In China, a substantial amount of dredged silt is generated annually, with solidification treatment being recognized as a crucial pathway for its resource utilization. Traditional cement-based solidification materials, while widely employed historically, have been associated with high energy consumption and substantial carbon emissions. To address these limitations, a novel approach based on the “using waste to treat waste” concept was proposed, whereby a technique for solidifying dredged silt using rice husk ash (RHA) and carbide slag was introduced. The mechanical properties and microstructural mechanisms of this composite solidification system were investigated through unconfined compressive strength (UCS) tests and scanning electron microscopy (SEM) analysis. The results show that significant strength enhancement of the silt is observed upon RHA incorporation, with an optimal mix ratio determined to be 15% rice husk ash and 7% carbide slag. Beyond strength improvement, the composite system is found to markedly increase soil toughness, achieving an ultimate strain of 3.1%~4.5%—a range exceeding that of traditional cement-stabilized soil. Hydration-generated calcium silicate hydrate (C-S-H) gel is identified as the primary strength-enhancing component, functioning through pore-filling and soil particle-binding mechanisms. Based on experimental data, two models were established: a predictive model for solidified soil strength incorporating material ratios and curing ages, and a complementary model elucidating microstructural evolution.