Abstract: Due to grain-size sorting in the mud slurry during hydraulic filling, the consolidation process of dredged slurry at different locations along the horizontal direction under vacuum preloading with prefabricated horizontal drains (PHDs) varies. To explore the uneven distribution of physical and mechanical properties in dredged slurry treated by vacuum preloading with PHDs, laboratory experiments were conducted using slurries with two different initial water contents. After 7 days of self-weight deposition, vacuum consolidation was applied for 12 hours at two different loading positions within the soil. Settlement, water content, the content of the 0~0.015 mm particle fraction, vane shear strength, and structural yield stress were measured at different regions of the soil. The aim was to discuss the horizontal distribution of physical and mechanical properties after reinforcement. The test results showed that grain-size sorting affected the transmission of vacuum degree in the soil. Vacuum loading at a position with a higher content of coarse particles resulted in more uniform settlement across different regions. The content of the 0~0.015 mm particle group gradually increased with distance from the grouting side. Soils with higher initial moisture content exhibited a greater degree of horizontal particle sorting, and the uneven settlement after vacuum loading was more pronounced. Due to the attenuation of vacuum degree, soil closer to the loading position achieved a higher degree of consolidation, characterized by lower water content, higher vane shear strength, and a stronger structure at its bottom.