Analysis on Mechanics of Vacuum Preloading Method

The consolidation of soil under vacuum preloading was induced by reducing pore pressure on the boundary and thereby forming of unballanced distribution of pore pressure between the boundary and soil mass. With the good drainage condition on the boundary, the reduction of pore pressue certainly leads to the increase of effective stress and hence to the consolidation of soil even though the total stress is kept constant. The consolidation induced by vacuum preloading proceeds during the whole process from the unbalance of the distribution of pore pressure to a new balance. It was shown by test and theoretical analysis that the vaccum preloading method is different from surcharge preloading method in some aspects, such as the way of consolidation, the characteristics in the process of consolidation, stress path and the effect of drains. The only one common feature of these preloading methods is that the consolidation is induced by the unbalanced distribution of pore pressure and can be described with the differential equation of consolidation. Then a model for consolidation induced by surcharge and reducing pore pressure directly on the boundary was presented. At last, the effective stress analysis on several kinds of consolidation was carried out.