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  Performance predictions in hard rock TBMs Experiences with NTNU and Q TBMmodels

  Performance predictions and cost estimates are often decisive in the selection of excavation methods and have a major influence on the planning and risk management of Tunnel Boring Machine (TBM) excavation projects. 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, and the geological risk involved becomes critical. There is an urgent need for reliable prediction to facilitate the control of such risk and to enable delays and budget overruns to be avoided. When using predictions models, an appropriate understanding of the model methodology and limitations is of great importance for a reliable application of the models and for consistent assessments. The NTNU and QTBM models have been applied for the evaluation of recently completed hard rock TBM projects, both during geological pre-investigations and prognosis and during later tunnel excavation. Not only hard mixed-face conditions but also numerous fracture zones have been described and predicted, and ultimately treated with pre-injection. The present paper evaluates and discusses the applicability of the NTNU and QTBM models in hard rock TBM projects with fracture zones.

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