Suffusion is a typical form of the internal erosion, which leads to worldwide failures of embankment dams. Extensive investigations have been carried out to characterize suffusion process. However, less research has been focused on the lasting heterogeneity development by suffusion physically and quantitatively, despite the phenomenon been found in literatures. This paper proposes a vertical layered theoretical model based on the force balance of movable particles under one-dimensional upward seepage on gap-graded specimens. In the model, the finer particles loss was deduced respectively in every layer, combined with the coupled calculation including the seepage flow, the soil particles movement and the soil structures changes. The model was verified with experiments and showed a good consistency in the critical hydraulic gradient, layered water head, seepage velocity, finer particle loss and hydraulic conductivity. Finally, suffusion induced soil grading changes and the implications to the suffusion development are discussed quantitatively. The results indicate that the theoretically modeled soil heterogeneity changes are consistent with the suffusion phenomenon and the experimental observations. The outlet and inlet are more sensitive to suffer suffusion under upward seepage, as the two layer have more violent fine particles loss and soil grading coarsening. The layered model can theoretically simulate the development of suffusion with the sequential changes of the soil structures and serves as a new approach to understand the process in cohesionless soil.
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