Backward erosion piping (BEP) is a type of internal erosion responsible for the failure of many dams and levees. BEP occurs when small, shallow erosion channels progress upstream through foundation sands beneath the structure. As analysis of BEP involves coupling two different sets of flow equations to describe the groundwater flow and erosion pipe flow, the solution contains a singularity in the gradient field at the juncture of the soil and pipe domains. In addition, the erosion process is highly localized, often occurring over length scales of 1 cm or less. While it is well known that singularities and localized phenomena cause high errors in numerical solutions, there has been no assessment of the magnitude of these errors in BEP numerical models. This study evaluates the magnitude of error in BEP finite element models through comparison of numerical results to measurements from a highly instrumented BEP experiment. The results indicate that discretization errors related to the pipe geometry can cause 50%–300% error in the solution near the pipe tip when the pipe is represented via linear, 1D elements. These errors are significant and must be considered for models that assess pipe progression based on the local solution near the pipe tip. Results also indicate that the pipe width must be modeled as twice the physical pipe width to accurately represent the pipe flow when assuming a rectangular cross sectional shape for the erosion pipe. ... Read more

Most research on backward erosion piping (BEP) focuses on the critical conditions leading to failure. This paper studies the development of piping over time once the critical conditions are exceeded, which is useful to estimate time to failure. A commonly used small scale rectangular box setup is modified in order to monitor pore pressures and pipe pressures with a high spatial and temporal resolution. The experimental program includes three different sand types to study the effects of grain size and compaction, and different degrees of hydraulic loading. The results indicate that the transport of particles in the pipe affects the progression rate, and that the progression rate is related to the bed shear stress in the pipe. ... Read more