Measurements of Soluble Salt Content of Soils from Arid and Semi-Arid Regions

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Courtesy of ASTM International

Soils with soluble salts occur in arid regions worldwide. Depending on the amount of soluble salts present, treatment of these soils may be needed before construction. In engineering, the amount present is usually determined gravimetrically by finding the weight loss for a soil diluted with a fixed quantity of water. However, if the soluble salt content is evaluated with an insufficient amount of water, some of the salt present may not dissolve. This condition, termed “salt saturation,” may cause the amount of soluble salts present to be underestimated. To identify the correct dilution, this paper proposes checking successive dilutions until an unsaturated solution is obtained. This can be accomplished using either gravimetric or electrical conductivity measurements to detect salt saturation. The volume of water used to determine percent soluble salts can then be adjusted accordingly. This paper describes how to find the most suitable dilution using either method and how to determine the percent of soluble salts. Using this approach, five different soils from Las Vegas, Nevada, were evaluated. Unsaturated water-soil dilution ratios ranged from 2:1 to 100:1. In two cases, the 2:1 dilution was adequate, but for the other three it was not. Soil “M” exemplified this best: percent soluble salts increased from 1% measured at a 5:1 dilution (indicating a leave-in-place/no-action recommendation) to 7% at a 100:1 dilution (indicating a removal recommendation). This result illustrates the importance of using an unsaturated dilution for determining percent soluble soil.

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