Prediction of penetration per revolution in TBM tunneling as a function of intact rock and rock mass characteristics

• An important aspect in the design of a tunnel is the evaluation of TBM speed
• Some formulations which predict the penetration per revolution are complex
• A new formulation is presented to estimate the penetration per revolution
• The proposed formulation is simple and requires a small number of parameters
• A comparison between the existing formulations and the one proposed is presented
• The results obtained with the new formulation are compared with a case history

A new empirical formulation is presented which can be used to estimate the penetration-per-revolution for TBM tunneling, derived from TBM monitoring data of alpine tunnels in the North-West of Italy. This formulation is easy to use and allows the contribution of both the intact rock and of the rock mass characteristics to be taken into account. The contribution of the intact rock is taken into consideration through the use of the uniaxial compression strength, while the influence of the rock mass is considered through the use of the GSI. A statistical interpretation procedure of numerous operative data from TBMs used for the excavation of tunnels in rock, and of the characterization of intact rock and of the rock mass, has been developed to determine the proposed formulation. In particular, the penetration-per-revolution (p) recorded during excavation, the forces applied to each disk (FN), the Geological Strength Index (GSI) and uniaxial compression strength of the intact rock (σc) along the stretch have been compared.The set-up formulation is simple to use and reliable for tunnels excavated in metamorphic rock, as it has successfully been compared with the TBM net advancement speed data of a well-known case history taken from the literature (the Maen tunnel in Italy). Comparisons with results obtained with the Norwegian School method (NTNU) and Barton׳s calculation model have also led to positive results.