Abstract: In order to reveal the mechanism of consolidation-creep of soft soil, the settlements of soft foundtions after the completion of projects are calculated. The triaxial consolidation and creep tests have been carried out which simulate of soft soils under consolidation by vacuum, surcharge, and combined vacuum-surcharge preloading. The microstructure tests of soft soils before and after triaxial tests have been carried out also. The elasto-viscoplastic (EVP) model which could consider the change of microstructure of soft soils is set up. The outcome is drawn as follows: The results of triaxial tests show that the course of consolidation and the course of creep of samples under the loading of three different preloading methods have the coupling effect. The results of microstructure tests show there are relationships of supplement each other between the change of microstructure and the change of engineering characters of soft soils. The specific stress path of change is weakened in EVP model, in which parameter reflected the elastic and parameter reflected the plasticity and viscosity of soft soils could be determined by the microstructure parameters. The improved EVP model not only can calculate the EVP deformation of soft soils but also considered the microstructure changes of soft soil, which can better reflect the essence of soil deformation.

Key words: preloading, soft soils, microstructure, elasto-viscoplastic (EVP) model