Source: https://guthlabs.ai/docs/instruments/slope-stability-infinite-slope-method/implementation/

instrument implementation / implementation-contract

# Slope Stability — Infinite Slope Method implementation

A source-bound implementation contract for Slope Stability — Infinite Slope Method; deployment and executable qualification remain separate.

Status: **VERIFIED_CLEAN**Lifecycle: **implementation-contract**

## Binding contract

This record describes what an executable surface must bind and validate. It does not claim that a public calculator, package, or production route is deployed.

**Record owner**: Guth Instruments

**Lifecycle**: verified-clean

**Evidence ID**: t5-147

**Effect**: Computation or source lookup only

## Input and validation requirements

The formula is undefined at phi=90° because tan(phi) requires division by cos(phi)=0; an implementation that returns a numeric FS instead of rejecting the input is broken. A second hazard is the undocumented interpretation of signed beta, which can produce a misleading negative factor of safety.

## Required corrections

No binding erratum is attached to this unique-name record. Implementers must still preserve the declared units, domain, and failure behavior.

## Inspectable interface fixture

The sample below is evidence for interface and validation tests, not a production implementation.

````
{
  "inputs": {
    "beta_deg": 45,
    "phi_deg": 45,
    "c_kPa": 10,
    "gamma_kN_per_m3": 18,
    "gamma_w_kN_per_m3": 9.81,
    "z_m": 2,
    "m": 0.5
  },
  "expected_outputs": {
    "FS": 1.28305556
  },
  "working": "Convert angles: beta = 45 degrees, phi = 45 degrees; sin(beta) = 0.70710678, cos(beta) = 0.70710678, cos^2(beta) = 0.5, tan(phi) = 1. Effective unit weight term = gamma - gamma_w*m = 18 - 9.81*0.5 = 13.095 kN/m^3. Numerator = c + (gamma - gamma_w*m)*z*cos^2(beta)*tan(phi) = 10 + 13.095*2*0.5*1 = 23.095 kPa. Denominator = gamma*z*sin(beta)*cos(beta) = 18*2*0.70710678*0.70710678 = 18 kPa. FS = 23.095/18 = 1.28305556."
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/slope-stability-infinite-slope-method/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/slope-stability-infinite-slope-method/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/slope-stability-infinite-slope-method/qualification/>)

## Sources and evidence

These pointers bind the page to evidence. They do not grant authority or collapse verification into deployment.

- `VERIFIED_LEDGER.json`

- `evidence-tranche5/tranche5-results.json`