Engineering geological information: Its value and impact on tunnelling

During the last decades it has become more and more obvious that decision and risk analysis provide a framework and wide variety of tools for approaching a problem in a logic and stringent way, also within underground construction. The technique has a potential or generally improving the decision process and the handling or engineering geological information. Engineering geological information and prognoses play an important role in decision-making within underground projects. The complex nature of geological hazards necessitates a stringent handling of engineering geological information and a comprehensive quality assurance which reach beyond the scope of traditional systems. As a consequence the concept of engineering geological information requirements EGIR, including a top-down philosophy starting with the decision when approaching geological problems, is introduced in this thesis. The four corner-stones within the concept are the decision, the quantification of uncertainty, the language and the quality assurance. All four are discussed in the thesis, however, the requirement on quantification of uncertainty is treated specially. It is shown that different statistical modelling principles, of which stochastic processes and bayesian principles are important, may be used for treating different common problems. It is also shown that the choice of modelling principle depends on a number of factors, such as geological regimes and homogeneity (geological logics), scale, project stage and type of decisions. Guidelines concerning the choice of model are given and three different statistical modelling principles for treating uncertainty related to some common geological problems within underground construction are presented. Results from application indicate that uncertainty may be treated in a stringent matter and the relevance of additional information may be evaluated. However, if an unsuitable model and/or wrong engineering geological information are used, the basis for decisions may be insufficient or wrong. Examples are given in the thesis. By fulfilling EGIR and applying a top-down working procedure starting with the decision one will get a system for forming, carrying and transferring engineering geological information and establishing prognoses. A system that has the potential of improving the overall execution of underground projects and especially serve as basis for decisions.