Georg H. Erharter , Suzanne Lacasse, Franz Tschuchnigg

Engineering geology is highly affected by uncertainty related to the geology, geotechnical parameters, models used and methods. While the technical aspects of ground-related uncertainty are increasingly investigated, the terminology to communicate uncertainty (i.e. phrases such as “it is very likely that”) has not yet been unified and experts use it however they see fit. The problem arises that due to varying levels of experience, personal biases and cultural backgrounds, people may understand uncertainty statements very differently, which is misleading and can even result in legal disputes. This contribution investigates the usage of uncertainty terminology in ground-related disciplines and finds that there is a pronounced prevalence of uncertainty terminology in disciplines dealing with geo-materials and that there is a special need to express uncertainty related to quantities (e.g. “most of the tunnel consists of…”). In response, we propose a consistent framework to communicate ground-related uncertainty consisting of three steps: 1. if facts are to be described, describe them as such; 2. assess and state the degree of confidence in a statement based on the quantity and quality of the available evidence vs. the agreement of the evidence; 3. if high or very high confidence is achieved, describe the likelihood or quantity in a consistent manner. Using consistent ground-related uncertainty communication is essential to avoid misunderstandings which can lead to dire consequences. The proposed approach is in line with new standards, such as Eurocode 7, that demand an explicit treatment of uncertainty.