Effect of the dry-wet cycle on the mechanical properties of Ili loess with different mica contents.

The mechanical properties of the loess in the Ili region of China deteriorate significantly when it is subjected to the dry-wet cycles. Attributed to the critical role played by the mica content for the mechanical deterioration of Ili loess, a series of laboratory tests, including the X-ray diffraction (XRD) tests, the triaxial compression tests, the scanning electron microscopy (SEM), and other methods, were carried out to investigate the macroscopic and microscopic properties of Ili loess under different dry-wet cycles (i.e., 0, 1, 3, 5, 10, 15, 20 cycles) and different mica contents (1.8, 3.8, 5.7, and 7.7%). The main research outcomes are as follows: (1) the cohesion of the loess generally exhibits a fluctuating downward trend under different dry-wet cycles, while the internal friction angle of which shows a slight overall upward trend; (2) the content of small particles for the loess with small mica content (1.8%) gradually increases with the increased number of dry-wet cycles, resulting in a loose structure. It is after 20 dry-wet cycles that the clump-like particles with large size was generated. With the increased content of the mica, a large amount of the mica minerals were embedded and interspersed between skeletal particles of the loess in the flaky form; (3) the pore fractal dimension is highly correlated with the cohesion, while both the equivalent particle diameter and equivalent pore diameter are more closely related to the internal friction angle, for which the pore area ratio shows the least correlation with other parameters; and (4) the mica with small values of content will be embedded and interspersed between skeletal particles of the loess, which restricts the relative slippage of the loess mass. However, the increased mica content leads to the oriented arrangements structures in the loess mass, resulting in the occurrence of sliding surfaces associated with the decreased strength.