SUBSURFACE MINING


Geophysics has many applications related to the mining and processing of coal, including:


  • Mapping abandoned mine workings
  • Determining the continuity of coal in advance of mining
  • Mapping seepage from tailings dams
  • Vibration and blast monitoring
  • Locating pathways of acid mine drainage
  • Defining geological/geotechnical models relative to subsurface layering
  • Mapping variations of the physical properties of coal refuse to enhance
    coal recovery
  • Locating longwall mining fracture zones


Geophysical techniques that are commonly used in coal mining applications include:

DC Resistivity – This method is effective in rapidly imaging mine workings to a maximum depth in the range of 50 to 100 feet, which encompasses the majority of situations where mine subsidence problems at the surface are occurring. A variation of the DC resistivity method (SP) has proven effective in defining zones of seepage in embankment dams.

Electromagnetic (EM) methods – EM methods have proven useful in measuring ground water seepage in zones of fracturing produced by deep coal mining and in tracking the flow paths of acid mine drainage. They have also proven useful in mapping variations of coal content with refuse impoundments for the purpose of coal fines recovery.

Gravity – D'Appolonia has applied microgravity measurement to mapping of underground voids. Not many situations are amenable to use of this technique, but where it can be applied, it can provide very definitive results.

Ground Penetrating Radar (GPR) – In some cases, GPR has proven effective in mapping shallow abandoned mine workings.

Seismic Refraction – We use the seismic refraction technique to obtain data for preparation of subsurface images, most often for mapping the top of bedrock or to assess the rippability of rock.

High-Resolution Seismic Reflection – D'Appolonia has conducted seismic reflection surveys to map the continuity of coal in advance of deep longwall mining.

Resistivity survey being conducted in the field at undermined site.



For many explorations, the best results are obtained when more than one technique is applied. For example, for the detection of voids, we have successfully employed a battery of geophysical methods including GPR, DC resistivity, and seismic reflection to provide the desired level of definition.

The decision whether to use a specific geophysical technique depends on its cost-effectiveness as compared to other technologies. At D'Appolonia we provide a wide range of geotechnical services, and we are well aware of the situations where use of geophysical techniques is likely to be beneficial. We strive to provide geophysical services only under circumstances where they can be expected to provide a clear benefit.


EXAMPLE PROJECTS


Mine Void Detection at Coal Refuse Disposal Site in West Virginia

D’Appolonia was retained by the Mine Safety and Health Administration (MSHA) to perform a demonstration of the Time Domain Electromagnetic (TDEM) and DC Resistivity surface geophysical methods for detecting mine voids and subsequent verification of the geophysical interpretation based on borings and imaging of parts of the mine workings in the Lewiston Coal seam at the Lots Branch Tailings impoundment site in Prenter, West Virginia.


Geophysical Characterization of Abandoned Coal Mine

D’Appolonia was retained to perform geophysical studies identifying optimum boring locations for a subsurface exploration program at a site that was heavily undermined. The results of the geophysical exploration program indicated that mine workings were not present over much of the site, greatly reducing the need for the drilling of exploration borings.


Geophysical Characterization of Fine Coal Refuse

D'Appolonia conducted a study to evaluate the potential for energy recovery from fine coal refuse using electromagnetics (EM) and DC resistivity. The study confirmed that geophysical techniques can be utilized to characterize fine coal refuse and are useful for planning coal refuse recovery operations.


Geophysical Characterization of Abandoned Coal Mine Workings

Geophysical techniques were employed at a proposed power plant site in south Indiana to supplement conventional subsurface exploration methods. DC resistivity proved to be an effective tool for locating subsurface mine workings and imaging subsurface cross sections.


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