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Physical modelling of landslides using scaled landslide models behavior began in 1970s in Japan at a scaled natural slope physical model. The laboratory experiments of landslide behavior in a scaled physical model (also called 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 October 2018, at the Faculty of Civil Engineering University of Rijeka, started a four-year research Project Physical modelling of landslide remediation constructions behavior under static and seismic actions, funded by the Croatian Science Foundation. The main Project aim is the modelling of landslide remedial constructions’ behavior in physical models of scaled landslides in static (rainfall triggered landslides) and seismic conditions (earthquake triggered landslides) and their combination under 1g conditions. In this manuscript we will present the preliminary results obtained in landslide initiation test of a sandy slope (constructed of 0-1.0 mm the Drava River sand) exposed to an artificial rain typical for local conditions in Croatia by rainfall simulator. The results of landslide development were monitored by observation of volumetric water content and pore water pressure as well as by of surface displacement by structure from motion (SfM) surface observation displacement monitoring inside the model displaced mass. In this paper the preliminary results of provided test will be presented related to initiation and development of the observed instability of the sandy slope model.

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 assessment of a hazard of further landslide movements. The estimated dimension of landslide body are length of 350 m, width of 135 m and 20 to 30 m of depth to the slip surface. The movement of approximately 12 to 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 Valići Reservoir 250 m away from the downstream located Valići 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. The landslide is located in the Rječina River Valley which is very well known as an area prone to sliding with a lot of massive and small landslides recorded in the past and recent history (Arbanas et al. 2014). The Rječina River is 18.7 km long, and the mouth is located in the centre of the City of Rijeka. The area of the valley is part of a dominant morphostructural unit along the Rječina River Valley. The Cretaceous and Paleogene limestone are located at the top of the slopes, while the Paleogene siliciclastic rocks and flysch deposits are situated on the lower slopes and the bottom of the valley consisted of silty marl, laminated silt to silty shale and fine- grained sandstones (Benac et al. 2011). 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 (Mihalić Arbanas et al. 2014). It was identified that the recent landslide is a reactivation of the dormant landslide which contours were clearly visible on LiDAR images. Borders of both dormant and reactivated landslides were confirmed by engineering geological mapping on the new topographic map. The reactivated landslide included only part of the dormant landslide area. 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 Valići Reservoir, forming a landslide dam so as possible overflow of the dam and forming the wave that can reach the centre of the City of Rijeka downstream the Rječina 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. The LS-Rapid software is the first landslide simulation model possible to integrate the whole process of stable state, failure, post-failure strength reduction, motion and deposit of sliding mass (Sassa et al. 2010, 2014). While the foot of the landslide is submerged in the reservoir, the magnitude of motion, run off sliding path and deposition of sliding mass significantly depend on the reservoir water level. The landslide simulations were conducted for four different reservoir water levels correspondent to full reservoir, overflow level, and two lower safety levels. In case of high reservoir water level 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 Valići Dam and cause significant damage downstream the Rječina River channel. At the overflow reservoir water level of 229.50 m asl, the total volume of about 300.000 m3 would slide in the reservoir and cause 220 m width landslide dam while the consequent water level rising would reach 2.55 m with additional 5.80 m height water waves. Lowering of a reservoir water level would have an important impact on reduction of sliding mass that would fill the reservoir and consequences caused by the water level rising and landslide caused waves. At the safety reservoir water level of 224.50 m asl, the total volume of about 90.000 m3 would slide in the reservoir and cause 90 m width landslide dam while the consequent water level rising would reach 0.50 m with additional 3.00 m height water waves. 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 Rječina River and Valići Reservoir flow regimes so as long term disruption of hydro power plant work that imply on necessary landslide remediation before further landslide reactivation.

The Grohovo Landslide is a reactivated complex landslide in the outback of the City of Rijeka, Croatia. Several historical episodes of landslide movements and consequences demonstrate the needs for a landslide forecasting and an early warning system in order to reduce related hazard and risk and to protect human lives. The part of the Rječina River Valley between the Valići Reservoir and the Pašac Bridge is the most unstable part of the City of Rijeka area, with a highest hazard of possible sliding. Numerous historical descriptions, figures and maps describing landslides were found in the Croatian State Archive in Rijeka. An early warning system for possible landslide occurrence and assessment of landslide risk in the Rječina River Valley should be established based on possibility of prediction of instabilities appearances in the zones where the monitoring equipment is installed. Prediction of possible movements would be carried out on the basis of the results of 2D or 3D landslide stability analyses of wider landslide area in combination with the results of existing monitoring data. Critical limit values must be also defined for indicating of new sliding appearance and starting up the alarm. The 3D landslide stability analyses enable indication of possible hazard and risk for further landslide occurrences under unfavorable hydrological conditions in the most unstable part of the Rječina River Valley. The 3D stability analyses were carried out using landslide simulation model software LS-Rapid. LS-Rapid software could integrate the initiation of the landslide process triggered by rainfalls and the development of sliding due to strength reduction and the entrainment of deposits in the run out path. Stability analyses are based on strength parameters obtained by laboratory test on soil samples taken from the zones in which should be developed sliding surfaces. Soil testing were conducted on representative samples in a portable ring shear apparatus ICL- 1 designed for testing the residual shear resistance mobilized along the sliding surface at large shear displacements under static and/or dynamic local conditions. The results of the ring shear tests are necessary to enable input data for analyses of the development and propagation of the sliding mass in LS-Rapid software. In this paper will be presented deterministic 3D stability analyses using LS- Rapid software applied on the wider zone of the Grohovo Landslide at the north-eastern slope of the Rječina River Valley. The results of these analyses enabled prediction of possible sliding zones so as critical groundwater conditions (expressed by saturation ratio) those will cause sliding. Critical groundwater conditions could be connected with precipitation values, run off coefficients and infiltration ratios and these correlations will be used as an indicator of possible sliding in an early warning system. The most important indicators for alarm decision should be measured values on installed monitoring equipment in the moment when measured values reach proposed critical values.

In most cases, once the slope stability analyses of future quarry cuts are completed and mine management accepts results and designs, the geotechnical consulting is outsourced from further activities such as excavation plan design, excavation and mining and necessary activities on engineering geological mapping of excavated cuts, geotechnical supervising and active geotechnical design are not carrying out. This approach often leads to occurrences of local or global instabilities of quarry cuts. This paper presents a case study of global instability of open pit slopes in the Torine open pit that is situated in the Pannonian Basin, near the city of Gradac Našički in Croatia. Exploitation zone of basalt rock mass is underlain by chlorite schist rock mass. Sliding of basalt rock mass was developed along the slip surface at the geological contact with chlorite schist. Exploitation has been continuing even after sliding occurrence, without any previous remediation. On the basis of engineering geological mapping results, three separate landslide phenomena were determined. Despite its fact, the exploitation in the Torine open pit is continued till nowadays.

Numerous instability phenomena have been recorded in the Rjeˇcina River Valley, near the City of Rijeka, in the past 250 years. Large landslides triggered by rainfall and floods, were registered on both sides of the Valley. Landslide inventory in the Valley was established based on recorded historical events and LiDAR imagery. The Rjeˇcina River is a typical karstic river 18.7km long, originating from the Gorski Kotar Mountains. The central part of the Valley, belongs to the dominant morphostructural unit that strikes in the northwest-southeast direction along the Rjeˇcina River. Karstified limestone rock mass is visible on the top of the slopes, while the flysch rock mass is present on the lower slopes and at the bottom of the Valley. Different types of movements can be distinguished in the area, such as the sliding of slope deposits over the flysch bedrock, rockfalls from limestone cliffs, sliding of huge rocky blocks, and active landslide on the north-eastern slope. The paper presents investigation of the dormant landslide located on the south-western slope of the Valley, which was recorded in 1870 in numerous historical descriptions. 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. To predict possible reactivation of the dormant landslide on the south-western side of the Valley, 2D stability back analyses were performed on the basis of landslide features, in order to approximate the position of sliding surface and landslide dimensions. The landslide topography is very steep, and the slope is covered by unstable debris material, so therefore hard to perform any terrestrial geodetic survey. Consumer-grade DJI Phantom 2 Remotely Piloted Aircraft System (RPAS) was used to provide the data about the present slope topography. The landslide 3D point cloud was derived from approximately 200 photographs taken with RPAS, using structure-from-motion (SfM) photogrammetry. Images were processed using the online Autodesk service “ReCap”. Ground control points (GCP) collected with Total Station are identified on photorealistic point cloud and used for geo-referencing. Cloud Compare software was used for the point cloud processing. This study compared georeferenced landslide point cloud delivered from images with data acquired from laser scanning. RAPS and SfM application produced high accuracy landslide 3D point cloud, characterized by safe and quick dana acquisition. Based on the adopted rock mass strength parameters, obtained from the back analysis, a stability analysis of the present slope situation was performed, and the present stability of the landslide body is determined. The unfavourable conditions and possible triggering factors such as saturation of the slope, caused by heavy rain and earthquake, were included in the analyses what enabled estimation of future landslide hazard and risk.

The Grohovo Landslide, the largest active landslide along the Croatian part of the Adriatic coast, is located on the north-eastern slope of the Rječina Valley. In 2009 the Croatian-Japanese research joint 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 consisted of geodetical and geotechnical monitoring. Installation of monitoring equipment started in March 2011 and will be complete to the end of 2011. Integrated monitoring system will be consisted of surveying system using GPS and robotic total station, so as geotechnical monitoring using pore pressure gauges, inclinometers, extensometers and seismographs. The main part of monitoring equipment was installed in July 2011, when complete geodetical monitoring equipment was delivered and installed. In the automated integrated monitoring system until December 2011 are included observation of geodetic prisms with robotic total station and system of 10 GPS rovers (including master unit). Immediately after starting on of the system, the measurement data from the GPS and robotic total station observations were starting to collect, and it was possible to analyze initial landslide monitoring data. First analyses were pointed to relatively high accuracy and data scattering inside the expected limited values for this type of measurement and high values scattering dependence on local weather conditions. From analyzed measurement results, it is very clearly visible that the collected data are liable to numerous influences such as daily, monthly and yearly temperature and humidity variation and local disturbing effects caused by deformations of poles on whose robotic total station and GPS master unit receiver are installed. It should be necessary minimum one year of data collection that these disturbing effects could be connected with their causes and to establish procedures for calibrating equipment and eliminating effects of weather impacts on measurements accuracy. In this paper we will present the initial monitoring results so as perceived local weather condition implications on values of collected measurement data.

The Grohovo Landslide, the largest active landslide along the Croatian part of the Adriatic coast, is located on the north-eastern slope of the Rječina Valley. It was noted that during 19th and 20th century a lot of instabilities on the Rječina Valley slopes were occurred. The last complex retrogressive landslide was reactivated in December 1996, after long time dormant period and about 1.0x106 m3 were moved down the slope and buried the Rječina river-bed and after initial movements, the landslide was retrogressively developed up the slope. Slip surfaces are considered to be on the contact of superficial deposits and flysch bedrock. In 2009 the Croatian-Japanese research joint 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 consisted of geodetical and geotechnical monitoring. Installation of monitoring equipment started in March 2011 and will be complete to the end of 2011. Integrated monitoring system will be consisted of surveying system using GPS and robotic total station, so as geotechnical monitoring using pore pressure gauges, inclinometers, extensometers and seismographs. The establishment of monitoring system was carried out in stages according delivery purchasing and delivery of monitoring equipment. Installation of inclinometer casing and pore pressure gauges was started in March 2011 and foundations and poles for long span extensometers were finished in May 2011. The main part of monitoring equipment was installed in July 2011, when complete geodetical monitoring equipment was delivered and installed. After monitoring system starting up, some problems in equipment operating were observed and equipment re-adjustment was carried out until the end of November 2011. Installation of long span extensometers was completed in same time. In next stages of monitoring equipment installation, the short span extensometers, vertical extensometers, pore pressure gauges data loggers and pluviometer will be installed. In the automated integrated monitoring system until December 2011 are included observation of geodetic prisms with robotic total station and system of 10 GPS rovers (including master unit). Rest of equipment will be included after equipment connection in unique system. In this paper we will described the planned monitoring system so as details from monitoring equipment installation in detail.

The Grohovo Landslide, the largest active landslide along the Croatian part of the Adriatic coast, is located on the north-eastern slope of the Rječina Valley. In 2009 the Croatian-Japanese research joint 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 will be consisted of geodetical and geotechnical monitoring. Installation of monitoring equipment started in March 2011 and will be complete to the end of 2011. Integrated monitoring system will be consisted of surveying system using GPS and robotic total station, so as geotechnical monitoring using pore pressure gauges, inclinometers, extensometers and seismographs. In the automated integrated monitoring system until December 2011 are included observation of geodetic prisms with robotic total station and system of 10 GPS rovers. Immediately after starting on of the system, the measurement data from the GPS and robotic total station observations were starting to collect, and it was possible to analyze initial landslide monitoring data. One of most important aim of the Grohovo Landslide monitoring system is establishment of the early warning system. In designing of early warning system it is necessary: to identify real hazard of further sliding and possible direct and indirect threats, to identify possible movements and landslide widening with high hazard, to select appropriate equipment relating to position in the field and measurement accuracy and to define critical limit values that indicating new sliding appearance and start up alarm. Analyses of the past and prediction of the future landslide behavior are the most important steps in early warning system consideration, while equipment selecting should depend on measurements of appropriate values with required accuracy. In this paper we will present consideration of early warning system establishment on the Grohovo Landslide analyzing all previously mentioned requirements.

Paper presents landslide hazard and risk assessment in the central part of Istrian Peninsula, Croatia. Investigation area of about 550km2 is formed in Paleogene flysch deposits with expressed frequent instability phenomena followed by damages on local roads, buildings and other facilities, fortunately without casualties. Considering available data about landslide occurrences in the past, as well as results of preliminary analyses of sliding mechanism conditions and triggering factors, deterministic approach was used to analyse landslide hazard using 3D simulation model. High landslide susceptibility was identified in the north-eastern part of the investigated area, on the contact of flysch and limestone rock mass complex. Landslide susceptible areas are present in construction zones, protected forest, manufacturing and commercial zones, as well as other valuable parts on investigated area, established according to the existing urban plans. Furthermore, a coarse qualitative landslide risk analysis was performed. Elements at risk (assets) in the investigation area have been determined from the topographic maps and orthorectified photographs (1:5, 000) and they included following components: roads, smal road viaducts, residential houses and farm facilities, cultivated areas, protected forests and crude construction areas, as well as human lives and socio- economic activities. Vulnerability was defined as degree of loss for the certain element at risk threatened by landslide hazard inside defined hazard zone. Analysed area was divided in 20 hazard zones which were individually analysed regarding landslide risks, considering probability of hazardous event, vulnerability of elements at risk and temporal exposure to landslide hazard. Landslide hazard zones include zone of depletion, landslide path and zone of accumulation gained from the 3D simulation of landslide initiation and sliding mass propagation in LS-Rapid software. Temporal exposure of elements to landslide hazard was analysed considering a number of landslides inside the landslide hazard zone. Landslide intensity was considered in respect to landslide area. According to the present number of elements at risk inside the landslide hazard zone, four levels of impact on the total risk were determined. Single asset method was used in the vulnerability analysis where damage or loss for every element at risk were determined individually, paying attention on the elements inside or near the landslide hazard zones and landslides. Vulnerability was assessed inside the following levels: no damage, minor damage, functional damage or structural damage. Presence of human lives and social effects, as elements at risk, was considered in the way that vulnerability was raised for one level. Total risk was categorized into five levels: very low, low, medium, high and very high. Results of these analyses allow changes in existing urban plans and an improvement of future land use management. Cognitions about landslide hazard and risk in the area can be useful to many direct and indirect users, scientists and engineers, local government, developmental agencies, construction and utility service departments, as well as insurance companies. Analyses could give considerable contribution to sustainable land use development, if they would be included in the urban planning by limitation of construction on zones with acceptable landslide hazard and risk level.

The Croatian-Japanese joint research SATREPS' project 'Risk Identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatia' was performed from 2009 to 2014. Key objectives of the project were landslides and floods hazard analysis and the development of guidelines for use in urban planning. The aims of the working groups dealing with landslides were to establish a methodology of comprehensive real time monitoring at two most important landslides in Croatia based on the results of previous investigations and new in situ and laboratory testing and behaviour analysis ; laboratory soil testing and numerical modelling of static and dynamic landslide behaviour ; development of landslide inventories using direct sensing and remote sensing techniques followed by the development of methodologies of landslide hazard analysis and zonation in three pilot areas in Croatia. In this paper we will present the most important achievements of working groups related to landslide studies at the one of the Project pilot areas: the Rječina River Valley near the City of Rijeka. The identification and mapping of existing landslides in the Rječina River Valley so as establishment and results of the monitoring on the Grohovo Landslide, the most recent landslide in the pilot area will be described. It will be also pointed on activities whose would be performed to improve results of conducted investigations and analyses.

The advanced comprehensive monitoring system was designed and applied to the Grohovo Landslide in the Rječina River Valley, Croatia, in the frame of the Croatian Japanese bilateral scientific project on ‘Risk Identification and Land-Use Planning for Disaster Mitigation of Landslides and Floods in Croatia’. The monitoring equipment was selected based on landslide characteristics, equipment possibilities related to field conditions, so as scientific requirements. The focus of the monitoring system establishment was on effective combination of sensors (equipment fusion) Necessary improvements of existing monitoring system have been analyzed and presented on the basis of 1.5 year period of measurement. The use of multiple sensors at the same measuring point should guarantee the possibility to check redundancy and correlation of measurements. Equipment fusion is also useful in prevention of losing data if one instrument fails. Usage of geodetical and geotechnical equipment fusion in combination with hydrological monitoring equipment, enables reconstruction of the relationships between rainfalls, groundwater levels and landslide response. The results of monitoring system should provide basis for development and validation of numerical models and adequate early warning system inside the landslide hazard management framework. In order to provide establishment of the reliable early warning system alarm thresholds should be based on existing cognition of the Grohovo landslide behavior, which depends greatly on the reliability of the gathered monitoring data. In this paper, an overview of the two years observations results of the Grohovo Landslide using an integrated remote monitoring system as well as brief overview of the latest upgrades in the installed system will be presented. Since the monitoring system on the Grohovo landslide integrates two different types of monitoring, data will be presented accordingly. The latest data from the overall geotechnical monitoring system, was collected in the early September 2013, during the system upgrade and maintenance works. Regarding the geotechnical part of the monitoring system, data presented in this paper includes records from long span extensometers, short span extensometers, vertical extensometers and inclinometers. Second part of the data presented in this paper refers to geodetic monitoring. This part of the Grohovo Landslide monitoring system includes geodetic surveys of 25 benchmarks (prisms) observed by robotic total station and measurements from 9 GPS receivers (rovers) connected in local GPS network. Analyses of equipment in fusion behavior will be presented trough the analyses of results of different monitoring sensors installed at the same points, which in case of this paper refers to poles containing both geodetic prisms and GPS rovers. Data reviews will include standard components used to describe chain of events recorded by installed sensor.

During the excavation of pit of Nautical High School Sport Hall in the City of Bakar, Croatia, a landslide is occurred on the slope upper of the executed excavation in autumn 1999. Through the landslide movement, the great part of landslide body was sliding in the pit and consequently the construction works were stopped. The landslide body are formed in the clayey slope deposits formed through the weathering of the flysch rocky mass. The slip surface was developed at the contact of the cover and the bedrock i.e. layers of clayey residual soils and siltstone in the bedrock. A high level of underground water and unfavorable hydrogeological properties in the slope also affected on the sliding occur. Complex geotechnical investigation works were carried out for the purpose of drafting a landslide remediation project. Based on the results of investigation works, a landslide remediation project and the new cut construction design were made. The basic reinforced wall structure was replaced by an anchored boring pile-wall structure. The landslide remediation was based on observational methods. The paper describes the remedial works and the behavior of the landslide based on the measuring results obtained during the performance of works in phases. Results obtained from observations of geotechnical structures indicate on the behavior of geotechnical structures and allows for po-tential corrections. This is especially useful in complex geological conditions where site investigation works are not enough to determine the condition of all site features.

Hazard of landslides appearance is dependent on slope conditions described with geometry, soil composition, structure and soil parameters, so as hydrogeological, climate and vegetation conditions as a time variable. This paper presents experiences in the landslide hazard and risk increasing during the Adriatic Highway construction in the flysch slopes of Draga Valley near Rijeka, Croatia. The geological fabric of Draga Valley is very complex: steep slopes are consisting of limestone rocks and flysch deposits in the bottom, mainly made of siltstones and covered with clayey slope formations. The route of designed highway is lying on lower parts of the flysch slopes, where the alignment is formed partially by slope cutting and partially by embankments filling. The consequences are steeper slopes, deficiency of masses in lower parts of the slope, increasing of hydraulic gradients of ground water flows and decreasing of run-off surface waters coefficients with significant impact on pre-existing high landslide hazard in the area. Hazard increasing was resulting with numerous landslides during the highway construction. Similarities of landslides in dimension, shape, depth of slip surface, mechanism of sliding so as risk consequences were indicating on relatively explicit pattern. Based on these facts, it was possible to identify the landslide risk on similar flysch slopes.

Grohovo landslide is situated in the central part of the Rječina River Valley. Rječina watercourse is 18.7 km long and its river mouth is in the centre of Rijeka city. The central part of Rjecina River is 1.8 km long, and 0.8 to 1.1 km wide and it represents a narrow flysch valley between a karst plateaus. The Cretaceous and Paleogene limestone rocks are situated on the top of the slope, while the Paleogene flysch is situated lower on the slope, including the bottom of the valley. South-western slope of the valley is covered by predominantly coarse soils of limestone composition. Crown of instability is clearly marked by cliffs formed in limestone rocks which are much disintegrated and recently opened fractures are visible. On the north-eastern slope, slope deposits are mostly a mixture of clayey silt that was formed by weathering of flysch bedrock and fragments to blocks of limestone originating from the cliffs on the top of the slope. On both slopes, different types of instabilities, according to type of movement, type of material involved and state of activity, can be found. The biggest instability is Grohovo Landslide on the northern slope downstream of the existing accumulation. This landslide is not a recent phenomenon, because the data concerning mass movements has been registered on the end of the 19th and during the entire 20th century, last in December 1996. The field investigations indicated a complex landslide and evidence of many individual movements could be distinguished. These are identified as initial (primary) landslide, landslides in talus material, lateral landslides in soil material, reactivated landslide near the toe, sliding of separated limestone blocks and rock falls from the limestone cliffs. On the basis of the geological mapping and geophysical surveys, the thickness of the displaced slide mass could be estimated and the position of failure surfaces could be determined. The geometry of the landslide is described below, following the WP/WLI Suggested Nomenclature for Landslides (IAEG, 1990): Total length L = 425 m ; Length of the displaced mass Ld = 420 m ; Length of the rupture surface Lr =405 m ; Width of the displaced mass Wd = 200 m ; Width of the rupture surface Wr = 200 m ; Depth of the displaced mass: Dd = 6–20 m ; Depth of the rupture surface: Dr = 6–9(20) m ; In this complex/composite landslide, 13 slide bodies were identified in addition to mega-block movement and separation of blocks from the limestone scarps. The Grohovo Landslide was never stabilized with adequate remedial measurements. Conducted analyses indicate that the upper part of the slope, at the foot of the limestone scarps, has only a low factor of safety, such that in this part of the slope new movements can be expected in the future, e.g. when provoked by unfavourable hydrogeological conditions and/or strong earthquakes. In this paper we will present analysis of the landslide development from the sliding in December 1996. till today. Based on these analyses so as identified state of stability in particular landslide bodies, the behaviour of the landslide is predicted. According predictions, the monitoring plan is defined.

During the construction of the Adriatic Highway section near Rijeka, Croatia, a landslide occurred on the slope alongside a highway cut. Through lateral expansion, the landslide also affected the partly finished highway cut. Consequently, the construction works were stopped. The landslide body affected parts of the clayey slope formations formed through the weathering of the flysch rocky mass, and parts of the loosely bound layers of breccia lying on the siltstone layers in the bedrock. Complex geotechnical investigation works were carried out for the purpose of drafting a landslide remediation project. The works included core borings works, geophysical works, laboratory testing of soil and rock samples, so as geological, and geotechnical mapping works. Based on the results of investigation works, a landslide remediation design and a new highway cut construction design were made.

This paper presents the origin and the type of instability phenomena in the Rječina and Sušačka draga valleys near the town Rijeka, Croatia. Both locations are part of unique morphostructural unit. Karstified carbonate rocks prevail in this area. Paleogene siliciclastic sedimentary rock complex, i.e. flysch, has a form of a squeezed syncline between carbonate rocks. Geological boundaries between carbonate and flysch rock mass are tectonic, but with different mechanism of origin. Erosion processes and gravitational forces have caused disintegration of the carbonate rock mass, separation of blocks and their sliding over the flysch bedrock, as well as the accumulation of talus on the toe of rocky scarps. During the time, coarse grained fragments originating from the rockfalls were mixed with soil-like material from flysch weathered zone. Disintegration of carbonate scarps, rockfall and talus displacements are a permanent phenomena. The comparisons of a recent instability show a distinction between Rječina and Sušačka draga valleys.

This piece of work presents the “small” landslide occurrences in the part of the Istrian peninsula, named “Grey Istria”, where the Paleogene flysch sediments shaped the terrain. This is the area of the very significant exogenetic processes, like erosion and accumulation of material. The fore mentioned landslides are of the relatively small dimensions and with landslide body volume lesser than 20.000 m3. The sliding of material regularly occurs inside the weathering zone or in slope formations, while the slide surface is formed in the contact with the flysch bedrock. This paper deals with the landslide in the vicinity of the Krušvari settlement, which caused the damage of the local road in the section of Cerovlje-Buzet. It could be said that particular landslide is the typical one for the “Grey Istria” area, while its causes and sliding phenomena are similar to the numerous landslides in this region.