Rainfall-induced hydrological triggers and static liquefaction: a case study of the Brumadinho tailings dam failure

Abstract
This study examines the Brumadinho tailings dam failure, focusing on the hydrological effects of intense and prolonged rainfall that preceded the collapse. A back-analysis calibrated with laboratory and field data was performed to quantify how rainfall infiltration increased the degree of saturation, elevated the phreatic line, and reduced matric suction in the upstream tailings. Parametric simulations indicate that rainfall-induced wetting weakens the unsaturated zone, reduces the internal friction angle, and increases pore-water pressures within the downstream slope. Even modest rises in the phreatic surface produced measurable reductions in the factor of safety, pushing the structure into a marginally stable undrained condition. Under these saturated states, the loose, contractive iron tailings transitioned from peak to residual undrained strength, resulting in a catastrophic loss of shear resistance characteristic of static liquefaction. The combined hydrological effects of rainfall, high phreatic levels, and suction loss created the conditions necessary for a sudden collapse. The findings demonstrate that the Brumadinho disaster was driven primarily by rainfall-triggered hydromechanical processes rather than unexpected anomalies, highlighting the need for improved water management, continuous monitoring, and hazard-informed design for upstream tailings dams.