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The small-scale physical model platform was developed as part of a four-year research project, "Physical modeling of landslide remediation constructions' behaviour under static and seismic actions, " to investigate the behaviour of slopes built of different materials with and without remedial measures under the influence of rainfall and earthquake. As in real landslides, the observation of a physical model consisted of a geotechnical and a geodetic monitoring system. In this paper, the behaviour of clay-like slopes during 1g artificial rainfall, with and without remedial measures will be described. Complex remedial measures included deep trench drains which reduced pore water pressure, and pile wall with head beam made with 3D printer, which increased shear resistance at the sliding surface. At the same rainfall intensities, the clay-like slope collapsed, while the slope supported with a pile wall at the slope foot remained stable. The results of the photogrammetric equipment and the complex sensor network measurements within a slope are presented and discussed, helping us to understand the different behaviour of slopes with and without remedial measures.

Small-scale physical models of landslides triggered by rainfall and seismic conditions provide a good insight into the initiation and progression of full-scale landslides in nature. In order to track and document the displacements on the surface of the small-scale model, a digital image correlation-based optical measuring system with high-speed cameras is used here. Each model is prepared for the optical measurements by adding specially chosen marker points (pins) that are monitored by a pair of high-speed cameras during each experiment. An additional set of non-high- speed cameras with higher resolution is used to monitor the deformation field on a selected smaller part of the model. This enables to obtain the 3D displacements and velocities of each marker point in order to detect any movement or crack opening on the surface both visually and accurately from the optical measurement results. The described system and established measurement procedure are advantageous as they provide the 3D displacement and velocity data for a large number of points on the surface with less equipment than conventional contact measurement methods. The collected data, in combination with other monitoring sensors, allow the observation of landslide initiation and the analysis of landslide evolution in all parts of the model slope during the sliding process. In this paper we present the measurement procedure and the results obtained optically in selected small-scale experiments.

This paper presents the application of Light Detection and Ranging (LiDAR) data for landslide identification and mapping in the pilot area at the Istria Penninsula (Croatia) and the analyses on the influence of expert knowledge on the quality of landslide inventory. Visual interpretation of landslides was carried out on high-resolution airborne laser scanning (ALS) LiDAR dataset. Scanning was taken in March 2020 for the pilot area in the City of Buzet. Based on the characteristics of the acquired LiDAR Point Cloud, a bare-earth digital elevation model (DEM) with 30 cm resolution was created. Different topographic derivative datasets such as slope, hillshade, contour lines, and roughness maps were created to interpret the LiDAR data. Eight experts with different levels of expert knowledge on LiDAR interpretation were given one week to carry out visual identification and mapping of potential landslides in the pilot area (0.3 km2) at a large scale (1:200) to provide detailed landslide mapping. Statistical analyses were performed based on the collected data to determine differences in the mapping accuracy and the number of recognized landslides by the experts. Results show that the experts familiar with the geology of the study area and potential landslide mechanics obtained better results than the experts who mapped landslides based on only ordinary topographic and geomorphological features specific for landslides.

The scientific research project Methodology development for landslide susceptibility assessment for land-use planning based on LiDAR technology (LandSlidePlan, HRZZ IP-2019-04-9900 ), funded by the Croatian Science Foundation, deals with new and under-investigated subjects in respect of inventory mapping of small and shallow landslides and presents innovative approaches to scientific research of landslide susceptibility assessment using cutting-edge LiDAR technology for collection of input data. The project has three main scientific goals. The first goal is to create the best optimal digital model of the bare-earth terrain that shows realistic landslide footprints and differences between disturbed and undisturbed land that may influence land use. The second goal is to create the most reliable large-scale landslide susceptibility map with the best differentiation of landslide-prone and non- susceptible areas using scientific methods customised to specific engineering geological conditions of Croatian environments with sliding threats. And the third goal is to create maps depicting information about landslides tailored according to the needs of the system of physical planning in Croatia (particularly land-use planning), encompassing local and regional levels under, harmonised at the national level. Due to different natural conditions and land uses in different parts of Croatia, the methodology will be developed for pilot areas in the City of Zagreb, Hrvatsko Zagorje and Istria, selected based on characteristic geological settings and degree of urbanisation.

Landslide maps produced by LiDAR (Light Detection and Ranging) are very clear and detailed representation of the phenomena and in many cases reveal evidence of past landslides that are virtually invisible by other detection techniques due to vegetation cover. Over the last decade, airborne laser scanning (ALS) has been made available and has been used to identify and map landslide. LiDAR elevation data prove particularly effective for mapping of small and shallow landslides in areas that are partially or completely covered by dense vegetation that are difficult or impossible to identify using conventional identification techniques. The first topic covered in the talk is landslide detection and mapping using very high-resolution LiDAR DTM to obtain complete historical inventories of shallow soil slides. Few examples of landslide inventory maps from different geomorphological environment of the Republic of Croatia will be presented to show typical landslide distribution. For landslide spatial prediction, the talk focuses on the results of landslide susceptibility modelling and zonation performed for a range of coverages, starting with the largest encompassing whole territory of Croatia. Landslide susceptibility zonation was also performed for areas of two counties (Primorsko-Goranska County and Karlovac County) and few smaller pilot areas of cities and municipalities in the Pannonian Basin and in External Dinarides. The main objective of presented susceptibility zoning in different scales (national, regional and local scale) is to enable analysis of usefulness and reliability of map information (i.e., spatial distributions and rating of the terrain units according to their landslide propensity) for application in physical and urban planning. The needs of the decision-makers, planners and other stakeholders involved in landslide risk prevention are analyzed through the series of round-table discussions organized in Croatia in the framework of the project of applied research PRI- MJER (KK.05.1.1.02.0020). The ultimate goal is to create maps depicting information about landslides tailored according to needs of the system of physical planning in Croatia (particularly land use planning), encompassing local and regional level, harmonized at the national level. The research of the mapping methodologies is part of the project “Methodology development for landslide susceptibility assessment for land-use planning based on LiDAR technology, LandSlidePlan” (HRZZ IP-2019-04-9900) fully supported by Croatian Science Foundation.

Earthquakes are one of the main landslide triggering factors. Earthquake induced cyclic shear strain and stress generate the rise in the pore water pressure and soil strength degradation which tends toward soil failure. Slopes in which shallow landslide can be formed due to geological conditions are most susceptible to such kind of loading mainly because of soil low confining stress. Confining effective stress has a significant role on the soil response during static and cyclic load. Tests performed on soil samples under monotonic shear indicate that the shear strength properties increase with decreasing effective stress due to dilatancy. This paper presents preliminary results of an undrained cyclic triaxial test on sand material used for modelling small scale shallow landslides under 1g conditions. Based on the scaling rules for 1g conditions, frequencies of straining amplitudes for undrained strain- controlled cyclic triaxial tests were defined. Undrained cyclic triaxial tests on the type of sand used in a small-scale landslide model were performed. Samples were consolidated on low confining stress which corresponds to an assumption of a shallow landslide used as prototype. All tests were conducted in the Laboratory for geotechnics at the Faculty of Civil Engineering in Rijeka, Croatia. The influence of loading frequency and low confining stress was investigated and a simple model for pore pressure build-up was proposed which can be used to estimate the increase in pore water pressure due to cyclic loading at low confining stress for frequencies of loading less than 1 Hz.

Physical modelling of landslides by analysing the behaviour of small-scale landslide models subjected to artificial rainfall can be divided into modelling under 1g conditions and under increased acceleration (n times gravity) in a centrifuge. In this paper, the landslide initiation, progression, and deposition caused by artificial rainfall in three small-scale models built with sand or sand-kaolin mixtures at the same slope angle will be described. The evolution of landslides is monitored by observation of volumetric water content, matric suction, and pore water pressure, as well as by monitoring slope deformations and failure development. Analysis of the factors affecting the landslide initiation, propagation and their relationship to the slope material, the infiltration process, and the overall resistance of the soil in a slope in terms of soil strength, effective pressure and the contribution of matric suction in the unsaturated part of the slope will be discussed. The main observations from the results of the tests carried out in relation to the initiation and development of the observed instabilities of sandy and clayey slopes are given.

The Špičunak location at the state road D3, near the Lokve settlement in the Gorski kotar region, Croatia, is well – known by numerous traffic interruptions caused by slide and rockfall occurrences. The rockfalls at the Špičunak location are mostly predisposed due to geological setting and heavy jointed rock mass in the road cut of approximately 180.0 m length and 23.0 m height. Structural and kinematic analysis of possible future rockfall were carried out following the modern approaches and recent techniques in rockfall hazard analysis. These approaches include application of remote-sensing techniques enabled to ensure digital terrain models (DTM) from three-dimensional high- resolution point cloud (3D HRPC) of the rock cut surface ; engineering geological mapping using combination of remote-sensing techniques and field mapping. The three-dimensional high-resolution point cloud (3D HRPC) were established based on terrestrial laser scanning (TLS) and photogrammetry survey employing unmanned aerial vehicle (UAV) using Structure form Motion (SfM) technique. Based on established 3D models, the cut was analysed to identify the main characteristics of the rock mass structure as well as to detect and map the discontinuities and discontinuity sets, orientation and dip of discontinuities, spacing of discontinuities, persistence of discontinuities and roughness of discontinues. Traditional geotechnical survey was conducted to determine the characteristics of the main discontinuity sets at the cliff, as well as to carry out a rock mass classification using Rock Mass Rating (RMR) system and Geological Strength Index (GSI). Detailed analyses of field survey and remote sensing data pointed to three different zones, based on their properties and rock block standings according to the general orientation and dip of the cut face. To identify possibility of failures associated with the present joint sets and their orientations, the kinematic analyses of plane, wedge and toppling failure mechanisms were carried out based on joint sets discontinuity features data collected by both traditional geological and geotechnical field survey and remote sensing survey and data analysis. Based on the kinematic analyses results, adequate protection measures to prevent further brock block detachments and rockfalls were selected and designed. In this paper we will describe field investigation, establishing of the rock cut model based on remote sensing and traditional geotechnical investigations, stability analysis, as well as design element necessary for ensuring of stability of the rock mass in the cut and safety of the traffic along the road.

The Raspadalica rockfall is well known location with numerous rockfall occurrences from 100 m high limestone cliff in the past that caused significant damages and victims at the railway Buzet - Pula in Istria, Croatia. Structural and kinematic analysis of possible future rockfall were carried out following the modern approaches and recent techniques in rockfall hazard analysis. Modern approaches include application of remote- sensing techniques enabled to ensure digital terrain models (DTM) from three dimensional high- resolution point cloud (3D HRPC) of the cliff surface ; engineering geological mapping using combination of remote-sensing techniques and field mapping. In this paper the methods and results of field and remote sensing investigation of the cliff structural and kinematic analysis results, identification of rockfall sources, as well as analysis of necessary protection measures and their positions at the slope above the railway route

Physical modelling of landslides using scaled landslide models behaviour began in 1970s in Japan on scaled natural slope models. The laboratory experiments of landslide behaviour in a scaled physical model (flume or flume test) started in 1980s and 1990s in Canada, Japan and Australia under 1g conditions. The main purpose of the landslide physical modelling in the last 25 years was research of initiation, motion and accumulation of fast flow like landslides caused by infiltration of water in a slope. In this paper the results obtained in landslide initiation test of a sandy and clayey slopes at different slope angles exposed to artificial rain by rainfall simulator are presented. The results of landslide development are monitored by observation of volumetric water content, matric suction and pore water pressure, as well as by monitoring of surface displacements and the displacements inside the sliding mass. The main observations from the results of provided tests related to initiation and development of the observed instabilities of sandy and clayey slopes are given.

On December 29, 2020 a magnitude 6.4 earthquake occurred in the Sisak-Moslavina county of Croatia. The earthquake occurred along the Popusko-Petrinja strike slip fault within the Eurasia plate at a depth of 10 km with an epicenter at 45.422°N 16.255°E, three kilometers (km) west-southwest of the city of Petrinja. The maximum intensity of the earthquake was VII (severe) on the Modified Mercalli Intensity (MMI) scale and VIII (heavily damaging) to IX (destructive) on the European Macroseismic Scale (EMS). Due to the earthquake and resulting damage, there were seven fatalities, 26 people were injured, and many hundreds of people were displaced from their homes. The most affected city was Petrinja, but severe damage also occurred in Sisak, Dvor, Glina, Topusko, as well as in Croatia’s capital Zagreb, located approximately 50 km northwest of the epicenter. Damage was also reported in neighboring countries, including Slovenia, located north of Croatia, and Bosnia and Herzegovina, located south of this region of Croatia. The purpose of this post-earthquake reconnaissance report is to provide, within a few days of the earthquake, an overview of the hazard characteristics and to summarize preliminary reports of damage to buildings, bridges, roads, and other infrastructure. Moreover, key findings are also summarized with regard to geotechnical failures that include liquefaction, lateral spreading, landslides, sinkholes and damage to the extended levee system along the Kupa, Odra and Sava rivers., Joint Reconnaissance Report, PRJ-2959