The determination of geomechanical properties of weak and complex rocks presents special difficulties due to the problems arising in sampling, specimen preparation, and testing this type of material. Questionable is also the representativeness of the results since the tests are usually conducted on small specimens that cannot depict the structure of a complex formation. One usually resolves these problems by using classifications and empirical relationships between rock mass properties and geomechanical indices. Nevertheless, such an approach yields questionable results, since defining the state of the parameters consisting the geomechanical classifications is difficult to say the least for complex and weak formations. A case is presented where an integrated approach was used, consisting of direct and indirect methods, aiming at overcoming these difficulties. 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 employed for obtaining in an efficient and economic manner specimens of weak rocks. The results of the different methods used indicate a good agreement between expected and observed-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.
