Full-scale field study on cyclic vacuum preloading for dredged slurry-reclaimed ground

Vacuum preloading with prefabricated vertical drains is a widely employed method for the treatment of slurry ground. Conventionally, a constant vacuum pressure of 85 kPa is maintained throughout the treatment, leading to significant energy consumption due to continuous vacuum pump operation. Moreover, this approach exacerbates clogging issues inherent in PVD treatment of clayey slurry when compared to a lower loading pressure. To address these challenges, this study adopted a cyclic vacuum loading mode, which not only reduced energy use but also mitigated the clogging problem. By periodically switching the vacuum pump on and off, the under-membrane vacuum pressure varied cyclically within a predefined range. Initially, the effectiveness and energy-saving potential of this cyclic vacuum loading mode were validated through laboratory tests on PVD treatment of slurry. Subsequently, a full-scale field trial on cyclic vacuum loading was conducted on dredged slurry-reclaimed ground. The cyclic vacuum pressure in the trial (Pmax=80 kPa, Pmin=50 kPa) was implemented using 15 minutes pump-on and 45 minutes pump-off cycle. Key treatment effects including the pore water pressure dissipation, ground settlement, water discharge and power consumption were monitored. In-situ vane shear and plate load tests were performed post-treatment to assess ground improvement. The results demonstrated that cyclic vacuum preloading reduced energy consumption by 74.4% while achieving 88.4% of the effects of traditional full vacuum loading.