We here at the Fish have been following the fate of Auckland’s motorway obsession with interest. It seems that NZTA (the former Transit) and their Infrastructure Minister Stephen Joyce, are more than a little bit cautious when it comes to building things in tunnels. As many of our commenters here have noted, projected costs of $540 million per kilometre of tunnels are more than a little bit ridiculous. If you’re paying $540 million / km – you’re just not doing it right !
And so, while you were all out larging it on a Friday night, the Maximus massive were researching the interwebz, trawling through the factoids and the spamdroids to bring you facts and intelligent discussion on tunnels. Why? I hear you ask? Well, it just so strikes the Fish that one day Wellington could need to install a few more fast-going linkages throughout the city, and seeing as we are short of road space in certain points, it seems likely that we’ll need to go underground. Yes, it could be a tunnel for cars, or alternatively, we could start to think long term – what if we were to tunnel for a light rail system?

So first up, is it a hard thing to do – to make a tunnel? Well: not really. Modern tunneling has moved on massively over the years. While the first few Wellington tunnels were built by hand (ie pickaxe, drills, dynamite, and horse and cart to pull the spoils away), more recently tunnels in NZ are being built with TBMs – Tunnel Boring Machines. They come in a range of different sizes, from one suitable for pedestrians and cyclists only with a 3m diameter, all the way up to a more typical 10m size, and on up to a 15m massive diameter as being used by the Chinese under Shanghai. So, being as the maximum is always more impressive than the minimum, just to give you an idea about how big these tunnels can be: here’s a picture of a huge TBM:

Yes, that is one massive machine. Depending on the cutting head, these machines can go through hard rock, crumbly rock, or even watery shingle. The UK-France Channel Tunnel was mostly through chalk: what a doddle! Auckland has a volcanic scoria rock that is strong, but heavily fractured and (but I’m no geologist) probably very easy to drill through. Wellington’s rock would be much denser stone, but again: its heavily fractured, and so not a problem for the right TBM. And for those of you that are asking “How does it work?”, watch this:

So the principle is still the same for small ones as it is for big ones. The thing is, of course, that a TBM costs a lot to buy and to set up, as well as an ongoing cost per kilometre. Mind you, once it is set up, it would surely be simpler to just keep it going: ie a longer tunnel should presumably cost less per kilometre than a series of shorter, stop / start tunnels. So how much does it cost to buy one? We had difficulty finding prices advertised on the net – there is only one US maker (Robbins) and the rest are either Swiss / Austrian / German (ie Herrenknecht) or Japanese (ie Mitsuibishi). But there is a site where you can go to buy a used one : here and there’s even a newish Robbins TBM for sale there (main beam, open gripper, 9.8m diam shaft) for just a smidgen under US$ one million (normal cost about $10-20 million US$). For heavens sakes: there’s even one for sale on Ebay.

If you want to know more about these beasts, here is a really good site all about the tunneling industry: The City of Ember Underground site. There are also many more sites that are just totally wacko – one alleging that the US has had nuclear powered tunneling machines that have been boring their way across America by using fusion to melt the rock into a smooth glassy opening, and others alleging that America is criss-crossed by these high speed tunnels in which travel trains traveling at over 14,000 miles/hr (thanks to jayseatee for that disturbingly fantastically weird link).
I’m inclined to be a little sceptical of claims of nuclear-powered, rock-melting TBMs (called NTBMs or Subterrenes) as I’m sure that as with everything military, clever civilians would have got hold of it and be making money out of it (Teflon, stealth technology, even the Internet): and I’m not sure anyone would want to be traveling through tunnels bored with controlled nuclear explosions, due to the small matter of radiation… besides – our famed Nuclear Free stance would stop NZ from using that technology.
So lastly: what about the costs? We haven’t got much info on the latest NZ costs, but some comparisons on overseas costs in year 2000 US$ went something like this:
Norway $ 3 million / lane / km
Sydney $ 15 million / lane / km
Boston $ 47 million / lane / km
Tokyo $ 230 million / lane / km

The Norwegian tunnels were on a very long stretch – over 50km long; the Sydney tunnels are more similar to the NZ situation; while both the Boston and Tokyo costs are extortionate due to the extreme urban nature of the scheme. The picture below of the Boston “Big Dig” through city streets will give an indication of why that project had massive costs: building a multi-lane motorway about 5 stories below ground through a dense and historic city streetscape with massive underpinning, and spanning over existing underground metro lines – no wonder it was expensive.
A 4 lane motorway ($540 million / km quoted) is therefore costing (in 2008 NZ$) some $135 million / lane / km. It seems just totally unlikely that in NZ, through basically virgin land in Auckland, that our tunneling costs should ever be as high as that. In Auckland, something just doesn’t add up.
Only one thing does add up – Let’s call in the Norwegians to build tunnels in Wellington!

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