Unsaturated permeability of clayey soil during desiccation: combined evaporation-shrinkage-cracking

Desiccation cracking significantly affects the unsaturated permeability (Kunsat), which governs the water diffusion in the soil in several engineering applications, such as slope stability, road embankments, long-term risk assessment from waste disposal sites, recharge for groundwater hydrogeology, petroleum, and CO2 storage. Cracking causes the permeability to increase, which is cited as the cause of failure and damage in a number of the aforementioned works. This paper aims to experimentally study the unsaturated permeability (Kunsat) of a clayey soil during desiccation. Similar to the instantaneous profile method (IPM), a new method was developed that is based on evaporation tests and water retention curve (SWRC) and takes into account the strains caused by shrinkage and cracks. Different initial states of a clayey soil are examined including a slurry soil prepared at the liquid limit water content and compacted soil with varying initial densities on the wet part on the normal optimum proctor (NPO). Two additional image methods were used: the DIC technique (digital image correlation) to investigate the strain field before cracking and the IAT (image analysis technique) to study the growth of cracks. It was demonstrated that Kunsat was well related to the initial state in terms of density and moisture content. When the suction reaches the entry suction value, Kunsat decreases when the suction increases without the appearance of desiccation cracks. Otherwise, it increases with the growing intensity of the cracks. The proposed experience protocol allowed for different initial states (density and water content) to be considered in a large suction range without the use of proximity sensors.