A HYDRO-MECHANICAL FINITE ELEMENT FORMULATION FOR LOCALIZED INTERNAL EROSION IN POROUS MEDIA, WITH APPLICATION TO BACKWARD PIPING IN COFFERDAMS

We have recently proposed a finite element formulation able to simulate the localization of propagating internal erosion in rigid porous media. In the present paper, such method is extended to deformable porous solids, in order to model also the interaction between backward erosion piping and soil movements. We present the equations governing the exchange and transport of solid and fluid mass in a saturated poro-elastoplastic solid embedding a propagating erosion conduit conveying a multiphase flow. The full set of coupled finite element equations is then obtained from the weak formulations of mechanical equilibrium and fluid mass balance. The performance of the proposed formulation is assessed through an analysis of the soil response to the progressive dewatering of a cofferdam. The hydro-mechanical coupling and the ability in capturing both the onset and propagation of piping are crucial for an interpretation of the limit states typically observed in these structures.