Sanja Dugonjić Jovančević

Study of Landslides in Flysch Deposits of North Istria, Croatia: Landslide Data Collection and Recent Landslide Occurrences

The northeastern part of the Istrian Peninsula in Croatia is built of Palaeogene flysch deposits, in which instability is common and where a large number of landslides, with significant consequences, have been recorded. Study of landslides in flysch deposits of North Istria will be conducted as one of the main activities of ongoing IPL-184 Project. It includes analyses and recognition of sliding mechanisms to use in landslide modelling and to determine landslide susceptibility and hazard in flysch rock mass deposits. Several landslide types, mechanisms and conditions occur in the study area. The majority of studied landslides occurred during the spring and winter. Generally, the landslides are of rotational and translational sliding type, and rarely rock falls and debris flows. Local roads and rarely other structures and facilities suffered major damage as a consequence of the landslides. Landslide inventories, as well as landslide susceptibility maps, have never been carried out in the study area. Today’s knowledge about landslides in this area is based on investigations of individual landslides and partial scientific research. After the project started, some of the activities from all stages of the project have been initiated. The proposed first stage of the project includes supplementation of the existing database, and field investigations of recent and existing landslides in the study area, as well as soil sampling for laboratory testing. Moreover, the methods used for landslide susceptibility and landslide hazard assessment are presented. This paper presents the current state of investigations and research in the initial stage of the IPL-184 Project.

A Landslide Monitoring and Early Warning System Using Integration of GPS, TPS and Conventional Geotechnical Monitoring Methods

An advanced comprehensive monitoring system was designed and used on the Grohovo Landslide in Croatia. Equipment selection was based on scientific requirements and consideration of possible ranges of monitored values and sensors precision. Establishment of an early warning system and defining of alarm thresholds is based on existing knowledge of the landslide behavior as well as collected comprehensive monitoring data. The focus of the early warning system establishment at Grohovo Landslide was on an effective combination of sensors (equipment fusion) with respect to detecting device malfunctions and reducing false alarms in the future. The weakest component in the Grohovo Landslide monitoring system is power supply based on solar devices, field data collecting and the data transmitting from the field PC to the control room at the University of Rijeka. This paper presents the main ideas and advances of the monitoring equipment fusion as well as weaknesses of the applied monitoring system at the Grohovo Landslide.

Geotechnical properties in relation to grain-size and mineral composition: The Grohovo landslide case study (Croatia)

The Grohovo landslide is the largest active slope movement along the Croatian coast, situated on the north-eastern slope in the central part of the Rjecina River Valley (north-eastern coastal part of Adriatic Sea, Croatia). Slopes in this valley are formed of siliciclastic rocks (i.e., flysch), while limestone rock mass is visible on the cliffs around the top of the river valley. The slopes are at the limit of a stable equilibrium state, and slope movement phenomena have been recorded since 19th century. Samples for laboratory testing were taken from the flysch bedrock, weathered zone and slope deposits to provide specimens for determination of their mineralogical, physical and geotechnical properties. Correlation between mineralogical and geotechnical properties and their influence on sliding processes are presented in this paper. Clay fraction in samples ranges from 17 % to 38 %. Clay activity of the tested samples is from 0.45 to 0.89, and the residual friction angle varies from 13.0° to 17.7°. These results correspond to the presence of kaolinite and illite groups of clay mineral. Mineral composition and decrease in strength of fine- grained soil materials, due to the increase of pore water pressures, contributes to the slope movements.

Landslide Susceptibility Assessment on Slopes in Flysch Deposits: A Deterministic Approach

This paper presents detailed landslide susceptibility analyses performed in an existing three dimensional model developed for simulation of progressive failure phenomena. Investigated area is built in flysch deposits, placed in the north-eastern part of the Istrian Peninsula, Croatia. This region is well known as an area of frequent, small and shallow instability phenomena, mostly triggered by rainfall. Performed analysis provided landslide susceptible areas which correspond to the real conditions in the slope. The results have shown that except for the detailed 3D analysis of slope stability at one specific location, LS-RAPID software can also be used for the deterministic landslide susceptibility analyses in wider area.

Coastal Erosion and Instability Phenomena on the Coast of Krk Island (NE Adriatic Sea)

This paper presents the influence of the marine erosion on slope stability in the south eastern coastal area of the Krk Island (north-eastern part of the Adriatic Sea). The bedrock (Paleogene marls and flysch) is occasionally covered with talus breccia from Quaternary period. The coast is strongly exposed to wave attack and thereby to marine erosion. Comparison of few orthophoto map generations shows significant coastal retreat during the fifty-year period. This phenomenon has been a fundamental trigger off different instability phenomena. The type of instabilities is a consequence of local geological fabric and resistivity of rock mass to marine erosion. In the investigated area, rock falls and slumps prevail in cliffs formed in talus breccias. Extremely high tides from 2008 and 2012 have caused significant coastal erosion. This is obviously an indicator of the possible higher hazard degree caused by the sea-level rise.

Insights from LS-RAPID Modeling of Montaguto Earthflow (Italy)

Open image in new window The paper deals with the numerical modeling of the Montaguto earthflow (Italy), as typical case of multi-stage flow-type landslide, formerly analyzed subdividing the whole process in subsequent stages. The paper proposed a unique simplified model including: (i) slope stability analysis to simulate the landslide initiation process due to pore pressure increase and (ii) landslide dynamic analysis for propagation, volume enlargement by entrainment and energy dissipation due to frictional, non-frictional and velocity dependent terms. The numerical results are capable to provide a substantial framework for interpreting the main kinematic and morphological features of the landslide.

Analysis of a historical landslide in the Rječina River Valley, Croatia

BackgroundLarge 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 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.Results2D 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.ConclusionsStability 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.

Marine Erosion and Slope Movements: SE Coast of the Krk Island

This paper presents the interaction of the marine erosion and slope movements on the south eastern coastal area of the Krk Island, Croatia. Larger parts of the coastal bedrock are carbonate rocks, and smaller parts are marls and flysch. The bedrock is occasionally covered with Quaternary sediments, which are characterized in terms of engineering soil properties. Complex geological fabric of the coastal area around Stara Baska settlement, in the south western part of the Krk Island, caused different movements on the coast. Due to the different grade of fissuring and karstification, as well as different weathering grade, carbonate and siliciclastic rock mass have wide range of resistance to the sea effects including wave attack. Exposure to the wave attack generated due to winds from the south directions contributes to the decreased resistivity. Additionally, occasional torrent flows and intensive erosion cause sporadic higher slope instability. The, effect of the previously registered extremely high tides, as well as the possible hazard increase due to the estimated sea level rise, is also analysed in the paper.

TXT-tool 3.385-1.2: Deterministic Landslide Susceptibility Analyses Using LS-Rapid Software

This paper presents the landslide susceptibility analyses on flysch slopes in Istra, Croatia, performed using deterministic three dimensional analyses in LS-Rapid software. The area of investigation is in the Pazin Paleogene Flysch Basin in the northeastern part of the Istrian Peninsula. Using deterministic approach in landslide hazard and risk analysis includes gathering of fundamental data about geometry, soil strength parameters, cover thickness and groundwater level, as well as the application of numerical models in safety factor calculation. LS-Rapid uses 3D models for simulation of progressive failure phenomena, developed to assess the sliding initiation and activation of landslides triggered by earthquake, rainfall or their combination. Detail distribution of pore pressures or the groundwater level inside the slope is taken into account trough the pore pressure ratio ru, which gradually increases until the failure appears in a certain part of the slope. If this approach is applied on the wider area, in which it is possible to define the relative position of the sliding surface, it is possible to obtain the values of the critical pore pressure ratio that causes conditions in which failures occur in specific parts of the investigation area. Connecting the critical pore pressure ratio with distribution of rainfall it is possible to obtain the landslide susceptibility and landslide hazard. The model was validated through the interpretation of stereopairs and engineering geological mapping, and the results have shown that landslides inside the zones in the model that were characterized as highly susceptible, occurred in the nearest of farthest past.

TXT-tool 3.385-1.3: Landslide Occurrence Prediction in the Rječina River Valley as a Base for an Early Warning System

This paper presents deterministic 3D stability analyses using LS-Rapid software applied to the wider area of the Grohovo landslide on the north-eastern slope of the Rjecina River Valley near the city of Rijeka, Croatia. Results of these analyses, in combination with results of existing monitoring data, are necessary for predicting future landslide behavior as a base for establishing an early warning system at the Grohovo landslide.