Abstract: The erosion degree at the root of the earthen site often exhibits variations with the height, correlating with the soil’s moisture content. This study investigates the effects of freeze-thaw cycles on the apparent morphology, mass loss, unconfined compressive strength, color difference, phase composition, and microstructure of lime-metakaolin (L-MK) improved soil under varying moisture (0−3%, 0−6%, 0−9%, 0−12%). All experiments used natural hydraulic lime (NHL) improved soil as the control. Results indicate that the surface deterioration and mass loss of L-MK and NHL improved soil samples correlate positively with the number of freeze-thaw cycles and moisture content. A threshold exists in the influence of moisture content on the compressive strength of L-MK improved soil samples. At a 0−3% moisture content range, compressive strength increases with freeze-thaw cycles. Beyond this, strength decreases inversely with freeze-thaw cycles, with the most significant drop occurring in the first cycle. In earthen site restoration projects, the soil at high moisture positions should be closely monitored and reinforced during the initial freeze-thaw stage. Microscopic analysis reveals that increasing moisture content leads to pore development in the improved soil’s microstructure after freeze-thaw erosion, accompanied by a noticeable reduction in hydration products like calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH). NHL improved soil exhibits recognizable color differences, while L-MK improved soil shows slight or perceptible changes. L-MK improved soil satisfies the restoration requirements for earthen heritage sites.

Key words: earthen site, lime-metakaolin, water content gradient, freezing-thawing