Research
Overview
Mines produce a significant amount of waste material in the form of finely crushed rock and process water, called mill sands or mine tailings, and the management of these tailings poses a signficant engineering challenge. Too often the conventional forms of tailings disposal and management, in particular slurry deposition into tailings ponds, have not performed well resulting in significant adverse impacts on the environment, surrounding communities, and the operation of the mine itself.
breach of a conventional tailings dam and flow of loose, wet tailings into surrounding areas
Our research examines the engineering properties and behaviour of tailings that have been dewatered to the extent that they are similar in consistency to toothpaste. Such materials are often referred to as thickened tailings or paste tailings. Paste tailings may be either pumped to surface and stacked, thereby eliminating the conventional ponds altogether, or they may be mixed with cement and pumped back underground as Cemented Paste Backfill in order to stabilize the large underground voids created by mining. We have researchers looking at the application of paste tailings for both surface disposal and underground backfill.
Resources
Field sites are an important part of our research strategy and we have worked with mines located in Canada, South America, Africa, Europe, and Asia. Closer to home, our research laboratories are located in the Galbraith Building on the downtown campus of the University of Toronto. In addition to standard geotechnical apparatus for stiffness, strength, and permeability testing, we have developed specialized facilities including the following:
- A Dispersion Technologies DT1200 Acoustic/Electroacoustic analyser for characterizing, amongst other things, particle size distribution and zeta potential, for suspensions up to 50% solids content by volume. This device is very useful when combined with rheometry equipment, for studying the properties and behaviour of flowing paste.
- An Environmental Chamber for simulating drying paste in arid conditions. The development of suctions and the movement of moisture can be assessed within the deposited layers.
- A high frequency (up to 70 Hz fundamental frequency) servo-hydraulic triaxial test device, with embedded ultrasonic p- and s-wave transducers for simultaneous monitoring of small and large strain stiffness. Blast time histories from in situ monitoring projects can be fed into this machine in order to subject cemented paste backfill samples to blasting loads under controlled laboratory conditions.
Projects
Previous in situ monitoring projects with Canadian mines have shown that the as-placed properties of cemented paste backfill can vary significantly from the properties of "similar" samples prepared under controlled laboratory conditions. This has important implications for underground mining operations, especially in terms of the procedures they use to fill the underground voids (i.e., fill rates and stages of filling), the design and construction of the barricades used to retain the fill, the time the mine must wait before they can resume production blasting in proximity to the fill, and the ultimate strength of the fill especially in critical design situations that involve mining through or under wide spans of fill. A multi-year, multi-university research program is therefore being initiated to better develop the science and engineering of cemented paste backfill systems. To find out more about this project, contact us.