The Wear of Tunnel Boring Machine Excavation Tools in Rock

Some of the most important aspects in the study of the fragmentation of rock due to the action of TBM disks concern the abrasiveness of the rock and the wear of the tools. The wear of the disks in fact means that they have to be substituted, with consequent effects on the efficiency of the excavation, on the speed of advancement and therefore, on the times and costs of constructing the tunnel. After having conducted a detailed examination of the methods that have become established in scientific literature to assess the degree of abrasiveness of rock and the potential speed of tools wear, the formulas that allow an estimation to be made of the mean advancement velocity of the excavation machine are presented, considering the effect of wear on the tools and the necessity of substituting them. By applying the Barton method to four different types of rock, for three types of tunnel diameter, it has been possible to obtain the trend of the global advancement velocity of a TBM with variations of the GSI index. It has been possible to note how the CLI parameter, which describes the potentiality of the rock to wear the disks, can influence the global advancement velocity of the TBM to a great extent. Data obtained during the recent construction of a tunnel in North Italy have made it possible to compare the currently available calculation methods and obtain the CLI parameter through back-analysis. A good agreement has been found, above all between the Barton calculation method and that of the Norwegian School, both of which have shown to be reliable systems for the forecasting of the wear of disks on a TBM and for the estimation of the advancement speed of the excavation machine.