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Comment by erikpukinskis | Hacker News Reader

They've mentioned water when asked about Hyperloop, to point out that standard tunnels are waterproof to a specification that they could also support the level of vacuum necessary for Hyperloop, without modification.

The SpaceX rep mentioned this in the recent Hawthorne city council meeting, and I believe Elon said the same thing in one of his presentations.

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It's not keeping water out of the tunnel once built that's hard. It's building the tunnel through water and mud that's hard.

Sure, but groundwater flow has to be accounted for. Hard engineering can lead to very bad outcomes. The Soviets tried to ignore the effects of disrupting thermal equilibrium in their attempts to build cities in permafrost areas. Their solution was prodigious volumes of concrete. It failed badly. These days geotechnical engineers try to work more harmoniously. For example, in areas with saturated soil one approach is to excavate an equivalent weight of soil to that of your construction, thus the building effectively floats, and there is no disruption to the local dynamics.

I cannot see that Elon can get around the need for proper geomorphological study here.

In the video two comments up, they explain that a different kind of TBM is used for waterlogged boring. Bentonite is used to keep pressure on the tunnel face instead of the bored material, the slurry is then separated with a centrifuge and piped back to the face/out of the tunnel.

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