The analysis of the flysch badlands inventory in central Istria, Croatia

The south-western part of Croatia, i.e. the area of central Istria (the research area, approximately 500 km2) is characterized by flysch complex with a great number of isolated relief landforms – badlands. The importance of badlands (areas with sparse or no vegetation) is in the fact that the sediment production from these areas is 8000 higher than from the areas with vegetation. In this paper the badland inventory for the area of research is presented with 5568 badlands (polygons) singled out with total badland area of 10.7 km2. Spatial analysis of the badland inventory showed that concentrated erosive channel flow at steep slope foot is the most important factor in the badland forming and development for the area of central Istria

Use of a LiDAR-derived landslide inventory map in assessing Influencing factors for landslide susceptibility of geological units in the Petrinja area (Croatia)

A landslide inventory was created for an area of 22.6 km2 near Petrinja city in northern Croatia, based on the high-resolution LiDAR data complemented by orthophoto maps. A total of 216 landslides were identified, covering 2.91 % of that area. Landslide polygons were overlain on geological units based on the Basic map of SFRY at a scale of 1:100,000 that is the largest scale geological map available for the whole of Croatia. The relationship between landslides and geological units was expressed as a landslide index. Three geological units displayed increased landslide susceptibility. A Pliocene unit clearly had the largest susceptibility, followed by a Palaeocene-Eocene unit, and finally a Badenian unit. Landslide density was analyzed within these geological units to identify influencing factors for landslide initiation. Each geological unit revealed different influencing factors. The Pliocene unit is mostly influenced by bedding plane orientation and local relief. Heterogeneousness lithology is the dominant factor in the Paleocene-Eocene unit, while the Badenian unit demonstrated the least certain interpretation as there are multiple factors involved. The forest road is presumed to be crucial, followed by spring occurrences and proximity to the tectonic boundary. The basic geological map of SFRY proved to be a viable source of geological information for the creation of landslide susceptibility maps at a scale of up to 1:100,000, but with limitations in the case of lithologically heterogeneous geological units. Larger scale maps require more detailed research as landslide susceptibility factors vary in each geological unit

Preliminary analysis of a LiDAR-based landslide inventory in the area of Samobor, Croatia

The paper presents an analysis of the LiDAR-based landslide inventory for the area near Samobor, in northwestern Croatia with two main objectives: i) to define the geological units (obtained from Basic Geological Map of Croatia) most susceptible to landslides, and ii) to analyse the limitations of the Basic Geological Map and its applicability in landslide susceptibility map design. Within the study area of 63.8 km2, 874 landslide polygons were manually outlined, covering an area of 2.15 km2. The landslide outline confidence level, landslide index and the relief energy map were used to analyse the landslide susceptibility of a particular geological unit. By that, units in the same state of stress, i.e., in the same relief energy group were compared. This preliminary analysis has shown that the geological units Pl,Q, M3 1,2, and 1M3 1 are the most susceptible to landslides and that older geological units, Pc and K1,2, are also prone to landslides. Still, landslides within those older units can be considered as old and inactive. As for the limitations of the Basic Geological Map of Croatia, three things emerged, namely scale, the geological unit defining approach, and the neglect of regolith. Despite the limitations presented, the usability of the Basic Geological Map of Croatia in the development of small-scale landslide susceptibility maps is emphasized. However, instructions that should attribute engineering geological features to the geological units outlined in the Basic Geological Map should be prepared in the near future

APPLICATION OF INDEX TESTING METHODS IN DETERMINING MECHANICAL PROPERTIES OF INTACT ROCK MATERIAL

U radu je prikazan pregled indeksnih metoda ispitivanja s detaljnijim osvrtom na primjeni postupka određivanja tvrdoće Schmidtovim čekićem te određivanja indeksa čvrstoće postupkom opterećenja u točki u procjenama mehaničkih značajki intaktnog stijenskog materijala. Uz to su prikazani i rezultati provedenih ispitivanja na utvrđivanju primjenjivosti spomenutih metoda u procjenama jednoosne tlačne čvrstoće, modula elastičnosti, vlačne čvrstoće te čvrstoće na savijanje za tri karakteristična tipa vapnenaca iz krovinskih naslaga ležišta „Korenići“.The review of index testing methods with detailed observations on the application of Schmidt rebound hardness and point load strength index in mechanical properties estimations of intact rock material is given in this paper. The results of conducted testing in determining applicability of the above-mentioned testing methods for the estimations of uniaxial compressive strength, elasticity modulus, tensile strength and flexural strength for three characteristic types of limestone from the roof layers of „Korenići“ deposit are also presented

PROCJENA JEDNOOSNE TLAČNE ČVRSTOĆE POMOĆU MODELA BAZIRANIH NA REGRESIJSKIM STABLIMA

This paper presents the estimation of the uniaxial compressive strength for mudstone and wackestone carbonates. The need for the estimation has occurred due to inability to fulfill the high quality requirements of sample treatment during direct determination of this physical and mechanical property on certain types of rocks. For the needs of modelling intact rock materials, extracted from six locations in Croatia, were tested. The following properties were examined: density, effective porosity, point load strength index, Schmidt rebound hardness, P-wave velocity and uniaxial compressive strength which was the target value of the used statistical models. The statistical models based on multiple linear regression and regression trees were considered and compared using cross validation, which showed that the most efficient estimation of the uniaxial compressive strength is obtained using random forestsOvaj rad bavi se procjenom jednoosne tlačne čvrstoće za karbonate tipa madston-vekston. Potreba procjene javlja se zbog nemogućnosti ispunjavanja propisane visoke kvalitete obrade uzoraka kod direktnog određivanja tog fizikalno-mehaničkog svojstva na nekim vrstama stijena. Za potrebe modeliranja, u ovom radu, ispitivan je intaktni stijenski materijal sa šest mjesta u Hrvatskoj. Ispitane značajke su: gustoća, efektivna poroznost, indeks čvrstoće, Schmidtova tvrdoća, brzina prolaza ultrazvučnog P-vala te jednoosna tlačna čvrstoća koja je bila i ciljana vrijednost procjene uspostavljenih modela. Prikazani modeli su načinjeni na temelju višestruke regresije i regresijskog stabla, a provedena unakrsna validacija, pokazala je kako najuspješniju procjenu jednoosne tlačne čvrstoće daje model slučajnih šuma (engl. random forests)

Engineering properties of marine sediments in Mali Ston Bay (Croatia) based on “Mainland-Pelješac” bridge investigations

The complete geological characteristics of the wider area of the Pelješac peninsula are presented: lithostratigraphical, structural/tectonic and seismotectonic. The main accent is put on engineering geological characteristics of clastic sediments in Mali Ston Bay encountered during investigations for implementation project of the “Mainland-Pelješac” bridge. The bridge large proportions with 2404 m in length and with 14 pylons under the sea, requested thorough and expensive in-situ and laboratory investigations which enabled development of detailed and reliable engineering model of quaternary clastic sediments at the explored site. The results clearly indicate three different engineering units which are predominantly classified according to the obvious difference in consistency: Unit A – very soft and soft soil; Unit B – soft to firm soil and Unit C – firm soil. Because of great soil total thickness, locally over 100 m, its generally poor engineering properties and great seismicity of the area the foundation surroundings are unfavorable. The mentioned units which are classified according to its engineering properties also tightly correspond to the deposition environments which represent much wider area than just exploration site. Therefore authors presume presence of units A, B and C in wider area with similar geological situations like proximities of the Zrmanja, Krka, and Cetina deltas. </p

ESTIMATION OF UNIAXIAL COMPRESSIVE STRENGTH BASED ON REGRESSION TREE MODELS

This paper presents the estimation of the uniaxial compressive strength for mudstone and wackestone carbonates. The need for the estimation has occurred due to inability to fulfill the high quality requirements of sample treatment during direct determination of this physical and mechanical property on certain types of rocks. For the needs of modelling intact rock materials, extracted from six locations in Croatia, were tested. The following properties were examined: density, effective porosity, point load strength index, Schmidt rebound hardness, P-wave velocity and uniaxial compressive strength which was the target value of the used statistical models. The statistical models based on multiple linear regression and regression trees were considered and compared using cross validation, which showed that the most efficient estimation of the uniaxial compressive strength is obtained using random forests

A case study in the research polygon in Glina and Dvor municipality, Croatia–landslide susceptibility assessment of geological units

In this paper, a preliminary analysis of the landslide inventory is presented for the wider area of the municipalities of Glina and Dvor, within Sisak-Moslavina County in Croatia, where LiDAR scanning for 45.85 km2 was conducted. Landslide polygons were outlined based on the visual interpretation of HRDEM derivates. In total, 477 landslides were contoured with an average landslide density of 9.85 per km2. Most of the landslides are characterised as moderate, shallow, and not recent. The spatial relationship between landslides and geological units is expressed with the landslide index. Subsequently, the geological units were grouped into four engineering geological units representing different susceptibilities to landslides. The geological units most prone to landslides are the Eocene, Oligocene, Palaeocene and Jurassic sandstones. Even though all geological units were analysed here, the majority of landslides are within sandstones. A particular emphasis was on landslide occurrence in metamorphic and igneous rocks of the ophiolite sequence, a distinctive characteristic of the research area where less susceptibility to landslide processes was observed. Moreover, to further distinguish the differences between the units in the area a morphometric characteristic (relief) and drainage network was also analysed. The purpose of this analysis was to additionally confirm the landslide susceptibility assessment and the division of geological units into engineering geological units, which again implied the different behaviours between landslides in igneous and metamorphic rocks compared to sandstones. Because the research area is poorly studied regarding landslide susceptibility, relief, and drainage networks, these findings will be a step forward in recognising the relationship between them and creating a base for the development of a landslide susceptibility map for this area