Enormous Tunneling Machine 'Bertha' Blocked By 'The Object' 339
An anonymous reader sends word that 'Bertha,' the world's largest tunneling machine, which is currently boring a passage beneath Seattle's waterfront, has been forced stop. The 57.5ft diameter machine has encountered an unknown obstruction known as "the object."
"The object’s composition and provenance remain unknown almost two weeks after first contact because in a state-of-the-art tunneling machine, as it turns out, you can’t exactly poke your head out the window and look. 'What we’re focusing on now is creating conditions that will allow us to enter the chamber behind the cutter head and see what the situation is,' [said project manager Chris Dixon]. Mr. Dixon said he felt pretty confident that the blockage will turn out to be nothing more or less romantic than a giant boulder, perhaps left over from the Ice Age glaciers that scoured and crushed this corner of the continent 17,000 years ago. But the unknown is a tantalizing subject. Some residents said they believe, or want to believe, that a piece of old Seattle, buried in the pell-mell rush of city-building in the 1800s, when a mucky waterfront wetland was filled in to make room for commerce, could be Bertha’s big trouble. That theory is bolstered by the fact that the blocked tunnel section is also in the shallowest portion of the route, with the top of the machine only around 45 feet below street grade."
And so it begins (Score:5, Informative)
This tunnel was locally controversial, with opponents arguing that
- it was expensive
- it wouldn't help with Seattle's traffic problems, AND
- these monster boring machines have a track record of getting stuck underground, and then what are you going to do? Call Roto-Rooter?
Sounds like it's starting to come true...
Re:Near the waterfront? (Score:5, Informative)
An anchor that can block a five-story-high tunneling machine? I've seen some massive anchors from old battleships, but to block this it would have to be an order of magnitude larger.
Best bet is either on a giant boulder of some hard rock, or maybe a buried building of some sort. It's not ship debris - this thing is the *size* of some large ships.
Re:Time to call in... (Score:3, Informative)
How do we know that the SCP Foundation wasn't already aware of this object, and the whole tunneling project wasn't actually a cover for securing it? Rest assured that whatever "it" is, "they" have a suitably mundane explanation already prepared.
Re:Doesn't sound very stable... (Score:5, Informative)
The machine puts up tunnel walls as it goes.
http://gizmodo.com/big-bertha-is-digging-seattles-massive-underground-fre-662469199 [gizmodo.com]
Concrete panels go in right behind the bore head. Infront of the maw is ground below the water table. The bore head forms a seal and the tunnel behind the bore head is pumped dry of water that leaks through.
Re:Near the waterfront? (Score:5, Informative)
They couldn't build an Earth tunneling machine that cant deal with a giant boulder ?
The cutter heads break apart stationary rock and other objects. The theory in the local press here in Seattle is that the bolder is being spun with the cutter head, thus the cutter teeth canâ(TM)t grip it, and itâ(TM)s too big to fall through the openings in the cutter head that channel debris to the exit conveyor.
Cannot back up (Score:5, Informative)
No can do. As the machine moves forward the tunnel walls are built behind it. TBM's have no reverse.
Actually the machine isn't stuck, yet. They stopped the machine because it encountered resistance. If it actually does get stuck the machine can't be dismantled underground and removed. They would have to dig it out from above, remove the TBM and install a new one. If it does get stuck let's just hope it's not under a skyscraper.
http://www.wsdot.wa.gov/News/2013/12/10_SR99tunnelingstatement.htm
http://www.thestranger.com/seattle/what-could-possibly-go-wrong/Content?oid=4399657
Re:Doesn't sound very stable... (Score:4, Informative)
They are concerned and not just about a cave-in. Vibration could cause lot's of damage. According to the WSDOT the machine is not actually stuck yet. They stopped it because they encountered resistance. The walls behind the machine are already built so there's not much risk of a cave-in. But there is a risk that nearby infrastructure could be damaged if they move forward. They can reinforce the infrastructure above but if they actually get stuck it could have enormous consequences. The machine would have to be dug out and replaced (at $80 million per borer). Add in the cost of reinforcements and digging a big hole, then consider that the $3.1 billion project is only bonded up to $500 million.
http://www.thestranger.com/seattle/what-could-possibly-go-wrong/Content?oid=4399657
http://www.wsdot.wa.gov/News/2013/12/10_SR99tunnelingstatement.htm
Picture of concrete panels lining tunnel (Score:4, Informative)
http://www.gizmag.com/worlds-largest-drilling-machine-bertha/28311/ [gizmag.com]
Re:Doesn't sound very stable... (Score:4, Informative)
I am not a tunnel excavating expert but my 5 year old thinks these are among the coolest machines that have ever been constructed and likes educational shows that are about tunneling where they use a TBM.
Re:No camera or observation hatch? (Score:4, Informative)
It's a TBM for waterlogged sand and dirt (Score:5, Informative)
This is an earth-pressure-balance type TBM built for soft sand and dirt, below water level. Compressed air is used to keep water out at the working face. That's what's needed for a tunnel under the Seattle waterfront. It can cope with rocks and boulders, but not a solid rock face. It's not a hard-rock TBM. Those have very different cutters, but can't handle waterlogged soil.
Tunneling is like that. Stuff like this happens. It will be handled.
Re:Doesn't sound very stable... (Score:4, Informative)