Study of a large landslide and mudflow at Gaspar, SC, Brazil

Marcelo Heidemann, Luiz A. Bressani, Juan A. Altamirano Flores

In the proceedings of: GEO2011: 64th Canadian Geotechnical Conference, 14th Pan-American Conference on Soil Mechanics and Geotechnical Engineering, 5th Pan-American Conference on Teaching and Learning of Geotechnical Engineering

Session: Landslides

ABSTRACT: In November 2008 after a 56 days long rainy period the North of Santa Catarina state suffered a severe rainstorm (450mm/2 days). The paper describes the studies that have been carried out on an extremely fast landslide which happened a week after this rainstorm. The slide involved a granulite residual soil which was classified as inorganic sandy silt but that showed large packets of kaolinite minerals. Its hydraulic conductivity was of the order of 5x10-8m/s. Triaxial, direct shear and ring shear tests have been carried out on the soil. Although in the back-analysis of the initial failure the peak shear strength was necessary to properly explain the slide, the liquefaction that followed was probably caused by a drop from peak to residual shear strength due to re-alignment of the clay particles.

RESUMEN: En noviembre de 2008 después de 56 días de lluvias, el norte del estado de Santa Catarina fue afectado por severas precipitaciones (450 mm / 2 días). Este artículo presenta los estudios realizados en un deslizamiento de tierra muy rápido ocurrido una semana después del periodo de lluvias intensas. El deslizamiento de tierra corresponde a un suelo residual que se clasifica como un silte inorgánico con arena, que presentó grandes agregados de caolinita. Su conductividad hidráulica es del orden de 5x10-8 m/s. En este suelo fueron realizados ensayos triaxial y de corte directo. Aunque en el retro análisis de la ruptura inicial la resistencia al corte de pico explicaría mejor el deslizamiento, todavía la licuefacción que se siguió fue causada, probablemente por reducción para la resistencia al corte residual debido al re-alineamiento de las partículas de arcillas.

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