Soft tailings bearing capacity

Soft tailings are often so weak that people and animals can't walk on them. A common solution is to cap them using geofabric, geogrid, and waste rock placed by small, expensive earthmoving equipment -- we often refer to this approach as the "fairies and teaspoons" method.

Gord standing on geofabric on soft tailings at the Wismut Uranium mines in eastern Germany in 1999

Soft tailings are those, that due to their low shear strength, present a challenge to stabilize, cover, cap and reclaim. Their very low bearing capacity requires use of special methods of stabilization before soil placement by normal earth-moving equipment. The cost of these special methods is usually high – often 20 to 50 times the cost (per unit area) of typical mine reclamation projects. The total costs required to stabilize and reclaim soft tailings is usually tens to hundreds of millions of dollars for typical mines, often comparable to the costs of tailings management during ore production. Although there are a great number of soft tailings sites worldwide, soft tailings stabilization and reclamation projects are done as one-off projects and little published guidance is available to practitioners. Sharing the experience from individual sites extends the range of reclamation solutions available and leads to better environmental and economic performance.

Other options, if well planned and executive, are available. We’ve summarized them in a recent paper (McKenna et al 2016) , and mostly boiled it down to two graphs (that continue to evolve):

Strength vs solids content compendium from our 2016 Lake Louise paper listed above.

Strength vs solids content compendium from our 2016 Lake Louise paper listed above.

 

Strength and density for soft tailings capping (from McKenna et al 2016)

Strength and density for soft tailings capping (from McKenna et al 2016)

 

Here are some examples of soft tailings reclamation technologies….

 

Water capped tailings

Floating water cap (Syncrude Base Mine Lake)

 

 

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Floating coke cap (Suncor Pond 5)

 

 

 

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Hydraulic (beached) sand capping — Syncrude Sandhill Fen

 

 

 

Fairies and teaspoons method of soft tailings reclamation - geofabric, geogrid, wickdrains, small equipment  (Wismut 2007)

Soft ground technique – – geofabric, geogrid, wickdrains, small equipment (Wismut 2007)

 

Conventional earthworks reclamation -- Elliot Lake Uranium Tailings 1996

Conventional earthworks reclamation — Elliot Lake Uranium Tailings 1996

 

Here are some papers on soft tailings you might find useful:

  • Consortium of Tailings Management Consultants (CTMC). 2012. Oil Sands Tailings Technology Deployment Roadmap: Project Report – Volume 2, Component 1 Results. Consultants report to Alberta Innovates – Energy and Environment Solutions. June 22, 2012. 112p.
  • Jakubick AT & McKenna GT. 2001. Stabilization of soft tailings. practice and experience. Eighth International Conference on Radioactive Waste Management and Environmental Management (ICEM’01). Brugge Belgium. American Society of Mechanical Engineers.
  • Jakubick AT, McKenna GT, & Robertson AM. 2003. Stabilisation of tailings deposits: international experience. Sudbury 2003. Mining and the Environment. Sudbury.
  • McKenna G & Cullen V. 2008. Landscape design for soft tailings deposit. Tailings and Mine Waste 08 Conference. Vail, Colorado.
  • McKenna G, Mann V, Fisseha B, Beier N, & Olmedo N. 2016. The geotechnical vane strength of soft tailings compared to soft foods. Fifth International Oil Sands Tailings Conference, December 4-7. Lake Louise, Alberta. University of Alberta Geotechnical Group, Edmonton. 11p.
  • McKenna G, Mooder B, Burton B, & Jamieson A. 2016. Shear strength and density of oil sands fine tailings for reclamation to a boreal forest landscape. IOSTC International Oil Sands Tailings Conference. Lake Louise. Dec 4 to 7. University of Alberta Geotechnical Group. Edmonton.