An expert panel hired by Vale SA to investigate the disintegration of a tailings dam at the Feijao iron ore mine in Brazil in January concluded that the failure and resulting flow slide was the result of flow liquefaction, or sudden loss of strength, within the tailings in the dam.
In the report commissioned by the miner, released in Dec. 12, the panel said dam failures are "rarely due to one cause" as multiple conditions contributed to the instability of the dam, which was built using an upstream method over a period of 37 years in 10 raises, with no additional raises after 2013.
Those factors included the design, water management and high iron content of the tailings and lack of internal drainage that led to a "persistently high water level" in the dam. Further, "high and intense" regional wet season rainfall also contributed to the failure.
The panel said that there were no "apparent signs of distress" to the dam structure prior to the burst that killed over hundreds. Extensive monitoring was conducted using various instruments to keep track of the movements inside and around the structure.
Meanwhile, German prosecutors opened an inquiry into TÜV SÜD AG, suspecting that it illegally signed off on the stability of a tailings dam at Feijao, Reuters reported Dec. 13.
The probe follows a criminal complaint filed on behalf of relatives of the disaster victims against two employees of the certification firm. A spokesperson for the prosecutors said they are seeking for incriminating and exonerating evidence.
TÜV SÜD certified the dam as safe in September 2018, months before it collapsed.
The Brazilian Senate called for the prosecution of TÜV SÜD over the disaster. Federal police in Brazil previously called for criminal charges against Vale, TÜV SÜD and 13 employees over alleged falsification of documents certifying the stability of the tailings dam.
Vale is facing multiple investigations over the dam failure, including a preliminary probe by the U.S. Securities and Exchange Commission that started in mid-November.