The influence of wear on the interaction between the cutting tools and the rock face

At present, the demand of long tunnels with high cover is growing. At these depths, a rock mass consists mainly on hard rocks, which are often excavated with hard rock TBMs, whose costs per meter are lower than conventional excavation methods. The excavation principal of the TBM consists on disc cutters distributed on the cutterhead, which is pressed against the rock face. These disc cutters interact with the rock and cause chipping of the rock. The distribution of the tools on the cutterhead, especially the spacing between adjacent tools, has an important impact on the interaction. The wear of the discs, which is a major cost factor, can have a significant impact on the efficiency of the cutting process. The main purpose of this work is therefore to investigate the impact of wear on this cutting process, which can be done by experimental tests or numerical simulations. In Politecnico di Torino, there is an Intermediate Linear Cutting machine (ILCM), which is able to test rock samples with different cutting configurations. Testing the same configurations with discs with different stages of wear would allow to identify the impact of wear. The ILCM could not be used in the scope of this work, but the data produced by this machine were analyzed and it was discovered that for the existing data points, the maximal normal force has a local minimum for the optimal cutting configuration and therefore, a connection between the two could exist. Moreover, a new theoretical force model is created and compared with an existing model and experimental data to provide a better basis for numerical simulations. The new model adapts better to the shape of the contact pressure distribution of the experimental tests. Finally, proposals are made in which direction research could be based on the results of this work.