Additional Analyses of the Fundão Tailings Storage Facility: In Situ State and Triggering Conditions

On November 5, 2015, the Fundão tailings storage facility (TSF) failed, resulting in significant tailings release and 19 deaths. Following the failure, a review panel was established to investigate the cause of the failure. This investigation suggested that the failure involved static liquefaction triggered by deformations in slimes underlying loose, saturated, sandy tailings. This conclusion was reached by interpretation of cone penetration tests (CPTu), laboratory testing of deformation-induced stress paths, and numerical modeling. However, the report did not clearly indicate what method was used to infer the in situ state ψ from the CPTu probes, and electronic data are not currently publicly available. To remedy both of these limitations, the CPTu data presented by the Panel were digitized to enable their more widespread use and to assess which methods likely were used to interpret the state. As part of this process, a zone of looser sandy tailings at the location where liquefaction was likely to have triggered was identified. Comparison of the state of this material to the overall sandy tailings state indicates that this loose zone may have played a role in the initiation of static liquefaction. Examination of historical data indicated a potential source for this loose material. This examination provides a slightly different perspective of the factors contributing to the initiation of static liquefaction at Fundão.