Progression rate of backward erosion piping in laboratory experiments and reliability analysis

Backward erosion piping is an important failure mode of dikes and dams. The time required for the backward erosion process to result in dike failure is expected to be an important factor in the safety of dikes. This holds especially in coastal and estuarine areas which are dominated by storm surge, and pipes may not fully develop during a storm. Furthermore, insight in the duration of the various piping stages can assist in developing effective emergency mitigation measures. However, the temporal development of piping is hardly studied quantitatively, as most experimental and modelling studies focus on the critical head. Also data of real breaches is generally insufficient to determine the time to failure. As a result, currently the contribution of time required for pipe growth cannot be quantified in a deterministic and reliability analysis. In this study, it is investigated how the pipe progression rate can be predicted and applied to dike reliability. The data analysis is based on a composition of 45 small, medium and large scale experiments from six studies. Advancement rates are related to the applied hydraulic gradient and soil properties using a multivariate analysis. From the analysis we derive an empirical model for the advancement rate, including a quantification of the uncertainty. This model is applied in a reliability analysis of a hypothetical coastal and riverine dike. The results of our analysis may be used to validate transient numerical piping models, perform time-dependent probabilistic dike safety analysis and support emergency response.