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Título

GEOLOGICAL AND GEOTECHNICAL BACK ANALYSIS OF THE PUNTA COLA ROCK AVALANCHE IN CHILE: A 3-DIMENSIONAL INTEGRATED APPROACH

Resumo

As a result of the earthquake of April 21, 2007, in the Aysén Fjord, Chile, a series of different types of landslides were generated, most of which affected the coastline surrounding the fjord. Among these landslides, a rock avalanche occurred in the Punta Cola sector, which resulted in a rock avalanche that reached the coast and produced a tsunami that affected populated sectors.
The main objective of the following work is to perform a back analysis of geological and geotechnical features and compare computation volumes obtained with limit equilibrium analysis and the onshore volume avalanche. All this within an interconnected workflow between implicit modeling for the determination of domains and geometry; and 3D limit equilibrium analysis.
For the definition of the geological domains, the information published by Oppikofer et al. (2012) was used to reference the digital elevation model and geological and geotechnical observations from field mapping. The integration of such data into a 3D environment eased the geotechnical definition of the 3D anisotropies and lithologies, also, the direct and explicit definition of the discontinuity's sets were fundamental for the subsequent determination of the landslide’s morphology.
Subsequently, the geotechnical domains containing the geomechanics properties and representative geometry were evaluated in terms of resulting factor of safety, and sliding mass volume, where different scenarios were selected: Base Case and Pseudo Static Analysis. Sensitive parameter variation was also conducted with the shear strength properties and discontinuities sets to determine the order of the avalanche's triggering factors.
The results highlight the complex structures and mechanisms involved earthquake-triggered landslides and driving forces on the minimum factor of safety. The 3D (3 Dimensional) slope stability captured the anisotropic influence on the sliding mass shape, and further comparison with digital elevation post event compared between the computed and observed landslide volumes.
This study presents the importance of the proper use of field data on the context of 3D model analysis, the benefits of a combined geological-geotechnical analysis schema and the use of limit equilibrium method for rock failure mechanism driven by discontinuities sets.

Palavras-chave

landslides, geological hazard, rock mechanics, 3D slope stability.

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