Studying Underground Cavity Progression and the Effects under Levees: A Numerical Investigation Using the Material Point Method

Earth-retaining structures are susceptible to uncontrolled seepage, e.g., due to defects in embedded pipes or conduits, which can result in internal instability and ultimately, full collapse. Understanding the process of cavity formation is vital to understanding the performance of levees in such complex scenarios while ensuring safety. Studying and predicting these failures requires advanced numerical tools to capture failure initiation and large deformations during collapse. This paper investigates the formation of underground cavities in levee systems using the Material Point Method (MPM). Different scenarios are analyzed, including two geometries, i.e., levee geometry with an opening close to the toe and levee geometry with an opening under the crest, and different soil conditions, i.e., one-phase effective stress formulation (neglecting seepage) and two-phase fully coupled effective stress hydro-mechanical formulation to determine the effect of seepage in the result. The soil characteristics and geometry of the model are inspired by a set of centrifuge lab tests conducted at the Engineer Research and Development Center (ERDC). Cavity progression is presented in terms of displacement and mean stress fields. Overall, the numerical models show reasonable agreement with the centrifuge test data. The findings also highlight the complexity of the problem, the importance of capturing the seepage, and the need for advanced numerical frameworks that can capture the complex soil behavior and soil-water interaction involved in these processes while avoiding numerical instabilities.