Analysis of the Tunnel Boring Machine Advancement on the Bologna-Florence Railway Link

Problem statement: The high-velocity railway link between Bologna and Firenze (Italy) is today under construction and several tunnels have to be excavated for this purpose, some of these using TBMs. A small diameter tunnel, named Cunicolo ginori, was realized by TBM parallel to a large railway tunnel (Vaglia), at the distance of only 35 m. Approach: The Vaglia tunnel had been excavated by conventional methods and provided, thanks to a detailed survey and a systematic geotechnical monitoring (rock quality evaluation and convergence measurements) the characterization data of the crossed rock mass; moreover the TBM performance data in Cunicolo ginori were continuously monitored. A tunnel stretch, 587 m long, was recorded and the analysis of the data from both surveys allowed to correlate the geomechanical parameters of the rock-mass to the TBM performances (net advancement rate, thrust, specific energy). Results: Based on this large amount of data a new system to predict the net TBM advancement rate for a tunnel in rock masses of known geological and geomechanical characteristics was then developed. Also the Utilization Coefficient (CU) can be correlated to the rock quality Indices: The net advance rate and the utilization coefficient provide a mean to foresee the gross advancement rate and to evaluate the suitability of a machine for the excavation of a tunnel. Conclusion: In this study, an analysis had been carried out on about 587 m of a service tunnel, excavated by a TBM in a flysch formation.