Elastic Visco-Plastic Model for Binary Sand-Clay Mixtures with Applications to One-Dimensional Finite Strain Consolidation Analysis

The pore water dissipation of sand-clay mixtures is significantly affected by the sand fraction due to nonuniform stress distribution. On the basis of the elastic visco-plastic modeling concepts of Yin and Graham, a new elastic visco-plastic (EVP) model based on Lagrangian formulation was proposed to consider the effects of sand fraction in a sand-clay mixture on the time-dependent stress-strain behavior at finite strain. In hydraulic dredging and marine deposit improvement projects, the initial water content of mixtures is relatively high, leading to a high compressibility. Therefore, the soil skeleton of the mixtures was fixed to Lagrangian coordinates to facilitate the definition of soil boundary. The governing equation was formulated by combining an equivalent time concept with the mixture theory. A finite difference method was adopted for the benchmark analysis of boundary-initial value problems. The proposed model contained eight parameters. Seven of them pertained to the clay matrix that can be calibrated from the reference time line, instant time line, and consolidation curves of the pure clay in the mixture. The structure parameter represented the intergranular structure and can be calibrated based on the compressibility of a sand-clay mixture. Two multistage oedometer tests (including unloading stages) can be performed to calibrate the model parameters, one on the pure clay and the other on the sand-clay mixture with a predefined sand fraction. A benchmark analysis of the proposed model revealed a significant difference in excess pore pressure dissipation between Eulerian and Lagrangian coordinates. The calibrated model based on Lagrangian coordinates was found to reproduce the effect of sand fraction on the overall responses of sand-clay mixture well when compared with the experimental data of sand-bentonite mixtures and sand-marine clay mixtures from the literature.