Dear Sir
The good sense of Nick Barton’s article (T&TI, June 2003), stating the need for a more balanced and realistic approach to proposals to use TBMs in rock, was highlighted by another near-tragedy reported from Yuncan HEP in the same issue. There is little question that the use of modern shielded TBMs provides a proven low risk and efficient method of tunnelling in soft ground conditions. However, the risks associated with ‘hard rock’ machines can be extremely high, and if we are honest, simply unacceptable.
We – meaning clients, consultants, contractors, manufacturers and media – have to get the message across that the choice of method for rock tunnels – particularly those of great length – must be based on a rigorous and properly documented assessment of risk, and if risks cannot be reduced to acceptable levels a method must be rejected. Difficult decisions must be made. Hybrid approaches suggested by Nick Barton may have to be considered more routinely as part of the selection process if we are to uphold the credibility of the industry and profession.
Nick Swannell
Associate Director (Engineering Rock Mechanics)
Halcrow Group Ltd
