Finite Element Analysis of Vacuum Consolidation With Modified Compressibility and Permeability Parameters

Laboratory tests and case history studies indicate that soil subjected to vacuum preloading may not behave the same as ground treated by traditional surcharge preloading. In detail, soil compression under vacuum pressure is smaller than or equal to that induced by positive pressure with the same magnitude; soil rebound after stopping the vacuum is not as high as after removing the surcharge; and the consolidation rate is usually faster under vacuum pressure than with surcharge preloading. Analysis of vacuum consolidation with existing methods cannot gain all these differences. Thus, in this study, three factors for adjusting compressibility and permeability are proposed based on past laboratory and field results which are used in a finite element analysis of soft soil foundation under vacuum-assisted preloading. This proposed method can be incorporated in existing computer programs associated with classical soil models (e.g., the modified Cam-Clay model and the Soft-Soil model); it is then examined via three distinct simulation scenarios including a laboratory model test and two prototype field cases. The improved accuracy in relation to consolidation by the proposed method is demonstrated and practical ranges for the adjustment factors are discussed.