The proposed approach combines geomechanical characterization, with the results of in situ testing, and back analysis. Especially for in situ testing, a new method is developed for obtaining in an efficient and economic manner specimens of weak rocks. The results of the different methods employed indicate a good agreement between expected and as monitored behavior. The paper is developed with reference to the design of the largest in cross-sectional area railway junction in Europe, the Borzoli Cavern.