PFEM to simulate earthen dikes failure due to overtopping: A coupled surface-subsurface approach

Delpierre, Nathan [UCL] Rattez, Hadrien [UCL] Soares Frazao, Sandra [UCL]

The majority of breaching of earthen embankments is triggered by overtopping flows or waves. With the increasing frequency of extreme precipitation events due to climate change, this type of failure will happen more often in the future. These failure mechanisms are usually simulated using the shallow-water equations complemented by the Exner equation to reproduce the progressive erosion of the embankment and the growth of the breached area. The dynamics of breach opening play a major role in the way water rushes into areas that should be protected by dams or dikes. This is why numerical models have been developed with the aim of making better predictions of breach outflows. Such an approach usually neglects the effect of the degree of water saturation in the embankment as well as the flow through the embankment that can alter the slope stability of this structure by reducing the soil’s mechanical strength during overtopping. Such slope instabilities greatly affect the breach opening evolution and should therefore be modelled. Here we present a numerical model in which the surface and subsurface flows are coupled with a geomechanical model of the earthen embankment. The Particle Finite Element Method (PFEM) is used to reproduce the large displacements that occur during the slope failure process generated by mechanical strength losses resulting from pore pressure variation and allow the simulation of the entire dike failure process. The groundwater flow is simulated by solving the 2D Richards equation, while the surface flow is simulated by solving the 1D shallow-water equations. The combination of these flows provides information regarding the pore pressure evolution inside the earthen embankment during the overtopping process. This evolution leads to severe decrease of the soil’s shear strength and eventually to complete failure. Several test cases were conducted to show the influence of the coupled flows process on the geomechanical failure. The effects of pore pressure fluctuation and of soil’s parameters on the geomechanical failure are studied. This work shows that the geomechanical failure should not be neglected in the process of earthen embankment failure simulation.