Enhancement of cemented rockfill design and practice

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Ore dilution is defined as the accidental contamination of the blasted mineralized rock (ore) with waste material such as mine backfill or waste rock. As a result, the economic value of the blasted (diluted) ore is reduced. Thus, it is important for a mining operation to take all possible measures to eliminate the occurrence of ore dilution. One important source of ore dilution is the backfill material that is used to fill previously mined blocks. When backfill is made of waste rock mixed with water and cement, it is called cemented rockfill (CRF). It is used to fill the cavities or empty stopes created after they have been mined out. When production takes place in a stope adjacent to a previously filled stope, the backfill material may be shaken by adjacent production blasts, and as a result, topples down right into the stope being mined. This problem is known as ore dilution due to backfill failure. CRF has been a subject of research for many years. Many researchers attempted to explain CRF failure but so far none has been able to determine the failure mechanisms of CRF. Little work has been done to determine how much blasting affects backfill failure. This project tackles the issue of ore dilution due to backfill failure that is triggered by blast vibrations, while parameters such as stope dimensions and planned stope production sequence. This project will take place at the Birchtree Mine of Vale Thompson Operations in Manitoba. The work comprises a detailed review of the CRF practices in North American mines, laboratory testing to determine the strength of CRF mixes, and in-situ experiments to measure the vibrations in a backfilled stope as the adjacent stope is being extracted by blasting. The results will be used to determine how much blast vibrations affect backfill failure. Three-dimensional computer modelling will be developed to simulate the Birchtree Mine stopes. Finally, a set of design guidelines will be developed in light of the knowledge gained from the laboratory and in-situ experiments and computer modelling. The project is expected to render great economic benefits to Canadian mines by reducing ore contamination with waste material from backfill.