Morphology-based mechanism of desiccation cracking in soil and montmorillonite

Abstract

Cracking from soil desiccation is a common phenomenon. Stress analysis based on transient spatial distribution of soil water and fracture mechanics has been extensively applied in studying the development of soil cracks. Nevertheless, the existing experiments and theoretical models for soil crack development generally ignore the interaction between cracks, and lack quantitative analysis of the transient evolution of crack length L(t) and crack strength I(t). This study explored the transient evolution of soil and montmorillonite shrinkage and cracking by analyzing the images from both field and laboratory experiments. Our study demonstrated that in the initial stages of drying, newly formed cracks accelerated the soil moisture evaporation near the crack opening interface, resulting in a rapid increase in stress, which promoted an exponential growth of the cracks. Subsequently, the general case where two or more parallel cracks have a mutual shielding interaction led to slowing down and saturation of their development. The experimental L(t) and I(t) curves for the S-shape could be well-fitted by introducing the existence of a competitive relationship between cracks. The experimental results also showed that the I(t) curve lagged behind L(t). The shielding effect between cracks was also supported by imaging of all crack samples. Hence, the single-crack model commonly used in traditional soil desiccation cracking studies is unsuitable for analyzing cracks in soil samples. Finally, the analysis of the concave-shaped soil shrinkage characteristic curve (SSCC) and the concave-shaped the soil water evaporation curve for all soil samples revealed that they could not explain the S-shaped L(t) and I(t) curves. Therefore, the plausibility of the single or isolated crack model for the evolution of soil drying and cracking was excluded. Finally, this experimental study proposed the hypothesis that the saturation phenomena of L(t) and I(t) are likely due to the competition between cracks for the release of strain energy caused by drying.