2
safety staff in Michigan and Minnesota, keeping them
apprised of operational status long-term planning and seek-
ing feedback as necessary (Cleveland-Cliffs, Inc. 2023b).
This paper focuses on the steps Cleveland-Cliffs, Inc.
navigated to reinforce a portion of the thousands of feet
of dam embankment at the company’s tailings storage
facilities at Hibbing Taconite Company, located 5 miles
north of Hibbing, Minnesota. Hibbing Taconite Company
produced 5 million longs tons of iron ore pellets in 2022
(Cleveland-Cliffs, Inc. 2023a) and approximately 18 mil-
lion long tons of tailings in 2022. The full site covers
approximately 30,670 acres of which the tailings facility
makes up approximately 6,500 acres as shown in Figure 1
on page 4. Approximately 13 miles of perimeter dams
impound the tailings facility and 5 miles of interior dam
allow for full tailings depositional utilization and improves
access to areas for dust control activities. The perimeter
tailings impoundment dams consist of earthen dams con-
structed over the life of the tailings storage facility from
1974 to the present. The tailings facility contains 3 active
tailings impoundment cells and one reclaim water reservoir
storing approximately 13,000 acre-feet of water depen-
dent on climate conditions. The perimeter dams are con-
structed mechanically, and interior dams are constructed
hydraulically with a coarse tailings handling (pumping)
system. Hibbing Taconite Company utilizes upstream,
offset upstream, centerline, and downstream methods of
construction. Native clay cores and random downstream
slope materials from a local borrow source were used in
starter dam construction, which was downstream.: In the
late 1980’s, dam construction moved to upstream still using
native materials from nearby borrow locations, and in the
late 1990’s, with the exhaustion on adequate native borrow
materials, Hibbing Taconite Company began to use offset
upstream construction. Tailings are deposited hydrauli-
cally using a coarse-tailings (+200 mesh) separating system,
pump house and pipeline and the fine tailings (–200 mesh)
flow via gravity from two launders from the concentrat-
ing portion of the iron processing facility allowing Hibbing
Taconite to avoid fines tailings thickening and pumping.
After the gravity deposition in tailings storage cells process
water is decanted through an open channel concrete spill-
way in the West Area of the facility and through a decant
drop structure in the East Area. The tailings process water
treated in the tailings facility is reclaimed from a clear water
(SD-3) Reservoir back to the plant through two 7-foot
diameter pipes from an intake structure in the and reclaim
pump house at approximately 120,000 gallons per minute
as shown in Figure 1 on the next page.
The Hibbing Taconite Company tailings facility is in a
broad, relatively flat-lying valley, situated north of the plant.
The surface geology below the facility and at the toe of the
perimeter dams mainly consists of lacustrine (clay), swamp
(peat and muck), and glacial (primarily till and outwash
sand) deposits underlain by bedrock. The bedrock generally
consists of intrusive and extrusive igneous rocks of Upper
Pre-Cambrian age, including granite and gneiss. Most of
the bedrock is massive, although the upper portions are
fractured. The degree of bedrock fracturing in the exposed
portions of the rock is variable, depending on elevation.
The glacial till consists primarily of fine-grained soils, but
contains a wide range of gravel, cobbles, and boulders. The
matrix is typically a reddish-brown, sandy silty clay of mod-
erate plasticity.
A PARADIGM SHIFT
A theory which overhauled human understanding of the
heavens was the heliocentric model, first proposed by Greek
philosophers, but it was not until Nicolaus Copernicus
presented the mathematical model in the sixteenth cen-
tury that the world accepted this new understanding and a
paradigm shift occurred. While it might be presumptive to
compare humanity’s understanding of the earth’s revolution
around the sun to a change in our mastery of hydraulically
placed fine tailings as a foundation to upstream dam con-
struction, for tailings and geotechnical engineers and the
paradigm shift we have seen over the last five years it is evi-
dent. In 1962 Thomas Kuhn wrote that a paradigm shift is
“sufficiently unprecedented to attract an enduring group of
adherents away from competing modes of scientific activ-
ity,” but that is simultaneously “sufficiently open-ended to
leave all sorts of problems for the redefined group of prac-
titioners to resolve.” (Kuhn 1962). When the Engineer of
Record informs Dam Owner that undrained shear strength
ratios for liquefaction in the fine tailings foundations below
upstream dams might shift from a value of 0.11 to 0.05,
a cohort of those that understand the importance of und-
rained shear strength ratios for liquefaction in upstream
dam design all realize that a paradigm shift is in the making.
Lessons learned from tailings dam failures around the
world drove the mining industry to review its standards
and in the case of upstream tailings dam construction the
understanding of foundational materials was intensely
reviewed. While recent events have highlighted the phe-
nomena of liquefaction, case studies from AECOM (2009)
and ASDSO (2023) point to liquefaction case studies back
into the 1970’s. Tailings storage facilities and their man-
agement have gained attention through world events, and
that attention has further elevated tailings management
safety staff in Michigan and Minnesota, keeping them
apprised of operational status long-term planning and seek-
ing feedback as necessary (Cleveland-Cliffs, Inc. 2023b).
This paper focuses on the steps Cleveland-Cliffs, Inc.
navigated to reinforce a portion of the thousands of feet
of dam embankment at the company’s tailings storage
facilities at Hibbing Taconite Company, located 5 miles
north of Hibbing, Minnesota. Hibbing Taconite Company
produced 5 million longs tons of iron ore pellets in 2022
(Cleveland-Cliffs, Inc. 2023a) and approximately 18 mil-
lion long tons of tailings in 2022. The full site covers
approximately 30,670 acres of which the tailings facility
makes up approximately 6,500 acres as shown in Figure 1
on page 4. Approximately 13 miles of perimeter dams
impound the tailings facility and 5 miles of interior dam
allow for full tailings depositional utilization and improves
access to areas for dust control activities. The perimeter
tailings impoundment dams consist of earthen dams con-
structed over the life of the tailings storage facility from
1974 to the present. The tailings facility contains 3 active
tailings impoundment cells and one reclaim water reservoir
storing approximately 13,000 acre-feet of water depen-
dent on climate conditions. The perimeter dams are con-
structed mechanically, and interior dams are constructed
hydraulically with a coarse tailings handling (pumping)
system. Hibbing Taconite Company utilizes upstream,
offset upstream, centerline, and downstream methods of
construction. Native clay cores and random downstream
slope materials from a local borrow source were used in
starter dam construction, which was downstream.: In the
late 1980’s, dam construction moved to upstream still using
native materials from nearby borrow locations, and in the
late 1990’s, with the exhaustion on adequate native borrow
materials, Hibbing Taconite Company began to use offset
upstream construction. Tailings are deposited hydrauli-
cally using a coarse-tailings (+200 mesh) separating system,
pump house and pipeline and the fine tailings (–200 mesh)
flow via gravity from two launders from the concentrat-
ing portion of the iron processing facility allowing Hibbing
Taconite to avoid fines tailings thickening and pumping.
After the gravity deposition in tailings storage cells process
water is decanted through an open channel concrete spill-
way in the West Area of the facility and through a decant
drop structure in the East Area. The tailings process water
treated in the tailings facility is reclaimed from a clear water
(SD-3) Reservoir back to the plant through two 7-foot
diameter pipes from an intake structure in the and reclaim
pump house at approximately 120,000 gallons per minute
as shown in Figure 1 on the next page.
The Hibbing Taconite Company tailings facility is in a
broad, relatively flat-lying valley, situated north of the plant.
The surface geology below the facility and at the toe of the
perimeter dams mainly consists of lacustrine (clay), swamp
(peat and muck), and glacial (primarily till and outwash
sand) deposits underlain by bedrock. The bedrock generally
consists of intrusive and extrusive igneous rocks of Upper
Pre-Cambrian age, including granite and gneiss. Most of
the bedrock is massive, although the upper portions are
fractured. The degree of bedrock fracturing in the exposed
portions of the rock is variable, depending on elevation.
The glacial till consists primarily of fine-grained soils, but
contains a wide range of gravel, cobbles, and boulders. The
matrix is typically a reddish-brown, sandy silty clay of mod-
erate plasticity.
A PARADIGM SHIFT
A theory which overhauled human understanding of the
heavens was the heliocentric model, first proposed by Greek
philosophers, but it was not until Nicolaus Copernicus
presented the mathematical model in the sixteenth cen-
tury that the world accepted this new understanding and a
paradigm shift occurred. While it might be presumptive to
compare humanity’s understanding of the earth’s revolution
around the sun to a change in our mastery of hydraulically
placed fine tailings as a foundation to upstream dam con-
struction, for tailings and geotechnical engineers and the
paradigm shift we have seen over the last five years it is evi-
dent. In 1962 Thomas Kuhn wrote that a paradigm shift is
“sufficiently unprecedented to attract an enduring group of
adherents away from competing modes of scientific activ-
ity,” but that is simultaneously “sufficiently open-ended to
leave all sorts of problems for the redefined group of prac-
titioners to resolve.” (Kuhn 1962). When the Engineer of
Record informs Dam Owner that undrained shear strength
ratios for liquefaction in the fine tailings foundations below
upstream dams might shift from a value of 0.11 to 0.05,
a cohort of those that understand the importance of und-
rained shear strength ratios for liquefaction in upstream
dam design all realize that a paradigm shift is in the making.
Lessons learned from tailings dam failures around the
world drove the mining industry to review its standards
and in the case of upstream tailings dam construction the
understanding of foundational materials was intensely
reviewed. While recent events have highlighted the phe-
nomena of liquefaction, case studies from AECOM (2009)
and ASDSO (2023) point to liquefaction case studies back
into the 1970’s. Tailings storage facilities and their man-
agement have gained attention through world events, and
that attention has further elevated tailings management