Another study explains the potential trigger of the Vale dam disaster in 2019 and blames a drilling occurring shortly before the failure. For the Vale organization, it shows a "particularly unfavorable combination of circumstances".
The failure of the dam holding residue of iron ore in Brumadinho resulted in the death of 259 people - 11 more are still missing - and an environmental disaster in Brazil.
At its request, the Federal Public Ministry received the results of a study conducted by the International Center for Numerical Methods in Engineering, a research organization part of the Technical University of Catalonia.
The report confirms that the failure of the dam was due to liquefaction. "It is undisputed that the failure of the Dam I involved the mechanism of flow liquefaction."
The report backs up a previous conclusion from the Federal Police and contradicts the version of Vale group, arguing the intense rainfalls in the previous days caused the dam to collapse.
Liquefaction occurs when the soil, saturated with water, loses its strength and act as a fluid. This effect can be caused by earthquake shaking, resulting in a mudflow and the collapse of buildings.
The ICNME analyzed several simulations of a numerical model that included the construction history of the dam, its movement in the years before the failure or rainfalls in the last 40 years.
The report points out that "most of the dam tailings were fluffy, contractile, saturated and poorly drained and therefore highly susceptible to liquefaction".
A contained liquefaction of the dam a year before
And for the university, the drilling of a hole that started five days before the tragedy was the potential trigger. In their analysis, "the characteristics of the rupture and the pattern of movements are consistent with the visual observations".
Simulations of drilling in other locations however didn’t end up in the collapse of the infrastructure.
In fact, the soil profile at the site of drilling was "especially unfavorable", causing water overpressure under the dam. The drilling was meant to install another piezometer, a device used to measure liquid pressure in soil.
Actually, the risks of liquefaction were not new. A year before the catastrophe, another drilling was performed to install drains and piezometers. A major incident resulted in visible mud leaks at various points of the dam which, for the university, provoked a contained liquefaction according to seismic graph records.
The study also excluded seismic or mining activities as potential triggers to the catastrophe.
Moreover, it found that the slow deformation of the dam and an increase quantity of precipitation would not make the dam unstable for another period of 100 years.
Earlier in February, the inspection carried out by the Federal police revealed an improper drilling caused the failure of the dam. It had concluded that Vale should have waited to receive technical results before carrying out the drilling.
For Vale, as reported by R7, the study shows there "was no indication prior to the failure of the structure, which occurred abruptly", and "attests that there was a particularly unfavorable combination of circumstances".
Vale agreed in February to a US $7 billion payout as a compensation for the disaster. Sixteen people have been charged of the homicide of 270 people and of environmental crimes, five of them are yet to be located.
Value was also involved in another dam disaster in 2015 in Brazil.