4
prominence in every mining company’s executive team. This
paper focuses on how Cleveland-Cliffs, Inc. and Hibbing
Taconite Company navigated the paradigm shift through
internal planning and budgeting, regulatory engagement,
evolving tailings guidance, and shifting industry standards.
Hibbing Taconite Company Tailings Storage Facility—
Technical Review Board
In 2017, Cleveland-Cliffs, Inc. began an independent
external peer review with the implementation of a technical
review board at Hibbing Taconite Company. The Technical
Review Board was made up of principal and project engi-
neers from the Engineer of Record, two independent sub-
ject matter experts, and a Cleveland-Cliffs management
representative and tailings engineering staff. The Technical
Review Board began to review geotechnical dam design
methodology used by the Engineer of Record for Hibbing
Taconite Company. The Technical Review Board started
by focusing on reviewing the controlling factor in dam
design, which is the foundational characteristics of the off-
set upstream dam on hydraulically deposited fine tailings as
highlighted in green in Figure 2.
In February of 2018 the initial findings of the techni-
cal review board indicated that the Hibbing Taconite Dam
Design Methodology had some room for further refine-
ment and verifications of methodology. Even though the
dam design methodology was deemed to be defensible and
prudent, The Technical Review Board for the Engineer of
Record included suggestions to enhance the tailings facility
design methodology. The report suggested looking further
into the parameters and methods used to determine und-
rained shear strength ratio for liquefaction of the fine tail-
ings foundation of the offset upstream perimeter dams. In
November 2018 the Engineer of Record followed the guid-
ance of the Technical Review Board findings and required
a re-evaluation of the dam design at Hibbing Taconite
Company. The re-evaluation of the dam design at Hibbing
Taconite Company focused on more significant geotechni-
cal investigation and confirming methods used to estimate
the undrained shear strength of the fine tailings. During
this process, tailings management gained a world-wide
audience with the video of a January 2019 liquefaction fail-
ure of a tailings storage facility in Brazil. This event, acceler-
ated and influenced the dam design re-evaluation path that
was already underway at Hibbing Taconite Company.
Throughout 2019, the Technical Review Board contin-
ued to review the findings of geotechnical investigations,
review new literature, and incorporate the subject mat-
ter expert’s suggestions to determine an appropriate und-
rained shear strength ratio for liquefaction to be used in
dam design. The variability of tailings, which range from
slimes/clays to silts to sands, while considering dilative and
contractive behaviors, all framed by the unique layering
of those tailings through hydraulic deposition can make
the determination of strength arduous and presents much
uncertainty as to the representativeness of the estimate
values. Interpretation of both laboratory and in-situ data,
given the variability of tailings noted above, is onerous and
time consuming. Given the timing of Hibbing Taconite
Company’s re-evaluation path relative to the Brazil tragedy
the Technical Review Board, at the request of Cleveland
Cliffs, decided to use a conservative worst case assumption
for undrained shear strength ratio for liquefaction of 0.05.
The alternatives analysis using the undrained shear strength
ratio for liquefaction of 0.05 was undertaken in March
2019 and involved the alternatives noted in Table 1 and
Figure 3.
In April 2019, the Technical Review Board selected
Alternative C noted above and Cleveland-Cliffs, Inc.
began budgeting and planning efforts for 2020 construc-
tion. During the remainder of 2019, the Technical Review
Board continued review of the work being completed
by the Engineer of Record to define an undrained shear
strength ratio for liquefaction based on extensive laboratory
Figure 2. Hibbing Taconite Company Tailings Facility Impoundment Dam Typical Cross Section
prominence in every mining company’s executive team. This
paper focuses on how Cleveland-Cliffs, Inc. and Hibbing
Taconite Company navigated the paradigm shift through
internal planning and budgeting, regulatory engagement,
evolving tailings guidance, and shifting industry standards.
Hibbing Taconite Company Tailings Storage Facility—
Technical Review Board
In 2017, Cleveland-Cliffs, Inc. began an independent
external peer review with the implementation of a technical
review board at Hibbing Taconite Company. The Technical
Review Board was made up of principal and project engi-
neers from the Engineer of Record, two independent sub-
ject matter experts, and a Cleveland-Cliffs management
representative and tailings engineering staff. The Technical
Review Board began to review geotechnical dam design
methodology used by the Engineer of Record for Hibbing
Taconite Company. The Technical Review Board started
by focusing on reviewing the controlling factor in dam
design, which is the foundational characteristics of the off-
set upstream dam on hydraulically deposited fine tailings as
highlighted in green in Figure 2.
In February of 2018 the initial findings of the techni-
cal review board indicated that the Hibbing Taconite Dam
Design Methodology had some room for further refine-
ment and verifications of methodology. Even though the
dam design methodology was deemed to be defensible and
prudent, The Technical Review Board for the Engineer of
Record included suggestions to enhance the tailings facility
design methodology. The report suggested looking further
into the parameters and methods used to determine und-
rained shear strength ratio for liquefaction of the fine tail-
ings foundation of the offset upstream perimeter dams. In
November 2018 the Engineer of Record followed the guid-
ance of the Technical Review Board findings and required
a re-evaluation of the dam design at Hibbing Taconite
Company. The re-evaluation of the dam design at Hibbing
Taconite Company focused on more significant geotechni-
cal investigation and confirming methods used to estimate
the undrained shear strength of the fine tailings. During
this process, tailings management gained a world-wide
audience with the video of a January 2019 liquefaction fail-
ure of a tailings storage facility in Brazil. This event, acceler-
ated and influenced the dam design re-evaluation path that
was already underway at Hibbing Taconite Company.
Throughout 2019, the Technical Review Board contin-
ued to review the findings of geotechnical investigations,
review new literature, and incorporate the subject mat-
ter expert’s suggestions to determine an appropriate und-
rained shear strength ratio for liquefaction to be used in
dam design. The variability of tailings, which range from
slimes/clays to silts to sands, while considering dilative and
contractive behaviors, all framed by the unique layering
of those tailings through hydraulic deposition can make
the determination of strength arduous and presents much
uncertainty as to the representativeness of the estimate
values. Interpretation of both laboratory and in-situ data,
given the variability of tailings noted above, is onerous and
time consuming. Given the timing of Hibbing Taconite
Company’s re-evaluation path relative to the Brazil tragedy
the Technical Review Board, at the request of Cleveland
Cliffs, decided to use a conservative worst case assumption
for undrained shear strength ratio for liquefaction of 0.05.
The alternatives analysis using the undrained shear strength
ratio for liquefaction of 0.05 was undertaken in March
2019 and involved the alternatives noted in Table 1 and
Figure 3.
In April 2019, the Technical Review Board selected
Alternative C noted above and Cleveland-Cliffs, Inc.
began budgeting and planning efforts for 2020 construc-
tion. During the remainder of 2019, the Technical Review
Board continued review of the work being completed
by the Engineer of Record to define an undrained shear
strength ratio for liquefaction based on extensive laboratory
Figure 2. Hibbing Taconite Company Tailings Facility Impoundment Dam Typical Cross Section