Ayecarumba
Ayecarumba
Joined: Nov 17, 2009
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June 25th, 2012 at 11:02:17 AM permalink
Construction is underway to dig a new "straw" under Lake Mead to provide water for the Las Vegas valley. The existing "straws" are at risk of becoming useless if the water level in the lake falls much further, so a new, deeper, inlet is required. Previous attempts to get this going have resulted in flooded tunnels (they ran into a previously unknown earthquake fault) and costly overrides due to lost equipment and time.

My question is, since the digging is starting outside of the lake, and coming up under it, what will they do to hold back the water, when the digging nears the point where the contents of the lake want to break through the remaining rock? I imagine it would be like trying to attach a hose to an open fire hydrant if they "punch" through before taking precautions.

Will they dig to a certain point then set explosive charges to blast away the last few meters? Perhaps they will drop a casing into the lake and pump the water out of it before digging out the last few meters of rock? If this is the plan, why didn't they just start from the lake and dig down, rather than the other way around?
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Nareed
Nareed
Joined: Nov 11, 2009
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June 25th, 2012 at 11:24:16 AM permalink
Quote: Ayecarumba

Will they dig to a certain point then set explosive charges to blast away the last few meters? Perhaps they will drop a casing into the lake and pump the water out of it before digging out the last few meters of rock? If this is the plan, why didn't they just start from the lake and dig down, rather than the other way around?



1) Because then you have to lower all the heavy equipment for digging through the lake.

2) You also need to hold back the water for the full length of the construction.
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98Clubs
98Clubs
Joined: Jun 3, 2010
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June 25th, 2012 at 11:28:52 AM permalink
Its so bad in Las Vegas, even Lake Mead is leaving.
Thought it was worth repeating here.

Sounds like a boondoggle, complete with unknown faults, and associated cost-overruns. They'd better have one heck of a check-valve ready. But as long as the tunnelling is in a "J" shape, the height of the stem might prevent loss of all water. But then again, this IS a boondoggle,
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rxwine
rxwine
Joined: Feb 28, 2010
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June 25th, 2012 at 12:19:54 PM permalink
Quote: 98Clubs

But then again, this IS a boondoggle,



And in the end, they will find out that it would have been cheaper to refill the lake with shipments of bottled water.


But if such has been done somewhere to the same depth with similar geology, they ought to be able to replicate it. If.
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