Internal erosion initiation processes in homogeneous earth fill dams: a case study

In a homogeneous earth fill dam, an initial process of internal erosion was observed near the base of the downstream slope, which is one of the main dam failure causes in the world. This problem was adequately solved, and research was started aiming to find the causes of the detected anomaly. The history of the structure was investigated, field testing results were analyzed and undisturbed samples were collected in different regions of the dam. Characterization tests, saturated permeability coefficients tests under different effective stresses and flow directions, and Filter Papel tests were run. Results were incorporated into computational models to investigate the behavior of hydraulic gradients and the height of the exit point of the phreatic line defined on the basis of monitored piezometers installed at the site. The software Plaxis LE was used in this study. It was evaluated whether the adoption of unsaturated parameters or 3D analysis would promote any change in the flow pattern in the studied structure, which did not occur. It was also considered whether the soil-atmosphere interaction could generate critical hydraulic gradients through rainfall and evaporation cycles, but there were no critical results either. Finally, it is concluded that effects of natural vegetation previously found in Dam X may have led to the observed internal erosion process. These somewhat unusual findings are relevant for improving the understanding of vegetation impacts on earth dam safety and can help guide future monitoring and, particularly, maintenance practices to prevent similar issues in other similar earth fill dams.