Any suggestions on how to set an alignment for a TBM 25 metres down a shaft? I need two points at the bottom for the alignment but can not see down into the hole. The dimensions of the hole are 3 metres wide by 6 metres long (usable space at the bottom).  the bore is 300 metres long so any error in the setout of the points at the bottom will make a great big ops at the end.

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Does Leica make a 90° eye piece? Maybe heavy plumb bob in oil? 25M prism pole? That last one was a joke....lol

Never been taxed with this job, sounds cool. Those would be my first thoughts though.

Good luck. Update if you can.
We use a Laserline Quad 1000 for our horizontal alignments in these situations. You will be hard pressed to find a better piece of equipment for carrying horizontal control vertically. It's an investment at just over $3k, but if you plan on getting more jobs like this, high rises, commercial work, monitoring...it will pay for itself in a few jobs, not to mention the ease in planning and loss of worry. It is almost fool proof to use as well!!!

We then transfer vertical using a weighted, oiled steel tape from a surface benchmark. The oil and weight greatly reduce any wind effects from the shaft.

This generally involves finding/building a way to mount laser targets at the top of the shafts that can be located from the surface before hand.

We have used this method for mine shafts over a mile deep up to a 63 story tall building. I am sure there are other methods and I hope you get other responses as I would be interested to hear them as well. Always looking for more methods to the madness!
I’d be looking at a system using INS and a gyrocompass.

This sounds like time for gryo station like this one,

https://us.sokkia.com/products/optical-instruments/monitoring-speci...

Tough problem. No idea where to start.

I have used a contruction line laser that we set up at night in the dark.  I have laser glasses that help me see the laser when I use artificial lighting to see what we are working on and lining into above ground.  I line the laser up above ground and it will also shoot down into the hole in the ground.  We have then set up a second laser underground and aligned it with the laser beam that is coming from our laser above ground.  This process worked well and we did not need to rent a gyrostation... we hit our mark as they bored straight down from the far site and it was just over 900 linear feet from end to end.

30 meter plumb Bob line like the Romans used.

If you dont want to invest more a heavy plumb bob should do the trick....but then it has to be suspended and air movement has to be accounted for.... else a plumb line laser should do the job but its costlier.

Well, it's VERY old school, but also very precise.  We used piano wire for a plumb-bob string (actually used 6 lbs of lead) lowered into 55-gal. drums filled with oil.  (Could use smaller barrels) Determine a precise position on the tops of the plumb wires, go into the tunnel and line the instrument on the bottom wires. Voila!   I'm sure you can figure out the rest.

(sometimes the "old Pharts" still know a thing or two.

This method is tested for accuracy and practical. No need for sophisticated tools. 

This is what I would do:

If you can, set up four or five retro targets around the top of the shaft and resect to all of them (using a 90 degree eyepiece - maybe rent one because they're pricey). You might need someone to hold up a target perpendicular to  each so you're not looking at them on too oblique an angle. Then just use ref line. As the tunnel progresses always set up in the same place and do the same resection, you shouldn't be too far out. Don't expect to be spot on with any method, as you know, an error of even 0.5mm in your line will make you 150mm out at the end. And your resection from the original control is unlikely to be without error. This is not a good construction methodology if your looking for perfection. Hopefully the tunnel diameter has allowed for some error.

The simple answer is don't worry about the tunnel just yet. Drill and locate prisms on the top of the beam mounted on spigots. Ensure these prisms are geocentric, ie whichever way you turn them, the centre will be the same. Once coordinated from control at the top, turn the prisms over and face down into the shaft. Resect at the bottom (diagonal eye piece is handy) ensuring your vertical readings are ok between face 1,2. Setout the alignment. For the tunnel checks, ask for a gyroscopic survey to give corrections in the tunnel. Depending on length of tunnel and tolerances required you should be fine. If tolerances are that tight, perhaps get a gyroscopic baseline within the base slab.

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