Technologies for Locating Mine Workings - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 93

in the expansion of the cleat void spaces, effectively increasing the hydraulic
characteristics of the coal. Therefore, additional data for coal under high
lithostatic pressure should be collected and evaluated for feasibility and
development of this method. Research should be performed to ascertain
whether hydraulic testing has merit as a cost-effective and accurate method to
aid in determining the extent of coal outcrop barriers and coal voids in mines
adjacent to coal waste impoundments.
SUMMARY
One of the critical tasks in site characterization is ruling out the presence
of voids. Invasive drilling programs can provide the necessary information.
However, they may compromise the hydrological integrity above the mine, and
their cost is often significant, both economically and environmentally. Well-
planned and appropriate use of geophysical techniques can often help to
minimize the amount of drilling required to detect mine voids. However, no
single geophysical technique will work at all depths in all types of geology.
From a practical standpoint, steep topography compounds the difficulty in
collecting, processing, and interpreting geophysical data when surface methods
are used, but these effects are minimized when borehole, cross-hole, and in-
seam methods are used. In addition, trees and cultural features such as fences
can impede geophysical data collection, processing, and interpretation. Multiple
geophysical techniques may be necessary to reduce the probability for error to
an acceptable level; drilling is required for confirmation.
The committee concludes that geophysical techniques are useful in some
cases in coal mine void detection, especially the use of seismic surface waves,
seismic reflection, ground-penetrating radar, and electrical resistivity methods.
The committee also concludes that geophysical techniques have been
underutilized in the coal-mining industry and could benefit from additional
research. The committee recommends that demonstration projects using
modern geophysical techniques be funded, and that the results be widely
conveyed to the mining industry and to government regulatory personnel
through workshops and continuing education. Continuing education could
include the opportunity to attend short courses and seminars that present the
latest technology along with case histories to support its use.
The committee notes that much more work has been done using
geophysical techniques on coal field problems than is indicated in the literature.
Since a large amount of the work is proprietary or involved in litigation, little
has been published. The committee notes that publication of case histories on
this work would be desirable.