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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. Physical modelling of landslide initiation began in Japan in the 1970s on scaled natural slope models. After initial experiences with field and laboratory researches, small-scale landslide modelling has found wide application around the world in various aspects of landslide investigations, analysing different types of landslides, different types of slope materials and landslide movements. The main task of landslide physical modelling has been to study the initiation, motion and accumulation of fast flow- like slides caused by infiltration of surface water. Studies that have included landslide mitigation measures in the small-scale physical model are rare and have not established correlations with the behaviour of on-site mitigation structures. This paper discusses the behaviour of a small-scale sandy slope supported by a gravity retaining wall in the foot of the slope, during artificial rainfall in 1g loading conditions. Two models of sandy slopes, with and without retaining wall applied, were exposed to identical intensities of artificial rainfall. The results of the simulations indicated that the slope supported by the gravity retaining wall at the toe remained stable under the same conditions under which the sandy slope collapsed. The supported slope also remained stable under much longer rainfall. At the end of the simulation, the supported slope was subjected to much higher rainfall intensities, well above the infiltration capacity of the sandy material, and surface runout was affected. The combination of surface erosion and saturation of the superficial layer of the slope led to the initiation of a debris flow, while the complete saturation of the slope at the moment when the ground water level reached the surface of the slope caused the soil strength to be exceeded and the formation of a surface of rupture and consequently movements of the formed landslide body. Although the landslide movement caused displacement and longitudinal deformation of the gravity wall at the slope foot after local shear failure in front of the wall foundation, in general the gravity wall significantly improved the stability of the slope. The results of the measurements carried out with the installed geodetic and geotechnical monitoring system allowed a comprehensive understanding of the whole process of infiltration of precipitation and reduction of soil strength until the development of the fracture surface in the slope, as well as the process of incremental load development on the retaining structure until the limit resistance of the structure.

Despite the considerable progress made in recent decades, there is still a need for a deeper understanding of the physical processes, mechanisms and crucial factors that lead to rainfall-induced landslides. With ongoing climate change affecting the frequency and intensity of meteorological extremes, and the imperatives of continuous urban expansion undoubtedly influencing the frequency and magnitude of landslides, it is no coincidence that the issue of rainfall-induced landslides has received increasing attention from both the scientific community and landslide practitioners in recent decades. Close observation of the hydromechanical response of slopes exposed to different rainfall loads plays a crucial role in understanding the driving mechanisms and factors affecting rainfall-induced landslides. In combination with appropriate monitoring techniques, small-scale physical landslide models can provide accurate insight into the relevant variables under precisely controlled initial and boundary conditions. This paper presents a model platform for physical modelling of scaled slopes under 1g rainfall infiltration conditions, developed at the Faculty of Civil Engineering, University of Rijeka, Croatia, within the four- year research project "Physical modelling of landslide remediation constructions' behaviour under static and seismic actions". Some of the main features of the model platform and the materials used for testing are described. Special attention is given to the sensor network that allows precise monitoring of soil moisture and pore water pressure in a scaled slope during rainfall simulation. Finally, two interesting examples of monitoring data are singled out and analysed with working frameworks relevant to the study of scaled slope models exposed to rainfall.

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.

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.

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.

Physical modelling of landslides has started in the 1970s in Japan on natural slopes exposed to artificial rain. Subsequently, small-scale laboratory models’ development began in the 1980s with the aim of studying landslide behaviour such as triggering, movement, and accumulation. The research presented here is part of the Project funded by the Croatian Science Foundation entitled “Physical modelling of landslide remediation constructions’ behaviour under static and seismic actions”. When remediation constructions become part of a small-scale model, the determination of a scale ratio and the need to establish, at least partially, similarity laws with regard to a real slope is inevitable. Although many studies use a small-scale model to research landslide behaviour of a real slope, there are only few studies that consider the scale ratio and similarity laws. In this paper, a summary of some of these studies is provided, along with an overview of all similarity laws and the characteristics that make them up in relation to landslides. Since the most important problem with small-scale models at 1g are low values of the overburden stresses in a model, laboratory tests are performed in an attempt to determine the relationship between the constitutive behaviour of the material in a small- scale model and a real slope. An example of geometric similarity is given here using the grain-size distribution curve and its influence on other similarities and their characteristics like infiltration rate, weight, and strength of soil, etc. Some preliminary results of laboratory tests are presented together with a discussion about possibilities and limitations in achieving better similarity of small-scale models to real slopes.