Loess is extensively utilized as a roadbed filler in western China's transportation infrastructure due to its widespread availability and accessibility. However, significant engineering challenges are posed by the inherent collapsibility and high compressibility characteristics of this material during road construction and operational safety maintenance. Four improvement schemes were systematically examined for over-wet loess treatment: fly ash, alkali-activated fly ash, slag-fly ash, and alkali-activated slag-fly ash. Comprehensive evaluations were conducted through multiple parameters including water content, grain size accumulation curve, shear strength, and compressibility to determine the optimal improvement scheme. The conclusions show these as follows. Grain composition optimization is achieved in all four improvement schemes compared with untreated natural loess, accompanied by water content reduction after 14 days curing. The most significant water content reduction is achieved in the alkali-activated slag-fly ash improve loess, with its water content decreasing from the 25% to 18.43%. Significantly shear strength improvement is observed in all four improved over-wet loess, with performance hierarchy established as: alkali-activated slag-fly ash improved loess > slag-fly ash improved loess > alkali-activated fly ash improved loess > fly ash improved loess. The alkali-activated slag-fly ash improved loess exhibited a 181.95% enhancement in cohesion and a 67.41% increase in angle of internal friction compared to natural loess. Compressibility characteristics are substantially improved across all improvement schemes, meeting the standard for low-compressibility soil. The compressibility coefficients are quantified in ascending order as: alkali-activated fly ash improved loess < alkali-activated slag-fly ash improved loess < slag-fly ash improved loess < fly ash improved loess. The alkali-activated slag-fly ash improved loess demonstrates superior engineering properties, exhibiting the lowest water content, optimal grain composition, highest shear strength, and exceptional compression deformation resistance. Therefore, it is deemed the most effective improvement scheme among the four over-wet loess improvement methods.