In France, levees remain most of the time badly maintained; these long linear structures show signs of weaknesses on numerous occasions. Only incomplete information is usually available. The general lack of data describing the behaviour of the infrastructure during unwanted events led to estimate their safety mainly from expert judgement. Thus the ability of the expert to predict the level of functioning of an infrastructure for a type of hazard and its intensity is crucial. An error of judgement can have very serious consequences and the production of reliable information requires the ability of the expert to report accurately the uncertainties in its estimations, as well as associated confidence. In order to meet this need, our research within Incertu project (French Ministry of Ecology funding) aims to produce relevant scientific approaches and tools for the collection and processing reliable experts' statements or combined with a confidence level in the context of uncertain information and input data.