Thursday, October 23, 2008

Big Becky Mired in La Merde

I was just wondering, what's happening with that dang tunnel? I had worked on it for a while, so it interests me. As well, with all the earlier bad experience we had with tunnels in the area, I recoiled at the thought. The old guys talked about the first tunnels, but they blasted the crap out of it, and had a very strong sandstone roof.

Then I came across this page, with is absolutely wonderful! It tells the current position, and how much rock is falling on their collective heads. Still a heck of a lot! When you use a tunnel boring machine (TBM), you expect precision to the inch. You use a TBM to get a wonderfully smooth concrete liner, at minimum cost.

Click on those pictures below on that page. They are fantastic! Look at the overbreak! Think of how they are going to line that sucker! I can't imagine that drill and blast would be any worse, so the TBM is a total waste of money here. When you line a long water tunnel, you want it as smooth as a baby's butt. This tunnel will not last 100 years, and you can't get back into it, after an earthquake tears it to shit, because you can't drain it!

When the rock is this bad, and the stresses are so high (note the classical shape of the overbreak), I wonder about the long-term stability of the tunnel. They are using steel mesh and shotcrete for the support, so I hope all the strains settle before the final liner. But the tunnel has such a bad cross-section that I'm not too sure.

What would have happened had the listened to the RockMeister Harold? No TBM for one thing, and more attention to the rock stresses. I would have either gone two stages, and put in a flatter, eliptical section.

So let's not look at this as a Total Financial Disaster (which it is), but as a great case study for future students of Rock Mechanics.


No comments: