Abstract
The desiccation cracks in expansive soil, which are a common natural phenomenon, have a significant negative impact on the engineering properties of the soil and are the direct cause of many engineering problems and geological disasters. This study aims to investigate the influences of sand content and particle size on desiccation cracks of the compacted expansive soil. First, samples of compacted expansive soil with five sand contents and four sand size groups were prepared. Then, a series of drying tests were performed. The dynamic variation of geometric parameters of the surface crack network during evaporation was quantitatively analyzed by using digital image processing technology and fractal theory. The results demonstrated that the increase of the surface‐cracking areas in the early and later stages was manifested by the increase of the crack length and crack width, respectively. In the same size of sand particle group (0.15, 0.3 mm), as the sand content (dry weight ratio of soil sample) increased from 0% to 40%, the surface‐cracking ratio (the ratio of the crack area to the total surface area of the soil sample) showed a decreasing trend (13.20%, 11.42%, 10.50%, 8.98%, and 7.71%, respectively). When the sand content (40%) was the same, as the sand size groups increased from [0.15 mm, 0.3 mm) to [1.18 mm, 2.36 mm), the surface‐cracking ratio also presented a decreasing trend (7.71%, 7.69%, 4.35%, and 3.73%, respectively). The changing law of the fractal dimension of cracks was the same as that of the surface crack ratio. During the drying process, the deformation of the sample was characterized by centripetal shrinkage or cracking, which were mainly affected by the boundary conditions of the sample. This research’s results verify the effectiveness of sand to improve the dry‐shrinkage characteristics of expansive soil, providing a reference for the improvement of roadbeds and the treatment of soil slopes in expansive soil areas.
Highlights
Expansive soil is rich in minerals with strong hydrophilicity such as montmorillonite and illite
E location of the collected soil is illustrated in Figure 1. e undisturbed soil samples were wrapped with plastic film and sealed with adhesive tape to prevent water loss. e water content and dry density of undisturbed soil samples were determined by the ring knife method in the laboratory. e soils were air-dried, crushed, and passed through a 2 mm sieve. e physical properties of the soil samples, such as specific gravity limit, water content, and free swelling rate, etc., were tested according to the Chinese standard for geotechnical testing method (GB/T 50123–2019)
Effect of Sand Content and Particle Size on Water Evaporation. e evaporation process of samples with different sand contents and particle size groups could be divided into three stages: constant evaporation, failing evaporation, and residual water content stage. e external factors affecting the evaporation rate mainly include temperature, relative humidity, and wind speed, while the internal factors mainly include the mineral composition, particle size, water content, and degree of compaction of the soil [14, 29]. e initial water content, dry density, and evaporation environment of the samples were the same in the test. e main factor affecting the evaporation rate was the changes in soil properties caused by the sand content and particle size group in soil
Summary
Expansive soil is rich in minerals with strong hydrophilicity such as montmorillonite and illite It is a kind of clay with significant swelling, shrinkage, and cracking properties, widely distributed in the world [1]. E cracks in farmland soil will aggravate drought, increase soil strength, and adversely affect plant root growth, resulting in the reduction of crop yields [4]. From another perspective, the cracks cause preferential flow during irrigation or rainfall, leading to a decrease in the efficiency of water and fertilizer utilization, but an increase in the risk of groundwater pollution [5, 6]. Desiccation cracks in the foundation or roadbed can reduce the bearing capacity of the soil, inducing some problems such as uneven settlement and pavement cracking [10]
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