Abstract:During the process of vacuum preloading,soil is consolidated when pore water pressure in the soil reduces and effective stress increases. According to the principle of effective stress,the mechanism of soft soil consolidation by preloading is studied. A series of new formulas are proposed to calculate incremental effective stress in different depths of the soft ground by vacuum preloading. These formulas can also provide a new way to estimate the effective consolidation depth of the soft ground by vacuum preloading. Based on the investigation of vacuum preloading project of Macao International Airport,relation between incremental effective stress and depth of the soil is presented;and the theoretical analysis is validated by in-situ results.