In order to obtain an accurate calculation of settlement after construction of soft soil foundation by vacuum preloading

surcharge preloading and vacuum combined surcharge preloading method

stress changes of soft foundation reinforced by the different preloading method is analyzed. Elasto-viscoplastic model which the specific stress path of change is weakened represents stress-strain relation of soft clay. Combined with classical Biot consolidation theory

the finite element method of calculation the settlement of the soft clay improved by preloading method is deduced. The proposed method is verified through the concrete example. The outcomes as follows: (1) Reinforcement mechanism and stress paths are not the same for the different preloading methods. Surcharge preloading method is an anisotropic consolidation process under positive pressure. Vacuum preloading method is the isotropic consolidation process under negative pressure. (2) elasto-viscoplastic model is a rheological model not affected either by transient stress or the specific influence of stress paths. It have superiority when applied it to the soft foundation reinforced by the different preloading method that neither need to consider stress paths nor need to consider the primary and secondary consolidation division. (3) In the Biot consolidation theory

using the elasto-viscoplastic model to reflect the physical equations of soft soil

consolidation settlement and settlement after construction of soft foundation could be accurately calculated. (4) The vertical displacement of soft soils is influenced obviously by viscosity parameter ? /V and plasticity parameter ? /V of elasto-viscoplastic model.