Effect of Mica Content on Shear Strength of the Yili Loess under the Dry-Wet Cycling Condition

Loess landslides caused by the dry-wet cycling processes are the most common geological disasters in the Yili region of China and have caused significant economic loss and casualties. Therefore, there is an urgency to study the mechanism of landslide disasters. However, research on loess landslide disasters under dry-wet cycling conditions in the Yili River Valley is still underdeveloped, and the research foundations are relatively weak. Based on the characteristics of high and stable mica content in Yili loess, this research probed the changes in shear strength and microstructure of loess with different mica contents (0%, 5%, 10%, and 15%) after different dry-wet cycles (0, 1, 3, 5, 7, 10, 15, and 20) using direct shear testing and a scanning electron microscopy. The results showed that the mica content had a negative relationship with the shear strength of loess. For the same number of dry-wet cycles, the higher the mica content was, the lower the loess’ shear strength, especially in the first five dry-wet cycles. The influence of mica content on shear strength parameters was not similar. The impact was more significant for cohesion. With increased mica content, cohesion gradually decreased. The effect was minor with the internal friction angle. With the rise in mica content, the angle slightly increased with slight variations. Under certain dry-wet cycling conditions, micro-particle content in the loess decreased continuously, the average reduction can reach 11.25%, the content of small and medium particles tends to increase, the average increments were 6.21% and 3.1%, and volatility changes in large particle content. However, the overall increasing trend remains. Accordingly, the number of micropores and small pores decreased, the average reduction was 7.63% and 5.48%, the number of medium pores and large pores increased, and the average increments were 6.13% and 6.99%, respectively. All these changes were more evident in the first three dry-wet cycles and when the mica content increased from 0% to 5%. This study will be beneficial as a reference for the occurrence mechanisms of loess landslide under dry-wet cycling conditions in the Yili area.