1. Andrzej Kotyrba Central Mining Institute Katowice, Poland
Application of geophysical methods for post mining rock strata characterization
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2. Common needs in process of post mining hazard evaluation for specific sites
spatial extent of mining workouts,
manner of workouts disposal,
spatial extent of impact zone in overburden of mining workouts,
structure of rock massive altered by mining,
physical and mechanical properties of rock strata,
contamination plumes and transport paths in ground water aquifers.
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3. Geophysical methods applicable
Division based on measurement environment
Surface Methods
Borehole Methods
Division based on physical principle of method
Geoelectrics (with Ground Penetrating Radar)
Gravimetric
Seismic
Geothermics
Radiometry
Borehole logging and wave or electrical tomography
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4. Main Objectives of Geophysical Research
Characterization of geological strata dezintegrated by mining operations
Contouring the anomalous, risky or hazardous regions
Assessing the probable origin of anomalies
Indication of best places for location of testing boreholes
Selection of test drilling methods (percussion or core)
Indication of boreholes probing needs and methods
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5. Tasks for geophysical measurements
Static
Post mining cavities detection and localization
Rocks strata characterization in terms of lithology, continuity of geological structures, water content, voidage, elastic or quasi elastic properties
Zoning of contamination plumes
Zoning of egzogenic events within rock mass
Monitoring of caves behaviour and contaminants motion
Monitoring of dynamic events within rock mass
Control of post mining site reclamation effects
Dynamic
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6. General remark on efficiency of geophysical methods application in post mining hazard assessment
There are a wide variety of geophysical methods and techniques, which can supply information about mined parts of deposit and overburden as well. They use out various natural or artificial physical fields and sophisticated numerical methods to find geological or geomechanical information directly from measurements data or to obtain reliable models of rock structure. Practically, their usefulness for post mine site characterizations depends on the actual surface conditions (technical availability to carry measurements in proper way) and local mining and geological conditions (rock and strata properties)
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7. Example 1 - ERT testing of damaged by sinkhole road substratum– area of abandoned silver mine in Triassic sediments /Poland/
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8. Example 2 - GPR results of testing the site shown on example 1 (silver mine)
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9. Example 3 - Local gravity field response for two geological cross sections of coal deposit with shaft and gallery – results of modelling
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10. Example 4a - The temperature of soil at depth 0
Example 4a - The temperature of soil at depth 0.7 m and air circulation scheme within bedrock strata (marked by green line) over fire spot in extracted shallow coal seam
Spontaneous combustion of coal in abandoned mine at urban area
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11. Example4b – Burning wastes in abandoned landfill from coal production
Localization of VES points on landfill surface
Resistivity cross sections of landfill after VES data inversion

12. Example 5- Contamination plume in quaternary water aquifer at vicinity of the Coal Mine Waste Dump (application of VES method)
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13. Geodynamic process/ type of mine openings
Suggested geophysical methods for post mining land screening - extremely shallow mining
Depth of exploitation
(Voids)
Geodynamic process/ type of mine openings
Method
Measurement Mode
< 30 m
Caving, subsidence, erosion, leaching, washing out/
Horizontal, vertical, inclined
Gravimetric
Surface measurements, in rock measurements
Electroresistivity
Surface measurements, borehole logging, tomography (ERT),
In rock measurements
GPR
Surface measurements, borehole measurements,
In rock measurements,
Tomography
Electromagnetic
Surface measurements,
Seismic
Combustion in coal, shafts
Geothermic
Surface measurements, borehole measurements
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14. Geodynamic process/ type of mine openings/extraction
Suggested geophysical methods for post mining land screening – moderately shallow mining
Depth of exploitation
(Voids)
Geodynamic process/ type of mine openings/extraction
Method
Measurement Mode
30 – 80 m
Caving, subsidence, erosion, leaching, washing out/
Horizontal, vertical, inclined
Electroresistivity
Surface measurements, borehole logging, tomography (ERT),
In rock measurements
Electromagnetic
Surface measurements,
GPR
Borehole measurements, cross hole tomography
Seismic
Egzogenic processes in coal
Geothermic
Borehole measurements
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15. Geodynamic process/ type of mine openings
Suggested geophysical methods of post mining land screening – deep mining
Depth of exploitation
(Voids)
Geodynamic process/ type of mine openings
Method
Measurement Mode
> 80 m
Caving, subsidence, erosion, leaching, washing out/
Horizontal, vertical, inclined
Electroresistivity
Cross hole tomography
Seismic
Surface measurements
GPR
Crosshole tomography
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16. Conlusions: ISRM Mine Closure Commission
In post mining hazard assessment procedures, geophysical surveys usually precede test drillings and rock sampling. For deep mining residues, where borehole techniques are necessary, the surveys are conducted together with test drillings.
If legislative procedure for methods and range of testing is not established (e.g. Poland), geophysical surveys are the first emergency tool choosen by investors or developers of postming lands when unexpected features are encoutered during geotechnical testing (examples on the left).
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17. Thank you for the attention