Abrasion law of dry and dense soil under the bombardment of sand grain flows

Abstract: Saltation bombardment is a well-recognized dominant dust emission mechanism in the dynamic of soil erosion by wind. Since the abrasion can be caused by the interaction of saltating grains and soil, this specific process of particle transport can be jointly controlled by the saltation parameters of sand grains and the mechanical properties of soil. However, many current models of wind erosion cannot fully consider the function of soil, although some new concepts were suggested previously, such as rupture modulus, binding energy, and surface strength. Particularly, it is still lacking in the soil mechanical properties in wind erosion. Fortunately, the theoretical models of rock abrasion were greatly improved in classical mechanics in recent years. Some types of soil can also share the common characteristics with rocks, such as elasticity and failure behaviors. Therefore, it is a high demand to develop the new abrasion models for soil or rocks. In the presented study, a robust abrasion model of soil was proposed to determine the abrasion variable, considering the comprehensive effects of the impact number per unit time, the yield stress and Young's modulus of soil, the kinetic energy and density of the impacting sand grains. A series of experiments were conducted to examine the interaction between abrasion rate and abrasion variable. Firstly, five types of cylindrical specimens were prepared to cover the man-made, uniform, dry and dense soil, i.e. clay, sand, loam, sandy clay, and loamy clay. Secondly, the compressive strength and Young's modulus of the soil were measured using a standard universal testing machine. Thirdly, seven abrasion experiments were performed on each soil type. Among them, a newly developed sandblasting gun was also utilized under different impact speeds of natural desert sand grains with a nearly uniform sieve size. An analytical balance was used to measure the mean abrasion rates or mass loss per unit time. Meanwhile, the abrasion variable was calculated after measurement. The results revealed that the compressive strength and Young's modulus were 0.823-4.092 MPa and 0.043-0.149 GPa, respectively. There was a linear correlation in the abrasion rate of dry and dense soil, where the slope and intercept were 3.27×104 and -0.027 kg/s, respectively, when abrasion variable is less than 3.0×10-2 g/s. The theoretical model was agreed with the experimental data, because the uniform, dry and dense soil fully meets the assumption of perfect elasticity, and more importantly, the soils in this study behave as the brittle materials, similar to impact targets in rock abrasion models. The abrasion area per impact was much smaller than the target size in the Hertz contact model. The non-positive intercept in the rate-variable relation indicated that the abrasion occurred, once the abrasion variable was larger than the threshold. In addition, the detailed abrasion expressions vary in the types of soil, in terms of the compressive strength, Young's modulus, slope, and intercept. The finding can provide the data support for the wind erosion of various natural features and artificial structures, such as farmlands, dried lake bases, ancient riverbeds, yardangs, and ancient city ruins, which are widely distributed in the arid region of Northwest China.