Investigation of a Deep-Seated Gravitational Slope Deformation in Western Carpathian Mts., Slovakia

Abstract

ABSTRACT: Deep-seated gravitational slope deformations (DSGSDs) are common but not highly investigated phenomena around the world. In the Carpathian mountains they played an important role during the Quaternary evolution of typical core mountain ridges. The collapsed Brdo DSGSD from Western Carpathians, Slovakia has been subjected to a detailed investigation involving geomorphic mapping, remote sensing analysis, structural data collection and numerical modeling. To improve our understanding of these gravity-induced processes, we performed a continuum-based finite-element modeling set up using the RS2 code (©Rocscience). We used geomechanical rock data from the field works and previous laboratory tests as well as interpretation of it in RSData software (©Rocscience) to obtain the major rock mass design parameters for the models. The results show that Brdo DSGSD is predisposed by regional geological structures given by the intersection of bedding planes, joint sets, and thrust faults. The main causal factors influencing development of DSGSD have been bedrock structure, the lithological composition of dolomite, limestone layers, thrust faulting, and deep weathering of the rock mass. 1. INTRODUCTION The Western Carpathian mountains in Slovakia represents a typical region with favorable predisposing conditions for landslides and other mass movements including the deep-seated gravitational slope deformations (DSGSDs). Recent studies in Alps (Della Seta et al., 2017; Crosta et al., 2013; Faccini et al., 2020; Discenza et al., 2021), Carpathians (Pánek et al., 2017) and Andes (Pánek et al., 2022) show that most of big scale slope deformations are controlled by already existing geological structures, such as joints, folds, faults and bedding planes which influence the kinematic conditions in rock massif and directly affect the geomechanical, rheological characteristics of the rock mass at the mountain scale (Jaboyedoff et al., 2013). In this work, we investigate a collapsed Brdo DSGSD case with a goal to deeper understand driving mechanisms and possible evolution scenarios of a typical relatively isolated DSGSD case. Finite element numerical modeling was performed to investigate the development and geomechanical characteristics of collapsed DSGSD as well as to reconstruct the stages and initial conditions of the deformation. We present an analysis of a mountain massif affected by large-scale DSGSD collapse which will let us evaluate stress and strain distribution, displacement rates, and vectors in the different DSGSD development stages. This case study shows well-preserved gravitational morpho-structures in relatively isolated and small-scale rock massif. However high slope (>400 m) geometry and volume of massif don't allow us to use traditional limit equilibrium slope stability models. In this study, we use a continuum-based finite element method which lets us reveal the main predisposing factor for DSGSD collapse in retrospective analysis and lets us predict the most possible areas and slip zones/surfaces for future slope collapses in the research area. We aim to introduce the complex methodology combined from field observation, structural, geomorphic, LIDAR data analysis, and numerical modeling which could be helpful for a more holistic understanding of the transition from DSGSD to its collapse.