Scope. Seepage through a porous media can cause the detachment and transport of soil particles. The type of internal erosion where finer particles are detached and transported through a coarse soil matrix is referred to as suffusion. Loss of particles in soil due to suffusion can significantly alter the hydraulic and mechanical properties of soil, potentially leading to damage or collapse. In tunnel construction, such risks include water inrush and sinkholes. This study introduces a numerical methodology of seepage-induced suffusion and an elastoplastic soil model describing the mechanical properties of eroded soil. It aims to consider both the removal and movement of fine particles through the soil matrix and its effect on the soil behavior by coupling the hydraulic and mechanical phenomena. Methodology. The numerical methodology of seepage-induced suffusion is derived from the framework of multiphase mixture and porous media theories. In this approach, soil is treated as a saturated porous media consisting of four constituents, erodible particles being one of them. The suffusion process is modeled as the phase exchange of erodible particles from solid to liquid phase, which occurs when shear stress exerted by the fluid is greater than soil critical shear stress. A soil elastoplastic model that considers particle loss is developed to account for the mechanical consequences due to suffusion. It follows the concepts of the changes in soil volumetric state. Volumetric change of the current state is defined through the volumetric variable where particle loss of solid volume has a direct impact on void space increase. The model is formed based on the subloading cam-clay model. Principal Findings. Numerical simulations reveal that following the onset of erosion, porosity increases, leading to a corresponding rise in permeability, while the concentration of eroded particles increases in the direction of flow. The simulations also show a reduction in soil strength due to suffusion. The loss of particles results in an increase in specific volume and volumetric strain, indicating that the soil becomes looser and transitions from a dilative to a contractive state. Additionally, it is observed that soils with lower compressibility experience a delayed onset of suffusion. Conclusion. This study utilizes a straightforward methodology for modeling seepage-induced suffusion, taking into account the changes in soil behavior resulting from particle loss. The findings offer insights into the evolution of porosity, the concentration of eroded soil particles, and pore water pressure distribution. Additionally, the developed soil model effectively captures erosive behaviors, including strength reduction and deformation.

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