ABSTRACT
The need for tunnels everywhere and in every kind of ground and environment is growing rapidly, especially for tunnels excavated in congested urban areas. Tunnel Boring Machines (TBMs) provide a number of technical alternatives for handling the specific issues associated with tunnelling in urban environments. Ground conditions play a key role in the type of TBM selected and in the TBM’s performance, for example, rock strength, fractures and abrasivity, presence of faults and the ground capability to accept an eventual groundwater level drawdown. Different TBM technologies may be used to cope with rock conditions, including pressurized and open mode excavation.
Tunnel diameter also influences the TBM choice and the associated progress rates, with high dependence on the rock strength and abrasivity. Rock TBM tunnels allow different lining alternatives including one or two pass linings, and allow several lining alternatives to simplify later tunnel connections with other tunnels or galleries.
These concepts will be analyzed in this paper, supported with examples of completed and ongoing projects that feature different TBM types in urban areas. These include the hard rock machines used in the recently opened East Side Access, Manhattan, New York and in the Sydney Metro Northwest project, the ongoing mega Earth Pressure Balance (EPB) TBM used in Subway Line 9 in Barcelona and the Slurry TBM used in the Joint Water Pollution Control Plan (JWPCP) in Los Angeles.
