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This research develops a physicochemical framework to understand the saturated–unsaturated behavior of low plasticity compacted clays. Test results indicate that matric suction covers the entire range of the water retention curve thereby allowing the determination of air entry and residual suction values. In contrast, osmotic suction is operative within a limited range such that it increased eight-fold and bounced back to a lower value. The swell-shrink path is a j-shaped curve for deionized water and has two cascading j-shaped curves for concentrated brine. The identical paths from 100 to 70% saturation are due to osmotic-induced consolidation whereas the remainder is governed by matric suction. On the contrary, transient swelling exhibits s-shaped curves for both fluids and comprises initial (ion hydration to develop a diffuse double layer), primary (formation of water menisci within the soil pores), and secondary (saturation of some clay particles in smaller pores) stages. Furthermore, the effect of pore fluid on consolidation is subdued as indicated by the compression index (0.13) and the rebound index (0.04). During consolidation, hydraulic conductivity decreased showing an initial steep slope (0.16) and a final mild slope (0.06); values for concentrated brine were lower than the deionized water by five times and ten times, respectively. The identical stress–strain trends showed no distinct peaks and values for concentrated brine were ~ 12% higher than those with deionized water. These findings illustrate that physicochemical interactions in low plasticity compacted clays govern the two independent stress state variables (applied stress and soil suction) thereby affecting soil behavior. [ABSTRACT FROM AUTHOR]

Severe climatic and environmental conditions warrant the use of stabilization agents in aid of compaction for sustainable improvement in engineering properties of clays. Physicochemical agents are a viable option because they are cost effective, environmentally friendly, and offer improved long-term performance of treated soils. This research developed a fundamental understanding of the clay–water–electrolyte admixtures relations. Based on a comprehensive literature review, the effect of nanomaterials, biopolymers, and geopolymers on the behavior of compacted clays was investigated. It was found that all of these admixtures facilitate the development of an aggregated soil microstructure through unique mechanisms. Biopolymers have the highest water adsorption capacity followed by geopolymers and then by nanomaterials. The effect of admixtures on optimum compaction properties follows a decreasing trend similar to untreated clays (S = 80% ± 20%). The variation of hydraulic conductivity, compression index, and compressive strength are largely within the family of curves identified by typical relationships for compacted clays. These preliminary findings indicate that not all engineering properties are improved to the same level by the different types of physicochemical admixtures. The specific nature of geotechnical engineering (soil type and site conditions) as well as the wide range of admixture types and potential biodegradation of some of the reagents are the major shortcoming of using this class of materials. [ABSTRACT FROM AUTHOR]

Water retention in compacted clays is dominated by multi-modal pore size distribution which evolves during hydro-mechanical paths depending on water content and stress history. A description of the evolutionary fabric has been recently introduced in models for water retention, but mostly on a heuristic base. Here, a possible systematic approach to account for evolving pore size distribution is presented, and its implications in models for water retention are discussed. The approach relies on quantitative information derived from mercury intrusion porosimetry data. The information is exploited to introduce physically based evolution laws for the parameters of water retention models. These laws allow tracking simultaneously the evolution of the aggregated fabric and the consequent hydraulic state of compacted clays. The influence of clay microstructure, mechanical constraints and water content changes on the water retention properties is highlighted and quantified from experimental data on different compacted soils with different activity of the clayey fraction. The framework is discussed with reference to a widespread water retention model and validated against experimental data on a Sicilian scaly clay compacted to different dry densities and subjected to a number of hydro-mechanical paths. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

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]

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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]