Backfill research

This paper describes a new methodology that can be applied to compare several bench extraction strategies requiring backfill. The method is applicable at the planning or operational stages and can be used to maintain dilution within design parameters and improve the overall economics of bench stoping operations. The parameters influencing bench performance have been empirically rated based on economical, geomechanical, operational and backfill properties. Four different extraction strategies have been considered and rated from most preferred to less preferred using an integrated approach to bench extraction.

Minefill operations are being introduced and implemented throughout the underground mining industry in Australia. In recent years, the Western Australian School of Mines (WASM) has carried out a number of research projects on behalf of a number of Western Australian mining operations to determine the most economically and geotechnically appropriate fill recipes. Recent research has shown that the fill material’s mineral components and oxidation, as well as the cement types have significant influences on the fill quality. This paper reviews fill quality issues related to cemented paste fill and cemented hydraulic fill during site practice and laboratory trials for two major Western Australian underground mines.

This paper summarizes research work carried out at the Western Australian School of Mines on mine backfill properties in the last few years. The fill properties presented relate to cemented aggregate fill and cemented tailings fill. Emphasis of these studies has been placed on the composition of backfill materials including aggregate particle size distribution, cement dosage and influence of cement admixtures. The unique features of the backfill research carried out at WASM during the last few years are the accomplishment of a study into the properties of large cemented rockfill samples by triaxial testing and the investigation of the properties of fill material made from highly saline ground water prevailing in the Goldfields region of Western Australia. Exploring different cost effective binding agents for mine backfill was also carried out at WASM. Special effort has been put on the development of fill materials compatible with hydraulic and paste fills. During the process, specific methods and procedures for laboratory testing of backfill material have been formalized.

The potential environmental impact of using cyanide-bearing tailing in the cemented paste fill (CPF) has been investigated. A series of laboratory tests were conducted to determine the total and WAD cyanide content in tailings, and CPF samples. In addition, a chemical analysis of water which could have been exposed to CPF during underground mining operations has been undertaken. In all cases the liberated HCN has been monitored. This study showed that, the total and WAD cyanide content increased with cement content in the CPF mixes. However, the values measured did not exceed recommended maximum level for acceptable environmental impact.

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Mine fill is the material placed underground to fill the voids created by mining excavations. It provides overall large scale ground stabilisation while allowing localized pillar recovery. In addition to providing a working floor or back, mine fill has the potential to reduce subsidence and minimize dilution. Mine fill is essential to cut & fill, benching and sublevel stoping mining methods. This paper describes optimisation research carried out at the Western Australian School of Mines (WASM) over the last few years. The research included cemented paste fill (CPF), cemented hydraulic fill (CHF) and cemented aggregates/rock fill (CAF/CRF) optimisation projects for a number of mines throughout Australia and overseas. The studies included composition of different mix designs to achieve the required strength at different mining stages. The paper also summarises key experimental observations, typical results and recommendation for CPF, CHF, CAF and CRF. The physical properties of different types of tailings, binder, mixing water and their influences on the physical and mechanical properties of mine fill at different curing times, temperature and humidity are presented.

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The Xstrata Nickel Cosmos Mine is located about 500 kilometres north of Kalgoorlie, Western Australia. This paper describes cemented rock fill (CRF) strength testing carried out at the Western Australian School of Mines (WASM). The studies included composition of different mix designs to achieve a target strength at different mining stages. The physical properties of waste rock, binder, mixing water and their influences on the physical and mechanical properties of CRF at different curing times, temperature and humidity are presented.

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Mine fill is the material placed underground to fill the voids created by mining excavations. It provides overall large scale ground stabilization while allowing local- ized pillar recovery. In addition to providing a working floor or back, mine fill has the potential to reduce subsidence and minimize dilution. Mine fill is essential to cut and fill, benching and sublevel stoping mining methods. This paper describes mine fill research carried out at the Western Australian School of Mines (WASM) over the last 10 years or so. The research included cemented paste fill (CPF), cemented hydraulic fill (CHF) and cemented aggregates/rock fill (CAF/CRF) optimization projects for a number of mines throughout Australia and overseas.

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Cemented rock fill (CRF) is often used to support open stope voids. This allows for the full recovery of ore while achieving global mine stability. In such cases, the exposed CRF masses require adequate compressive strength and stiffness to resist the forces and limit the displacement associated with movements in the rock mass surrounding the excavations. The CRF material preparation often involves the use of large particles, either from crushed rock or development mining waste. This means that conventional laboratory samples cannot be readily used to determine the laboratory strength. Consequently, a research project was undertaken to determine the influence of sample size on uniaxial compressive strength. This paper presents the results from CRF samples that were prepared using the same mix design and then cast into moulds with diameters of 150, 240, 300 and 400 mm. The laboratory testing also allowed a better understanding of the effect of particle size distribution upon the overall strength of a rock fill mass. The laboratory results were compared to a database of large-scale results from the testing of fill masses from a number of mine sites.

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