Multiscale modeling of flood-induced piping in river levees

A three-dimensional transient fully coupled fluid-particle model is utilized to simulate flood-induced piping under river levees and taking into account the effects of soil-fluid-structure interactions. The porous soil medium is modeled as a mixture of two phases, namely the fluid phase (water) and the particulate solid phase. The fluid is idealized as a continuum by using an averaged form of Navier-Stokes equations that accounts for the presence of the solid particles. These particles are modeled at a microscale using the discrete element method. The interphase momentum transfer is modeled using an established relationship that accounts for the dynamic change in porosity and possible occurrence of nonlinear losses. The hydraulic structure (levee) is modeled as an impervious rigid block and its motion is described by a combination of external and internal forces from the surrounding fluid and solid particles. A computational simulation is conducted to investigate the response of a granular deposit when subjected to a rapidly increasing head difference. The simulation provided information at the microscale level for the solid phase as well as at the macroscopic level for the pore-water flow. The settlement and failure mechanism of the structure were captured as the hydraulic head difference gradually increased and the solid phase underwent subsequent deformations. The results suggest that failure of such structures may occur suddenly and at hydraulic gradients well below the critical gradient. The proposed computational framework for analyzing river and flood-protection levees would provide a new dimension to the design of such vital geotechnical systems. The technique can be effectively used to investigate failure mechanisms under complex loading and flow conditions.