TUNNEL BORING machines that can produce square, figure-of-eight- shaped or elliptical cross sections will soon be available in Europe, a packed meeting of the British Tunnelling Society heard last week.
'Even triangular is possible,' said Kawasaki tunnelling department general manager Yasunori Kondo, whose presentation on 'Exotic TBMs' was described from the floor as 'the most interesting talk I've heard in nearly 30 years of BTS meetings'.
Kondo gave details of a wide range of advanced equipment unknown to European tunnellers. Some were already in use on projects in Japan, others are still at the prototype stage.
The square TBM now on trial uses a conventional rotating shield fitted with supplementary planetary-action cutters. However, more unusual cross sections will be possible with a new generation of 'parallel link' excavating shield machines. Here the shield oscillates rather than rotates, ensuring even wear across all the cutters and so longer maintenance intervals.
The first parallel link TBM to go into service will be circular, but Kawasaki hopes tunnel designers will take advantage of the new technology to economise on excavation by specifying more efficient cross sections.
Also in service are 'mother and child' TBMs, used for tunnels with branches. Normally a shaft would be needed to install a second separate TBM to bore a branch tunnel. Instead, Kawasaki's 'mother' TBM carries up to three 'child' TBM kits. These emerge at junctions and carry on independently.
A full report will appear in ICE News next week.