msquared48 - Is this your doing?

[IRstuff]

The article nicely explains why the machine can't back up.

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[bridgebuster]

I wonder if they could do some soil grouting behind the TBM, remove some lining, then back the machine up? Just a harebrained idea.

 

[MikeHalloran]

Now I'm getting the impression that what they were tunneling through is not monolithic rock, but dirt with rocks in it. I.e., if you remove a segment of tunnel liner behind the machine, the roof will cave in, and the dirt will keep pouring in until the tunnel fills or until the resulting cavity reaches the surface. Dangerous, indeed.

Also, because it's the largest such machine ever built, they can't just buy a used one, or parts of one, from somewhere else.

I wonder if they could leave it where it is, buy two (used?) TBMs of ~half the size, and drive two smaller tunnels instead of one big one?

Doesn't matter, really. It smells like the dispute over cost overruns, from estimates based entirely on fantasy, with local and state politicians trying so hard to screw each other, will spend decades in court.





Mike Halloran
Pembroke Pines, FL, USA

 

[msquared48]

You got it Mike. Part of the reason we have so many problems with landslides here - locally unstable glacial till soils.

Mike McCann
MMC Engineering

 

[dik]

Ron:
"Any chance of starting another boring machine at the other end of the tunnel and working back toward the broken one, then removing both when old one repaired?"

Great, now we have two machines stuck... the tunnel isn't really needed... matter of filling the void with CLSM or something and forgetting about it...

Dik

 

[btrueblood]

"I'm guessing the well casing/ whatever was made of steel, and tough enough and ductile enough to get wrapped around the cutter head like fishing line around a propeller."

Can't disagree, Mike, but the point is/was that the bore path was known to intersect a number of these casings (18 or so if I remember right), the casings were left by borehole wells made by the state DOT for soil/rock sampling. Point being, if you knew the casings were in the way, would you not have designed/programmed the cutter head to manage them?

The surrounding earth being drilled is mostly compacted mud/clay and glacia "till" (mixed gravel and mud). Oh, and below sea level in a wet climate, so really wet too. Pretty much guaranteed to collapse unless you seal it. So, whent the seal failed...well, now we have a driller head buried up to its figurative armpits in mud.

 

[msquared48]

Was there ever any mention if this was the first casing encountered?

Mike McCann
MMC Engineering

 

[davidbeach]

Ya know, following the 1989 earth quake, San Francisco just took down their equivalent of the Alaska Way viaduct and didn't replace it with anything. Seems to have turned out ok.

 

[IRstuff]

Yeah, but that section was relatively short, and in both directions, the traffic is pretty messy these days.

Nevertheless, whatever the problems there, they pale in comparison to the southbound 80 to Bay Bridge transition, which, on, say, Friday nights, can take a couple of hours or more to get through to the city. I once decided to head down to the San Mateo bridge to cross the Bay, just to avoid the Bay Bridge. The Bay Bridge seems to do little relieve the congestion on the approaches.

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