Physical Modeling of Backward Erosion Piping Phenomenon in a Geotechnical Centrifuge

Backward erosion piping is a mechanism of internal erosion that has been widely recognized as a potential hazard for water-retaining structures, such as dams and levees, that are founded on granular materials. Backward erosion piping initiates toward the downstream zone of the structure by the concentration of flow at an exit point acting as drainage, which leads to a localized loosening of the soil and eventually to a continuous migration of grains from the foundation following a piping path pattern. Such piping path extends backward toward the impoundment once a certain critical hydraulic condition is met, resulting in the loss of stability of the structure and leading to failure. Despite the numerous studies aimed to provide new insights into backward erosion piping prediction, detection and remediation, there is still a need to develop experimentally validated methodologies that allow linking results from physical and analytical models to field behavior. This is due to, among others, the difficulty to replicate the field behavior in small-scale models and the limited understanding of parameters that are interrelated and affect the evolution of the phenomenon. The geotechnical centrifuge modeling technique has the potential to model complex geotechnical mechanisms and stress conditions that occur in large-scale prototypes (i.e., field conditions) using models with reduced scale, which saves cost and time in model construction. This is done by imposing a simulated gravitational acceleration field to the model that is higher than the Earth’s gravity applied to the prototype. However, the use of centrifuge modeling to study backward erosion piping is limited due to the complexity of the phenomenon and the limited understanding of the effects of the increased gravitational acceleration field on parameters, such as head and pressure losses, flow regime and critical hydraulic conditions. A few research studies have attempted to assess backward erosion piping in the geotechnical centrifuge, but the associated scaling effects are still insufficiently explored or validated. The goal of this study is to advance the understanding of the backward erosion piping phenomenon by implementing the geotechnical centrifuge modeling technique. A series of centrifuge modeling experiments were performed to model the different mechanisms involved during the development of backward erosion piping. The scaling effects derived from the implementation of this technique are evaluated to allow the interpretation, conformation and validation of existing theoretical scaling laws. Results from this study provide new insights into the impact of exit drainage and seepage length on the global and local hydraulic conditions developed during different phases of the phenomenon. Critical hydraulic conditions were obtained and compared with data available in the literature. Overall, this study provides a new experimental protocol and analysis procedure for conducting centrifuge modeling studies of backward erosion piping. This study is a first step towards the full understanding of the complex field conditions