Experimental study on structural effects of particle migration in Malan loess under different dry and wet conditions

Malan loess is a wind-deposited sediment that is loose and porous and has high water permeability. It has experienced many dry–wet cycles during tens of thousands of years, resulting in unique engineering properties. The unique properties of loess are closely related to its texture and microstructure formed during dry–wet cycles. This paper investigates the influence of dry–wet cycles on the microstructure of Malan loess and its formation mechanism. The results show the following. (1) In an open environment, the ion content of the loess samples decreased after the dry–wet cycles, indicating that the cementation of the loess particles had weakened and the structural strength of the loess has decreased due to the loss of cementation materials as the cycle number increased. (2) The ion content of the soil samples did not change significantly after dry–wet cycles in a closed environment. However, after several cycles, the clay and colloid particles migrated and were adsorbed around the skeleton particles, and soluble salt ions were enriched in the form of cementation, with a slight increase in structural strength. The proposed dry–wet cycle model in this paper showed that the loess structure property was weaker in an open environment and stronger in a closed environment, revealing the formation and evolution of loess structure at the microscale. The results of this study provide very important theoretical and practical engineering significance for deep understanding of the mechanical and hydraulic properties of loess and the prediction and prevention of geological disasters.