ABSTRACT
Tunnel Boring Machine (TBM) method is widely increasing its applicability and often TBMs must deal with hard-to-very hard, massive, and abrasive, rock mass conditions (i.e. very to extremely low rock boreability), which is associated with high risk to advance rate and cutter consumption, and where the machine specifications and operational parameters approach are of great relevancy.
The high risk to advance rate and cutter consumption must be limited based on a proper pre-investigation, tailormade design of the machine according to the expected geological conditions and appropriated approach of the TBM operation, where personnel knowhow, at all levels, is required. At the project planning stage, when characterizing rock boreability for hard rock TBM projects, more emphasis should be put on the areas with the extreme rock mass conditions (i.e., low penetration rate, high cutter consumption). The tailormade design of the machine, according to the expected geological conditions, must include design of cutters, cutterhead, main bearing assembly and the rest of the TBM system as well. Strict requirements to the TBM design must be considered from the very beginning (i.e. tender stage). The operation of the TBM in hard rock should focus on efficiency to maximize production and limit the construction cost. The relationship between cutter thrust and penetration rate is exponential. High cutter thrust combined with optimal RPM, which means increasing penetration per revolution as much as possible, will be beneficial for the rock breaking process and cutterhead wear and cutter consumption.
The present paper discusses the main risks when boring in hard-to-very hard, massive, and abrasive rock mass conditions providing guidelines for the design of the machine (i.e. machine specifications) and the most optimal and efficient approach for the TBM operation and maintenance in such challenging conditions.
