Experimental Study on the Micro-mechanism for Strength Anisotropy of Intact Loess

Abstract

To investigate the micro-mechanism for the anisotropy in the strength of intact loess in Xining, China, a series of consolidated-undrained shear tests were carried out, with a triaxial apparatus, on intact loess at different shear angles and depths. In this study, a scanning electron microscope (SEM) was used to examine sheared samples and generate their scanned images, which were used to analyze the morphology and the connection mode of soil particles qualitatively. Also, a particles and cracks analysis system (PCAS) was used to estimate the porosity, the probability entropy, and the porosity fractal dimension quantitatively. Test results reveal that the morphology of soil particles was mainly circular or oval at the direction parallel to the natural sedimentary surface. Soil particles were mainly in direct contact. The porosity of the soil was relatively lower when the pores were arranged in a regular pattern. With an increase of the shear angle, the morphology of soil particles gradually became schistose and the connection between soil particles turned into indirect point contacts. The porosity of the soil was gradually enlarged when the pores were not arranged in a regular pattern. The normalized pore size firstly decreased and then increased with the increase of the shear angle. Based on the analysis of the micro-mechanism for the anisotropy in the strength, the relationship between the macro-mechanism and the micro-mechanism for the anisotropy in the strength of intact loess was established and proved.