Effect of Microstructural Evolution of Loess under Infiltration on Soil Strength

Shallow loess landslides typically occur under the influence of rainfall and irrigation, where hydrodynamic processes significantly affect soil strength and stability by altering particle gradation, soluble salt content, and mineral dissolution. Loess, characterized by high porosity and low density, is highly susceptible to structural changes under water infiltration. These microstructural changes not only exacerbate the collapsibility of loess but also weaken its strength, thereby increasing the risk of landslides. However, most existing studies focus on infiltration tests conducted in laboratories using collected samples, lacking long-term monitoring of the microstructural properties of in-situ loess slopes. As a result, these studies fail to ensure that their findings accurately reflect the actual conditions of natural slopes.

To address this gap, this study conducts long-term monitoring of a typical loess slope in the field, with regular artificial irrigation and natural rainfall recording, alongside borehole sampling. Using techniques such as Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Laser Granulometry, and Particle Flow Code (PFC), this research systematically examines the effects of water infiltration on loess microstructure, particle migration, and mineral dissolution. It also explores the spatial and temporal evolution of loess properties at different depths. To date, two sets of loess samples have been used to establish a quantitative relationship between water infiltration and microstructural characteristics (e.g., porosity, mineral dissolution rate, and particle migration rate). The results indicate that during long-term infiltration, the content of cemented minerals in the shallow soil decreases, fine particles are lost, and the pore structure evolves toward a single large-pore form. Furthermore, PFC-based simulations reveal the weakening process of soil strength under water infiltration, providing an in-depth analysis of the particle-level mechanisms underlying strength degradation. This study offers a theoretical basis for the design and optimization of monitoring and early warning systems for loess landslides.