Characteristics of loess wind sorting and its structural mechanical significance

Abstract

As loose sediment transported and deposited by wind, changes in the grain size of loess is the main source of changes in its macromechanical properties, mesostructural characteristics and microparticle effects. However, at present, there is almost no relevant research on the relationship between grain size and structural mechanics of wind-sorted loess, which significantly restricts the in-depth understanding of the mechanism and evolution of geological disasters and resulting engineering damage. In this paper, grain size optimization is performed by a wind sorting device developed in this laboratory to reveal the intrinsic mechanism associated with sorting, structural mechanics and particle interactions. The results show that the average grain size is positively correlated with the wind speed and negatively correlated with the transport distance. Further study finds that the grain size of aeolian loess consists of superimposed medium and fine particle fractions with good distribution sorting and coarse particle fractions with poor distribution sorting. Under the same conditions of water content and dry density, cohesion increases with increasing transport distance and wind speed. However, the internal friction angle first decreases and then slowly increases during the whole wind transport process. Fine particle content is the decisive factor for the change in shear parameters. Microscopic analysis shows that the contact mode, pore characteristics, azimuth of particles and variations in coarse, medium and fine ternary particle accumulations are closely related to the grain size distribution caused by wind sorting. The negative (loosening, wall, wedge) and positive (filling, adsorption) effects in these microstructures correspond to the structural characteristics of soil at different transport distances, and different structural characteristics correspond to different mechanical properties. This correspondence fully reveals the close relationship between the grain size characteristics produced by wind sorting and structural mechanics. This study helps to elucidate the relationship between grain size variation and mechanical characteristics of aeolian loess and provides theoretical references for relevant applications in the fields of geological and geotechnical engineering.