Effects of salt content on desiccation cracks in the clay

On the whole, if the climate of the saline soil distribution area is arid or semi-arid, with small precipitation and large evaporation. Thus, soil desiccation cracks are a common phenomenon in saline soil. The cracks of soils cause serious problems in several fields (e.g., agriculture, geotechnical engineering, and engineering geology). The type and amount of salt in saline soil have important effects on its mechanical and hydraulic characteristics and cracking behavior. The purpose of this study is to quantitatively analyze the effects of salt content on the characteristics of crack development and water evaporation in clay. Laboratory experiments were carried out on six groups of samples with thin layers of saturated clay slurry with NaCl content of 0, 1%, 2%, 4%, 8%, and 16% by weight of dry soil under controlled temperature and humidity. During the drying process, the mass of the samples was recorded using an electronic balance, and photographs were taken with a digital camera to record the development of surface cracks. The geometric parameters of the crack images, such as the crack ratio and the total length of the crack network, were determined using digital image processing technology. Combined with the fractal theory, the development process of cracking was analyzed quantitatively. The results showed that water evaporation and crack development were both reduced with increases in NaCl content. The evaporation process of water could be divided into three stages: the steady, falling, and residual rate stages. With increases in NaCl content, the crack ratio, total length of the crack network, average crack width, and fractal dimension of the crack all decreased. When the NaCl content was equal to 16%, the surface of the soil was covered by a layer of salt due to salt crystallization, and no cracks appeared on the surface to the end of the evaporation process. The study results would contribute to hydrological analyses in arid and semi-arid lands with potential applications in water and land resources management.