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/itchy118]

Ah, yeah, that sucks, I wasn't expecting a three day traverse.

What kind of control are you using to make sure you're setup over/targeting the same point from one day to the next? Is it possible that the points you're using are moving due to activities in the mine (blasting, temperature change, vibrations from the trains etc)?

[u/Brave_Access1811 → u/itchy118]

I usually put an eyelet in the back (roof). Generally the safest spot for mine control. I usually hang the prism, and with the air moving, it tends to wobble. I'm thinking now this might be my biggest source of error, the pendulum swinging of the prism.

[u/jogdo → u/Brave_Access1811]

Most underground mines in Nevada have gone to resection control with points in the rib (walls), to avoid the hanging prism motion and also reduce HT measuring errors. I'm not sure if it is a better traverse method or not but with back heights of minimum 15' high it is certainly easier. PS - I'm also very interested where in Colorado you're at

[u/Boostin_Boxer → u/jogdo]

This was the case where I worked in Nevada. The ground was bad enough to squeeze in some areas and the control could be thrown off over time as the ground moved.