Experiences from tunnel boring when hard-to-very hard rock with focus in performance predictions and cutter life assessments

Abstract

The use of hard rock tunnel boring machines (TBMs) has become widely and generally used with success but in too many cases, due to inappropriate assessments, with undesirable consequences. A process of great complexity is involved during tunnel boring. When hard-to-very hard rock (i.e. low-to-extremely low boreability), the complexity is accentuated becoming, in many cases, critical for the achievement of the final schedule and reasonable tunnelling cost. Performance predictions and costs estimates have a major influence on the planning and risk management of TBM excavation projects. A proper understanding of tunnel boring and wear processes in hard rock enhances an appropriate applicability of the models for performance prediction and cutter life assessments. The paper compiles experiences and outcomes from research and consulting collaborations on several hard rock TBM projects and during the revise and extend of the current version of the NTNU prediction model for TBM performance and cutter life.