Consolidation mechanism of vacuum preloading for dredged slurry and anti-clogging method for drains

Considering the key problem that the vacuum preloading method cannot efficiently improve dredged slurry, the research findings over the years obtained by the author's research team are comprehensively summarized, including the following four aspects: (1) A large number of consolidation-hydraulic conductivity tests are performed using the modified consolidation apparatus under low initial stress. Based on the test results, the influences of the initial water content and the liquid limit on the compression-permeability properties are discussed. The evolution laws of the permeability coefficient during the compression are obtained quantitatively. (2) The development laws of displacement and strain of soils and the formation mechanism of soil column during the vacuum preloading consolidation of the dredged slurry are illustrated. By utilizing the particle image velocimetry (PIV) and the particle tracking velocimetry (PTV) techniques, the development laws of the displacement and strain of soils during the vacuum preloading consolidation process are obtained. Furthermore, the consolidation process of the dredged slurry is revealed. Besides, the formation process of the soil columns under different initial water contents and particle-size distributions is obtained. (3) The analytical and numerical methods are proposed to calculate the consolidation of dredged slurries improved by vacuum preloading. Based on the uneven strain assumption, the consolidation solutions are derived for the clogging zone and the intact zone, respectively. Subsequently, the consolidation behaviors are studied under various distributions and development laws of vacuum preloading at the permeable boundaries. Besides, the consolidation model considering the formation of the soil columns is also established to investigate the relevant influences. (4) Based on the laboratory and field tests, several methods are proposed by enhancing the vacuum seepage fields, slowing the formation of soil columns, and improving the soil properties, to increase the consolidation efficiency. These methods include applying staged vacuum preloading, booster PVDs, multi-flocculant treatment, and appropriate pore size of PVD filters. Using these methods, the clogging of the dredged slurry during the treatment process can be reduced, and then the consolidation speed and improvement quality can be increased. The research findings are of great significance to developing and utilizing dredging slurry sites, alleviating the shortage of urban land resources, and promoting the sustainable urban development. © 2021, Editorial Office of Chinese Journal of Geotechnical Engineering. All right reserved.