Have you seen this?

https://surveyorconnect.com/community/surveying-geomatics/gyro-tunnel-surveying/

I recently spoke to someone about doing gyro obs at the bottom of a shaft to orient for tunneling to another shaft for deep stormwater tunnels. It was from a 25' diameter shaft to a 5 foot diameter shaft about 900 feet away.

I think that is becoming more common now, I recently found out that they are going to be doing similar work in Pittsburgh where I live...16 miles of tunnels 150 feet deep along and under the rivers. These are large diameter tunnels?ÿ

https://www.alcosan.org/clean-water-plan/regional-tunnel-systems

?ÿ

Several of those have been constructed here in StL.?ÿ Some are still ongoing.?ÿ I was monitoring a flood wall weekly that they were blasting underneath.?ÿ I'm looking out my window now at one going under the river.?ÿ Used to have a good rattle every afternoon that would wake me up.

@jflamm Do you have any link of them or a website? Also you know someone to the sell them used?

@ars-mine-surveyor Yeah but most attache links are not working anymore...

High-Precision Directional Surveying in Tunnelling, Mining and Shipbuilding (Webinar)