Source: https://guthlabs.ai/docs/instruments/pavement-thickness-simplified-aashto-cbr-method/implementation/

instrument implementation / implementation-contract

# Pavement Thickness — Simplified (AASHTO/CBR Method) implementation

A source-bound implementation contract for Pavement Thickness — Simplified (AASHTO/CBR 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**: t7-121

**Effect**: Computation or source lookup only

## Input and validation requirements

The specification has multiple failure points: CBR = 0 produces an undefined division, the required fit constant A and logarithm base are unspecified, and no selector or applicability rule distinguishes the CBR thickness formula from the AASHTO structural-number branch.

## 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": {
    "method": "CBR_empirical_fit",
    "CBR": 5,
    "design_ESALs": 1000000,
    "A": 100,
    "A_units": "mm",
    "log_base": 10
  },
  "expected_outputs": {
    "estimated_pavement_thickness_mm": 268.328157
  },
  "reference_data": {
    "calibration_row": {
      "A": 100,
      "units": "mm per [log10(ESAL)/sqrt(CBR)]",
      "source_convention": "Illustrative user-specified calibration; no universal AASHTO table value"
    },
    "logarithm": {
      "base": 10,
      "source_convention": "Widely tabulated standard mathematical convention for common-log pavement curve fits"
    }
  },
  "working": "t = A·log10(ESAL)/sqrt(CBR)\nlog10(1,000,000) = 6\nsqrt(5) = 2.2360679775\nA·log10(ESAL) = 100·6 = 600 mm\n t = 600/2.2360679775 = 268.328157 mm"
}
````

## Other records

[01**Overview**](<https://guthlabs.ai/docs/instruments/pavement-thickness-simplified-aashto-cbr-method/>)[02**Mechanism**](<https://guthlabs.ai/docs/instruments/pavement-thickness-simplified-aashto-cbr-method/mechanism/>)[04**Qualification**](<https://guthlabs.ai/docs/instruments/pavement-thickness-simplified-aashto-cbr-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-tranche7/tranche7-results.json`