Granular soil in construction of earth works can be solicited by hydrodynamic and mechanical forces. Fine particles constituting these soils may be eroded by the flow leading to a modification of their mechanical behaviour. Classically, the susceptibility of granular soils to internal erosion is assessed by internal stability criteria. In this paper, numerical modelling using discrete elements method is performed to study the mechanical behaviour of eroded soils on triaxial paths. Soils samples were generated according to known particle size distribution and void ratio. Triaxial test have been simulated on samples with the same initial void ratio and same confining stress. Relation has been established between soil mechanical behaviour and its internal stability. Finally, taking into account the relationship between the internal erosion parameters and the mechanical properties of granular materials, a new approach to assess the soil stability has been presented.