Abstract：Elastoviscoplastic properties，especially viscous properties of water-saturated or air-dried sands，were investigated based on the results of a series of plane strain compression(PSC) tests. Loading rate effect，creep and stress relaxation should be attributed to the viscous properties of the sand specimens，but not to the delayed dissipation of excess pore water pressure. The strain rate was changed stepwise several times；and stress relaxation tests and a set of creep tests were performed during otherwise monotonous loading at a constant strain rate. It was found when the strain rate suddenly changed，the stress also changed sharply with a very high stiffness，being close to the elastic value. Then，with an increase in the strain，the viscous stress component gradually rejoined the essentially unique stress-strain curve after having exhibited clear yielding. Similar behaviors were also found when monotonic loading was restarted at a constant stain rate following a creep loading or stress relaxation stage. An elastoviscoplastic constitutive model，described in a nonlinear three-component framework，was proposed to predict the effects of viscous property on the stress-strain relationship of sands observed in plane strain compression tests. The model is able to simulate the viscous effects of sand for arbitrary loading history，including the stress-strain behaviors during monotonic loading with step changes in the strain rate and the one after creep or stress relaxation. The results of the tested sands have been used to validate the proposed model. It is shown that the three-component elastoviscoplastic model can simulate the viscous properties of sands reasonably
