,
    "diameter": 0.9,
    "elasticModulus": 28000000,
    "unitWeight": 24
  },
  "soil": {
    "layers": [
      {
        "type": "cohesive",
        "top": 0,
        "bottom": 8,
        "gamma": 18,
        "cohesion": 60
      },
      {
        "type": "cohesionless",
        "top": 8,
        "bottom": 16,
        "gamma": 19.5,
        "sptN": 28
      },
      {
        "type": "cohesive",
        "top": 16,
        "bottom": 24,
        "gamma": 19,
        "cohesion": 120
      }
    ],
    "waterTableDepth": 4,
    "waterUnitWeight": 9.81
  },
  "serviceLoad": 1000,
  "segments": 240,
  "loadSettlementPoints": 160,
  "maxTipSettlement": 0.12,
  "bellDiameter": 1.8,
  "bellHeight": 0.45,
  "fsTip": 2.5,
  "fsSide": 2,
  "fsWeight": 1.5,
  "fsUplift": 2.5,
  "convergenceTolerance": 0.05
}'

The GET variant returns allowableDown,allowableUplift,service.settlement 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

• allowableDown applies fsTip and fsSide separately (side resistance mobilizes at much smaller displacement than base bearing).
• With a bell, tip and tipPressure are computed on the bell base area, and bellUplift adds the inverted-bearing uplift contribution.
• The FHWA five-foot top exclusion is applied only for surface clay; the bottom one-diameter (plus bell-height) exclusion is applied only for cohesive base soil.
• service is a t-z/q-z load-transfer result at serviceLoad, not an ultimate-capacity settlement estimate. Rock-socket service response remains disabled until a named public rock load-transfer method is implemented.
• The bearing stratum is the layer immediately below a tip interface. The response records that convention and the fine/coarse convergence check. Jointed-rock side resistance uses the declared Table 11.4 column, but jointed-rock base resistance fails closed.