One-dimensional elasto-viscoplastic model for structured soft clays

The purpose of this study is to present the development of a one-dimensional elasto-viscoplastic (1DEVP) constitutive model to describe the destruction effects on the time-dependent behavior of structured soft clays. Firstly, the new concept of viscoplastic strain rate lines is proposed based on the Bjerrum's concept of time lines, and the 1DEVP model for unstructured soft clays is established. Secondly, with the variation law of compression index with void ratio with one-dimensional compression being revealed, a new description for the progressive destruction during 1D loading is proposed for the structured soft clays. Thirdly, based on the definitions of "intrinsic volume" and "intrinsic strain", the intrinsic compression law for soft clays is obtained consequently. And after the derivation of creep function for the structured soft clays, 1DEVP model considering destruction effects is established, with all model parameters being calibrated in a straightforward way. Furthermore, the newly developed model is used to simulate the conventional oedometer tests and long-term creep oedometer tests on Ningbo natural clays as well as the CRS oedometer tests on Berthierville clays and Ariake clays. The comparisons between the simulated and experimental results show that the newly proposed 1DEVP model can reasonably describe the coupled effects of the time dependence and the bond degradation of soft sensitive clays. Although the model is proposed for 1D analysis, it is helpful for providing the theoretical basis for establishing 3D elasto-viscoplastic models for the structured soft clays.