Back-analysis; Flysch rockslide; Geomodelling; Internal fracturing; Numerical modelling; Slope reconstruction; 3d distinct element methods; Dynamic numerical modeling; Geomodeling; Romania; Seismic landslides; Vrancea; Geotechnical Engineering and Engineering Geology; Geology
Abstract :
[en] Ancient landslides of unknown origin can be found in large numbers in mountainous regions; some represent valid markers of (pre-)historic natural regimes referring to either long-term evolution or short-term peak events of climatic and seismotectonic nature. An example is represented by the Balta rockslide in the Romanian Carpathian Mountains. Its location in the seismically active Vrancea-Buzau region, as well as its morphological features, deep-seated rupture surface and large debris volume, raise the question of its failure history with regard to a possible co-seismic triggering. A 3D volume based reconstruction of the slope morphology together with field measurements of elasto-plastic in-situ rock properties allow to estimate pre-failure conditions of the slope, with special regards to the geological, i.e. flysch bedrock of poor to fair rock quality, and structural settings, i.e. anti-dip slope bedding crossed by the main joint family. The reconstructed slope behaviour was tested under static and dynamic forces with the 3D distinct element code 3DEC, subsequently used to simulate a failure scenario with a 120 s long real earthquake record that leads to the realistic post-failure morphology of Balta. For the latter, we observe a principally joint-controlled failure combined with internal fracturing of the undamaged rock mass. After 230 s of simulated time, the landslide debris reaches the valley bottom with maximum displacements of 1350 m and is marked by a lateral expansion to a broader extent than the source zone width, as observed in the field. Extension of this work to other pre-historic slope failures in the valleys of Vrancea-Buzau yield valuable new information for future seismic hazard estimations of the region.
This research was partly funded by the WBI (Wallonie - Bruxelles International, with the bilateral project ‘Evaluation des risques long-termes liés aux mouvements de masse déclenchés par les séismes dans la région de Vrancea, Roumanie’), as well as by the F.R.S-FNRS Belgium in the frame of the FNRS-SNF collaboration project ‘4D seismic response and slope failure’. We further acknowledge the FRIA-FNRS research fellowship granted to Anne-Sophie Mreyen during the years 2016–2020. Finally, we thank the editor and the reviewers for their helpful suggestions that improved the quality of this work.
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