b'the soil.Generally, when the soil resistivity is Soil resistivity can be measured in the field usinghigh (measured in ohm-cm); the rate of corrosion asoilresistivitymeterorbyobtainingasoilandlossofsteelislow.Corrosivesoil sample from the site and testing it in a laboratorycharacteristicallyhaslowsoilresistivity.Low usingaresistivitymeterandasoilbox.Thissoilresistivityusuallyoccursinfine-grained equipmentisgenerallyavailabletothesoilssuchassilts,loams,clays,andpeat;and geotechnical engineer.thereforehasthegreatestcorrosion SoilpH:Thisisthemeasureofacidityorsusceptibility.Table1belowillustratesthe alkalinity in a solution and is given a pH number.average corrosivity range for common soil types, ValuesofpH7areconsideredacidicandandTable2providesameasureofsoil valuesofpH7to14arealkaline.Purecorrosivity based upon the soil resistivity . distilled water is neutral and has a pH = 7.pH isSandy soils have the higher resistivity values are ameasureofthedegreeofhydrogenionmost often found to be the least corrosive.Clay concentration in the water.When a sample ofsoils generally have higher corrosivity especially soil is mixed with distilled water in the lab, thewhen clay soil is in an area of saline water.In solution can then be tested with a pH meter tothis case the soil can be highly corrosive to steel. arrive at the soil pH number.Table 1.Soil Resistivity Ranges For General Soil TypesSoil Type 1 Resistivity Range (ohm-cm) Soil Type 1 Resistivity Range (ohm-cm)Gravel 40,000 to 200,000 Fine Silts & Organics 2,000 to 10,000Sand 10,000 to 100,000 Loams 3,000 to 10,000Silt 1,000 to 2,000 Humus 1,000 to 4,000Clay with Silt 3,000 to 5,000 AshesCinders 500 to 5,000Clay 500 to 2,000 Peat 100 to 2,000Heavy Plastic Clay 5,000 to 20,000 Marshy Deposit 50 to 300Notes: 1. High soil moisture content decreases the resistivity making the soil more corrosive.2.Freezing the soil dramatically raises the resistivity, thus reducing the corrosivityTable 2. Soil Resistivity and Relative While soil corrosivitycanexistwithinabroad Corrosivity Rating range of soil conditions, the amount of acidity,Resistivity Corrosivity pH 7 (organic reducing soils) or alkalinity, pH(ohm-cm) Rating 7influencescorrosionsusceptibilityandcorrosion rates.MostsoilshaveapHthatfalls 10,000 Non-Corrosive within the range of pH 3-1/2 to pH 10.5,000 to 9,999 Mildly Corrosive Soils that are highly acidic (pH 4-1/2) or3,000 to 4,999 Moderately Corrosive highly alkaline (8 pH 10-1/2) have1,000 to 2,999 Corrosive significantly higher corrosion rates than soils500 to 999 Highly Corrosive within the mid-range 4-1/2 pH 8. 500 Extremely Corrosive Alkaline soils that have a pH greater than 10-1/2will have a significantly decreased corrosion ratedue to passivation.Range forSoilspH 0pH 7(Neutral) pH 14pH 4 Acidic Soils Alkaline Soils pH8pH 10Range forRange forHigh Corrosion High CorrosionFigure 1. Corrosion of metals within soils can occur over a broad range of pH.ECP Technical Design Manual Corrosion Life2021 Earth Contact Products, L.L.C.2021-09 Chapter 8 - Page 148 All rights reserved'