Andrzej Kotyrba Central Mining Institute Katowice, Poland Application of geophysical methods for post mining rock strata characterization ISRM Mine Closure Commission

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. ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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) ISRM Mine Closure Commission

Example 1 - ERT testing of damaged by sinkhole road substratum– area of abandoned silver mine in Triassic sediments /Poland/ ISRM Mine Closure Commission

Example 2 - GPR results of testing the site shown on example 1 (silver mine) ISRM Mine Closure Commission

Example 3 - Local gravity field response for two geological cross sections of coal deposit with shaft and gallery – results of modelling ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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

Example 5- Contamination plume in quaternary water aquifer at vicinity of the Coal Mine Waste Dump (application of VES method) ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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 ISRM Mine Closure Commission

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). ISRM Mine Closure Commission

Thank you for the attention