Mechanism of combined action of seepage force and surface pressure difference in vacuum-preloading method

According to the basic equation of seepage, consolidation analytical solution of the vacuum-preloading method is deduced. It is considered that there are two kinds of seepage in foundations, i.e. the consolidation seepage and instantaneous steady seepage due to the negative boundary pressure. The force of instantaneous steady seepage results in the vertical stretching of the foundation under geomembrane and the lateral compression, which make the foundation in the state of pure shear stress with small volumetric compressive deformation, thus, the foundation cannot be reinforced effectively. The deviatoric stress caused by surface pressure difference is in the opposite direction to that caused by the seepage force, and the counteraction of the stresses makes the foundation under the flexible membrane in the state of spherical stress. Therefore the surface pressure difference is the main load for reinforcement of foundations and the key factor that determines the consolidation character and final consolidation effect of foundations.