Conference Paper

Optimal Operational TBM Parameters for Efficient Hard Rock Tunnel Boring on the Basis of Rock Boreability and 'On-Site' Testing

Authors:
  • JMConsulting-Rock Engineering AS
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Abstract

Hard rock tunnel boring has become widely used and is currently an important method employed by the tunnelling industry. The development of tunnel boring machine (TBM) technology has made the approach applicable in an increasingly wider range of rock mass conditions. Technically speaking, excavations can now be carried out in almost all rock conditions using this method, given certain economic constraints. Hard rock tunnel boring leads the interaction between the rock mass and the machine, which is a process of great complexity. The tunnelling system around the excavation process has a great relevance in the final goal of performance predictions for hard rock TBMs, which is the estimation of time and cost. Operational parameters, applied thrust and cutterhead velocity (rpm), have a significant influence during TBM excavation. On the aim of efficient tunnel boring, operational parameters should be adapted to the rock mass conditions and machine specifications. 'On-site' testing has the main purpose of evaluate machine performance under a given set of geological conditions. 'On site' testing involves the commonly used penetration test and the recently introduced ‘RPM test’ and it should be followed by detailed engineering geological mapping and rock sampling for drillability assessments. A penetration test consists of a measurement of cutterhead penetration over a given time at a variety of logged thrust levels carried out at constant cutterhead velocity while an ‘RPM test’ measures cutterhead penetration over a given period at a variety of cutterhead velocities under constant cutterhead thrust. This paper analyses the influence of the operational parameters, cutter thrust and cutterhead velocity (rpm), in hard rock tunnel boring efficiency on the basis of rock boreability and 'on-site' testing.

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