Numerical modeling of collapsed deep-seated gravitational slope deformations: insights from Velka Fatra Mts., Slovakia

Large-scale 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 formed by crystalline basement and surrounded by Mesozoic deposits. There is evidence that most of the biggest catastrophic rock slope failures (collapses) in the Carpathian Mountains appeared exactly in areas that are affected by DSGSDs. Two DSGSD-affected slopes (Brdo and Žlebiny) on the northeast side of the Velka Fatra Mountains (Western Carpathians, Slovakia) have 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 back-analysis of collapsed DSGSDs through a 4-stage continuum-based finite-element model set up using the RS2 code (Rocscience). We used geomechanical rock data from fieldwork and previous laboratory tests, as well as interpretation in RSData software (Rocscience), to obtain the major rock mass parameters for the models. Results show that these DSGSDs are strongly predisposed by regional geological structures given by the intersection of bedding planes, joint sets, and thrust faults. The numerical modeling approach and performed back-analysis have enabled a better view of the development of these deep-seated slope failures in the Velka Fatra Mountains. It suggests a high diversity of mechanisms leading to the origin of these DSGSD cases. The main causal factors influencing their development have been bedrock structure, the lithological composition of dolomite and limestone layers, thrust faulting, and, finally, deep weathering of the rock mass. Both cases have deep basal shear zones and a few series of gravitational faults associated with complex joint sets. According to the numerical modeling results, Brdo DSGSD shows a typical scenario of a symmetrical sackung surrounded by shallow landslide areas, while Žlebiny DSGSD developed into a one-sided deep-seated slide with a few large-scale tilted rock blocks.