<p>Grouting-vacuum preloading is a recently developed efficient soft soil improvement technique that enhances soil consolidation efficiency by promoting soil particle flocculation. However, as the grouting pipe lifting rate governs soil flocculation, its optimal value remains undetermined in engineering practice, making it necessary to identify the optimal rate. To address this gap, grouting-vacuum preloading tests under different lifting rates were conducted in this study. Pore water pressure dissipation, settlement, and drainage volume were monitored during the test, while the vane shear strength and water content of the consolidated soil were systematically measured. The results showed that excessively high or low lifting rates reduce the soil consolidation efficiency by inhibiting pore water pressure dissipation and decreasing drainage capacity. When the lifting rate was 35&#xa0;cm·min⁻¹, pore water pressure dissipation was significantly accelerated, drainage volume markedly increased, and settlement substantially enhanced, with the consolidation time shortened by 69.21% relative to the worst-performing group. Correspondingly, the average vane shear strength of the treated dredged sludge was increased by 31.81%, and the water content was reduced by a maximum of 25.2%. This study confirms that 35&#xa0;cm·min⁻¹ is the optimal lifting rate for grouting-flocculation-assisted soil consolidation, which maximizes treatment efficacy by promoting soil flocculation and enhancing drainage consolidation.</p>