API: global slope stability

Compute global, unreinforced slope factor of safety with the Bishop simplified method for static, two-dimensional circular surfaces. Terrain must descend left to right; strata are horizontal and contiguous. Total soil unit weights, base strength parameters, a prescribed piezometric line and vertical strip surcharges define the slice forces.

Endpoint

Use explicit candidate circles or a bounded center/radius grid of at most 1,000 circles. Refine and widen the search and compare slice meshes. Piezometric pressure is water unit weight times head above the slice base; suction is not credited. Ponded surface water and water-filled cracks are rejected. An optional dryCrackDepth introduces an empty vertical entry crack of that depth for every circle. Without it, crestTension sets how tensile base forces near a cohesive crest are handled: "minimum-fs-dry-crack" (default) re-analyses each circle with an empty crack at the depth giving the minimum FS, and "permit" leaves the tension in the solution, as Rocscience Slide2 does by default, with a warning.

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/global-slope \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "method": "bishop-simplified-circular",
  "unitSystem": "si",
  "terrain": [
    {
      "x": -20,
      "elevation": 10
    },
    {
      "x": 0,
      "elevation": 10
    },
    {
      "x": 20,
      "elevation": 0
    },
    {
      "x": 40,
      "elevation": 0
    }
  ],
  "layers": [
    {
      "topElevation": 10,
      "bottomElevation": -30,
      "unitWeight": 20,
      "cohesion": 0,
      "frictionAngleDeg": 25
    }
  ],
  "water": {
    "mode": "dry"
  },
  "surcharges": [],
  "search": {
    "mode": "candidates",
    "circles": [
      {
        "id": "trial-1",
        "centerX": 8,
        "centerElevation": 18,
        "radius": 22
      }
    ]
  },
  "slices": 100
}'

The GET variant returns critical.factorOfSafety,search.coverageComplete 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.

The method satisfies vertical force and overall moment equilibrium, not horizontal force equilibrium. Base normal forces are checked on the continuous slip surface, so the result does not depend on the slice count: tension from pore pressure above the total overburden rejects the circle, and tension from the cohesion intercept is treated as set by crestTension. Warnings for crest tension and m_alpha below 0.2 are appended to limitations. Interslice tension and water in the crack require independent review. No pile contribution, seismic force, noncircular slip or Spencer verification is included. No design acceptance is reported.

Source: USACE EM 1110-2-1902 (2003), Appendix F Eqs F-4/F-5, Appendix C-3, para 2-2.f and Appendix C-10.c (tension cracks). The implemented pore-pressure projection follows F-4 (u times horizontal width), independently checked by vertical and tangential equilibrium.