Volume 34, N. 2

May-August 2011

Back Analysis of a Landslide in a Residual Soil Slope in Rio de Janeiro, Brazil


Volume 34, N. 2, May-August 2011 | PDF (3 downloads)


After a short period of relatively intense rainfall, a deep-seated landslide occurred in a slope in Rio de Janeiro. On the following day, field inspection revealed full saturation of the failure mass, despite the inexistence of groundwater in the slope. A comprehensive experimental investigation was undertaken to determine the geotechnical parameters of the residual soil. A numerical modeling study of the infiltration processes revealed that the rainfall amount was insufficient to reproduce the saturation condition of the failure surface. This paper introduces the slope stability approach aiming to verify if the factor of safety would reflect a stable condition under the pluviometric records that occurred before the landslide. Therefore, 2D limit equilibrium analyses were accomplished, considering the different hydrological scenarios that were conceived for the flow simulations. The geotechnical parameters were defined according to laboratory test carried out on samples extracted from the slide surface and from an undisturbed site. Pore pressure distributions were obtained from previous results of flow simulations. Regardless of the geometry of the failed mass, the analyses indicated that the landslide could not be triggered solely by rain infiltration. Amongst various alternatives, a preferential flow through the bedrock fractured layer revealed to be the only feasible scenario that could reproduce not only the saturated condition, but also a FS value close to 1. Despite the usual approach of identifying the landslide as a rainstorm-induced mechanism, it appears to be more complex and other infiltration sources may play an essential role.

Keywords: unsaturated soil, residual soil, transient flow, rainfall, stability analysis, landslide,

Submitted on July 15, 2010.
Final Acceptance on January 11, 2011.
Discussion open until December 30, 2011.