An example of back analysis of the geomechanical properties of a rock mass in “flysh” concerned with an highway tunnel driving

This work has been developed to compare the geomechanical behaviour of a rock mass concerned with a highway tunnel drilling to the design previsions. This study starts from the analysis of the geomechanical parameters as estimated during the design phase after the survey. Hereafter, we report the elaboration methodology, the adopted classification criteria and the main quantitative evaluations that permitted to rebuild the geological and geomechanical outline. Then, a comparative analysis has been performed between the results of the design calculation procedures and those calculated work in progress to interpret the indications and the values of the monitoring measures of this excavation. After having synthetically described the main geological and geomechanical features of the excavated rock mass, we briefly relate on the adopted calculation procedures and, at last, we compare the different parameters. As the geomechanical behaviour of the various lithofacies are naturally different, only the “flysh” lithofacies has been analysed, as it presents a more complex and interesting behaviour from the scientific point of view. Some closing considerations have been made to assess the results obtained from the different procedures.