Suction measurement and SWRC modelling for reconstituted salt-laden soils in earthen heritages

Under the long-term impacts of influencing factors including water and soluble salts, the Site of Yarkhoto Ancient City which is a precious earthen heritage is subjected to irreversible deterioration. Exfoliation of surface crusts on the remaining walls is one of the commonly observed pathologies. The behaviors of unsaturated soils are dependent on suction, thus making it crucial to obtain reliable soil-water retention curve (SWRC) for investigating the deterioration mechanisms of earthen heritages. The slurries with different NaCl contents are prepared from the local soils. The total suction and matric suction during desiccation are determined using five methods (vapor equilibrium, water potentiometer, filter paper, pressure plate and high-capacity tensiometer), and the discrepancies are further discussed. Meanwhile, two models, i.e., van Genuchten (vG) and Fredlund & Xing (FX), are adopted to model the SWRC. The results show that NaCl has insignificant effect on the matric suction but induces osmotic suction, leading to a great increase in the total suction especially at high water contents. The general trend of water retention behavior of soils obtained by various methods is consistent. Based on the data obtained by different methods, the errors of curve fitting can be minimized, and a reliable SWRC on drying path is acquired in the full suction range. Both vG and FX models can model the experimental data well, which provides a scientific basis for further quantitative analysis of the evolution process of surface crusts cracking in earthen heritages.