Soil curling process and its influencing factors

Abstract

Soil curling is a common phenomenon in nature due to the rearrangement of soil particles caused by moisture loss. The occurrence of curling in soils significantly affects soil performance in various disciplines. Despite its importance, most existing studies describe the soil curling process within the context of soil desiccation cracking, where boundary conditions facilitating soil curling are not well controlled, or often use the final stage of the desiccation process to infer the soil curling behaviour. Consequently, the underlying soil curling mechanism, the state of the curled soil, and the influencing factors (i.e., clay type, drying temperature, initial water content, and sand content) are not fully understood. In this study, soil curling tests were conducted to study the above-mentioned issues in different types of soils under well-controlled boundary and environmental conditions. It was found that natural clays consisting of higher portions of smectite underwent both upward curling (concave-up) and downward curling (convex-up), while artificial clay experienced only concave-up curling. Concave-up curling initiated when the samples were almost in the saturated condition, while convex-up curling started when the water content of samples was close to their plastic limits. The influencing factors had a profound effect on the moisture evaporation and thus on the soil curling state and its lift-off height. Finally, a conceptual model isproposed to explain the soil curling mechanism and factors influencing soil curling.

Modeling of Drying‐Induced Soil Curling Phenomenon

“…Environmental temperature or relative humidity would affect the evaporation rate by changing the saturated vapor pressure (Ben Neriah et al., 2014). Laboratory studies show that a higher drying temperature would increase the lifted height and shorten the total drying period in soil curling (Tran, Bui, Kodikara, & Sánchez, 2020).…”

“…For Group B, it is able to present convex curling when bonded with moisture gradient. Tran, Bui, Kodikara, & Sánchez (2020) conducted laboratory curling tests on three types of soil. One of them curled up slightly in the final state while two of them formed evident convex curl in the end, as observed in this study.…”

“…Since the early stage of drying shrinkage in the slurry sample is dominated by vertical subsidence, curling often occurs after the sample detached from the container and started to experience horizontal shrinkage (Tran, Bui, Kodikara, & Sánchez, 2020). From the experimental result in Figure 6 we can see that the evident curling development and the increase of water content difference started from the average water content of 60%.…”

“…The types of curling and the degree of curvature are also controlled by soil properties such as clay type and grain size distribution. Tran, Bui, Kodikara, & Sánchez (2020) found that clays composed mainly of smectite minerals develop both concave‐up curling and convex‐up curling, while clays with more kaolinite minerals develop only concave‐up curling. Bradley (1933) reported that the direction of the curl depends on the vertical grain size distribution and graded soil would curl toward the finest grains where the shrinkage capacity is the largest.…”

Cracking to curling transition in drying colloidal films

“…In addition to patterned cracks, delamination of films is another important failure mode during the drying of colloidal films. However, only a few studies deal with the delamination crack [33,34]. Compared to crack propagation, the delamination of a film is considered to be more complex and difficult, due to additional deformation modes.…”