Jul 26, 2018
After a rupture in the containment structure at the Fundão dam at the Germano plant in Mariana, Brazil, nearly 32.6 million m3 of mining tailings were released on November 5, 2015. Downstream, the Santarém dam retained a large portion of the tailings, however, the remaining portion flowed on to Bento Rodrigues located 8 kilometres away [1].
Samarco and co-owners, Vale and BHP Billiton retained the law firm Clearly Gottlieb Steen & Hamilton LLP, to coordinate an independent investigation with the support of a board of geotechnical specialists to identify causes of the dam’s failure [1]. The panel did not assign liability or fault in its findings. The following are excerpts from the report:
The Fundão Tailings Dam failed on November 5, 2015 in a liquefaction flowslide that initiated at the dam’s left abutment.
Hence the failure of the Fundão Tailings Dam by liquefaction flowsliding was the consequence of a chain of events and conditions. A change in design brought about an increase in saturation which introduced the potential for liquefaction. As a result of various developments, soft slimes encroached into unintended areas on the left abutment of the dam and the embankment alignment was set back from its originally-planned location. As a result of this setback, slimes existed beneath the embankment and were subjected to the loading its raising imposed. This initiated a mechanism of extrusion of the slimes and pulling apart of the sands as the embankment height increased. With only a small additional increment of loading produced by the earthquakes, the triggering of liquefaction was accelerated and the flowslide initiated [2].
The panel’s review of on-site instrumentation revealed the following: Inclinometer data at Fundão is limited [2].
After the failure of Fundão, Samarco contacted Measurand to determine if ShapeArray would be a suitable monitoring instrument for the site. As part of the automation of geotechnical instrumentation at the Samarco Mine, Samarco Mineração S.A. selected SAAF model ShapeArrays for installing in key geotechnical structures on site. Measurand and our Brazilian distributor TecWise, assisted Samarco with the installation of vertical ShapeArrays in boreholes located in the Sela and Tulipa Dams to monitor for lateral deformation, and the installation of horizontal ShapeArrays in the Santarem Decant Gallery to monitor settlement.
References:
[1] “Understand the collapse – Samarco.” [Online]. Available: https://www.samarco.com/en/rompimento-de-fundao/. [Accessed: 12-Jul-2018].
[2] N. R. Morgenstern, S. G. Vick, C. B. Viotti, and B. D. Watts, “Fundão Tailings Dam Review Panel Report on the Immediate Causes of the Failure of the Fundão Dam,” Cleary Gottlieb Steen & Hamilton LLP, New York. Aug. 2016.