A Laboratory Investigation of Factors Influencing the Electrical Resistivity of Different Soil Types

Abstract

Abstract Field-based electrical resistivity methods offer a nondestructive and rapid means to collect continuous subsurface data. As such, these types of geophysical methods are becoming increasingly popular tools for geotechnical engineers; however, it is challenging to derive geotechnical information, such as soil type, density, and water content, from the field measurements. Laboratory-based soil-box resistivity tests, such as AASHTO T 288-12, Standard Method of Test for Determining Minimum Laboratory Soil Resistivity, are also being used to examine the electrical resistivity of soils; however, it is unclear how density and a number of other factors may affect the results. A laboratory geophysical investigation was carried out to gain a better understanding of the parameters that affect the electrical resistivity of soils and to improve estimates of soil group classifications based on resistivity measurements. Nine different benchmark soils were tested, representing most of the major soil groups according to the unified soil classification system. The effects of water mineralization, water content, degree of saturation, density, and temperature on the measured electrical resistivity of the soils were investigated. The parameters that were found to be most effective in the identification of soil type are bulk density and degree of saturation. While the general trend between saturation and resistivity is known, results indicate that resistivity values reach a lower threshold at around 60 % saturation and that density and water mineralization become less influential as the saturation increases above this threshold. Regardless of the density or saturation, temperature was found to be an important parameter and should be monitored and corrected for in laboratory tests such as AASHTO T 288-12 when results are compared to field data. The influence of particle size and obtaining representative specimens in laboratory soil box testing were also shown to be important.