Multiphysics modelling of a river levee affected by mammal bioerosion

The levee embankment along the Secchia River (San Matteo locality, Emilia Romagna) was the protagonist of a disastrous failure on 19 January 2014, resulting in the release of large water volumes and significant damages for the surrounding area. The failure mechanism is attributed to the presence of local heterogeneities or cavities, such as an animal burrow, as supported by photogrammetric images that provide evidence of existing dens along the damaged levee. A finite-element multiphysics approach is used to fully describe the hydraulic behaviour and the geotechnical stability of the levee in the presence of a preferential channel flux, such as an animal burrow, recognised as the primary trigger of the levee failure. To fully capture the hydraulic interaction between the levee and the cavity, this work proposes to describe the cavity initially as an empty domain and subsequently as a highly permeable porous medium. Finally, the stability analysis is carried out by the combination of poroelasticity and elastoplasticity theories together with the second-order work criterion (Hill’s stability). The results show that the presence of a burrow locally modifies the hydraulic head distribution within the levee, producing higher pressure gradients around the cavity. When the hydraulic response is coupled with mechanical behaviour, the analysis based on Hill’s second-order work criterion highlights zones potentially prone to instability near the burrow. These results suggest that biological cavities can locally weaken levee stability by altering the seepage pattern and stress distribution.