Expansive soils, rich in hydrophilic clay minerals, respond sensitively to changes in ambient humidity. Repeated wetting-drying (W-D) cycles induce desiccation cracks that markedly degrade their engineering performance. This study systematically elucidates the evolution mechanisms of desiccation cracking in compacted expansive soil through laboratory simulations of repeated W-D environments. Nine different evaporation conditions were established based on varying temperatures (30, 40, 50 °C) and humidities (25%, 55%, 85%), which were quantified by the environmental evaporation rates (\(\:{E}_{er}\)). Samples under different \(\:{E}_{er}\) were subjected to seven W-D cycles and crack development was quantified using automated digital image analysis, complemented by Scanning Electron Microscopy (SEM) and Mercury Intrusion Porosimetry (MIP) to capture microstructural evolution and pore-scale changes. The results indicate that the water loss in compacted soil samples follows an exponential decay process. During desiccation, crack width development lags behind crack length extension. Higher \(\:{E}_{er}\) leads to faster growth in both crack length and width. As water content decreases, the crack length tends to stabilize first, while the width continues to rise. After reaching its peak, the crack width stabilizes or partially decreases depending on \(\:{E}_{er}\). The crack ratio, length, and average width display an initial increase during early W-D cycles and subsequently attain a stable state. Higher \(\:{E}_{er}\) is associated with more pronounced initial growth trends. Additionally, broader water content ranges during W-D cycles aggravate internal structural deterioration, ultimately leading to higher crack lengths and widths. For narrower water content ranges, cracks tend to form from the boundaries, with crack development primarily driven by lengthening. More W-D cycles are required for cracks to reach a stage of stabilized development. SEM and MIP results further reveal that repeated W-D cycles shift pore-size distributions toward larger pores (> 1 μm) and drive the formation of multi-scale pore networks, particularly under higher \(\:{E}_{er}\) and broader water content variations. This work introduces an innovative approach to elucidate the synergistic influence of environmental factors on desiccation cracks which may hold instructive significance for geotechnical engineering under repeated W-D environments.
