Due to the high water content and poor compressive strength, dredged sediment cannot be recycled directly. Alkali-activated industrial wastes can serve as an alternative to cement for stabilizing sediment, offering the benefits of lower costs and reduced carbon emissions. However, pure chemical stabilization often shows limited effectiveness in treating sediments with high water content. This study develops a mixed binder including incinerated sewage sludge ash (ISSA) and ground granulated blast-furnace slag (GGBS) to stabilize Hong Kong marine deposit (HKMD) together with vacuum preloading. The research evaluates the new binder's effectiveness in treating HKMD with water content up to 200% and compares the performance with and without vacuum preloading. The results demonstrate that ISSA and GGBS can be used as cement alternatives to stabilize dredged sediment, and the composite stabilization method (VP-CSM) significantly outperforms the pure chemical stabilization method (CSM). The strength and stiffness of VP-CSM increase at least five times compared to CSM. Additionally, the treated HKMD exhibits a larger elastic range than pure clay and a smaller stiffness degradation rate than cemented clay. The treated HKMD exhibits cross-anisotropy in stiffness, which is caused by the anisotropic microstructural fabric and is further enhanced by vacuum preloading. The coupling effect of vacuum preloading and chemical solidification includes two main aspects: (1) vacuum preloading reduces the water content of the dredged sediment, which lowers the water-cement ratio and densifies the soil; (2) the solidification reaction increases the permeability coefficient of the mud in the early stage, thereby accelerating the efficiency of vacuum preloading.
