ABSTRACT:

The use of cemented hydraulic backfill in underground mines has gained momentum in many parts of the world. The effect of material composition on the hydraulic backfill material in South African gold mines has been determined through research. A high level of variation of backfill strength results was obtained from a deep-level gold mine in South Africa and factors causing this variation were determined. Factors such as tailings material properties, binder flow rate and curing affect the strength of backfill material. A strategy to maintain backfill strength consistency and improve backfill performance on the mine was developed. Possible solutions to the current operational constraints causing inconsistent backfill strength and quality control and monitoring procedures on the current backfill practice were developed. A new improved backfill strategy will help maintain consistency of the backfill quality at the plant and improve backfill performance underground. Improved backfill quality will ensure long-term stope stability, improve safety, and reduce backfill operational costs.

1. Introduction

Backfill is an important component of underground mining operations and is a critical part of the mine design process. The increase in mining depth poses a need for improved ground control and maximum ore recovery which is essential in ensuring safe and economic mining (Kluge, 2011). The performance of backfill in deep-level mines is determined by its ability to support underground mining voids effectively and efficiently. The strength of the backfill placed underground can be affected by a wide range of factors that can be identified and controlled to maintain consistency of the strength achieved by the backfill material. Understanding the impact of factors affecting backfill strength can assist in optimising the backfill operation and save cost for the mine.

Most underground mining environments have predominant stress conditions where compressive stresses exist. It is important to assess the behaviour of rock masses and backfill placed underground to ensure the stability of underground excavations (Masniyom, 2009). The strength of backfill placed in underground stopes must be sufficient to provide stability throughout the stope. This allows even distribution of stresses within the filled stope and maintains stope stability. The effectiveness of backfill as a support medium depends on inherent material properties and conditions of placement (Clark, 1988). To maintain consistency of backfill strength, these properties must be monitored and controlled during preparation, mixing and placement.

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