Date of Award

8-1-2013

Degree Name

Master of Science

Department

Mining Engineering

First Advisor

Spearing, A. J. S.

Abstract

Research and experience using various types of mine backfill - hydraulic, rock, paste, and blended - has indicated several benefits to the mining industry. Backfill is a general term that refers to any waste material that is placed into underground mine workings. Paste backfill in particular has shown environmental and economic benefits. Paste fill is generally produced from total mine tailings, meaning that it can include waste rock, sands, and clay-sized particles. It also contains no free water, meaning that water will not flow freely through it after placement causing post filling shrinkage. These characteristics make it the most environmentally "friendly" backfill option currently available. In addition, paste backfill is non-segregating and stackable, containing about 80% solids by weight, and having the consistency of medium-slump concrete, containing a cementitious content. These characteristics make paste backfill the best option for post-mining ground control in room and pillar coal mines. There are two main bodies of research regarding paste backfill. The first studies its composition, application, and performance in past and present mining environments; the second studies its theoretical application for both mine support and waste disposal. While this research has provided much for the burgeoning technology of paste backfill, little has been done to investigate its economic application to the industry in room and pillar coal mines. At present, surface disposal of waste is generally cheaper than underground disposal. The goal of this thesis is to initiate discourse investigating the hypothesis that paste backfill may be used in such a way as to allow for increased coal extraction, which may then not only cover the additional costs of underground waste disposal, but potentially increase overall mine profitability. Inherent to this discourse will be a consideration of the following issues: * The potential for increased extraction. * The preservation of long-term pillar stability. * Improved floor stability. * Diminished environmental impact at surface. * The cost benefits associated with all of the above. Data from three Illinois Basin room and pillar coal mines were collected and used for this thesis. Theoretical computer modeling using LaModel and Phase2, empirical analysis of mine stability, physical testing using simulated paste backfill models, and comparative cost analyses considering current and hypothetical mining scenarios were conducted to identify these potential benefits and their consequences, both theoretical and practical.

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