Barnes Survey

Cathodic Protection

Layer resistances and resistivities from successive Wenner measurements.

App id: SOIL-06. Reference version 1.0.

How to fill it

Add rows as you need them. The tool uses every row you enter.

On the tool screen, Calc is the working sheet. Presets stores values you reuse. Reference is the formula, assumptions, and provenance below.

Formula

R_n,layer = R(n-1) R(n) / (R(n-1) − R(n)); ρ_n,layer = 2π S_n,layer R_n,layer

Inputs

Name	Unit
Electrode spacing	`ft`
Measured resistance (camera)	`ohm`

Outputs

Name	Unit
Apparent resistivity	`ohm-cm`
Layer thickness	`ft`
Layer resistance	`ohm`
Layer resistivity (hero result)	`ohm-cm`

Diagnose

Observations are context. They do not pass or fail a structure. See Diagnose.

Screening bands in the app: Very Low · Low · Moderate · High · Very High.

When	Observation	Severity
`resistivity < 1,000 Ω·cm`	Very Low	info
`1,000 ≤ resistivity < 3,000 Ω·cm`	Low	info
`3,000 ≤ resistivity < 10,000 Ω·cm`	Moderate	info
`10,000 ≤ resistivity < 30,000 Ω·cm`	High	info
`resistivity ≥ 30,000 Ω·cm`	Very High	info

Assumptions

Successive Wenner measurements treated as parallel paths.
Spacings are strictly increasing. Adjacent equal resistances make a layer unstable.

Provenance

NACE/CP2 training material describing Barnes Layer calculations.
Seattle Public Utilities Cathodic Protection Design Standards.