Evaluation of the Failure Mechanism of an Unsaturated Tropical Soil Slope

The paper presents results of studies performed at PUC-Rio to evaluate the mechanism of failure of a natural slope in Nova Friburgo, Rio de Janeiro, Brazil. The slide provoked the death of two people and important material losses. It happened in a profile of unsaturated gneissic residual soil. Failure occurred in a period of low precipitation, a few days after the rupture of a water pipe buried in its top portion. In an attempt to understand the mechanisms that caused failure, field and laboratory investigations were carried out and stability and flow analyses were performed. Flow analyses were executed using a 2D finite element saturated-unsaturated flow program. Resulting pore pressures were used in 2D stability analyses under different scenarios. Also analyses were run to have an assessment of 3D effects on the slope failure. It was verified that failure was caused by the rupture of the water pipe.