Investigating Soil Desiccation Cracking Using an Infrared Thermal Imaging Technique.

Soil desiccation cracking is of great concern in many fields such as hydrology, geology and agriculture, whereas its multi‐physical governing mechanism remains unclear up to now. As evaporation is a key influencing factor to soil cracking, capturing the evaporation‐induced soil temperature will significantly contribute to the improved understanding of soil cracking behaviors. Infrared thermal imaging enables the surface temperature measurement through converting infrared radiation into visible images, and has not been applied for soil cracking characterizations in the past. In this study, the fundamental mechanisms of soil desiccation cracking are investigated through the combined usage of three noninvasive techniques including infrared thermal imaging, particle image velocimetry, and digital image processing. Experimental results reveal the correlation between the evaporation‐related temperature of soil and its hydro‐mechanical behaviors. The evaporation rate is proportional to the soil‐atmosphere temperature difference. The soil body with a higher water content corresponds to a larger temperature difference, with the more apparent correlation observed in the unsaturated state of soil. Furthermore, as indicated in a nonuniform soil temperature field, the pore water migrates from the soil body with high temperature into the body with low temperature, similar to the soil particle motion under drying. Hence, the soil body with low temperature attracts additional water to maintain a high water content, resulting in a fast evaporation rate and a low temperature field for a long time. The evolution of the desiccation crack network is also related to the temperature distribution. Soil desiccation cracks tend to form in a lower temperature area, whereas the soil body with a higher temperature presents a more remarkable volume shrinkage. Primary cracks (defined as those first to develop and cause the breaking up of the intact material into separate clods) propagate along the isotherm, while the propagation path of secondary cracks (defined as those sub‐cracks initiated from primary cracks and subdivide soil to smaller clods) is first orthogonal to the isotherm and then rotates to gradually overlap with the isotherm. This study highlights the potential application of the infrared thermal imaging technique to investigate the underlying mechanisms of soil‐atmosphere interaction and perform soil desiccation cracking prediction. Key Points: Soil‐atmosphere temperature difference is proportional to soil evaporation rate, with a higher value corresponding to more pore waterThe horizontal movement tendency of pore water is similar to that of solid particles, toward evaporation‐induced low temperature areasDesiccation cracks are prone to formation in the low temperature area and lengthen parallel to the isotherm [ABSTRACT FROM AUTHOR]