They Said “It Will Never Work” – 25 Years of Paste Backfill 1981 – 2006

Authors: Landriault, D Paper is not available for download Contact Us

DOI https://doi.org/10.36487/ACG_repo/663_24

Cite As:
Landriault, D 2006, 'They Said “It Will Never Work” – 25 Years of Paste Backfill 1981 – 2006', in R Jewell, S Lawson & P Newman (eds), Paste 2006: Proceedings of the Ninth International Seminar on Paste and Thickened Tailings, Australian Centre for Geomechanics, Perth, pp. 277-292, https://doi.org/10.36487/ACG_repo/663_24



Abstract:
As a young mining engineering graduate in 1975, I joined Inco Limited in Sudbury, Ontario, Canada with all the idealistic ambitions and fears of any young graduate starting their career in any industry. My initial aspirations, like many of my young colleagues, were to be the Chief Operating Officer (COO) of the company. I quickly realized after six months that the normal path to COO was not for me and I turned some of my efforts to understanding the science of mining. I initiated several studies at the mine to define the true cause of the mine’s productivity problems at that time. This led to studying the mine’s backfill system performance and the resulting in situ behaviour of the two major roles backfill plays in a mine, an underground construction material and a ground support method. These extra curricular efforts led to me being transferred to the newly formed Mines R&D group, where I was given a laboratory dedicated to backfill research and the responsibility to optimize the nine hydraulic slurry backfill plants operating at the Inco, Sudbury basin mines. In studying the interaction between the different backfill plants (many of which used classified mill tailings as the backfill material), the mills and the surface tailings disposal system, I learned the third major role of underground mine backfill, which is as a means of waste disposal. The mandate of the backfill laboratory was to optimize the backfill performance at all the mines with respect to all three of the major roles played in the mine, while reducing the overall cost of backfilling underground stopes. This led us to the development of alternative binders such as iron blast furnace slag which has been in use in Inco’s Sudbury mines since 1983, producing backfill strengths twice those attainable with Portland cement and reducing binder consumption at many Inco mines by 40%. The other main effort at cost reduction was to improve the water:cement ratio of the cemented slurry backfill; typically being placed underground in the mines at solids content between 65 and 70 wt% solids. This effort turned our attention to the concrete industry which routinely pumped concrete short distances on construction sites through similar diameter pipelines, both horizontally and vertically (up and down). To lower Inco’s binder consumption, I asked the question “Why couldn’t backfill be transported at similar solids content and water: cement ratios as being used in the concrete industry?” When this concept was presented to the company research review board for funding, it was viewed with great scepticism. This was mainly due to the mining industry’s limited experience with underground pipeline transport of concrete which centred around the use of vertical slick-lines to free-fall concrete down a Paste2006–R.J.Jewell,S.Lawson,P.Newman(eds) ©2006AustralianCentreforGeomechanics,Perth,ISBN0-9756756-5-6 Keynote Address Paste2006,Limerick,Ireland 277 hoisting shaft during development. Many attempts had been made to transport concrete down the shaft and horizontally into the shaft stations where related concrete construction work was underway. All attempts were met with limited success or disaster. This resulted in the vertical and horizontal (over 30 m) transport of concrete being divided into two separate operations. Concrete was free-fallen down the shaft slick-line into an oversized pipe or hopper (mixing boot) from where it would overflow into a concrete pump hopper and get pumped horizontally (30-150 m) to the construction location. When the concept of transporting cemented paste backfill by gravity, in a pipeline, thousands of metres underground (vertically and horizontally) was presented to the research review board, the overwhelming response was “It will never work”.

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