Experimental study on the disintegration characteristics of undisturbed loess under rainfall-induced leaching

Loess is prone to collapse as the soil approaches saturation, leading to severe geological hazards. However, how the undisturbed loess microstructure evolves due to rainfall-induced leaching is poorly understood and a detailed assessment of the corresponding disintegration characteristics is lacking. In this study, we conducted a series of leaching and disintegration tests on undisturbed Q3 loess from Yan'an, China. Loess disintegration on a macroscopic level were characterized using a self-developed disintegration apparatus, and the relationship with influencing factors such as moisture content, temperature, and salinity were explored. At the microscopic scale, scanning electron microscopy (SEM) was performed to qualitatively probe the underlying mechanisms of loess disintegration under varied leaching conditions. The microstructure properties of the loess samples revealed in the SEM images were examined using Image-Pro Plus (IPP) software. A quantitative relationship between the microstructural parameters of the pores and particles with disintegration was established based on the grey correlation theory. The results show that the disintegration process of undisturbed loess under the action of leaching can be divided into three stages: soaking, softening, and collapsing. Compared with samples without leaching, the study demonstrates that leaching can facilitate the loess disintegration. Under otherwise similar conditions, loess disintegration ratio decreases with increasing moisture content and salinity, whereas it increases with water temperature. In addition, microstructural observation shows that the undisturbed loess microstructure changed from interlocking to overhead with increased leaching, inducing favorable conditions for loess disintegration. Moreover, grey correlation analysis shows that the particle size distribution and macropore content of undisturbed Q3 loess yields a satisfactory correlation with the loess disintegration ratio. In general, rainfall-induced leaching effect is conducive to the disintegration of loess by degrading its internal structure.