Studies carried out to analyse the risks of levees must include an evaluation of the probabilities of occurrence of different failure mechanisms (overflow, internal erosion, sliding and scouring). The probabilistic quantitative evaluation of these mechanisms remains difficult due to often insufficient input data, the natural variability of the materials, structures of very long length, the availability of mechanical models for certain failure mechanisms, and the random nature of the stresses involved. This makes it necessary to call for expert judgement to evaluate the probabilities of failure. However, expert judgement is generally associated with a qualitative and subjective dimension, and it comprises biases liable to impair the capacities of an expert to elicit their evaluations. This article proposes an approach to processing expert judgement that includes the modalities of Individual expert Elicitation, Calibration, Aggregation, and Debiasing of expert judgement (IeCAD). This IeCAD approach has been developed for river levees in view to correcting biased expert evaluations in the case of evaluating the failure probability of structures.