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The use of resistivity imaging (RI) in subsurface investigation has increased in recent years. RI is a non-destructive method and provides a continuous image of the subsurface. However, only qualitative evaluation of the subsurface can be obtained from RI. The correlations between RI results and geotechnical engineering properties of soils have become important for site investigation using this method. The primary objective of the current study was to determine the geotechnical parameters affecting electrical resistivity of compacted clays. Understanding the influential factors will be helpful in determining the correlations between RI results and geotechnical properties of soil. The effects of moisture content, unit weight, degree of saturation, specific surface area, percentages of pores, and ion composition on soil resistivity were investigated. Soil samples used were classified as highly plastic clay (CH) according to the Unified Soil Classification System. High-energy X-ray fluorescence tests indicated the presence of high percentages of aluminum, silicon, and calcium ions in the samples. In addition, scanning electron microscope images were analyzed to identify clay structure and the distribution of pores. It was determined that the dominant clay mineral in the soil samples was montmorillonite. Soil resistivity tests were conducted in the laboratory at varying moisture contents and unit weights. Based on the experimental results, the average reduction in soil resistivity was 13.8 Ohm-m for an increase of moisture content from 10 to 20%. Test results indicated that soil resistivity decreased with an increase in moist unit weight. In addition, soil resistivity increased from 4.3 to 14.2 Ohm-m for an increase of surface area from 69.6 to 107.1 m2/g at 18% moisture content and 11.8 kN/m3 dry unit weight. Soil with high surface area required more water for the formation of water film and bridging between the particles. This might cause an increase in soil resistivity with an increase of surface area. Moreover, specific surface area also controlled resistivity when soil resistivity was plotted against calcium ions and pore spaces of the soil samples. Therefore, in addition to moisture content and unit weight, specific surface area of soils was identified as an important factor influencing soil resistivity. [ABSTRACT FROM AUTHOR]

Considering the relevance of clay mineral-bearing geomaterials in landslide/mass movement hazard assessment, various engineering projects for resource development, and stability evaluation of underground space utilization, it is important to understand the permeability of these clay mineral-based geomaterials. However, only a few quantitative data have been reported to date regarding the effects of the clay mineral type and hydraulic gradient on the permeability of clay mineral materials. This study was conducted to investigate the permeability of clay mineral materials based on the clay mineral type, under different hydraulic gradient conditions, through a constant-pressure permeability test. Comparative tests have revealed that the difference in the types of clay mineral influences the swelling pressure and hydraulic conductivity. In addition, it has been found that the difference in water pressure (hydraulic gradient) affects the hydraulic conductivity of clay mineral materials. The hydraulic conductivity has been found to be closely associated with the specific surface area of the clay mineral material. Furthermore, the hydraulic conductivity value measured is almost consistent with the value calculated theoretically using the Kozeny–Carman equation. Moreover, the hydraulic conductivity is also found to be closely associated with the hydrogen energy, calculated from the consistency index of clay. This result suggests that the hydraulic conductivity of clay mineral materials can be estimated based on the specific surface area and void ratio, or consistency index of clay. [ABSTRACT FROM AUTHOR]