Accounting for Uncertainty in Geotechnical Design using a Probabilistic Approach
A simple but systematic probabilistic approach was adopted for the preliminary design of an example tunnel alignment for the Egnatia Odos Highway in a heterogenous molasse formation. The purpose of this investigation was to discern sources of geotechnical uncertainty, and evaluate its effect on the output design parameters. Rigorous analyses of the key parameters and factors were undertaken following a standardised method for the design of underground structures. Statistical analysis of the intact rock strength parameters and project specific influencing factors allowed the determination of sources and quantification of uncertainty. Furthermore, it enabled the geological units encountered to be classified into geotechnical units or Rock Mass Types (RMTs). Finally, the results of the numerical modelling allowed the classification of the different behaviours into the pre-defined Rock Mass Behaviour Types (RMBTs), which subsequently led to the preliminary design of the respective support sections.