Abstract: The vacuum preloading technology is widely used in the treatment of large-area silt foundations formed by dredging. In order to improve the traditional vacuum preloading reinforcement effects, a method of vacuum preloading combined with alkali residue treatment is proposed for dredging silt foundations. By conducting the indoor vacuum preloading model experiments and microscopic tests, the reinforcement effects and mechanisms are explored and analyzed. The research results show that compared with the conventional vacuum preloading method, the new method has significantly improved the reinforcement effects, with an increase of about 20% in the drainage and surface settlement. After reinforcement, the water content of the soil is reduced by 34.9% from 90%, and the maximum vane shear strength is increased by 1.33 times. Through the SEM and mercury intrusion tests, it is found that the alkali residue can promote particle aggregation, reduce the content of fine particles in the soil, and increase the permeability of dredged sludge. Strong hydration reactions may occur between alkaline slag and clay minerals, generating products. This study provides a theoretical basis for the technological development of improving the vacuum preloading methods and the efficient utilization of alkali residue.