Colloid effect on clogging mechanism of hydraulic reclamation mud improved by vacuum preloading

Many cases of artificial soft clay foundation constructed by hydraulic filling and improved by the vacuum preloading show the clogging phenomenon in the surrounding soil, which compromises the improvement quality. To clarify the clogging mechanism and the formation of soil columns, the vacuum process was tracked from macro to micro by laboratory model tests. Results show that the soil column with higher strength (density) and lower water content was formed surrounding the prefabricated vertical drainage (PVD). Mercury intrusion porosimetry (MIP) tests revealed that the pore-entrance diameter of the soil column after 50 and 43 days of vacuum application ranged from 100 to 600 nm, and that at peak it is 300 nm. However, the mean diameter of the colloidal particles in tail water decreases from 1000 to 100 nm with continuous vacuum application, and then becomes stable at about 100 nm after 43 days. After re-visiting the vacuum process of the hydraulic reclamation mud, the pore-size distribution of surrounding soils and particle-size distribution of the tail water, the clogging was explained by the filling of the pores of the soil column by the colloidal particles in pore water. This mechanism differentiates the artificial foundation improved by vacuum preloading from the natural foundation for the presence of rich colloidal particles in pore water.