Experts Blame Deadly Vale Dam Collapse on Drainage Problems
December 12 2019 - 01:33PM
Dow Jones News
By Samantha Pearson and Luciana Magalhaes
SÃO PAULO -- Vale SA said experts hired by the miner have
concluded that drainage problems were largely to blame for the
collapse of its dam in January that killed 270 people in
Brazil.
The original design of the dam and the way it was built up over
decades allowed dangerous amounts of water to accumulate inside the
structure, meaning it was only a matter of time before it gave way,
according to the report released by Vale on Thursday.
The failure of the mine-waste dam, one of the world's deadliest
in decades, is the subject of criminal investigations in both
Brazil and Germany, home to TÜV SÜD, the dam's Munich-based safety
inspector.
The report was commissioned as a technical study, designed to
spell out the specific engineering shortfalls and causes of the
collapse. It wasn't designed as a report to affix blame or
responsibility, the report's drafters said.
When the dam was first built in 1976 by Ferteco Mineração, a
Brazilian miner that Vale acquired in 2001, its design prevented
correct drainage at its base, according to the panel of four
international engineering experts hired by Vale's lawyers. The dam
was also initially constructed with a particularly steep slope,
leaving the structure more unstable as subsequent layers of the dam
were added over the next 37 years, they said.
The dam was built via the so-called upstream method, the
cheapest design, whereby dried out mining waste is gradually piled
up over time to form the wall of the structure. Vale built the last
layer in 2013, taking the dam to a height of 280 feet, and stopped
depositing mining waste there in 2016.
The experts said the mechanisms introduced at later stages of
its construction were also insufficient to solve the structure's
drainage problem, which was exacerbated by intense rainfall during
Brazil's wet season at the end of last year.
Adding to the dam's problems was the stiff and heavy nature of
its contents, the so-called tailings. The tailings contained a
particularly high level of iron ore, making the structure more
brittle, according to the experts from universities in Canada,
Australia and the U.S.
When the dam finally ruptured at 12:28 p.m. on Friday, Jan. 25
-- as many workers were having lunch in the mine's canteen lower
down the valley -- the heavy weight of the tailings meant they also
burst out with great force. The slope of the dam collapsed in less
than 10 seconds. About three quarters of the dam's contents rushed
out over the next five minutes, obliterating the canteen, as well
as nearby homes and a small guesthouse.
This occurred via a process called liquefaction, a trick of
physics that makes solids behave like a liquid, the report said.
Liquefaction was also responsible for the collapse in 2015 of
another mine-waste dam jointly owned by Vale in the nearby town of
Mariana.
The experts ruled out seismic activity or detonations in
neighboring mines as the trigger, saying that the dam was under so
much internal stress that it likely underwent a gradual deformation
and collapsed.
In September, Brazilian federal police accused 13 mostly
lower-level employees from Vale and TÜV SÜD of covering up
structural dangers at the dam.
A spokeswoman for Vale said the company wasn't aware of any
imminent or critical risks at the structure before it collapsed.
She said the company was also carrying out a detailed technical
investigation into all its upstream dams, and would share the
findings of Thursday's report with the authorities.
TÜV SÜD, who police said were aware of the dam's drainage
problems, has declined to comment on the police inquiry, saying the
company was cooperating with the authorities.
Write to Samantha Pearson at samantha.pearson@wsj.com and
Luciana Magalhaes at Luciana.Magalhaes@wsj.com
(END) Dow Jones Newswires
December 12, 2019 13:18 ET (18:18 GMT)
Copyright (c) 2019 Dow Jones & Company, Inc.
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