Three-dimensional hydro-mechanical modelling of suffusion in gap-graded granular soils for engineering practice

Currently, numerical studies at the real scale of an entire engineering structure considering suffusion are still rare. This study presents a 3D hydro-mechanical continuous modeling approach considering suffusion in gap-graded granular soils for engineering practice. It requires a relevant hydraulic model for suffusion to evaluate the changes in the fines content and a mechanical model for granular soils considering the fines content dependency. To this purpose, the saturated soil has been considered as a mixture of four interacting constituents: soil skeleton, erodible fines, fluidized fine particles, and fluid. The detachment and transport of the fine particles have been modeled with a mass exchange model between the solid and the fluid phases. An elasto-plastic constitutive model for sand-silt mixtures has been developed to monitor the effect of the evolution of both the porosity and the fines content induced by internal erosion upon the behavior of the soil skeleton. For each component of the approach, alternative choices are provided. Simulations of laboratory tests demonstrated the reliability and applicability of this coupled numerical approach for internal erosion problems. Afterwards, to describe more accurately the seepage within the earth structures, an unsaturated flow condition has been implemented into this coupled hydro-mechanical model. A stabilized finite element method was used to eliminate spurious numerical oscillations in solving the convection-dominated transport of fluidized particles. This numerical tool was then applied to the specific case study of a dike-on-foundation subjected to internal erosion. Different failure modes were observed and analyzed for different boundary conditions