How do you keep water out of a tunnel when building an underwater crossing?

Seems like the water would just rush in to ruin everything. or:Seems like the water would just rush in to ruin everything.or:U have to go deep enough

Seems like the water would just rush in to ruin everything.

or:Seems like the water would just rush in to ruin everything.

or:U have to go deep enough so that there is solid rock between the water and where the tunnel is being dug. They had a problem with the overburden rock while digging the chunnel. Something about it being too weak and fractured at one point. Forget how they solved it.

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