Two-dimensional probabilistic slope stability analysis of Fundão dam

Abstract

The failure of the Fundão Dam was considered, at its time, the biggest environmental disaster in Brazil and the biggest in the world involving tailings dams. Studies of the failure that followed adopted a deterministic approach, discarding the formal approach to the uncertainties involved in the design. It was identified that the non-designed presence of mud near the downstream zone impaired drainage conditions and simultaneously caused stress redistributions raising the shear stresses in the sandy tailings and leading to contractile rupture and liquefaction. This paper presents two-dimensional probabilistic analyses developed by Monte Carlo methods and following a hybrid point estimation method, considering parameter uncertainties and spatial variability inherent in the materials. With the available data, it was found that the average factor of safety decreases when the section is in the undrained condition. Evaluating the work against traditional limits of threat degrees, it was found that the left section in the undrained condition extrapolated the acceptable limits for ore dam works. However, mainly due to the lack of a borehole or cone penetration test through the total depth of the tailings of the left abutment, where the rupture started, the analyses indicated that the right hand shoulder had a higher probability of rupture.

Presentation: Two-dimensional probabilistic slope stability analysis of Fundão dam by Murray D. Fredlund