Abstract: Rainfall-evaporation cycles constitute a critical environmental factor inducing structural degradation of expansive soils and slope instability. To elucidate the evolution of cracking behavior and the mechanisms governing hydraulic deterioration under cyclic conditions, evaporation, cracking, and permeability tests were conducted on compacted expansive soils with varying thicknesses subjected to rainfall-evaporation cycles. The results indicate that cyclic wetting and drying markedly alter moisture migration pathways and evaporation stage characteristics, with specimen thickness exerting a controlling influence on evaporation intensity and stage evolution. During the early cycles, the evaporation intensity in the constant-rate stage of thicker specimens increased in response to crack development. Cracks continuously initiated and propagated as water content decreased, exhibiting cumulative growth with increasing cycle number. Active crack development was primarily concentrated within a water content range of 12.5 %-20 %, and thicker specimens demonstrated higher crack density and connectivity. With increasing cycles, the volumetric deformation mechanism gradually transitioned from being dominated by overall shrinkage in the initial stage to crack propagation in later stages. The formation of a crack network significantly enlarged effective seepage channel dimensions, resulting in an order-of-magnitude increase in hydraulic conductivity with continued cycling.