Geotechnical and Geophysical Assessment of the 2021 Tamban Chimbo Landslide, Northern Andes of Ecuador

Abstract

The recent landslide at the Tamban site, on 21 December 2021 (23:30 local time), provides relevant information on the trigger mechanisms and their relationship with geological factors. Therefore, the predominant aims of the current study were to identify the lithological units in the rocky substrate and subsoil from geophysical surveys, delineating the thickness of the tuff- and lapilli-supported fall layers. Additionally, we evaluated the deformation dynamics from probabilistic and deterministic analysis, where a plane with well-differentiated discontinuities of normal-type geological fault was evidenced. This deformation feature was associated with a planar-type landslide that reached a debris flow up to 330 m distance, with varied thicknesses. Furthermore, we conducted a probabilistic analysis, which started from the characteristics of the post-slide material analyzed through triaxial trials that were conducted to a retro-analysis in order to obtain the parameters of the moment the event occurred. With the base parameters to perform the landslide analysis and determine its safety factors in compliance with current regulations, a reinforced earth configuration was applied using the Maccaferri’s Terramesh method. Hence, it was possible to provide an analysis methodology for further geological scenarios of landslides that occurred in the province of Bolívar, the northern Andes of Ecuador.