Trimble X7 - Best practice in tunnel surveying

Discuss Trimble hardware here.
User avatar
landmeterbeuckx
V.I.P Member
V.I.P Member
Posts: 1616
Joined: Tue May 01, 2012 5:19 pm
11
Full Name: Lieven Beuckx
Company Details: Studiebureau Beuckx
Company Position Title: Owner
Country: Belgium
Linkedin Profile: Yes
Has thanked: 183 times
Been thanked: 548 times

Re: Trimble X7 - Best practice in tunnel surveying

Post by landmeterbeuckx »

smacl wrote: Fri Jan 21, 2022 7:50 am
stutosney wrote: Wed Jan 19, 2022 10:25 am I had the 'pleasure' of surveying 13 tunnels over 200km of rail several years ago. The longest tunnel was about 700m in length and at no point did I ever consider C2C. We ended up drilling into the tunnel wall and installing spigots which can attach a survey prism as well as a scanner target (same offsets). We set a spigot on each side of the tunnel every 25m or so, so every scan had 4 targets in (in front and behind). After scanning, we traversed through with a theodolite.
Agreed entirely. In additional to the traverse, longer tunnels and those where tolerances are very tight with limited external control may also require a gyroscope to be used and included as part of the network adjustment. Tunnel surveying is all about robust control.
A gyro may be a bit overkill if thee is control at the start and end of the tunnel. Best is control at start and end which is 2x the length of the tunnel.
LSBbvba
Surveying services - 3D Laserscanning
Tel : +32477753126
www.lsbbvba.be
[email protected]
Ioannis
V.I.P Member
V.I.P Member
Posts: 628
Joined: Sun Jul 24, 2016 6:19 am
7
Full Name: Ioannis Papas
Company Details: techical office
Company Position Title: CEO
Country: EU
Skype Name: -
Linkedin Profile: Yes
Has thanked: 99 times
Been thanked: 62 times

Re: Trimble X7 - Best practice in tunnel surveying

Post by Ioannis »

Why gyro is overkill is the best solution for underground.
https://www.dmt-group.com/products/geo- ... romat.html
User avatar
landmeterbeuckx
V.I.P Member
V.I.P Member
Posts: 1616
Joined: Tue May 01, 2012 5:19 pm
11
Full Name: Lieven Beuckx
Company Details: Studiebureau Beuckx
Company Position Title: Owner
Country: Belgium
Linkedin Profile: Yes
Has thanked: 183 times
Been thanked: 548 times

Re: Trimble X7 - Best practice in tunnel surveying

Post by landmeterbeuckx »

Ioannis wrote: Fri Jan 21, 2022 10:05 am Why gyro is overkill is the best solution for underground.
https://www.dmt-group.com/products/geo- ... romat.html
A gyro is fine when you cannot get through a tunnel, when you only have a start position but no end. If it has openings at both sides a 1" gun will do just fine.
LSBbvba
Surveying services - 3D Laserscanning
Tel : +32477753126
www.lsbbvba.be
[email protected]
User avatar
smacl
Global Moderator
Global Moderator
Posts: 1409
Joined: Tue Jan 25, 2011 5:12 pm
13
Full Name: Shane MacLaughlin
Company Details: Atlas Computers Ltd
Company Position Title: Managing Director
Country: Ireland
Linkedin Profile: Yes
Location: Ireland
Has thanked: 627 times
Been thanked: 657 times
Contact:

Re: Trimble X7 - Best practice in tunnel surveying

Post by smacl »

landmeterbeuckx wrote: Fri Jan 21, 2022 10:10 am
Ioannis wrote: Fri Jan 21, 2022 10:05 am Why gyro is overkill is the best solution for underground.
https://www.dmt-group.com/products/geo- ... romat.html
A gyro is fine when you cannot get through a tunnel, when you only have a start position but no end. If it has openings at both sides a 1" gun will do just fine.
Depends on how many instrument setups you have and what accuracy specification you are working to. Even tripod to tripod on a 0.5 second instrument you will incur an incremental error based on the number of setups you are away from a fixed base line. If you have a look at the error ellipses on a tunnel traverse (or any other link traverse) this becomes obvious. The other issue you encounter is short base lines and/or short legs in your traverse where there is significant curvature. These can lead to more serious incremental angular errors. Having some gyro observations to introduce fixed or constrained bearings is a huge help here. Having retro targets on the walls can also add useful additional redundancy. Working in rail tunnels in built up areas can be very challenging in terms of meeting control specification and being able prove that specification has been met. As with most things in the survey world, the instrument dealer may imply the solution is about buying the highest end piece of kit but having the correct working method and QA is all important.
Shane MacLaughlin
Atlas Computers Ltd
www.atlascomputers.ie

SCC Point Cloud module
Post Reply

Return to “Trimble”