On 25 January 2019, Dam B-1 at Vale S.A.'s (Vale) Córrego do Feijão Iron Ore Mine, located nine kilometers northeast of Brumadinho in the state of Minas Gerais, Brazil, suffered a sudden failure, resulting in a catastrophic mudflow that traveled rapidly downstream.
The failure extended across much of the face of the dam. The collapse of the slope was sudden and complete, with 9.7 million cubic meters of material flowing out of the dam in less than five minutes.
An investigation into the technical causes of the failure was commissioned by Vale. This was carried out by a panel of four experts in geotechnical engineering with special expertise in water and tailings dams. The panel was instructed to use its expertise and professional judgment to review and assess requested relevant data and technical information. The results of the panel's work were published on 15 December 2019. Lucas de Melo of Geosyntec participated as a member of the expert panel and Geosyntec also assisted the panel by providing engineering support.
Geosyntec's Scope of Services
To determine what triggered the failure of Dam I and why the failure occurred when it did, the Panel carried out an investigation into the causes of the failure, including: (i) evaluating the nature of the materials in the dam and their properties, (ii) assessing the dam construction and operation methods and their impact on the dam and tailings material properties, (iii) assessing the condition of the dam before and during the failure using analyses of available images, such as video, ground-based radar, laser (LiDAR), satellite (InSAR and photographs), drone videos, and (iv) numerically modelling the conditions just prior to failure. The assessment of material properties included sampling and laboratory analysis of materials from the site to allow critical state deformation and stability analyses of the tailings dam structure, and numerical analyses of water flow through the tailings and dam were performed to assess the impact of pore water pressures on the stability of the structure. The Panel's assessment was informed by detailed assessments of the history of construction, historical geotechnical data, historical instrumentation data, and seismic evaluations of the region around and at the site.
The panel concluded that the failure and resulting flow slide were the result of flow liquefaction within the tailings in the dam resulting from the presence of the loose, saturated, heavy, and brittle tailings under high shear stress conditions. This resulted in a marginally stable dam that was close to failure in undrained conditions. Laboratory testing showed that the amount of strain required to trigger strength loss could be very small, especially in the weaker tailings, making flow liquefaction possible.
Geosyntec worked with the expert panel in an accelerated pace, performing numerous tasks in parallel with the panel members and other consultants, to complete our tasks quickly and accurately. The results of the work were published in December 2019.
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- Location: Brumadinho, Minas Gerais, Brazil
- Client: Skadden, Arps, Slate, Meagher & Flom LLP
- Project Practice Areas: Geotechnical
- Type of Facility: Tailings storage facility
- Services Provided: Expert Panel participant, Failure investigation support to Expert Panel
- Type of Work: Slope failure investigation
- Governing Regulation: National and local