A Finite Element Analysis of the Fundão Dam Failure

ABSTRACT: The Fundão tailings dam failure of November 2015 in Brazil is one of the deadliest and most environmentally damaging tailings dam breaches in recent history. Roughly 32 million cubic meters (Mm3) of iron mine tailings were accidentally released in this catastrophic collapse, claiming the lives of nineteen villagers, and causing major environmental concerns after polluting local water systems. As part of the forensic investigation that followed, a finite difference analysis (FDA) simulation using the NorSand constitutive model in FLAC software was conducted by the Panel to test the hypothesis of lateral extrusion triggered failure. The purpose of the present study is to simulate the triggering of static liquefaction failure of the Fundão dam using a finite element analysis (FEA) approach in which the NorSand constitutive model is adopted in Rocscience RS2 software. A selected number of the Panel’s laboratory test results were simulated in a series of FEA models to determine the validity of the numerical results and the strain-softening behaviour of the tailings. Drained triaxial compression tests were simulated to confirm calibration of the constitutive model. A computer model of the failing section of the dam’s left abutment was subsequently generated for numerical analyses following the depositional details provided in the Panel’s report. The results of the FEA are compared with the FDA shear stress-strain behaviour of the tailings reported by the Panel on a laboratory scale and for the dam’s failing section, thus supporting the hypothesis of a slope failure triggered by a lateral extrusion mechanism. The implications and limitations associated with the FEA are further discussed in this paper.