FINDING COAL ADITS: WHAT CLIENTS WANT EXAMPLE: MINE TUNNEL UNDER ILLINOIS LANDFILL

摘要

Geotechnical issues arise when surface structures are proposed above abandoned subsurface mine structures. This is particularly true for landfills where liner integrity is of paramount importance. When an abandoned coal mine tunnel (70 feet below ground surface) was encountered along the slope of a newly developed landfill expansion cell in eastern Illinois, the extent of coal mining in the area became an issue. Typically, the owners of such situations acknowledge that using drilling alone to map the extent of subsurface mine workings is cost-prohibitive. However, using the "time is money" cliche, they then demand prompt action with "Tricorder-like" precision and low-cost subsurface investigative methods. Following discussions with owners in which possible methods of investigation and their limitations are introduced, the next course of action commonly includes: 1. A test program to prove the efficacy of the proposed methods 2. A production phase investigation program to map the mine workings if the test program proves successful 3. Selection of drill locations to test subsurface targets. A test program was implemented at the aforementioned landfill location to determine the most effective geophysical method(s) for an expanded investigation. Seismic reflection, electrical resistivity/induced polarization (IP), and ground penetrating radar (GPR) methods were tested in an area thought to contain the extension of a known mine tunnel. Following the test program, an expanded survey was conducted using all three methods along the main access road and on a cut bench along the slope of the new cell. Based on the results of the expanded investigations, drilling targets were identified and ranked according to the spatial concentration of geophysical anomalies and the confidence level of their interpretation as possible mine structures. Boreholes were drilled to confirm the subsurface targets.