Formation of Crusts and Initiation and Development of Cracks in Them Following Soil Wetting and Drying

Abstract

【Objective】 Crust is a thin soil layer formed on soil surface when water on the soil surface recedes; continuing soil drying after that could result in cracks to develop. Crusts and cracks could significantly affect water infiltration and soil water evaporation, and the purpose of this paper is to experimentally study how crusts form and cracks subsequently develop following a rainfall on a slope. 【Method】 The experiment was conducted on a slope watered by artificial rainfall. After the rainfall stopped, we measured physical properties of the crusts, imaged the initiation and development of cracks in them at different locations on the slop. These images were processed using MATLAB to quantify their morphological characteristics as well as their relationship with soil water content. 【Result】 Based on where the crusts were formed, they can be classified into structural crusts, depositional crusts and transitional crusts, with different physical properties. The depositional crusts have the highest volumetric weight and clay content. In contrast, the structural crusts have the greatest sand particle content. The morphology of cracks developed in the crusts at different locations in the gully differed from each other significantly. For crusts where the cracks developed, their impacts on crack area ratio (RC), length density of the cracks (LC), and the average width of the crack (Wi) were ranked in the order of depositional crusts<transitional zone crusts<structural crusts. The connectivity index of cracks developed in different crusts was not significantly different. The formation of cracks was mainly affected by physical properties of the crusts, decreasing rate of the soil moisture, and the initial soil moisture content. The cracks developed in the structural crusts were in arch-shape. Relevant analysis showed that RC, LC, and Wi of the structural and depositional crusts increased as the soil moisture decreased. After crack development was completed, the soil moisture content of the structural and depositional crusts was 11.88% and 20.57% respectively. The maximum duration for cracks in the depositional crusts to develop was 357 hours. 【Conclusion】 Crack development depends on the physical properties of the crusts there they initiated. The cracks in structural crusts are most visually visible, while the cracks in the depositional crusts were morphologically complex and took more time to develop.

Keywords

• soil crust
• cracks
• soil moisture content
• microtopography