Underground GPS?

[ChrisB]

I've read a few articles about the Crossrail tunnels now being built under London. They all make the bland statement that the tunnelling machines are guided by GPS, with no further explanation. But a GPS needs to see the satellites. I'm wondering whether this is just journalists copying what other journalists write, or is there a new way to apply GPS that could be useful for caving?

I've done a bit of searching, not found much but the link below is interesting

http://www.defensenews.com/article/20090801/C4ISR02/908010316/Tunnel-vision

ANyone know any more?

 

[Les W]

I would guess they are using GPS to precisely position access shafts and the like, and then using highly accurate surveying techniques with lasers to ensure the passages don't intercept things they shouldn't, such as building foundations, sewers, other tunnelt, etc. And of course to ensure they ultimately meet up.

Just a guess though.

 

[Maggot]

Back in 2005 I remember reading 'Earthcore', a horror novel by Scott Sigler. In the novel, he came up with the idea of an underground GPS type system using seismic signals from 'thumpers', surface based stations that pounded on the rock with a weighted striker. These were recieved by a portable bit of kit carried by the underground crew (before the monsters down there hacked them to bits, of course).

 

[maxf]

I have had a look at some of the data from these surveys... I am in the marine surveying field. They were worried about the thames scouring down to the top of one of their tunnels so we did a survey of the river bed and tied it in with the underground tunnel data.

Back to the main point, they use inertial and laser systems when surveying tunnels. They start at a known location and work from there.

Sent from my BlackBerry 9900 using Tapatalk

 

[bograt]

Seem to recall being involved in radioloction in Peak a few ( about 30) years ago, gave us accurate details of underground to surface, tie these into GPS from the surface and  we could get some really useful information to relate surveys to surface details.
Dr. Harold Lord (RIP), ex BSA could have given you more details (he did predict a big shaft between Cavedale and Rowter in the 1960's - what happened there ?)

 

[TheBitterEnd]

I think the use of the term "GPS" in relation to tunnelling is just an analogy to explain the technology to journalists. What I think they are probably referring to is laser guidance, the TBM steers itself based on a laser pointed at a sensor on the back of the shield. The laser has to be moved forward and surveyed in by conventional surveying techniques.

 

[kdxn]

Geodetic GPS(Glonass too sometimes) is used to establish mm accurate control points at access tunnels and shafts usually using the OS GPS network. This control is extended underground using zenithal plummets and conventional total stations.

The TBM's are guided using a laser beam fixed to the tunnel wall putting a spot on a target grid on the TBM. Tunnel curves can be created by allowing the beam to move on the target grid and periodically resetting the laser position n the tunnel. Conventional traversing is done in a zig-zag pattern down the constructed tunnel to check the face position. Other checks can include very accurate inertial systems. The zig-zag observation pattern from one side of the tunnel to another is to balance the atmospheric effects because they have found that surveying along just one side of the tunnel will bias optical data.

Unfortunately journo's dum stuff down, hype or downright lie in order to sell their "words of wisdom" and photos.

Having said that, some companies have used the term GPS or SatNav to market highly technical navigational systems because these terms have become ubiquitous for positioning. There is a working technical system that has been called "GPS 2.0" which has been created by a company called Locata and is now being used for deep pit mining and warehouses where there are few or no satellite signals. This uses the 2.4Ghz frequency to transmit GPS like signals from ground stations. A number of mining companies would like to see this or something like it underground so that vehicles can become unmanned.
http://www.locatacorp.com/about/

BAE have recently demonstrated a positioning system, NAVSOP, that uses existing Radio transmitters to surface position. Whether this could be extended underground............?

As to mapping underground tunnels. A swiss company InfraSurvey has developed a UGPS (underground GPS) which uses an 8kg underground magnetic transmitter which is received by four or more GPS co-ordinated surface receivers. This requires someone to carry it underground and the range is limited to 200m.
http://www.infrasurvey.ch/?page_id=730&lang=en

 

[graham]

Seem to recall being involved in radioloction in Peak a few ( about 30) years ago, gave us accurate details of underground to surface, tie these into GPS from the surface and  we could get some really useful information to relate surveys to surface details.
Dr. Harold Lord (RIP), ex BSA could have given you more details (he did predict a big shaft between Cavedale and Rowter in the 1960's - what happened there ?)

You need to have Geodetic GPS to make radiolocation worthwhile, unless you are dealing with sump surveys, which are still much less accurate than ordinary cave surveys. Our lot recently surveyed a through trip in Ireland using DistoX & pocket Topo on a PDA. The tie in points at the entrances gave a 20 m error after a traverse of about  650 m. I know which I believe.