Prediction of Soil Moisture Content through Photographs of Cobalt Chloride Filter Paper in Contact with Soil Specimens

Abstract

Abstract Measured soil moisture content is a useful geotechnical engineering property for a variety of analyses. The laboratory determination of soil moisture content can be time consuming, labor intensive, or both; the field determination of soil moisture content may require additional certification, as associated with the use of the nuclear density gauge. The objective of this research was to identify a method that could be used to determine the soil moisture content without the aforementioned disadvantages. This objective was achieved through the use of cobalt chloride filter paper being placed into contact with the soil. The cobalt chloride filter paper changes color in the presence of moisture (a blue color when the paper is dry and a pink color when the paper is wet). A membrane separated the cobalt chloride paper and the surface of soil specimens (kaolinite, bentonite, Donna Fill, and a silty sand) to prevent cobalt chloride migration. The soil specimens were prepared at different moisture contents, and photography-based hue values were determined for each soil/cobalt chloride filter paper pair at given time intervals. Linear correlations were observed to exist between the soil moisture content and the slope of the linear portion of the hue-time relationship for all of the investigated soil types. The coefficients of determination (R2) ranged from .91 to .99. All soils showed a strong positive linear relationship between the slope of the cobalt chloride hue and soil moisture content. This use of hue may provide a rapid determination of in situ soil moisture content.