Percolation Behavior of Soft Clay under Vacuum Suction

The clogging induced by particle transport is often mentioned in the practice of vacuum preloading, but the percolation behavior of soft clay under negative pressure is still not clear. To understand this, the percolation behavior was investigated using an artificial paste of silica sand and kaolinite under different hydraulic pressures. The hydraulic conductivity under positive pressure (90 kPa) was about twice as high as that of negative pressure (−90 kPa). However, the transport capacity and leached particle size under negative pressure were more significant than those under positive pressure, despite the same tendency of the porosity under the positive or negative pressure. This is an interesting and paradoxical finding, suggesting complexity accompanying the erosion and clogging under the nominal hydraulic gradient, where a higher concentration of the hydraulic gradient occurs under negative pressure. The percolation under negative pressure––a self-adaptive process––included three elements: (1) the colloidal transport of clay minerals; (2) colloid accumulation and clogging in the seepage channel close to the outlet; and (3) a gradient concentration close to the outlet.