Siting of Prison Complex above Abandoned Underground Coal Mine

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This paper discusses in detail the process undertaken to mitigate the effects of any future mine subsidence on prison structures proposed above old abandoned underground workings. The site for a proposed prison complex purchased by the state of Indiana was located in west-central Indiana and was undermined by an old abandoned room and pillar mine. The original plan for construction consisted of one phase. Based on a study of the mine map and subsurface verification of the extent of mining it was determined that all prison buildings and important structures could be placed above solid coal to the north. However, one masonry building was located within the potential draw zone of mine works that still contained significant mine voids. Based on empirical data the subsidence potential was estimated and the building was designed accordingly to be mine subsidence resistant. It was decided that a phase II prison complex should be constructed adjacent to and just south of the phase I complex. This complex would be directly above the underground workings. The first stage of design was to minimize by positioning the exposure of significant structures to the subjacent mining assuming the mine map was sufficiently accurate. Subsequently, an extensive subsurface investigation program was then undertaken to (1) ascertain whether or not mine areas where buildings would be located were already collapsed and thus only nominal, if any, subsidence could occur in the future and (2) verify the presence of solid coal areas within the mine as indicated on the mine map. Based on all the site information gathered subsidence profiles were developed from an empirical database of subsidence events in the Illinois coal basin. As a result of this work many structures on the site required no or nominal subsidence considerations. However, for others that could be affected potentially by future subsidence movement preliminary subsidence resistant designs were completed using the expected level of potential subsidence movement. The estimated costs to make each of these structures subsidence resistant was significant. Mine backfilling measures were taken at these structure locations.