Gyro tunnel surveying

Kelly Johnson

There is a lot of literature that can be found on the Internet and in books and journals on the gyrotheodolite.

To start with you can find some info. in Dr. Ogundare book "Precision Surveying"

You will want to look at Dr. Mark Breach web page; www.markbreach.co.uk/Gyrotheodolite.htm. You can
purchase a DVD on the use of the Wild GAK azimuth gyro (very interesting---I bought it).

Also do an internet search on the " gyromat". Of all gyrotheodolite on the market this is the best (most accurate and costly).
www.gyromat.de/gyromat-5000.html

Hopes this helps.

JOHN NOLTON

PS Sokkia also has a azimuth gyro

Thank you, John. I appreciate the input. I will look into ordering Mr. Breach's DVD.
I have looked at the Gyromat 5000 that you mentioned. We are hoping to get some information and maybe a demo from DMT at my firm as well.

I have worked on two projects where our network was confirmed by Gyro. The general strategy has been to have them come in at 2/3 completion of the drive to check the azimuth of the network. The first part of the campaign is to calibrate the equipment to local gravity on known control above ground and then measure select vectors in the tunnel and adjust the network. After hole through the network is adjusted again by conventional traverse and made final.

We have used DMT http://www.dmt-group.com/en/services/exploration/surveying-geoinformation.html

It has just been one geodesist who works with my boss in the field, each campaign takes 3-5 days, adjustments have been sub 40 mm.

My exposure being so limited that the only piece of practical advice I can offer is to build strong brackets or pedestals, with a nice canopy if under the conveyor.

Personally I would consider subbing it out to the DMT guys to get a feel for the practical implications before going all in.

I don't go underground very often these days, but have the equipment to do the work. I don't work on tunnels, only hard-rock metal mines. The gyros allow me to map stopes, carry bearings from one level to another and verify that my control survey is accurate for situations where I need to break through from one drift to another. When surveying underground refraction can become a problem. The general method to avoid this is to alternate the instrument's position from one side of the "tunnel" to the other. The horizontal errors from refraction can be compensated using this method.

My equipment consists of two Wild-Heerbrugg GAK gyros (I have a third for parts) and several illuminated targets. The GAK gyro is a separate unit that mounts onto an old Wild theodolite. I have an old T-2 and T-16 both with the appropriate mounting bracket. The T-16 has a special endless horizontal tangent screw to advance the instrument back and forth. After setting up the instrument, the instrument is oriented to north (+/- 30 degrees), the gyro is powered up and released from its housing. The gyro spins at 20,000 rpm and will oscillate back and forth from astronomic north.

There are two methods of observations, one requires a time piece and some minor calculations. The other is to follow the oscillations back and forth and observe the horizontal angles at "east and west elongation". I use that term because the method is similar to observing Polaris at elongation. The gyro has a mark that you keep centered by slowly turning the instrument until it reaches elongation. The more observations (4 to 6 sets) you have the better the accuracy. The only computation is to mean the observations. The instrument should be calibrated prior to and after the underground work to verify that the instrument constant (the difference between the direction the gyro determines and the direction the theodolite is pointing) has not changed during the survey.

The accuracy of the GAK gyros depends on the instrument used and the latitude and usually is between 20" and 30". I do not make observations at each station unless I am mapping out a stope. The equipment for modern tunnel work has superior accuracy to this, say on the order of 2" to 3". However, the gyro costs over $250,000 and you still need a high end total station to mount onto it. There was an article several years ago about using a gyrotheodolite for survey control of new infrastructure tunnels under Atlanta in one of the survey trade journals. The gyro was either the Gyromat 2000 or Gyromat 3000 with a Leica total station. Here is a link to Leica's website.

http://www.leica-geosystems.us/en/Gyromat-3000_1743.htm

I see that the German manufacturing company now sells a Gyromat 5000. Here are two links to what is touted as the most accurate gyrotheodolite available.

http://www.dmt-group.com/en/products/geo-measuring-systems/gyromat.html?key=1-2

http://www.gyromat.de/gyromat-5000.html

The GYROMAT 5000 is the latest product for high precision direction measurement with an accuracy of 0.8/1000th gon, which corresponds to a deviation in arc of about 1.2 cm over a distance of one kilometre.

I know that John Hamilton has a gyro that he has used in the past for underground control for a job in Peru. Scott Zelenak and John Nolton also have/share a Wild GAK so hope they will chime in with their experiences. John Nolton has kindly sent me several articles on gyrotheodolites. You may wish to contact him about those articles.

P.S. I see that Mr. Nolton responded whilst I was typing. Were your ears burning John? 😉

I did a couple of long hydro tunnels in Peru, pretty much as stated above. I first did some gyro obs above ground on pedestals that they had built for triangulation, that is to "calibrate" the gyro. This is done for two reasons. First, there is a bias that is dependent on latitude, and also you want to make sure that if there is a bias in the local network, you can get rid of that bias.

My unit (WILD ARK-2, military unit similar to T1 with GAK bolted on, all one piece)) is less accurate than these fine electronic units available today (and much less expensive). But it did the trick, it was done inside two 20+km tunnels as they were about to meet.

It is an acquired skill to operate the old ones, I imagine the newer models are more automated. Takes a lot of concentration to follow the oscillating "pendelum", especially with a lot of activity going on around you, like water gushing out of the walls, heavy equipment driving by, etc.

I finally found the Professional Surveyor article from 2006. Here's the link to the PDF file hosted by Leica on tunneling under Atlanta.

http://www.leica-geosystems.pl/pl/Jun2004_professional_surveyor_tunnel.pdf

If I recall correctly, DMT had a very long wait time to get the Gyromat 3000 back in 2006. I believe it was over a year wait to get one in your hands. Hopefully the turnaround is better now. If your company gets one Kelly, I hope you post a bunch of photos of it here!

P.S. Since John and John have posted, I'll ask them a general question. I believe that the gyrotheodolite determines astronomic north rather than geodetic north because the gyro is operating in a "gravity well". A professor informed me that my thinking was wrong, but that hasn't changed my mind.

Gene Kooper ask the question; gyrotheodolite determines Astronomic north rather than geodetic north.

YES Gene you are correct it gives Astronomic Azimuth.

Now if you calibrate it above ground you can get geodetic or grid inside the tunnel.

JOHN NOLTON

I agree with John Bolton's answer. That is another reason to observe a line if know azimuth in the surface network.

John Hamilton don't be so fast on the keyboard on the computer. Its NOLTON not Bolton.

JOHN NOLTON 🙂

JOHN NOLTON, post: 416281, member: 225 wrote: John Hamilton don't be so fast on the keyboard on the computer. Its NOLTON not Bolton.

JOHN NOLTON 🙂

Oops...Typing on my phone. Sorry about that Mr Nolton. It just spell checked it again to Bolton but this time I caught it.

Kelly Johnson, you are very welcome for the help. If you need more after you search more just ask.
Can you tell me about the job? I might be able to give more and better information.

JOHN NOLTON

JOHN HAMILTON the misspelling of my last name was no big deal. I got a laugh out of it----- thanks for your reply.

JOHN NOLTON

I guess Google spell check knows about ambassador John Bolton and not geodesist John Nolton!

Thank you John and John. I wanted to make the point about astronomic north because I work in the mountains where the Laplace correction is not trivial. If one does the pre- and post-calibration at the the job site then the instrument constant will account for the Laplace correction. John Hamilton noted that he did his calibrations at the job site, which is the proper place for doing the calibrations. Note that he mentioned the calibration accounts for the latitude. Using John Hamilton's method the resultant azimuth will be geodetic +/- the error in the local network.

I may have one more job this summer checking the alignment of a new mine drift, but I'm getting too old to haul all that equipment underground.