Coupled backward erosion piping and slope instability performance model for levees

Abstract

While backward erosion piping (BEP) and slope instability failure mechanisms have been investigated independently, they are not analyzed concurrently despite that the response of levees embankments to the BEP may likely impact the stability of the slope, especially if levees were to fail. This study presents a framework towards interfacing soil instability and BEP simulation with the goal of producing a performance model that considers the hydro-mechanical coupling between the material properties. This is afforded by updating the stiffness and strength properties of eroded zones based on the porosity changes that are determined according to a critical diameter model. The framework is then applied on a levee without a cutoff wall built on a silty sand foundation. The results show that the captured coupling between these two failure mechanisms crucially enhances our understanding of the performance of levee systems. Specifically, the results show that coupling effects are more substantial in cases where pipes extend to more than 50% of levee’s bottom width. Furthermore, the results indicate that ignoring the softening in the strength properties of the eroded zones due to BEP leads to overestimation of the slope’s factor of safety against instability by as much as 40%.