Characterization of water retention behavior of cracked compacted lateritic soil exposed to wet-dry cycles

Abstract

Alternate precipitation and evaporation often cause desiccation cracks in clayey soils, which necessarily change the soil water retention capacity. This work aimed to examine the influence of wet-dry cycles on the water retention behavior of compacted lateritic soil and further model the soil water characteristic curve (SWCC) of the soil containing cracks. Different wet-dry cycles were imposed on compacted lateritic soil specimens to produce desiccation cracks. Microscopic tests were performed to reveal the microstructural change of the soil. The SWCCs of the specimens after various wet-dry cycles were then measured and analyzed. The early six wet-dry cycles contribute most to the development of desiccation cracks. At microscale, some soil aggregates are broken into individual clay particles and further lost during wet-dry cycles, producing numerous microcracks and mesopores, which accounts for desiccation crack development. The SWCC of compacted lateritic soil changes from a unimodal form to a bimodal form under wet-dry cycles because of crack occurrences. With increasing cycle number, the first air entry value decreases and the reduction in volumetric water content becomes more evident, leading to a weaker water retention capacity of the soil. An empirical equation of the bimodal SWCC was proposed by incorporating a sigmoid function into the van Genuchten model and then verified with the experimental data. This equation can provide continuous and smooth bimodal SWCCs with all parameters having clear physical meanings.