The worst traverse conditions...

john-hamilton · 2021-11-04T14:22:00Z

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 ?ÿ ?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). ?ÿ 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 ?ÿ 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 ?ÿ

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Strictly Surveying

Last Post by Moe Shetty 5 years ago

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Moe Shetty

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@john-hamilton check with Gavin Schrock about tunnel surveys: he sent me, years ago, how the supercollider tunnels got their controls measured. Cool details with the Invar ribbon measuring instruments and so forth.

Posted : November 24, 2021 12:18 pm

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The worst traverse conditions...

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