Piping erosion safety assessment of flood defences founded over sewer pipes

Piping erosion is one of the major causes of failure of flood defences. The occurrence of this failure mechanism is difficult to predict and it can be triggered during a flood event. The inclusion of hard structures under flood defences will change the probability of occurrence of this erosion process. The present study aimed at understanding the effect of an embedded sewer pipe under the flood defence foundation in its safety assessment for piping erosion failure. This was done by setting a probabilistic analysis framework based on emulation of finite element models of porous media flow and the fictitious permeability approach. The effects of size and location of the sewer pipe were evaluated via a deterministic safety factor approach. Afterwards, emulators of the most safe and unsafe models were trained and used for probabilistic assessments. The results showed that the embedment of a sewer pipe in the flood defence foundation has a significant effect on its safety. The magnitude of the effect is highly dependent on the size and location of the sewer pipe. Furthermore, the foundation permeability uncertainty shows a conditional effect with respect to the sewer pipe size and location.