Josip Peranić

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.

Preliminary Investigations and Numerical Simulations of a Landslide Reactivation

Open image in new window A large landslide occurred near the Grohovo Village in outback of the City of Rijeka, Croatia, on 13 February 2014 after long term period of heavy rain. The preliminary surface observation was carried out immediately after sliding appearance enabled estimation of site condition, dimension of the landslide so as an assessment of a hazard of further landslide movements. The estimated dimension of landslide body are length of 350 m, width of 135 and 20–30 m of depth to the slip surface. The movement of approximately 12–15 m down the slope caused the complete damage of the local road over the landslide body. The toe of the landslide reached the bank of the Valici Reservoir 250 m away from the downstream located Valici Dam. Based on hazard assessment of further landslide movements, a lowering of the water level in reservoir and surface drainage from the landslide body were conducted as emergency landslide mitigation measures but the main reason for further landslide movements reduction was the end of heavy rain. Although the detailed filed investigations were not carried out, the analysis of possible further development of sliding was conducted. To establish the engineering geological model of the landslide, the analyses of existing LiDAR imagery and engineering geological mapping were carried out. It was identified that the recent landslide is a reactivation of the dormant landslide. Since a slip surface position was not identified by field investigation, a numerical analysis of a slope using the strength reduction method was introduced to determine the shape of a zone of rupture which would be used in landslide simulation. As a main hazard of further landslide movements, the filling of the Valici Reservoir, forming a landslide dam so as possible overflow of the dam and forming the wave that can reach the center of the City of Rijeka downstream the Rjecina River were identified. To determine possible scenarios those could be realized in case of new long term rainy period and raising of ground water level in the landslide body, a numerical simulations of further landslide development were conducted using LS-Rapid simulation software. In case of high reservoir water levels correspondent to the dam overflow, the sliding mass would significantly fill the reservoir and cause the landslide dam, while the water level rising and landslide caused waves (tsunamis) would overflow the Valici Dam and cause significant damage downstream the Rjecina River channel. Conducted LS-Rapid simulation results enabled a selection of relatively safe reservoir water level at which, in case of further landslide movements, no current harmful consequences would be realized. The reservoir filling by sliding mass would cause significant reduction of reservoir volume, disturbances in the Rjecina River and Valici Reservoir flow regimes so as long term disruption of hydro power plant work that imply on necessary landslide remediation before further landslide reactivation.

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 2.385-1.2: Landslide Comprehensive Monitoring System: The Grohovo Landslide Case Study, Croatia

The Grohovo Landslide is located on the north-eastern slope of the Rjecina Valley, Croatia and it was reactivated in 1996 at the location of the landslide from 19th century. In 2009 the Croatian-Japanese joint research project “Risk identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatia” was initiated and the Grohovo Landslide was chosen as a pilot area for monitoring system development. A comprehensive monitoring system was designed and installed. Integrated monitoring system consists of survey using GPS and robotic total station so as geotechnical monitoring using long span and sort span wire extensometers, inclinometers, pore pressure gauges and rain gauges. All measurements will be integrated in GIS for landslide risk management and early warning system. The monitoring results should provide a basis for develop and validate confidential numerical models and adequate hazard management.

Soil-Water Characteristic Curve of Residual Soil from a Flysch Rock Mass

Depending on the nature of the material and suction range, laboratory measurements of the soil-water characteristic curve (SWCC) can be time-consuming and expensive, especially for residual soils, in which a wide range of particle sizes and soil structures typically results in SWCCs that cover a wide range of suction. Investigations of the SWCCs of residual soil from flysch rock masses are rare, and so far, no results were presented in the literature which were obtained by performing measurements on undisturbed specimens. In this paper, a detailed examination of water retention characteristics is performed for a specific type of residual soil (CL) formed by the weathering of a flysch rock mass. Measurements performed by using different techniques and devices on intact specimens were successfully combined to obtain the SWCC during both drying and wetting processes, under different stress conditions, and from saturated to air-dried conditions. Used procedures are suitable for the determination of SWCCs of soils that undergo volume changes during the drying or the wetting process, since instantaneous volumetric water content can be determined. Results presented in this paper can be used to assess the influence of desaturation of the residual soil covering flysch slopes during dry summer periods by providing key-in material properties required to analyze the transient rainfall infiltration process.

Landslide Risk Reduction in Croatia: Scientific research in the framework of the WCoE 2014- 2017, IPL 173, IPL 184, ICL ABN

In this paper scientific activities of the Croatian Landslide Group (CLG), World Centre of Excellence on Landslide Risk Reduction (WCoE) of the International Consortium on Landslide (ICL) for the period 2014–2017, are shortly described. The results of scientific research are presented through the fields of landslide science: landslide identification and mapping, landslide investigation and testing, landslide monitoring, landslide modelling and landslide stabilization and remediation. It is concluded that the resulting landslide inventory maps, regional empirical rainfall intensity-duration thresholds, kinematic landslide models and soil strength parameters, landslide movement prediction models, numerical models and simulations and behavior of geotechnical construction for landslide stabilization provide necessary information for landslide risk management in Croatia. Besides applied scientific research, the general objectives of ICL WCoE are achieved in the framework of two Croatian IPL Projects and regional ICL Adriatic-Balkan Network.