Effect of Vertical Spacing Between Prefabricated Horizontal Drains on Vacuum Preloading of Dredged Slurry

The vacuum preloading combined with prefabricated horizontal drain (PHD) is an effective foundation treatment method for high‐water‐content dredged slurry. As the key design parameter of PHD vacuum preloading technology, the vertical spacing of PHD directly affects dredged slurry consolidation efficiency. However, its optimal value has not been clearly determined yet, so it is necessary to systematically identify the optimal vertical spacing for this technology. In this study, indoor model tests were conducted to assess the impacts of two primary variables: variable PHDs vertical spacing and differing distances of the upper/lower PHD layers from the slurry surface and bottom. The variation of mass of drained water, dissipation of pore water pressure, and surface settlement were monitored. Meanwhile, the water content and vane shear strength of the consolidated dredged slurry were measured. The results show that the optimal spacing for the PHDs arrangement is 450 mm, with the upper layer 200 mm away from the slurry surface and the lower layer 100 mm away from the slurry bottom. Compared with the worst group, the optimal group showed a 22.51% increase in mass of drained water and a 14.02% increase in surface settlement. Additionally, it had a 6.15% decrease in water content and a 6.99% improvement in vane shear strength. This study confirms that optimizing the vertical spacing and layer arrangement of PHDs can improve the vacuum pressure transmission efficiency and enhance the overall consolidation effect of dredged slurry. It provides key technical parameters and a scientific basis for the design of vacuum preloading combined with PHD in practical engineering.