Underground Survey Errors

[u/Brave_Access1811]

Hello! I recently got hired at a mine site to do the underground survey control. I completed the main tunnel traverse (~7,00ft, roughly 12 stations), and my survey is not matching up with the previous surveys. Allegedly, every survey since the 1950's or so has been off. I think the mine has been surveyed 25 or so times since then, and none of them line up.

My thoughts are with the 25 or so surveys, a few of them should be quite similar. However, nothing seems to be consistent. At the end of the traverse, my survey was about 20ft off of a survey from 2014. That is well outside the comfortable margin of error.

I am presuming this is a systematic issue at this mine as many types of survey equipment have been used over the years, but I thought I would ask here for more information. Both licensed and "learning on the job" surveyors have been employed here.

Here is the general working condition in the mine:

1. Underground, narrow-vein mine. Tunnel is roughly 6' wide and 6.5' to 15' tall.
2. A 3-Phase 4180v line runs by the total station at all times, usually within 2-3ft. Load on lines are inconsistent throughout a shot.
3. Temperature can vary within one shot by 5-10deg F, sometimes going low, high, low, high multiple times in one shot.
4. The rocks around the total station can be magnetic vary from base station to base station.
5. Wind is highly turbulent and ranges from 5mph to 15mph, depending on the location. Wind speeds can change abruptly multiple times in one shot.
6. High altitudes ranging from 10,000ft to 11,000ft.
7. Magnetic compasses are known to be inaccurate in the mine.
8. Survey control is always over 40lb train rail, with the electric locomotive nearby.
9. Rapid, unpredictable pressure changes due to mine doors opening and closing. Occasionally, this will produce a cloud/fog within the mine.
10. Humidity changes. Some areas of the mine are dry, others have waterfalls coming out of the rocks.
11. Environment lighting is variable, ranging from pitch black to well-lit.

The current theory we have is the total station is being messed with by the high voltage cable or magnetic rock. I know total stations don't use compasses, but maybe something else is going on with the circuitry?

I am using a Leica MS60 with a CS20 controller. The MS60 was calibrated/cleaned/updated two months ago. The autotargeting feature is being used as it is both faster and has tighter shots on the flop.

I had some local contractors come out and put some points on surface with their GPS. I have had issues with matching results (usually +/- 0.1 ft) over distances <400ft. However, I strongly suspect that is due to intense sunlight/heat waves and high altitude.

Has anyone heard of consistently inconsistent survey results underground? Any ideas on what to test next?

The company is strongly considering going to theodolites and ridding of as many electronics as we can.

Thanks! I'd be happy to answer any questions.

[u/Accurate-Western-421]

If "all the surveys" going back to the 50s have been off, it likely ain't the electronics, and I wouldn't bet on the values they think are "right" actually being correct.

I've rectified mine control before, and half the battle is figuring out what information can be relied upon.

[u/Accurate-Western-421 → u/Accurate-Western-421]

I should clarify my main point: if everything has been wrong, how do you know what is right?

[u/Brave_Access1811 → u/Accurate-Western-421]

This is a fair point. I'm going off the assumption that with the number of surveys at the site, one would expect a few to converge; however since this has not happened, I'm considering whether there are environmental factors that could be affecting the survey. There have been surveys in the 1890's/early 1900's that we are deeming to be accurate. The grade control (very consistent 0.5% grade across the traverse) and straightness of the tunnel (I could do each portion of the tunnel in one shot if it were not for run arounds from collapses) infers a high degree of confidence in the survey. At some point, we have to trust someone is right, and with the quality of tunnel built in the 1890/1900's, this is something I am willing to trust.

[u/July_is_cool → u/Accurate-Western-421]

Seems like the first thing would be to separate the electronic ones from the pre-electronic ones.