Member Update Presentation for the Abandoned Underground Mine Workshop
IOWA Department of Transportation, Matthew Trainum
ITGAUM 2006
June 14 – 16, 2006 – Rochester, NY
Within the last two years, the Iowa DOT has done some drilling investigations for two potential mine problems within the state. One investigation was in WapelloCounty(within the known mining district west of the City of Ottumwa) as a response to a reported minor subsidence of a portion of US 34,and the other in the PolkCounty (within the City of Des Moines) in conjunction with the re-construction of I-235.
In July 2004, the Soils Design Section, of the Office of Design, IDOT was informed of a continued pavement subsidence/settlement problem on US 34 in Wapello County. A previous investigation with drilling and resistivity (in 1996) did not find any cause for the settlement. A new investigation was initiated beginning with a Geographical Information System (GIS) review of Iowa DNR data (mine locations, etc) and followed up with drilling along both sides of the roadway. The regional field office recorded the subsidence weekly (between July and October 2004). The maximum subsidence was 0.03 ft. The DNR information showed a mine on the south side of the roadway and that it apparently did not extend north (under the roadway). Borings were drilled to a maximum depth of 105 ft. Although no mine was encountered on the south side, three voids were discovered on the north side at depths between 46 and 54 ft. A review old design plans and profiles from the drilling information indicated that these voids were probable mine adits and/or inclined shafts extending to the known mine on the south side. Drilling was spatially dense enough to rule out the possibility of a mine under the road; mines in this area are generally between 80 and 100 ft. The water table was found to be above the voids. Conclusion: considering the small amount of subsidence, the mine apparently not below the roadway, and the probability of the mine and adits being flooded, it was concluded there was no identifiable eminent danger. It was proposed that short pavement overlays be installed where and as needed to address the minor subsidence. This area will continue to be monitored.
In June 2005, while drilling afoundation boring for a noise wall design, as part of the re-construction of I-235, the Soil Survey Crew encountered what was thought to be a potential mine, mine shaft, or similar feature, at 33 ft. Further investigation of this was pursued with several additional borings and other research (Iowa DNR GIS data). The GIS data indicated a mine on the west side of I-235. The additional borings were drilled to between 45 and 60 ft, surrounding the initial boring as completely as possible. None of the other borings encountered anything but glacial clay with sand and gravel seams. Conclusion:There is no definite indication that an adit or horizontal/slanted shaft is present. The closest known mine is roughly 900 ft to the west. Coal mines within the area are generally 100 feet or more below the surface and within shale bedrock. It is unlikely, though not impossible, that there is any direct connection to the existing coal mine on the west side of I-235 (because a final excavation extent is often uncertain for many of the coal mines in Iowa). It appears, however, that this apparent void was a sand pocket in the upper part of a glacial till and therefore did not require any changes to the design of the proposed noise wall.