ABSTRACT
The assessment of risks associated with the use of a shielded TBM to excavate a hard rock tunnel is presented in Table 3, and that for drill and blast excavation is presented in Table 4.
5 RESULTS AND DISCUSSION
It can be seen from an initial inspection of Tables 3 and 4 that the number of hazards associated with a shielded TBM at Young Dong would be much greater than for the drill and blast method. The principal reasons for this include the:
• The sophistication of modern TBMs which require a high level of technological input for their successful operation and maintenance
• The relative inflexibility of mechanized excavation and lining systems to deal with conditions for which they may not have been specifically designed
• The dependence of the tunnel progress entirely on the performance and reliability of a single item of mechanical plant.
