The purpose of this study is to present the development of a 1D elasto-viscoplastic (1DEVP) constitutive model to describe the time-dependent behavior of soft clays. Firstly

based on Bjerrum’s concept of time lines

a new concept of viscoplastic strain rate lines is proposed

and after the relationship between viscoplastic strain rate and viscoplastic strain increment is deduced

the 1DEVP model for soft clays is established. Secondly

the relationship between the newly developed model and other three well-known elasto-viscoplastic(EVP) constitutive models are theoretically discussed. It demonstrated that the new model with no essential difference from the other three EVP models is simpler in form and clearer in physical meaning than others. Thirdly

the established 1DEVP is used to develop analytical solutions for consolidation-creep coupling effect

strain rate effect

stress relaxation effect. Lastly

based the one-dimensional consolidation tests on Ningbo soft clays

the model parameters is calibrated. Furthermore

the model is used to simulate 1D consolidation-creep tests on Ningbo soft clays

1D staged constant rates of strain tests on Wenzhou soft clays and 1D relaxation tests on Hongkong marine clays. The comparisons between experimental results and simulations show that the newly proposed 1DEVP model has a good predictive ability for the one-dimensional time-dependent behavior of soft clays.