SALT LAKE CITY Radar,
prisms and robots would seem more appropriate in the latest
Hollywood blockbuster than in a mine in Utah, but exactly this
kind of technology helped Rio Tinto Plcs Kennecott Utah
Copper avert what could have been a major human catastrophe
Kennecott, which operates the
vast Bingham Canyon Mine near Salt Lake City, for years has
used the most advanced technology available to detect, monitor
and plan for slides, an infrequent but anticipated occurrence
Kennecott was particularly
vigilant at part of the northeastern wall of Bingham Canyon,
the location of a geologic structured element known as the Main
Fe Fault. It was here that one of the biggest mine wall slides
in history took place April 10, which despite the collapse of
around 150 million tonnes of overburden into the pit resulted
in no human casualties.
The company uses a combination
of GroundProbe radar, Ibis radar and a prism network to give it
comprehensive data on even the slightest movement in the mine
slopes, Bingham Canyon Mine general manager Matt Lengerich told
AMM. The mine also uses extensometerswhich
measure displacements on highwallsto monitor very
specific, localized changes.
The company also has a team of
geotechnical staff and mining engineers trained to recognize
potentially dangerous movement.
"We had that northeast wall
under surveillance, as we had a number of concerns along that
wall. In early February, geotechnical staff noticed data on our
Ibis radar units that highlighted what looked to be point spots
of movement, less than a tenth of an inch a day," Lengerich
said. "Isolated movements had consolidated and the entire mass
above the Main Fe walltechnically referred to as the
hanging wall of the Main Fe Faulthad started to
The consolidated nature of the
movement rang alarm bells, and Lengerichs team sprang
into action. "On Feb. 12, our geotechnical staff said they
thought we had a problem. That day we engaged our network of
worldwide experts and said, we think we have a major
issue on our hands and we want to get as many opinions and eyes
on this as quickly as possible," Lengerich said.
Just like predicting landfall
for a hurricane, working out when the wall might fail also was
possible. Engineers used the movement rates to plot an inverse
velocity graph, showing the number of inches the mine moved per
day and the acceleration of that movement.
"In February, the geotechnical
engineers predicted the failure would happen in mid- to late
April. As the date became closer, their projections became more
focused," Lengerich said.
Using a Homeland Security-style
threat advisory scale, Kennecott set about removing people and
infrastructure, and established operating and contingency
plans. "Our primary purpose was to protect people, then the
sustainability of operations and then protection of
infrastructure. On April 9 we crossed the threshold to shut
down the 10 percent rampthis was the last failure zone
area we were usingand we continued to run some operations
in the bottom of the pit via the light vehicle access
Kennecott closed operations in
the lower pit at 11 a.m. April 10. "By (8:30 p.m.) that day the
geotechs said, the movement rates are so high that the
walls going to go at any time, and at (9:30 p.m.)
it failed," Lengerich said.
What Kennecott could not predict
was how much material would move and where it would end up.
"Those were the two variables
that were the most difficult to predict. We had modeled several
scenarios, which ultimately guided our planning," Lengerich
said. "We knew wed lose the 10 percent ramp, and that it
would impact lower pit operations, which would affect all lower
The slide took place in stages:
an anticipated initial failure at 9:30 p.m. filled the bottom
of the pit, and an unexpected second failure at 11 p.m. covered
the initial failure and a lot of the equipment the company had
carefully positioned in the pit to allow it to resume
operations more quickly.
The equipment loss included 13
trucks and three shovelsonly about 10 percent of the
companys equipment fleet, but a blow to Kennecott because
it had lost the mines heavy vehicle access road, leaving
it with just one shovel and 18 trucks in the restricted
Lengerich said that the shape of
the failure, how far back it went and where the material ended
up all surprised Kennecott. "We obviously wouldnt have
staged the equipment in those locations in the pit if we had
known what was going to happen," he said. "Wed have
staged it somewhere else."
Kennecott recently recovered
another truck from the affected area, taking its total to 19
trucks in the lower pit.
The mine is currently stable,
and no further slides are anticipated in the near future.