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Tunnel boring alignment

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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  • Land Surveyor

    http://www.moussystems.nl/nl/producten/lasers.html

    A product from The Netherlands, It can made a verticaal laser-line. 

    MOUS Systems
  • 1201335009?profile=original?width=721Thank you for the responses all really good stuff. I think I am going to try the resection to confirm my work. I did use a string line strung between two surface nails on line and an optical plummet to align myself  along the string at the bottom ( checked with my Total station & 90 eye piece set to zenith). Cool 360 pic of the pit  if you are instructed, https://theta360.com/s/fU87ypFQzcbBtFLy8CTgSNA4O

    Plate setting Nov 21. #theta360
    See Spherical image of RICOH THETA
  • Land Surveyor

    the better way for me is rent a laser proyector to transport a coordinates vertically to the bottom of the shsft, and a giroscopic theodolite to transport your azimuth from the surface.

  • Land Surveyor
    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.
  • Land Surveyor

    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.

  • Land Surveyor

    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. 

  • 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.

  • Land Surveyor
    30 meter plumb Bob line like the Romans used.
  • Seeking Employment

    Tough problem. No idea where to start.

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