Static Liquefaction Analysis of the Fundão Dam Failure

Abstract

On November 5, 2015, roughly 32 million m3 of iron mine tailings were accidentally released in the collapse of Fundao dam in Minas Gerais, Brazil. Totaling about 61% of the impoundment’s contents, the spilled tailings buried the town of Bento Rodrigues, claiming the lives of 19 villagers, and causing major environmental concerns. This study presents a comprehensive static liquefaction triggering analysis performed on the failing section of the dam prior to its collapse, with the goal to determine its susceptibility to liquefaction under its ultimate loading condition. The method of analysis implemented accounts for variations in mode of shear, anisotropic consolidation, and lateral load transfer along the failure surface normally encountered in the field. The instability line and flow liquefaction concepts are used in conjunction with in-situ test data to estimate liquefaction triggering and post-liquefaction undrained shear strengths for loose saturated tailings in the dam’s section. These are subsequently applied in iterative limit equilibrium analyses to obtain the factors of safety for liquefaction triggering and flow failure. After convergence in this process, the failing dam’s section was found to be susceptible to static liquefaction flow failure with a factor of safety of 0.56.