Prediction of Wetting Hydraulic Characteristics of Compacted Bentonites in Isochoric Conditions

Abstract

Unsaturated hydraulic characteristics of compacted smectite clays are essential in many engineering applications. The knowledge of the accurate soil-water characteristic curve (SWCC) and hydraulic conductivity function (HCF) is vital for simulating the transient water flow through bentonites. HCFs are routinely estimated from SWCCs using the statistical models that consider probabilistic soil pore-size models. Recent studies, however, emphasize a strong influence of adsorption saturation on the wetting of smectite clays. In this work, the hydraulic diffusivities of four different bentonites at different compaction densities were estimated by back-analysis from water imbibition tests. A constant hydraulic diffusivity with water content was found to be a good approximation, and the diffusivity was equivalent to the self-diffusion coefficient of water due to the influence of adsorption forces in bentonites. A novel procedure is proposed based on the identified dominant mechanism to predict the HCFs and diffusivities directly from the wetting SWCCs of compacted bentonites. The proposed approach was used to predict the HCFs, and transient water flows of four Indian bentonites at dry densities of 1, 1.4, and 1.6 Mg/m3 and other bentonites from the literature. The proposed approach was superior to the existing statistical methods and provided excellent agreement with the back-estimated conductivity data from the water imbibition tests. On the other hand, the existing statistical models severely underpredicted the conductivities, especially in the higher suction range, due to the dominant influence of adsorption saturation.