A report commissioned by Brazilian miner Vale SA last year to look at the stability of a residue ham that tore on January 25, confirmed it as healthy, but raised concerns about its drainage and monitoring systems.

The report by the German TÜV SÜD, which was reviewed by Reuters on Tuesday and was last updated in August 2018, made a number of recommendations to improve the safety of the construction. The report also stated that the dam meets the minimum legal requirements for stability.

Some of the identified problems were cracks in the drainage channels, which are shown in the report. The audit also recommended the installation of a new monitoring system that can accommodate small movements in the ground.

The findings of the audit were reported earlier Tuesday in the Brazilian newspapers Folha de S.Paulo and O Estado de S.Paulo.

Vale said in a statement that it had followed the recommendations in the report that the & # 39; routine & # 39; called.

The disaster at the residendam in Vale's Corrego do Feijao iron ore mine in the mining area of ​​Minas Gerais in Brazil killed at least 134 people, with 199 missing.

The report seemed to be at odds with a statement by TÜV SÜD the day after the leak, which said "based on our current knowledge, no damage was found" during their inspection of the dam.

Issues with drainage can be crucial in investigations into the causes of the dam break, where an official environmental official told Reuters that there were indications that the burst was caused by liquefaction.

Liquefaction is a process in which solid material such as sand loses strength and stiffness and behaves more like a liquid.

It is a common cause of the collapse of upstream dams that contain mine waste, also called tailings, because their walls are usually built with dried residues of sand and clay-like mud. Drainage problems can cause water to seep into the dried residues, changing their consistency and stability.

"In order to improve the safety of dams with regard to the failure of liquefaction, it is recommended to take measures to reduce the possibility of a trigger," TÜV SÜD said in its evaluation of the dam.

"To this end (Vale) must avoid vibrations, avoid nearby detonations, avoid heavy machine traffic on the dam, prevent higher water levels in the residues, do no work to remove material from the feet of the slopes or carry out work that causes overloading of the reservoir of the reservoir. the dam, "it said.

"The installation of seismological measuring equipment is also recommended in the vicinity of the dam."

TÜV SÜD did not respond to a request for comment.

(Reporting by Ricardo Brito, additional reporting by Stephen Eisenhammer in Belo Horizonte, Jake Spring in Brasilia and Edward Taylor in Frankfurt, editing by Bernadette Baum)

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