Experimental study on the shear strength influencing factors and shear surface characteristics of Malan loess

In this paper, the Malan loess is considered as the research object, through the direct shear test and electron microscope scanning test (SEM test), and based on studying the macroscopic shear deformation of loess, the formation and evolution of the shear surface of Malan loess are analyzed from the macroscopic, microscopic and granular scales, and the microscopic mechanism of the shear deformation characteristics of Malan loess is deeply revealed. The test results show that the shear strength of soil is controlled by the moisture state and the stress state, and the shear strength parameters c and φ are mainly related to the moisture state. The dry density highly affects the cohesion, but has a small influence on the internal friction angle. On the macroscopic level, the larger the vertical load, the smaller the shear surface roughness. In addition, the higher the water content, the higher the flatness of the shear surface. On the microscopic level, some skeleton particles near the shear surface are damaged and rearranged along the shearing direction during the shearing process, and some surface scratches appear. On the granular level, the basic shearing structural functional units mainly include the “core–coat” covering structure and the aggregate structure, and the performance of the basic structural functional units is related to the moisture state and the stress state. The results and conclusions obtained in this study have an important reference significance for the in-depth understanding of the strength characteristics and microscopic mechanisms of loess as well as similar soil materials.