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Technology News 387 - abandoned mine lands program TN #3: foaming mud cement controls underground coal mine fires and subsidence.

Washington, DC: U.S. Department of the Interior, Bureau of Mines, TN 387, 1991 Jul; :1-2
Objective: Develop a cost-effective, flexible method for extinguishing underground coal mine fires that can be readily used in fire conditions encountered in both abandoned mines and coal outcrops. In addition to he abatement of an underground coal fire, a secondary objective was to prevent subsidence by filling the voids with a material having sufficient compressive strength to minimize subsidence. Approach: The Colorado School of Mines Research Institute was awarded a research contract to determine the viability of using Foaming Mud Cement for abating underground coal mine fires and preventing subsidence. The program consisted of a laboratory and pilot scale investigation and process development. An extensive, controlled test program was conducted simulating floor, rib, roof and rubble fire conditions. Field demonstrations were conducted after the pilot scale research was completed. How It Works: Traditional techniques have targeted the control of burning by eliminating the air, fuel source or heat. This has been accomplished by trenching, quenching, smothering or combinations of these three methods. These techniques were not always successful, particularly in the case of fires in abandoned mines. Foaming Mud Cement (FMC) on the other hand, may be formulated to span a wide range of parameters with respect to its composition. The base components of the FMC mixture typically consist of soil materials, Portland cement and flyash. The mixture has the ability to control a fire by encapsulating the burning coal in a thick, foam-like slurry. The encapsulation isolates the burning coal from any oxygen source and prevents further oxidation or combustion of the coal. The FMC fills the voids left by the burning coal and once hardened, provides a support for the overburden, thus minimizing surface subsidence. The FMC can be designed for the compressive strength needed for site specific engineering requirements. Various mix designs can provide strengths from 200 psi to more than 2000 psi depending on the expansion of the material. Although a variety of gasses may be used to effect the expansion, normal air performs as effectively as any of the gasses tested. A primary consideration in the development of FMC was to produce a product that was effective for its intended purpose, economical and practical. The resulting product has proven to be workable over a wide range of sub-surface soil types. The range included soils with a clay component in excess of 50% and other's with a high organic content. These conditions have traditionally been incompatible in the area of cementatious products. FMC is easily produced using standard equipment available at most concrete bulk plants. Benefits: 1. Local soils, mine waste and spoil material are suitable for making FMC, eliminating the need for a high cost "specification" aggregate. 2. The slump of the material can be controlled for the requirements needed in building barriers with low slump FMC, or it can be made extremely fluid if the application requires. 3. Plowable FMC can be placed by gravity, eliminating pumping costs and volume restrictions of using conventional concrete pumps. 4. Up to 900 cubic yards of FMC can be produced and placed in an 8 hour operational day. 5. The cost of FMC is approximately 50% to 70% of the cost of a conventional concrete grout mixture. Applications: Approximately 30,000 cubic yards of FMG have been placed in the four sites listed below: 1. A multiple seam outcrop fire in Arizona; 2. An abandoned coal mine fire in West Virginia; 4. An outcrop fire in Utah; 3. An abandoned coal mine in Montana.
Mining-industry; Mine-fires; Fire-extinguishing-agents; Fire-fighting; Land-reclamation; Subsidence; Abandoned-sites; Cements; Fly-ash; Compressive-strength; Aggregates; Foam; Containment; Barriers; Backfills; Underground-mining; Stowing; Abandoned-shafts; Coal-mines; Concretes
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Washington, DC: U.S. Department of the Interior, Bureau of Mines, TN 387
Page last reviewed: September 2, 2020
Content source: National Institute for Occupational Safety and Health Education and Information Division