Investigating the curing time effect on water retention property and microstructure of lime-treated Ili loess

Water retention is an important soil property affecting the hydro-mechanical behavior of unsaturated soils. This study investigated the water retention property and the microstructure of lime-treated Ili loess from Xinjiang in China. Such material is a typical central Asian loess characterized by high salt content and strong collapsibility. The matric suction and total suction were measured by the filter paper method and saturated salt solution method. The microstructure characteristics of untreated and lime-treated loess were analyzed by scanning electron microscopy and mercury intrusion porosimetry, and the influence of the microstructure variation on the macroscopic water retention property was analyzed by introducing the parameter of fractal dimension, which is commonly used to describe the characteristic of pore shape and size. Results showed that, along the curing time, the lime treatment induced a change of the soil microstructure in terms of pore distribution with a consequent increase of the matric suction and overall water retention capacity. However, the osmotic suction decreased during curing. During curing, the lime treatment reduced the percentage of macro-pores and increased the nano-pores. Then, the soil microstructure was characterized by the fractal dimension, which increased with the curing times. Finally, the proposed fitting model of water retention consisting in introducing the fractal dimension into the Van-Genuchten model appeared adequate with good accuracy.