Salient factors controlling desiccation cracking of clay in laboratory experiments

Abstract

This paper elucidates some of the controlling factors governing soil desiccation. The desiccation tests were conducted on three materials -clay, potato starch and milled quartz sand -all three featuring similar fracture energy. Two controlling factors were identified in desiccation cracking, regardless of the material. The first is the tensile stress and strain energy development within the material when the material is restrained against shrinkage. The distribution of the tensile stress will depend on the boundary conditions and material stiffness, and will dictate where cracks are likely to originate. The second factor is that the exact positions of crack initiations will be controlled by the flaws and/or pores within the material. For materials such as clay, with very fine particles, the cracking mechanism is governed by flaws, since the desaturation of fine pores would require very high suction stress, and this requirement leads to sequential cracking and orthogonal crack patterns. If the material has particles giving relatively large and uniform pore sizes with high moisture diffusivity leading to high shrinkage energy prior to cracking, then the fracture energy balance indicates that cracking can occur in near hexagonal patterns with 1208 crack initiations, which occur predominantly simultaneously. However, even for materials with lower moisture diffusivity, such as for clay, high desiccation rates can give rise to an 'effective layer' over which high suctions and strain energy develop, leading to almost simultaneous dense cracking.

Observations on the desiccation and cracking of clay layers

“…These outcomes have been later corroborated by other researchers, such as Kodikara et al (2000) who analyzed the data of Corte and Higashi (1960) and Lau (1987), Nahlawi and Kodikara (2006), Lakshmikantha et al (2006) and Costa et al (2013). Tang et al (2008), Tang et al (2010a) and Costa et al (2013) were able to show that there was an influence of the desiccation rate in the amount of cracks produced. Rodríguez et al (2007) observed that the effects of soil thickness on the cracking water content were not noticeable for very thin soil layers.…”

Morphometric analysis of polygonal cracking patterns in desiccated starch slurries

“…Earlier studies have elucidated the mechanism of desiccation crack formation for various grain-liquid mixtures [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] . The mixtures typically consist of a skeleton of solid grains and pore spaces that are filled with either liquid or air bubbles.…”

Desiccation-crack-induced salinization in deep clay sediment

“…Expansive clay soils, which are dominated by 2 : 1 clay minerals, crack during desiccation when substantial matric suction in the pore structure of the fine-grained clays develops and the tensile strength exceeds the cohesive strength of the soil matrix (Mermut et al, 1996;Nahlawi and Kodikara, 2006;Costa et al, 2013). Desiccation cracks can serve as water conduits and preferentially transport water and solutes into deep sections of the vadose zone during the generation of local runoff or occasional flooding (Bronswijk et al, 1995;Kurtzman and Scanlon, 2011;Baram et al, 2012a).…”