Effect of Temperature and Water Salinity on Electrical Surface Conduction of Clay Particles

Abstract

In this study, the combined effect of temperature (T) and pore water salinity on electrical surface conduction parameters was investigated. Two new electrical surface conduction parameters, namely, electrical conductivity of effective solid (σs) and size of diffuse double layer (DDL) water per unit volume of soil (χ), were considered in this study. The tested samples included two commercially available clays and four natural clay soils with diverse physico-chemical properties. The two surface conduction parameters were also used to assess the influence of temperature (T) and pore water salinity, as well as the electrical conductivity of free water (σFW), on the evolution of the free swelling index (FSI) of clays/clay soils through experimental methods. The findings suggested that elevated temperature and σFW increased σs but reduced χ, as well as the FSI of clays/clay soils. Furthermore, the rate of reduction for both χ and FSI augmented under the influence of increased free water salinity, particularly for clays/clay soils with high swelling capacity. The combined reductions of χ and FSI provided substantial evidence that clay DDL thickness decreases as T and σFW increase concurrently.

Determining Liquid Limit and Plastic Limit of Clay Soils by Electrical Surface Conduction and Diffuse Double Layer Thickness

“…The presence of water within a soil-water mixture can be divided into two parts, namely free water and DDL water. Each clay particle and its surrounding DDL forms a single conductive unit called an effective clay particle [8,9]. Therefore, the total volume of saturated clay (V c ) can be written as the following [8]:…”

“…Each clay particle and its surrounding DDL forms a single conductive unit called an effective clay particle [8,9]. Therefore, the total volume of saturated clay (V c ) can be written as the following [8]:…”

“…Clay-rich soils require rational treatment in geotechnical engineering to implement any structural designs safely. These soils exhibit substantial characteristics due to their differences in mineralogy [1,2], degree of saturation [3], water content [4,5], micropore structures [6], particle size distribution [7], temperature [8], and level of anisotropy [9,10]. Without analysing those geotechnical properties efficiently, any construction site may experience a detrimental impact.…”

“…Since the liquid limit and plastic limit of clay soils are unique and contain specific water contents, it is possible to implement an EC approach to determine those metrics. Several discussions already exist in the literature that aimed to establish the connection between EC and clay properties [8,9,16,30]. In the past, soil was considered to be an insulated material, and the EC measurements were dependent on the clay-water interaction within the suspension and pore water conduction only [32][33][34].…”

“…Clay-water interaction can be further discussed by considering the surface conduction layer, which is known as the diffuse double layer (DDL). The electrical properties of the DDL are controlled by the pore water salinity and surface charge of clay particles [8]. This DDL can form an effective solid by surrounding each clay particle, which is electrically conductive.…”