This paper describes the behavior of soft soil foundation under vacuum-assisted preloading at the Second Bangkok International Airport, Thailand. An analytical solution considering the variation of soil permeability and compressibility is proposed. The associated settlement and excess pore pressure at the embankment centerline are predicted and compared with the available field measurement. The field data show that the efficiency of this improvement technique depends on the magnitude and distribution of vacuum pressure as well as on the extent of air leak protection. The height of sand surcharge and consolidation time can be significantly reduced in comparison with the conventional method of surcharge alone.