Mechanical properties and microstructure evolution of Malan loess

Abstract

At the top of the Pleistocene Loess-Paleogene sequence, Malan loess is the main substrate for industrial production, daily life, and construction activities. The Malan loess at different depths from the Chinese Loess Plateau was used as a test material to gain insights into its mechanical properties and microstructure evolution. The direct shear test and, collapse test were conducted to study the mechanical properties of the original loess. The microstructure evolution was displayed by the scanning electron microscopy (SEM) imaging and particle size distribution. Meanwhile, The microscopic properties of the loess pores were quantified by an Image-Pro Plus (IPP) software. Pearson's correlation was used to analyze the mechanical properties of the loess at different depths by selecting basic physical properties and microstructural parameters. The results show that with increasing depth, the Malan loess gradually becomes denser, the pore area ratio and the proportion of macropore area decrease, and the pore shape tends to be flat. However, the particle size varies slightly. Furthermore, the cohesion of the Malan loess is positively correlated with the dry density, liquid limit, and clay content, while negatively correlated with the silt content and macropore area ratio. There are positive correlations between the internal friction angle and the silt content and macropore area ratio, and a negative correlation between the clay content and water content. The silt content and macropore area ratio play a positive role in the collapse coefficient, while the dry density, liquid limit and clay content exhibit a negative impact on the collapse coefficient. Finally, a schematic diagram of the basic physical properties and microstructure evolution of the original loess at different depths was established. These findings provide a guidance for construction and conservation of related loess engineerings.