Reinforcement mechanism and effect of S-PVD vacuum preloading method for dredged sludge

The conventional vacuum preloading method using prefabricated vertical drains (PVDs) suffers from vacuum pressure attenuation with depth. To address this limitation, this paper proposes a novel stacked PVD (S-PVD) vacuum preloading method that enhances vacuum pressure transmission and consolidation efficiency. Comparative laboratory tests were conducted on conventional PVD, reverse prefabricated vertical drain (R-PVD), and S-PVD to evaluate the reinforcement effectiveness, with particle migration patterns during the reinforcement process being systematically analyzed through particle image velocimetry (PIV) techniques. The test results indicate that the S-PVD vacuum preloading method represents a rapid and effective enhancement. Compared to the conventional PVD method, S-PVD achieved significant improvements in various indicators, such as water discharge and surface settlement, within 75% of the reinforcement period. Furthermore, the soil reinforced with S-PVD exhibits superior uniformity, with a 32.37% improvement in vane shear strength uniformity between the top and bottom of the drainage board. For the soil at the bottom of the drainage board, pore water pressure dissipation increases by 97.17%, and the radius of the influence area expands by 84.59%. This demonstrates that S-PVD effectively facilitates the transmission of vacuum pressure into bottom soil layers, thereby enhancing reinforcement efficacy and enabling synchronous and efficient consolidation at various depths.