Assessing unsaturated permeability of loess under multiple rainfalls

Multiple rainfalls may give rise to changes in the microstructure of loess which in turn alter its unsaturated permeability. This study evaluates the unsaturated permeability of compacted loess using an infiltration device. In addition, Scanning Electron Microscopy (SEM) and Nuclear Magnetic Resonance (NMR) are used to document the microstructure before and after rainfall. The results demonstrated that the void ratio mostly controls permeability. In particular, the unsaturated permeability of loess samples featuring a low dry density (≤1.35 g/cm3) displays a decreasing trend with increasing rainfall times due to the occurrence of pore collapse. In contrast, rainfall events lead to an increase in pore size for loess samples with high dry density (≥1.45 g/cm3) as a result of the dissolution of soluble salts and cement inside the soil samples, leading to an increase in unsaturated permeability. Based on the experimental results, a novel model is developed to estimate the unsaturated permeability of compacted loess. •The unsaturated permeability of compacted loess under multiple rainfalls are classified.•The evolution of compacted loess microstructure by multiple rainfalls is explored.•The change mechanisms of unsaturated permeability are disclosed at the micro-scale level.•The model for estimating the unsaturated permeability of loess is proposed.