TunnelTalk reporting

Confirmation of an order with Herrenknecht for the world's largest ever TBM at 19.25m for the River Neva highway crossing in St Peterburg, Russia is followed by news of new 14m-plus mega-TBMs needed for new large diameter highway projects around the world.

With the new data in hand, our tracker of the world's mega-TBM tunnels is revised and updated.

* TunnelTalk reference below.

It is hard to say when the era of the mega-machine started. There was a time when 10m in diameter was considered the largest likely, or indeed possible. But whatever was once considered the technological limit for the size of TBMs, there are now many dozens of machines exceeding the 10m diameter size. This, of course, increases the benchmark for current mega-machine criteria. The need for ever-larger diameters is driven by the demand for ever-larger diameter tunnels able to incorporate extra and wider traffic lanes for heavy freight trucks as well as cars. Larger diameter bores are also needed to accommodate the latest in multi-modal transportation tunnels which will house both road and rail services as well as pedestrian and cycle-ways and perhaps also utility corridors.

Discussions in the past have considered the manufacture of the main bearing a limiting factor but these can now be designed and delivered in sections. Precision machining and welding has these vital components of the new mega-machines completed and built into them on site. A limit to the size and load of a single component to job sites was also considered a controlling barrier but first time on-site assembly, as promoted by Robbins in particular, overcomes some of these limitations.

Another consideration, as explained by Yasunori Kondo San at Kawasaki in Japan, is application of the thrust needed to advance such mega machines. For soft ground TBMs this force is applied directly to the precast concrete segments of the tunnel lining. These, as well as the number and size of the thrust rams around the perimeter of the machines, must be designed to take and deliver the powerful forces needed to move a mega-machine forward. There is a controlling factor on the number and power of the thrust rams needed to apply the force, as well as the surface area and ability of the precast concrete lining segments to accept the load.

Other considerations will be explored and added to the Discussion Forum as they are contributed.

References

New Zealand joins the mega-TBM tunnelling set - TunnelTalk, August 2011
Russia confirms order for largest TBM ever - TunnelTalk, Aug 2011
A second mega-TBM river crossing for Nanjing - TunnelTalk, Aug 2011
Robbins TBM rolls into hard rock history - TunnelTalk, May 2011
Nanjing Highway Tunnels - TunnelTalk, Sept 2009
Seville SE-40 Highway Tunnels - TunnelTalk, April 2010
Giant TBM accepted and heading for Italy - TunnelTalk, Dec 2010
Seattle Alaskan Way bored highway tunnel - TunnelTalk, Oct 2009

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