Salinity effects on cracking morphology and dynamics in 3‐D desiccating clays

Abstract

Saline conditions induce not only chemical but physical changes in swelling clays, and have a significant influence on the crack dynamics and morphology of desiccating clays. In this study, we used Xray microtomography to experimentally investigate the effects of sodium chloride on the morphology and dynamics of desiccation cracks in three-dimensional mixtures of sand-bentonite slurry under varying rheological conditions. Rectangular glass containers were packed with slurries of different salt concentrations, with the top boundary exposed to air for evaporation. The growth and propagation of the cracking network that subsequently formed was visualized in 3-D at multiple intervals. The characterization of cracking and branching behavior shows a high extent of localized surficial crack networks at low salinity, with a transition to less extensive but more centralized crack networks with increased salinity. The observed behavior was described in the context of the physicochemical properties of the montmorillonite clay, where shifts from an ''entangled'' (large platelet spacing, small pore structure) to a ''stacked'' (small platelet spacing, open pore structure) network influence fluid distribution and thus extent of cracking and branching behavior. This is further corroborated by vertical profiles of water distribution, which shows localized desiccation fronts that shift to uniform desaturation with increasing salt concentration. Our results provide new insights regarding the formation, dynamics, and patterns of desiccation cracks formed during evaporation from 3-D saline clay structures, which will be useful in hydrological applications including water management, land surface evaporation, and subsurface contaminant transport.

Patterns of Desiccation Cracks in Saline Bentonite Layers

“…6 can be also described by considering the chemistry and colloidal interactions of the clay particles as influenced by the ion concentration (Van Olphen 1963, 1964Luckham and Rossi 1999;DeCarlo and Shokri 2014b). Several studies have been conducted in the past to delineate the structure of bentonite and its characteristics when dispersed in a liquid (Goehring et al 2010).…”

“…Several studies have been conducted in the past to delineate the structure of bentonite and its characteristics when dispersed in a liquid (Goehring et al 2010). The interaction among the negatively charged clay particles is influenced by a phenomenon referred to as the 'Electric Double Layer' (EDL) (Gouy 1917;Grahame 1947;Van Olphen 1963, 1964Luckham and Rossi 1999;DeCarlo and Shokri 2014b). EDL plays an important role in the stability of the colloidal system.…”

“…This considerably reduces the repulsive forces among the particles that influence the configuration of particle association in the colloidal system. At low and high salt concentrations, clay particles form entangled and stacked clay network, respectively, which significantly modifies the mechanical properties of the slurry (Luckham and Rossi 1999;DeCarlo and Shokri 2014b). Entangled clay network includes formation of a threedimensional 'voluminous card-house structure,' and stacked clay network exhibits a highly compact, thicker and possibly larger flakes described as quasi-continuous layers of flexible units (Van Olphen 1963;Van Damme and Ben Ohoud 1990;Luckham and Rossi 1999).…”

“…Thanks to the recent advances in imaging techniques, a few studies have emerged which help to understand the desiccation cracks in three-dimensional systems (see Goehring 2008;Gebrenegus et al 2011;DeCarlo and Shokri 2014b). For example, Gebrenegus et al (2011) studied the crack dynamics of sand-bentonite mixtures by using X-ray computed tomography.…”

Influence of Soda Content on Desiccation Cracks in Clayey Soils

“…The morphology of desiccation cracks depends on the salt content (Lima and Grismer, 1992; Pauchard et al, 1999). DeCarlo and Shokri (2014) examined the effects of salt (NaCl) on desiccation crack morphology and behavior in a sand–bentonite slurry via X‐ray microtomography and found that crack networks consolidated with increased salinity. Sun et al (2015) stated that the saline content in soil has impacts on the desiccation cracking process; a decreasing trend in the rate of the evaporation of water in soil was found with increased salinity and cracking was delayed during desiccation.…”