Frozen Backfill for Underground Mine Applications

Vassilios Kazakidis,
Abstract Frozen backfill for mining operations in permafrost must be delivered in such a state so as not to thermally impose on the host rock surrounding the filled stope. The placement process, the material strength demand, and the freezing time delay are the parameters that control the applicability of the method. The thermal properties, initial temperatures, and mix ratio of the constituent materials can be used in a simple thermodynamic equilibrium model to predict the final temperature of the backfill upon placement. The frozen rock and tailings must be at a below zero temperature and get fully wetted so the surfaces cause adherence of the particles to one another and enhance the solidification of the poured backfill.
Results are based on a two-year research program carried out in the field and using a laboratory-scale apparatus, designed to simulate a pour of frozen backfill, to study the mixing, thermal properties and segregation. The results provided a recipe and a process for mix design for open stoping operations in cold regions. The testing evaluated the sensitivity of the test parameters that included:
o amount of water added in the mix;
o temperature of water;
o rockfill/tailings ratio;
o temperature of solid constituents.

Detailed thermal measurements were taken during sample preparation, during and after the pour, to determine the temperature ranges needed to provide a suitable material upon placement. The paper presents the result of this environmentally friendly, innovative technology. The distribution of the materials and the mixing process are instrumental in achieving the properties required for open stoping applications.
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