The effect of excavation boundary conditions on the design of mine backfills

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Mine backfill is the material, or materials, used to fill underground excavations created by mining so as to establish and retain safe working conditions economically. Today, high quality backfill mixes can be engineered at reduced cement content and are able to meet stricter production and environmental requirements with minimal risk to the operations. A well-engineered backfill design, process or practice must be safe, in particular for operations employing undercut mining methods. Even though the engineering design of backfill mixes has been well developed, there is much in the interaction between the backfill mass and the excavation boundaries that is not known, understood or applied, particularly when dealing with mining under fill (undercut mining) situations. When mining under fill, the bottom of the fill column is fully exposed and, because of minimum underpinning, the fill mass could fail with dramatic consequences. A number of improvements in current backfill design and placement are still required to establish safer, more efficient and less costly undercut mining practices. This research aims at establishing the effect of critical excavation boundary parameters, such as wall roughness and wall closure on the performance of different backfill mixes used for sillmat construction placed in excavations of differing dimensions. A 30 g-ton centrifuge constitutes the primary modeling tool, supported by analytical and numerical modeling methods. The expected significance of this research is the development of an improved and accurate procedure for sillmat design and will improve present techniques that are based on experience and trial and error methods. Detailed methodologies, test protocols and benchmark procedures for industrial designs of sillmats will be developed.