Non-uniformity In The Consolidation Process Of The Dredged Clay Under The Vacuum Pressure

Recently,clay deposited on the sea bed are dredged with water for the reclamation engineering in the east area of China.And vacuum preloading with the plastic vertical drain is adopted to reduce the water content and improve the strength of the dredged clay.Because of the high water content and drainage path,there is non-uniformity in the process of the consolidation,which contributes to the clogging of the drainage path near the PVDs.So,the study on the effect of non-uniformity induced by consolidation process is not only helpful to research the consolidaiton mechanism of the soil,but also have significant application valuable.Firstly,one consolidation experiments of the dredged clay are designed to obtained the soil samples in the consolidation process conveniently.And sealed effected are kept by the dredged clay itself.Variation of the porous ratio and permeability is studied by the soil samples got from different consolidation process,ignoring the gravity of the dredged clay.Research results show that the porous ratio and permeability of the dredged clay near the drainage channel increase more quickly than that far from the drainage channel.This phenomenon indicates permeability of the dredged clay near the drainage channel is less comparing to the dredged clay in the whole influence area of the vacuum pressure,which repents the clogging of the consolidation path.Then,depending on the sealed effect of the dredged clay,the PVD consolidation by vacuum preloading experiments without the sealed membrane are operated.Soil samples are obtained from the dredged slurry near the PVD by the small-scale cutting ring.Research results show that under the vacuum pressure,the porous ratio of the soil sample decrease from 2.4 to 1.37 in 30 minutes and the consolidation process comes to the end approximately.While the consolidation process of the clay far from the PVD just begins,which indicates to an obvious clogging phenomenon.Finally,by the pressure valve,different values of the vacuum pressure are applied to the PVD consolidation process of the dredged slurry.And influence of the different value of the vacuum pressure on the non-uniformity is studied.Research results show that the water content and porous ratio of the soil sample under the lower vacuum pressure decrease more slowly than that under the higher vacuum pressure.So,the lower vacuum pressure could reduces the non-uniformity and clogging in the consolidation process of the dredged clay.