Last week I had to run a traverse into a cable tunnel (actually two parallel tunnels) that ran from some hydro turbines to a switchyard and survey 54 points on the floor for movement.
To start, I had to remove a metal plate and shoot through it down to the tunnel...
The tunnels were narrow with cable trays carrying dozens of cables with 13.6 KV carrying 270 MW...I couldn't really feel or hear anything, but when my LED light got close to the wires it would vibrate.?ÿ
There were three crossover points between the tunnels, one at the far end, one about 1/3 of the way back, and one near the near end. There were several distances in the traverse around 2.5 meters to get around bends and crossovers. We were using forced centering.?ÿ
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?ÿI adjusted the data in Star*Net.?ÿHere is what the network looked like, with error ellipses. The 95% semimajor and semiminor axis at the first station in the tunnel were 0.005 m and 0.004 m respectively, and 0.130 m and 0.039 m at the far end (SW).
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Another company had done the exact same survey in 2019 (which I computed and adjusted at the time) using the same type of instrument (Trimble SX10) and similar methodology. The difference in our adjusted coordinates was -0.003 m N, -0.005 m E (0.006 m distance) at the first station and +0.024 m N and -0.020 m E (0.031 m distance) at the far station. Actually, except for the pair of stations at the far end, that were 2.5 meters apart and were traversed through, not sideshot, all other stations agreed at worst 0.013 m.
Here is the configuration at the furthest crossover point, which was at the NE end of the two long parallel legs at the far end of the traverse
103A to 203 was 2.89 meters, shot both ways as we traversed through each tunnel. 103 agreed between the two surveys -0.005 m N and -0.009 m E.?ÿ
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So the agreement between two independent traverses with different instruments was way better than the error ellipses would seem to indicate.?ÿ
Both surveys had leveling as well, coming off of the monument in the map above top middle, then down those steps using invar rods (different instruments and rods, but same type). Those all agreed at worst 0.002 m.?ÿ
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Neat post. ?ÿThanks, John.
I wish metric units were more intuitive in my mind.
I see that 0.005 m is roughly ~0.01 ft ? (flame away).
Very cool! Thanks for sharing.
I toured the inside of the Hoover Dam so I can relate to those conditions but just walking through vs surveying are much different situations.
0.003 m=0.01'
I have been using metric since about 1986, and all of my projects are done in metric (converted to FT if client wants that), but I still have to think in FT/miles and convert. I guess what we learn as kids is more ingrained into the brain than what we learn later.?ÿ
That's?ÿSUPER COOL!!!!!!!!!!
THANKS FOR THE POST!!!??ÿ
I wanted to post some more pics, but I ran up against a restriction on the number of attachments. Maybe I will post some later...
In order to get agreement like that 2 groups of surveyors have to do their work super well. So kudos to the un-named surveyor from 2 years ago as well.
Well, for full disclosure he worked with us on several deformation projects to see how we did things, so the procedures were very similar. They are my client and we get maybe 10 to 20 deformation projects a year through them and they do 1 to 3 themselves., but I do all the data processing and computations.?ÿ
Soooo... how many blows of the 8lb sledge does it take to adjust the dam back the 0.020m to where it belongs? ?????ÿ
the pair of stations at the far end, that were 2.5 meters apart and were traversed through, not sideshot,
Why would you not do a control network with the longer shots and side-shot the short one(s) ?
Not possible at all. The tunnels had 45?ø and less angles to accommodate the cables, I guess.?ÿ So to make a change in direction it would be a 45?ø, then about 10 feet straight, then another 45?ø. There was no way to get around the short sights inside there. For example, at the end where we crossed from one tunnel to the other, it was only possible to have a sight of 2.55 meters between them, so a 72 meter shot, then a 2.55 meter at a 90?ø angle, then a 100 meter shot at a 90?ø to head up the other tunnel. there were several angle points. Here is what it looked like to get from one to the other, we had to go through this door?ÿ
Then after the 100 meter shot, we had another short sight, here I am taking the picture from the next traverse station, 5.5 meters away back to the one that was 100 meters from the last one.?ÿ
and here is the next station, where I was standing when I took the picture
which then went 41 meters to the next traverse at an angle point, etc. We side shot any pins in between, and only occupied what we had to. Actually, going down tunnel 1 we set random points, and going back in tunnel 2 we occupied the points at the angles because it didn't have the short tangents as tunnel 1 did.?ÿ
Tough job indeed.
Frozen storage. Traversed from the outside Houston summer, through a below freezing storage, back out into the heat again.
That was something.
Back in my construction days, we were running new steam lines for Oregon State University to meet up with the old underground tunnels. Hot as hell and we are running levels separate from horizontal. They would put a line on an underground wall just like your pictures where they had to start. The engineers would plan the pipe route for nuclear steam pipes to meet grade for condensation and miss all existing utilities. We would traverse and level off there line up out of the tunnels, across campus and back down and mark a bottom of pipe line that was always field engineered by the US and the guys building it because heaven forbid an engineer ever be heald accountable with information on the plans????
Anyways, that kind of stuff is why I went into the woods???
@jed a friend was standing on the ground over a steam line at a University, the pipe failed and burned his foot, he didn??t fall in, it was a big pipe. Won a big settlement from the University.
