Integrating internal erosion into risk charts: a simplified approach for earth dams

Risk evaluation of embankment dams is typically based on slope stability analyses considering rising piezometric levels and their impact on safety factors. However, these methods often overlook internal erosion, which may lead to failure before slope instability occurs. This study presents a methodology to incorporate internal erosion into dam risk classification charts, enhancing current assessment models. The approach uses hydraulic gradient analysis to better capture internal erosion mechanisms and avoid unrealistic assumptions related to elevated phreatic surfaces. The method was applied to a case study considering two failure modes: sliding instability and internal erosion. For internal erosion, hydraulic gradients within the dam were calculated and compared with critical thresholds. Safety factors were defined as the ratio of critical to observed gradients and linked to monitoring data to determine risk levels. Gradients were also translated into equivalent piezometric surfaces to align with conventional slope stability analysis. The framework classifies risk into four categories (normal, attention, alert, and emergency) based on the more severe result between failure modes. This integration allows for clear and actionable decision making. Overall, the results demonstrate that including internal erosion in dam risk evaluations leads to more realistic assessments and improved safety by reducing overly conservative assumptions.