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
(https://papers.acg.uwa.edu.au/p/663_24_Landriault/)
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 
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©2006AustralianCentreforGeomechanics,Perth,ISBN0-9756756-5-6
Keynote Address
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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”.