Abstract: The application of underwater vacuum preloading technology has long been limited by difficulties in stabilizing vacuum pressure in marine environments, which restricts its effectiveness in deep-water conditions. To address this bottleneck, this paper proposes a novel underwater vacuum preloading method, which utilizes a large-diameter sleeve anchored in marine clay as the waterless operation system of the vacuum pump, thereby overcoming vacuum-pump pressure loss in the marine environment. Four model experiments compare the consolidation performance of the new underwater vacuum preloading method at different overlying-water depths with a traditional vacuum preloading method that has no overlying water, using underwater soft clay as the test material. Results show that the new method achieves significant consolidation, and the reinforcement effect increases with greater overlying water depth. Compared to the control test T4 with an overlying water depth of 0 m, the reductions in average water content for tests T1, T2, and T3 with overlying water depths of 7.2 m, 4.6 m, and 1.4 m were 43.8%, 31.3%, and 12.5% greater, respectively. The average undrained shear strength of the soil of tests T1, T2, and T3 increased by 39.5%, 25.7%, and 8.7%, respectively, compared to test T4. According to the improved Asaoka’s method, the consolidation degrees of tests T1, T2, T3, and T4 after 40 days were 90.2%, 90.2%, 92.7%, and 95.3%, respectively. This study provides an effective approach for applying underwater vacuum preloading technology in deep-water regions, presenting significant prospects for engineering applications.

Key words: underwater vacuum preloading, consolidation, ground improvement, marine clay