Brumadinho: combination of deformations caused dam rupture

Dec, 13, 2019 Posted by Sylvia Schandert

Week 201951

The result of the technical investigation of the breaking of Dam 1 of the Córrego do Feijão Mine, in Brumadinho (MG), showed that the cause of the tragedy was the critical combination of continuous internal strains due to creep and a strength reduction due to the loss of suction in the unsaturated zone caused by the intense rainfall accumulated on the site towards the end of 2018.

The dam broke in January this year, killing hundreds of people, many who are still missing.

The result was presented by expert panel leader Peter Robertson, PhD in geotechnics at British Columbia University in Canada. The group’s conclusions were released this Thursday (12/11) in São Paulo.

“Creep occurs when the material has a constant load and slowly deforms. This happens with some materials, which are very heavily loaded, such as a steep slope with excess water, which will suffer the effect of creep, with shear stresses [stress generated by forces applied in the same or opposite directions, in similar directions, but with different intensities] in the material analyzed,” explained Robertson. “It is a deformation that happens slowly, but the rupture is abrupt,” added the expert.

According to Robertson, the novelty of the study is the identification of cementation between the particles. “In lab tests, the effect of cementation [was found], and this created a much more brittle material that lost strength much faster,” he noted.

According to the expert panel report on the technical causes of the breakdown of Dam I, stress state analyzes within the structure also showed that significant parts of it were under very high loads due to its slope, high tailings weight, and water level. “The construction of a steep upstream dam [method in which the containment barrier receives layers of the mining tailings material itself], the high level of water, weak fine tailings within the dam and the fragile nature of the tailings have created the conditions for the disruption,” concludes the study.

The panel was hired by a law firm on behalf of Vale SA to investigate the technical causes of the breach. The full report is available at www.b1technicalinvestigation.com.

Source: Agência Brasil

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