Mining Contract: Assessment of Technology for Non-destructive Testing of In-situ Underground Mine Seals
Mine seals are a critical component to keeping an explosion that occurs in a sealed area from entering into the active parts of a mine. An ongoing concern of coal industry stakeholders is the structural integrity of coal mine seals over prolonged exposure to the mining environment; however, no technology currently exists to evaluate the integrity of these structures once built. Currently, visual inspection is the only means for evaluating the integrity of an as-built seal; making it impossible to know if the structure meets the regulatory requirements or continues to meet the regulatory requirements over time. Therefore, it is difficult to determine if a faulty seal is present and should be repaired or replaced.
Contract Status & Impact
This contract is ongoing. The contract final report is scheduled for delivery by the end of 2014.
The proposed research aims to design and construct MUSSEL, a mobile underground laboratory, and employ it to assess the feasibility of utilizing several types of existing technology for non-destructive testing of the integrity of in-situ seals with the objective of identifying damage due to improper construction or damage that occurs after installation due to movement of equipment, ground conditions, or chemical reactions.
This project will assess four different non-destructive testing (NDT) technologies for detecting imperfections such as cracks, voids, and composition variations, which could affect the structural integrity of an as-built coal mine seal. A proven NDT method should provide a clear diagnosis of a seal’s condition and provide guidance to mine operators on whether to replace or repair a faulty seal, or do nothing to a competent seal. The four NDT methods being assessed are ground penetrating radar (GPR), ultra-sonics (US), radio frequency identification tags (RFID), and passive tracer gas (PTG).
The project final report will provide an assessment of the four NDT techniques evaluated by the research. At this time, the RFID technique is not receiving further consideration because it cannot penetrate more than one foot into typical seal materials. The US technique, too, may be unable to penetrate deep into a seal, but laboratory work is continuing. The GPR technique is able to detect anomalous features at depth within four-foot test blocks. Analysis of GPR scans and evaluation of this promising technique continues. The PGT technique may provide an assessment of coal mine seal integrity that is completely independent of the other geophysics-based methods.
The final report may recommend that seal plans include quality control tolerances in the design such as (1) allowable variations in mix density, (2) allowable amount of fractures in the seal, and (3) allowable amount of voids in the seal. The NDT techniques developed by this project could provide a quantitative means to gauge imperfections within the as-built seal.