Source: https://guthlabs.ai/docs/instruments/soil-bearing-capacity-terzaghi-simplified/mechanism/

instrument mechanism / verified-clean

# Soil Bearing Capacity — Terzaghi Simplified mechanism

The inspectable method record for Soil Bearing Capacity — Terzaghi Simplified, kept separate from implementation and qualification.

Status: **VERIFIED_CLEAN**Lifecycle: **verified-clean**

## Model scope

The arithmetic and the stated conventional Terzaghi strip-footing equation are valid for a preliminary estimate. Verdict is NEEDS_REVIEW because the specification does not define q versus depth, the Nγ table convention, or whether qallow is gross or net, and it omits the required applicability constraints and correction factors for non-strip or nonideal loading.

- The strip-footing Terzaghi equation is standard only for the stated simplified assumptions: homogeneous soil, vertical centered loading, horizontal ground, a long strip footing, and drained or undrained parameters used consistently.

- The input list gives footing depth but the formula uses surcharge q; q must be explicitly defined as q=γDf, or as effective surcharge when groundwater is present.

- Nc, Nq, and especially Nγ depend on the selected Terzaghi convention and table. Nγ values vary among Terzaghi, Meyerhof, Hansen, and Vesic conventions; the instrument must identify one fixed table convention.

- qallow=qu/FS is ambiguous unless it is explicitly labeled gross allowable pressure. Net allowable pressure would normally use net ultimate capacity and net surcharge, with surcharge added back as appropriate.

- The formula does not include shape, depth, inclination, eccentricity, groundwater, or load-inclination corrections, so it must not be presented as a general shallow-foundation bearing-capacity calculation.

## Units and conventions

- c is effective or total-stress cohesion in kPa, used consistently with φ.

- φ is in degrees and is used to select or interpolate the bearing-capacity-factor table.

- γ is soil unit weight in kN/m³; Df and B are in m, so q=γDf has units kPa.

- qu and qallow are pressures in kPa, numerically equal to kN/m².

- FS is dimensionless and must be greater than zero; the examples interpret qallow as gross allowable pressure.

- The reference factors use the conventional Terzaghi strip-footing table values, with linear interpolation between tabulated φ rows.

## Inspectable vector

One of 4 source-bound review vectors:

````
{
  "inputs": {
    "c_kPa": 25,
    "phi_deg": 0,
    "depth_m": 1.5,
    "B_m": 2,
    "gamma_kN_m3": 18,
    "FS": 3
  },
  "expected_outputs": {
    "qu_kPa": 169.5,
    "qallow_kPa": 56.5
  },
  "reference_data": {
    "phi_deg": 0,
    "Nc": 5.7,
    "Nq": 1,
    "N_gamma": 0,
    "source_convention": "Widely tabulated standard value: conventional Terzaghi strip-footing bearing-capacity-factor table"
  },
  "working": "q=γDf=18×1.5=27 kPa.\nqu=cNc+qNq+0.5γBNγ\n=25×5.7+27×1.0+0.5×18×2×0\n=142.5+27+0\n=169.5 kPa.\nqallow=qu/FS=169.5/3=56.5 kPa.\nThe φ=0 row is used exactly: Nc=5.7, Nq=1.0, Nγ=0.0."
}
````

## Failure boundary

**BREAK_CLAIMED** · SELF_FLAGGED

The allowable-capacity calculation is undefined when FS=0, so the instrument must reject that input. The specification also leaves depth/surcharge sign conventions and factor-table regime handling insufficiently explicit, creating additional hazard potential.

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/soil-bearing-capacity-terzaghi-simplified/>)[03**Implementation**](<https://guthlabs.ai/docs/instruments/soil-bearing-capacity-terzaghi-simplified/implementation/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/soil-bearing-capacity-terzaghi-simplified/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-tranche7/tranche7-results.json`

- `BOUNDARY_HAZARD_CATALOG.json`