Abstract
Large landslides triggered by rainfall and floods were registered on both sides of the Rjecina River Valley, near City of Rijeka, in Croatia, where numerous instability phenomena in the past 250 years have been recorded, and yet only some locations have been investigated. The paper presents investigation of the dormant landslide located on the south-western slope, recorded in numerous historical descriptions from 1870. Due to intense and long-term rainfall, the landslide was reactivated in 1885, destroying and damaging houses in the eastern part of the Grohovo Village. 2D stability back analyses have been performed based on landslide features, in order to approximate the position of the sliding surface and landslide dimensions. Because of the very steep landslide topography and the slope covered by unstable debris material, a Remotely Piloted Aircraft System (RPAS) was used to provide the data about the present slope topography. The landslide 3D point cloud was derived using Structure-from-Motion (SfM) photogrammetry. In order to verify the cloud of georeferenced sliding points obtained from images, it was compared with the existing models acquired from terrestrial photogrammetry and laser scanning, showing good accordance and small changes through the years. Based on the classification and Uniaxial Compressive Strength test results, rock mass strength was defined using generalised Hoek-Brown’s failure criteria. Stability analysis results of the present slope conditions show that the slope is marginally stable for dry conditions, and that the critical seismic coefficient of about 0.14 would generate inertial forces corresponding to the factor of safety equal to 1. Analyses were performed with the purpose to predict the possible reactivation of a dormant landslide, and the presented results could be used in the establishment of an early warning system.
Highlights
Large landslides triggered by rainfall and floods were registered on both sides of the Rječina River Valley, near City of Rijeka, in Croatia, where numerous instability phenomena in the past 250 years have been recorded, and yet only some locations have been investigated
The superficial contact point between flysch and limestone was acquired from the point cloud data and the contact plane orientation was assumed in the model
Many activities were initiated through different investigation periods, focusing on reduction of the possible landslide hazard in the Rječina River Valley, near City of Rijeka, in Croatia, where numerous instability phenomena, in the past two centuries, have been recorded. 2D stability back analyses were performed on the SW slope of a dormant landslide, in the Rječina River Valley, with the purpose to predict the possible reactivation, on the basis of landslide features present on the field
Summary
Large landslides triggered by rainfall and floods were registered on both sides of the Rječina River Valley, near City of Rijeka, in Croatia, where numerous instability phenomena in the past 250 years have been recorded, and yet only some locations have been investigated. The bottom of the Valley is 150 to 200 m above the sea level, while the highest peaks are at elevation 432 m in the south western and 412 m in the north-eastern part of the Valley This is the most active area in terms of geodynamic and seismic activities, with daily rockfall events and numerous catastrophic floods recorded in the past centuries, presenting the area with expressed landslide and flood hazard. I.e. flysch (sandstones, siltstones and marls in alteration) have a form of a squeezed synciline between karstified carbonate rocks (Upper Cretaceous and Paleogene limestone) which prevail in a wide area of the mentioned morphostructural unit Neotectonic and recent tectonic movements have caused irregular subsidence of flysch areas and the uplifting of the surrounding karstic terrain, whereupon karstified limestone rock masses are visible on the top of the slopes and the flysch rock mass can be found in the bottom of the Valley
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