The Weakest Link: Spatial Variability in the Piping Failure Mechanism of Dikes

Abstract

Piping is an important failure mechanism of flood defense structures. A dike fails due to piping when a head difference causes first the uplift of an inland blanket layer, and subsequently soil erosion due to a ground water flow. Spatial variability of subsoil parameters causes the probability of piping failure to increase, often to unacceptable levels. The general research question is: How can we incorporate spatial variability in a flood defense system design dealing with the piping failure mechanism? The question in solved in three steps: first by quantifying the spatial variability in subsoil parameters, second by assessing the influence of this spatial variability on the piping mechanism and third by analyzing optimal decisions to deal with unacceptable situations. There are two new models presented in this thesis. The first model, is a simple design model that uses historical failures to assess the piping safety. The second model describes the formation of piping erosion paths in spatial variable soils. Especially the second model might potentially lead to improvements in piping modeling and potentially in cost reductions. The main conclusions from this thesis is that the piping mechanism and influence of spatial variability in the subsoil are a very significant threat to flood defenses. However, performing local soil measurements in combination with local dike improvements can be a cost-effective method to deal with unacceptable piping failure probabilities.Hydraulic EngineeringCivil Engineering and Geoscience