Approach to Estimate the Probability That Internal Erosion Will Initiate a Breach through an Embankment Applied to Levees with an Important Linear and Heterogeneous Facies

Internal erosion in embankments and their foundations is one of the main cause of levee failures. Unfortunately, this potential failure mode cannot be easily analyzed using numerical equations or models and the associated risk is difficult to quantify. This issue was studied within the hazard studies of the Drac river levees system in Grenoble city in France, maintained by the SYMBHI (Syndicat Mixte des Bassins Hydrauliques de l'Isère) and EDF (Electricité de France) as part of the new French "levees" regulation of 2015. To evaluate the probability of failure of the levees system due to internal erosion mechanisms, a probabilistic model is developed based on an empirical approach combining a back-analysis of levees behaviour during the impoundment of part of the levees system and the probability assessment proposed by Vick (2002). This approach allows the definition of a hydraulic gradient used in the assessment of the probability of failure. The need for such method was motivated by the important levee linear to be studied (about 36 km) and the heterogeneous facies of the levees system due to the successive construction stages and the heterogeneities of the foundation materials. Indeed, this heterogeneity makes the deterministic approach illusory. The defined approach is applied to the whole embankment system in order to identify, for a given flooding scenario, critical profiles where the risk of internal erosion could be significant. A detailed analysis of these critical profiles is then carried out in order to refine the probability of failure due to internal erosion.

Keywords: internal erosion, levee, failure, risk, probability, embankment