Soil Bearing Capacity — Terzaghi Simplified mechanism

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

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