In Chapter 4, Rémi Béguin, Pierre Philippe, Yves-Henri Faure and Cyril Guidoux devote their attention to a still under-researched mechanism of erosion, but which can be found in numerous dikes: contact erosion between two types of soil. The description of the mechanisms that take place at grain level allows for a better understanding of the conditions under which they occur as well as of the kinetics of erosion. Finally, several possible scenarios that might lead to a failure of hydraulic structures are being suggested.