Water State of Soil Experienced Wetting–Drying Cycles

Abstract

Owing to rainfall and evaporation in nature’s water succession, clay soil inevitably experiences wetting–drying cycles. In the present study, experiments are carried out to investigate variations in the water state (i.e., adsorbed and bulk) during the wetting process and again after experiencing 0–4 wetting–drying cycles. Mathematical connections between the water content, wetting–drying cycle, and the water state are analyzed using nuclear magnetic resonance (NMR). The experimental results show a defined T2 cutoff (T2C) where T2 = 1.84 ms is selected as the critical value of the water state. Based on this T2C, water in the testing specimen is divided into adsorbed water (T2 < 1.84 ms) and bulk water (T2 ≥ 1.84 ms). Adsorbed water shows a faster spreading speed, but bulk water possesses advantages of quantity. With a lower water content (ω < 19.0%), these two states show similar proportions during the wetting process. A significantly larger proportion of bulk water is observed after the water content exceeds 19%. Wetting–drying cycles enlarge the space between soil particles, and the cycle number shows a linear relationship with the bulk water. However, the cycle has less influence on adsorbed water. This paper presents change laws governing the water states during soil wetting and after experiencing wetting–drying cycles. Based on the achieved results, a simplified model containing initial porosity and cycle number is achieved for computing the permeability of clay soil experienced wetting–drying cycles.