The resistivity is the main character of the soil in cathodic protection calculations and its corrosivity evaluation. In CCPTools, it is possible to approximate the soil resistivity range based on the soil type and humidity.
General Analysis of Soil Resistivity
Using certain reference books we have provided an option to approximate soil resistivity. We make this approximation based on the water content and type. According to Tagg’s work, increasing water content will reduce soil resistivity. For example, dry red clay has more resistivity than topsoil and sandy loam. For all three mentioned types, 16% water content is sufficient to reduce the resistivity to less than 200 Ω m. Likewise, moisture of more than 25% will reduce soil resistivity to less than 100 Ω m, independent of the soil type.
Application
Soil resistivity approximation based on humidity and type is helpful in the CP industry. In cathodic applications, it is impossible to get precise data about the soil type at different depths. Sometimes the only available data is the water level. Therefore, by following this general guideline, we know that if the soil is saturated with water (for example, close to rivers), the soil resistivity in the worst scenario is less than 100 Ω m. Moreover, when we are close to the sea, the resistivity of soil saturated with seawater is less than 10 Ω m. Accordingly, this general guideline is sufficient for the preliminary evaluation and design of cathodic protection.