Saturated–Unsaturated behaviour of compacted clays
Clayey soils are often compacted for geotechnical and geo-environmental construction such as hydraulic dams, road embankments, tailings containment facilities, and municipal landfills. Post construction, these earthworks are exposed to variations in seasonal weather and extreme climatic events (drought, flood, and freezing), contaminations (deicing salts, ion-rich slurries, and toxic leachates), and applied stresses (self-weight, vehicular traffic, and heavy equipment), thereby affecting the integrity of civil infrastructures. The geotechnical behavior (flow through, volume change, and shear strength) is governed by soil composition and compaction, soil-water-electrolyte mechanisms, soil-atmosphere interactions, and field conditions. This research focused on developing a clear understanding of saturated–unsaturated behavior of compacted clays. For this purpose, a representative clayey soil possessing a moderate water adsorption capacity (liquid limit of 29% and plastic limit of 15%) was characterized to provide baseline geotechnical properties. This material was classified as lean clay according to the Unified Soil Classification System. Field behavior was simulated using regional climatic conditions and environmental loading along with test results. The compacted clay was found to have an air entry value of 700 kPa and a residual suction value of 5 × 104 kPa along with s-shaped swell-shrink curve for dry of optimum and j-shaped for wet of optimum. At optimum, osmotic suction was operative within the 70-100% saturation range and showed a j-shaped swell-shrink curve for deionized water and a cascading j-shaped curve for concentrated brine. The transient swelling potential exhibited s-shaped curves irrespective of the degree of compaction and the type of pore fluids. Likewise, the hydraulic and thermal properties of the soil were found to be governed by net water flux and air temperature. Based on the coupled hydraulic-thermal model, the active depth of soil was found to be about 4 m for degree of saturation and 3 m for heat flux. Furthermore, slope stability investigations showed that the environmental loading and soil properties were effectively captured but construction practices and site geology were only partly incorporated. The main innovative contributions are the development of the following: (i) simplified approach for volumetric constitutive relationships using soil suction and applied stress through normalized void ratio; (ii) soil-water-electrolyte framework to capture the effect of soil contaminations; (iii) coupled hydraulic-thermal model to predict the soil behavior under extreme climatic conditions; and (iv) systematic design approach for selecting the most stable geometry. The findings and the contributions of this research are useful for better design, effective construction, and long-term performance of earth structures.
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Faculty of Graduate Studies and Research, University of Regina