36
Geotechnical News • June 2017
WASTE GEOTECHNICS
consolidation but do little to enhance
the strength at the mudline unless
there is a sand cover.
Post-reclamation settlement of
oil sands tailings
Settlement of soft tailings deposits can
be a significant design issue. Figure 7
presents modelled consolidation settle-
ment for oil sand tailings deposited
into a 40 m deep mined-out pit. These
large settlements are typically accom-
modated by water capping the soft
tailings to become a lake – the water
cap becomes thicker as the tailings
mudline settles. But if settlements are
small (less than a few metres), they
can be managed with design of the
outlet and hummocky topography to
preclude large areas of open water
forming.
Small settlements are associated with
firm to stiff tailings deposited at their
final density or that largely reach their
final density before reclamation. These
technologies include dried fine tail-
ings, cement-amended tailings, filtered
tailings, non-segregating tailings, and
co-mixing tailings and overburden, all
of which are under development (see
CTMC 2012). Most are capital- and
energy-intensive. There is optimism
that firm to stiff tailings can be
produced economically with enough
strength and density to allow capping
and reclamation with limited post-
reclamation settlement.
Matching tailings management
to landscape performance
objectives
By considering both operational
and landscape performance objec-
tives in tailings management, mine
operators can meet their short-term
mining business needs, reduce their
long-term liability, and create a legacy
of landscapes with value to future gen-
erations. Integrating mining and recla-
mation goals and objectives improves
business performance and reduces
environmental risk. Understanding the
links between tailings deposit strength,
density, and settlement to the declared
reclaimed landscape performance
objectives is a critical component in
tailings R&D, tailings management,
and landform design.
Further reading
(most available
online, or call for a copy)
Ansah-Sam, Hachey, McKenna, &
Mooder. 2016. The DBM approach
for setting engineering design cri-
teria for an oil sands mine closure
plan. IOSTC. Lake Louise.
CCA. 2015. Technological Prospects
for Reducing the Environmental
Footprint of Canadian Oil Sands.
Council of Canadian Academies.
Ottawa.
CEMA. 2012. Oil Sands End Pit
Lakes Guidance Document.
Cumulative Environmental Man-
agement Association. Fort McMur-
ray.
CTMC. 2012. Oil Sands Tailings
Technology Deployment Road-
maps Project Report. Consortium
of Tailings Management Consul-
tants report to COSIA. Calgary.
Houston & Mitchell. 1969. Property
interrelationships in sensitive
clays. ASCE Journal of the Soil
Mechanics and Foundations Divi-
sion.
Jakubick, McKenna, & Robertson.
2003. Stabilisation of tailings
deposits: international experience.
Mining and the Environment.
Sudbury.
McKenna, Mooder, Burton, & Jamie-
son. 2016. Shear strength and
density of oil sands fine tailings
for reclamation to a boreal forest
landscape. IOSTC. Lake Louise.
McKenna, Mann, Fisseha, Beier, &
Olmedo. 2017. This tailings has
the consistency of chocolate pud-
ding: a formal comparison of the
geotechnical vane shear strength of
food and soft tailings. Geotechni-
cal News.
Wells & Caldwell. 2009. Vertical wick
drains and accelerated dewatering
of fine tailings in oil sands. Tail-
ings and Mine Waste. Edmonton.
Gord McKenna, PhD, PEng, PGeol
Principal Geotechnical Engineer,
BGC Engineering Inc
#500-980 Howe Street, Vancouver,
BC, Canada, V6Z 0C8
Phone: 604-838-6773; Email:
Brent Mooder, MSc, PEng
Principal Hydrogeological Engineer,
BGC Engineering Inc
#500-980 Howe Street, Vancouver,
BC, Canada, V6Z 0C8
Phone: 604-684-5900; Email:
bmoode
Bill Burton, MEng, PEng
Principal Geotechnical Engineer,
BGC Engineering Inc
#500-980 Howe Street, Vancouver,
BC, Canada, V6Z 0C8
Phone: 604-684-5900;
Email: bburto
Andy Jamieson, PEng
Geotechnical Engineer,
BGC Engineering Inc
#200-1121 Centre Street NW,
Calgary, AB, Canada, T2E 7K6
Phone: 403-250-5185; Email:
Derrill Shuttleworth, Illustrator.
956 Chichester Road, Gabriola
Island, BC, Canada, V0R 1X1
Phone 250-618-2119; Email:
Figure 7. Oil sands soft tailings
settlement based on large-strain
consolidation modeling.
