This study aims to reveal the mechanisms of the microstructural evolution of remolded loess under different molding water contents and overburden stresses. Utilizing L6 loess from Yan’an, remolded soil specimens were fabricated under various pressures and moisture contents, followed by conducting one-dimensional consolidation tests. The macroscopic porosity, pore size distribution curves (PSD), and microstructure of these remolded loess samples were examined. Experimental findings indicate that an increase in molding water content leads to an augmentation in macroscopic pore volume and elongated pore shapes, concurrently exerting substantial influence on the primary pore size and pore volume of both macropores (>0.4 μm) and minipores (0.4–4 μm), with minimal impact on micropores (<0.4 μm). The escalation of overburden stress solely contributes to the reduction in pore size and pore volume of macropores. Variations in the Menger fractal dimension occur only beyond the optimal water content, while overburden stress exhibits a minimal effect on the Menger fractal dimension. Furthermore, remolded loess exhibited a certain yield stress, and when the overburden stress was lower than the yield stress, there was almost no change in various types of pores. Finally, a microstructural evolution model of remolded loess under different molding water contents and overburden stresses was proposed. These findings are expected to provide new insights into the microstructural evolution and deformation mechanisms of loess in high embankment construction sites.

Expansive soils are widely distributed and the landslides happened in these area cause significant economic losses. The sliding surface records crucial information about landslides, providing insight into the mechanisms behind their occurrences. This research delves into the microstructural features of landslide surfaces in expansive soils. Various sliding surfaces were created through direct shear tests under different water contents (10%, 20%, 30%) and normal stresses (50 kPa, 100 kPa, 200 kPa, 400 Pa). Scanning electron microscopy (SEM) was used to observe the surfaces and based on their structural morphology and formation mechanisms, we categorized the surfaces’ structure into scratch, tension crack, and residual pore. Four parameters, porosity, average pore area, probability entropy, and area probability distribution index, were calculated and used to quantitatively characterized the surface structures. By correlating field landslide surface features with geological survey data, it was inferred that the triggering moisture content was 25.3–26.8% at least, the sliding surface was situated 10 to 12 meters deep within the slope, and multiple sliding events occurred. The water infiltration from the slope top and precipitation along fractures coupled with rising irrigation water levels that saturated the slope base ultimately leading to fracture layer breakthrough and slope failure.