The influence of dry-wet cycles on loess erodibility and microscopic interpretation based on SEM and NMR

• The shear strength and disintegration of loess in different compacted states under dry-wet cycles were presented. • The microstructural evolution of loess with varying compaction states and dry-wet cycles was investigated. • The relationship between erodibility indicators and microstructure parameters was explored through multivariate statistical analyses. • The underlying micro-mechanism of the change in loess erodibility was disclosed. Soil erodibility in the Loess Plateau is intensely exacerbated by climate-induced dry-wet (DW) cycles, yet a quantitative linkage between the concomitant evolution of macro-erodibility and microstructure remains inadequately established. In this study, compacted samples with varying dry densities (1.35, 1.45, 1.55 g/cm 3 ) and initial water contents (10 %, 14 %, 18 %) were subjected to up to 13 DW cycles, with alterations assessed via direct shear tests, disintegration tests, scanning electron microscopy (SEM), and nuclear magnetic resonance (NMR). The results reveal that the shear strength decreased by 21.32–33.73 %, accompanied by 35.94–82.82 % acceleration in the disintegration rate. Notably, a distinct threshold effect governs DW-induced deterioration, beyond which mechanical parameters stabilize. This critical threshold increases from 3 to 7 cycles with higher compaction water content while remaining insensitive to dry density variations. In terms of microstructure, the surface roughness of loess particles decreased by 0.92–2.50 %, while the arrangement orientation increased by 2.11–2.59 %. Concurrently, the volumes of macropores and mesopores expanded by 14.09–19.02 %. The resultant decrease in contact area between skeletal particles and coarsening of pore spaces collectively degrade interparticle cohesion and capillary forces, constituting the fundamental mechanism through which DW cycles enhance loess erodibility. A mathematical model based on this was proposed to predict the decay of erosion resistance from microstructure evolution. This deterioration process is exacerbated by higher water content and lower dry density. It is thus recommended to compact soils both on the dry side of optimum water content and at the maximum dry density to improve the dry-wet resistance of earth-works within loess regions.