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Underground mining case studies for ground stability using LiDAR and Photogrammetry
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Photogrammetry: Successes and Lessons Learned Brent Slaker Ground - - PowerPoint PPT Presentation
Photogrammetry: Successes and Lessons Learned Brent Slaker Ground - - PowerPoint PPT Presentation
Change Detection in Underground Limestone Mines Using LiDAR and Photogrammetry: Successes and Lessons Learned Brent Slaker Ground Control Branch NIOSH Mining Program Underground mining case studies for ground stability using LiDAR and
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Which method should be used for which application?
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- It’s very difficult to generalize because the methods are changing constantly and
every application has different requirements.
- In our experience the most important thing is to…Kno
now w your r accur curacy cy and preci cisi sion
- n
requi quirement ments s and size ze of the e job
- In underground mining, stationary methods will be poorly suited for
measurement sites >1-2 km long. Mobile methods will be poorly suited for detecting movements <1-2 cm. Many people report the theoretical precision of the instrument instead of the accuracy of the final product.
Stationary LiDAR (how we actually performed this): 4 hours Mobile LiDAR (hypothetical alternative): 20 minutes
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Pleasant Gap Mine – Stationary LiDAR
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Pleasant Gap Mine – Stationary LiDAR used for ground movement detection
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Warm colors = Rock disappearing Cool colors = Rock moving into the opening
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What to make of the apparent widespread and random movement?
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Scan Source Actual Rock Surface Reconstructed Rock Surfaces
- Point
nt densi sity and distance ce to target get – Not only will precision
- f the measurement tend to degrade with distance, but the
resolution of the subject will decrease. When performing time-lapse analyses on surfaces, two coarsely reconstructed surfaces will show a lot of false movement.
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Subtropolis Mine – Mobile LiDAR and Photogrammetry
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It’s important to understand precision requirements and the size of the job
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Error source examples: Surveying Drift = 1 cm/100 m Registration Error = 1 cm Instrument accuracy at 100 m = 5 mm Points at Time 2 Points at Time 1
100 m 1.5 cm 2.5 cm
Point movement will not be noticed because it falls within the expected error of the data Points at Time 3 Movement is higher than expected error, so it will be noticed, but quantifying the magnitude will be difficult because the movement is still a small distance relative to the error
- Error – If performing a job that spans a large continuous distance, registration
error (how well scans are stitched together) and surveying drift (compounding error as you get further away from a known point) can be far more important than instrument precision. Minimize scan length or have a plan to account for this error.
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LiDAR for Monitoring Mine Roof Movement
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Analysis performed on one scan: areas
- f higher roof elevation (red) indicate
damage before scan occurred Analysis performed on two wo scans: areas of higher roof elevation (red) indicate falls between scans
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Photogrammetry for Monitoring Floor Movement
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Reconstruction using ~30 photographs Note how some areas are missing due to poor photograph overlap or water
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Photogrammetry for Monitoring Floor Movement
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Heave
N
Crack
1.0 0.8 0.6 0.4 0.2
- 0.2
- 0.4
- 0.6
- 0.8
- 1.0
Displacement (in)
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Early detection of ground movement is beneficial, but not straightforward
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Ground Displacement Time
Where you observe a potential problem Failure Monitoring starts Movement exceeds error in instrument Injury/Fatality Damage Remediation Design change Supplemental support (bolting, mesh, shotcrete, cribs, etc.) Area is abandoned
Cost of the problem Increasing
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Final Considerations
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- Vegeta
getati tion – Growth or change in vegetation will appear as movement of the surface.
- Who can spot the hill underneath my
- vergrown backyard?
- Weather
er – Fog, dust, water, etc. can interfere with picture quality or laser reflection.
- Don’t trust your data; triple check everything.
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Disclaimer: The findings and conclusions in this report are those of the author(s) and do not necessarily represent the official position of the National Institute for Occupational Safety and Health, Centers for Disease Control and Prevention. Mention of any company or product does not constitute endorsement by NIOSH, CDC.