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The Use of Geophysical Methods to Detect Abandoned Mine Workings
Prior to the mid 1900s, significant coal mining was conducted in the Front Range of Colorado. Most of the mines extracted coal from relatively thin seams located at shallow depths using room and pillar mining techniques. Subsequent to mine abandonment, the remaining coal pillars and weak rocks above the "rooms" have tended to degrade and ultimately cause either gradual or abrupt subsidence of the overlying ground. Development in these undermined areas must consider the potential risk and magnitude of future subsidence. Mine subsidence studies in Colorado have traditionally employed widely spaced exploratory borings to detect the thickness and extent of remaining voids in mined areas. However, due to the limited area explored, such studies do not necessarily provide sufficient data for an accurate assessment of future mine subsidence. In recent years, geophysical testing has been used as a tool to initially screen undermined sites in an effort to detect the location of possible voids or disturbed geologic strata. Using geophysical data, borings may be located in areas underlain by anomalous conditions, rather than on an arbitrary grid pattern. Two methods that appear to show promise for use in this regard include Refraction Microtremor and multi-channel resistivity testing. This paper presents several project examples that demonstrate the use, effectiveness and limitations of these geophysical testing techniques within undermined sites north of metropolitan Denver.
The Use of Geophysical Methods to Detect Abandoned Mine Workings
Prior to the mid 1900s, significant coal mining was conducted in the Front Range of Colorado. Most of the mines extracted coal from relatively thin seams located at shallow depths using room and pillar mining techniques. Subsequent to mine abandonment, the remaining coal pillars and weak rocks above the "rooms" have tended to degrade and ultimately cause either gradual or abrupt subsidence of the overlying ground. Development in these undermined areas must consider the potential risk and magnitude of future subsidence. Mine subsidence studies in Colorado have traditionally employed widely spaced exploratory borings to detect the thickness and extent of remaining voids in mined areas. However, due to the limited area explored, such studies do not necessarily provide sufficient data for an accurate assessment of future mine subsidence. In recent years, geophysical testing has been used as a tool to initially screen undermined sites in an effort to detect the location of possible voids or disturbed geologic strata. Using geophysical data, borings may be located in areas underlain by anomalous conditions, rather than on an arbitrary grid pattern. Two methods that appear to show promise for use in this regard include Refraction Microtremor and multi-channel resistivity testing. This paper presents several project examples that demonstrate the use, effectiveness and limitations of these geophysical testing techniques within undermined sites north of metropolitan Denver.
The Use of Geophysical Methods to Detect Abandoned Mine Workings
Niehoff, James W. (author)
Biennial Geotechnical Seminar 2010 ; 2010 ; Denver, Colorado, United States
GeoTrends ; 119-128
2010-10-27
Conference paper
Electronic Resource
English
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