7
undrained shear strength ratio for liquefaction of tailings at
Hibbing Taconite was determined. That determination was
reviewed and approved by the Technical Review Board in
the fall 2021. Figure 4 aided in the communication of the
many steps for the Engineer of Record to get to a defensible
undrained shear strength ratio for liquefaction of tailings.
Finally, given the scale of the proposed downstream
improvement project, and considering available construc-
tions materials, construction rates and improvement work
needed on 8 miles of upstream tailings impoundment
dams a construction schedule was in order. A reasonable
construction schedule that could be logistically achieved
was prepared for and discussed with the State Dam Safety
Engineer. Figure 5 is a map showing the downstream
improvement plan schedule, which will be further discussed
in the next section. The first dam safety permit amendment
for the downstream improvements was issued on October
27, 2020.
Turning Multiple 300-Page Design Reports into a dam
A paradigm shift involving the undrained shear strength
ratio for liquefaction of tailings is a difficult subject to
explain, and when that paradigm shift means a very signifi-
cant shift in the tailings facility operating plan, a very well
thought out explanation should be prepared to ensure the
dam owner fully understands the project need and budget
appropriately.
Distilling a design report or multiple design reports
into an operating plan that can be easily understood and
accepted by a dam owner is a key first step in internal
Figure 5. Hibbing Taconite Company Tailings Facility Downstream Improvement Plan
undrained shear strength ratio for liquefaction of tailings at
Hibbing Taconite was determined. That determination was
reviewed and approved by the Technical Review Board in
the fall 2021. Figure 4 aided in the communication of the
many steps for the Engineer of Record to get to a defensible
undrained shear strength ratio for liquefaction of tailings.
Finally, given the scale of the proposed downstream
improvement project, and considering available construc-
tions materials, construction rates and improvement work
needed on 8 miles of upstream tailings impoundment
dams a construction schedule was in order. A reasonable
construction schedule that could be logistically achieved
was prepared for and discussed with the State Dam Safety
Engineer. Figure 5 is a map showing the downstream
improvement plan schedule, which will be further discussed
in the next section. The first dam safety permit amendment
for the downstream improvements was issued on October
27, 2020.
Turning Multiple 300-Page Design Reports into a dam
A paradigm shift involving the undrained shear strength
ratio for liquefaction of tailings is a difficult subject to
explain, and when that paradigm shift means a very signifi-
cant shift in the tailings facility operating plan, a very well
thought out explanation should be prepared to ensure the
dam owner fully understands the project need and budget
appropriately.
Distilling a design report or multiple design reports
into an operating plan that can be easily understood and
accepted by a dam owner is a key first step in internal
Figure 5. Hibbing Taconite Company Tailings Facility Downstream Improvement Plan