2006 Volume 55 Issue 8 Pages 777-784
The rapid excavation with TBMs is an ultimate dream to tunnelers in the world. In order to establish a useful and practical guide several ideas and concepts have been proposed up to the present. For example, there are the Tarkoy's Total Hardness (1975), Sanio's relation between rolling and penetration forces (1985), the Estimated Rock Strength by Fukui and Okubo et al. (1996), the Specific Energy in Rock Drilling by K. Ryoke et al. (1998), the Torque Variation by T. Aoki (1999), β-value by Hashizume (2000), etc. Considering the papers in the past, the authors propose the concept of the TBM Excavation Index (TEI) so as to generalize the relationship between excavation rate and variation in geological condition. This concept came from the analyses of three TBM applications to sedimentary, metamorphic, and igneous rock formations. The proposed index is based on dividing the total TBM's workload into the primary fragmentation for excavation and the secondary fragmentation for the other activities. And it is calculated with torque, thrust and penetration, excluding any uncertain constants. In conclusion, the standard deviation of 0.2 in the TBM Excavation Index clearly suggests the remarkable variation in geology, and when the standard deviation exceeds 0.2, excessive cutter wear occurs due to hard rock with low brittleness and less cracks and TBM operation is forced to be halted due to the instability of a face and its vicinity.