Let's get (geo)physical

29 May 2008

Flicking through the articles in T&TI this month, shows to a certain extent the degree to which the tunnelling industry can cope with fresh challenges in adverse situations. Installing yielding concrete elements within steel rib supports to deal with highly squeezing ground is well in effect at the St Martin La Porte access adit on the Lyon – Turin rail tunnel (p15). The re-designed lining method is now allowing steady advances to be made on a project that had been virtually stopped by bad ground.

Another example of ingenious engineering can be seen in Istanbul (p21), where a method of docking slurry TBMs with an immersed tube element is to be tried for only the second time ever (note: I believe this has been done once before in Hong Kong, but am happy to be corrected!). Also, and unusually for T&TI, we have handed over five pages this month for part one of a two part article describing the history and future development of the Herrenknecht Mixshield TBM (p35). Without a doubt, the Mixshield has revolutionised the way tunnelling is carried out in difficult ground conditions.

So, with all of this modern technology available to us, and a host of engineers capable of using it, it’s ironic to see that ‘unforeseen ground conditions’ have been put forward as largely responsible for the collapse of the Pinheiros Station shaft on São Paulo’s Metro Line 4 last year, that killed seven people (p27). Sadly, this tragic event will live on in the public’s memory far more than the positive ones mentioned before it.

With all the technology and experience we have, our major nemesis is still the medium we work in. Extensive traditional site investigations are said to be overly costly and virtually physically impossible in some sub-urban construction projects resulting in a call for a costlier, deeper positioning for tunnel structures and stations in such areas. These additions in cost will only prove prohibitive in getting any underground urban projects built.

The expression ‘unforeseen ground conditions’ is so commonplace that maybe it’s time to invest far more into a new type of technology to make it less ‘unforeseen’. What happened to all the research we heard about a few years ago into 3D geophysical predictions of the ground? Has it really proved impossible to do? With all of our technological advances in other fields, I find it hard to believe we can’t hone our understanding of geophysical modelling.

More reliable modern site investigation methods could not only go a long way to preventing such tragic incidents as the Pinheiros collapse, but actually make urban projects more financially viable, which for the industry can only be a good thing.

Tris Thomas


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