[Cementjungle]

engineers might have to work "at atmospheric pressures similar to what a diver would experience," the New York Times adds, and even spend "time in a decompression chamber" on their way back up to the surface, to find out.

How deep is this tunnel? I thought that it was for a road... how are drivers going to get through it if they'll need time in a decompression chamber after driving through?

[21twelve]

https://twitter.com/BerthaDigsSR99

The above is a link to Bertha’s twitter account!

This object was encountered over two weeks ago. The face of the tunnel is about 80 feet deep at the moment, not sure what the greatest depth will be - but would guess 120 feet or more as it goes under a hill. Inside the tunnel it is pressurized. But the workers need to get outside the tunnel to take a look at what is going on.

I’m surprised they didn’t just drill into the area directly in front of the object. Although I guess if they think it is manmade (building support, etc.) they don’t want to damage it. But I think at that depth and in those glacial deposits, that is highly unlikely.

I’m guessing it is a house-sized boulder dropped by a glacier.

[Windflier]

How deep is this tunnel? I thought that it was for a road... how are drivers going to get through it if they'll need time in a decompression chamber after driving through?

Consider that the NY Times is the source of that comment.

[Boogieman]

Good questions. I know cities sometimes dig deeper tunnels for drainage, but I wouldn’t think they would be deep enough to need decompression.

[Gandalf_The_Gray]

How deep is this tunnel? I thought that it was for a road... how are drivers going to get through it if they'll need time in a decompression chamber after driving through?

While the tunnel is under construction the ground water around the bore hole is kept out by introducing compressed air to keep leakage to a minimum. The rough hole cut by "Bertha" is immediately lined with interlocking ring segments which support the tunnel walls and prevent them from collapsing. The rings are assembled directly behind the machine as it moves forward.

The segmented rings are not watertight and so the contractor uses air pressure to keep the tunnel free from major flooding. Once the boring is complete, the bore hole is lined with concrete which permanently caulks the leaks in the ring structure and the air pressure is allowed to return to normal atmospheric pressure.

During the drilling phase when the bore is pressurized, workers pass through an air lock to enter and leave the work site. I would guess that they use the air lock for a decompression chamber. It's function would be prevent the workers from getting the bends (nitrogen dissolved in the blood stream while working under elevated pressure from forming bobbles if they were returned too rapidly to normal atmospheric pressure).

Once the tunnel is lined, the roadway finished, and ventilation is added to remove exhaust gasses, vehicle traffic can pass through from end to end with no change in pressure to worry about.

Regards,
GtG

[Gene Eric]

Exactly... I guess the air is ‘heavy’.