Although the highest part of the Czech Outer Western Carpathians lacks significant recent landslide activity, the vast area (∼20%) of their territory is occupied by relict deep-seated landslides and ...deep-seated gravitational slope deformations. Dating these deformations might help to determine degrees of present-day landslide hazard in that area. Based on the 10Be exposure dating of eight rocky scarps and walls of ridge-top trenches, we estimated the minimal ages of the deep-seated landslides (DSLs) and one deep-seated gravitational slope deformation (DSGSD) in the Satina River basin in the Moravskoslezské Beskydy Mts. The obtained ages (∼9.7–2.9 ka) suggest Holocene slope instability in the area with a pronounced cluster of ages spanning from ∼6.0 to 2.9 ka. Except for one DSL, the ages reveal rather episodic activity of gravitational movements. Mid-to early Late Holocene activity of large landslides in the study area corresponds to the ages of several previously dated landslides both in an adjacent region as well as within the Central European context. With respect to the historical quiescence of the DSLs and DSGSDs in the area and because the slopes have not been destabilized, even during the most extreme hydrometeorological events within the last few decades, we infer that the hydrometeorological thresholds necessary for their activation are seldom exceeded in this area. Therefore, the highest parts of the Carpathians built by rigid thick-bedded lithology reveal a rather lower frequency of events in comparison with adjacent parts formed by claystone-dominated flysch, where several large DSLs originated in the last few decades as a consequence of heavy rainfalls.
•The first TCN (10Be) dating of deep seated landslides and DSGSD in the Flysch Outer Western Carpathians was obtained.•Twenty-one 10Be exposure ages were obtained from eight DSLs and DSGSD rock scarps.•Pronounced Mid-to early Late Holocene activity of DSLs and DSGSDs was determined.•Anomalously humid prolonged periods are likely candidates for DSL/DSGSD triggering in the sandstone-dominated flysch.
According to various studies, the degradation of marly lithologies that constitute heterogeneous rock masses such as flysch, can trigger and condition many slope instabilities. However, not all marly ...lithologies degrade in the same way, exhibiting considerable differences in the rates and ways of degradation. Therefore, it is very important to know the degradation behaviour of different lithotypes against environmental conditions, characterizing their weathering patterns and quantifying their rates of deterioration. This issue has been widely studied trough different approaches: a) through laboratory tests, mainly based on the slake durability test (SDT); b) through the study of monitored natural slaking behaviour; and c) by means of the characterization of in situ observed patterns and natural degradation rates. The main aim of this work is to link these different approaches used to perform this characterization. For this purpose, an experimental test, in which various samples have been exposed under monitored natural climatic conditions for 12 months and have been characterized through the study of the fragment size distribution curves of the degraded particles, has been developed. Additionally, these samples have been also classified based on the Potential Degradation Index (PDI) determined through laboratory tests. Finally, the in situ weathering behaviour profiles have been also logged. Preliminary results of this research suggest the existence of a clear relation between the different classes of degradation stated by the Potential Degradation Index (PDI), the behaviour of the fragments retained in the drum along the SDT cycles, the slaking behaviour under natural climatic conditions and the weathering behaviour patterns and rates observed at weathered profiles in the field.
This paper attempts to show the relationship between joints observed in flysch formations in the field and microfracture fabrics invisible to the naked eye in hand specimens. Ultrasonic measurements ...demonstrate that the intensity and orientations of domains “memorised” by rock specimens are associated with the historical stresses within the rock mass rather than the rock lamination. The spatial orientations of these microfractures have been measured, and their dynamic-elastic properties have been found to correlate with the orientation of macroscopic joint sets measured in the field. The elastic properties measured vary because of sedimentary diagenetic processes that occured during the tectonic deformations of these flysch rocks in the Podhale Synclinorium of Poland. The structural discontinuities detected by ultrasonic measurements can be perceived as an incipient phase of the macroscopic joints already visible in the field and are attributed to the in situ residual tectonic stresses. Such historical stresses impart a hidden mechanical anisotropy to the entire flysch sequence. The microfractures will develop into macroscopic joints during future relaxation of the exposed rock mass. Understanding the nature and orientation of the invisible microfracture anisotropy that will become macroscopic in the future is vital for the safe and efficient engineering of any rock mass.
Using detailed field mapping, an analysis of landslide risk has been undertaken in the flysch highlands of the Outer Western Carpathians. The standardized Czech methodology of expert derived ...susceptibility zonation widely used for land development planning purposes and deterministic modeling of shallow landslides was used to separately assess the susceptibility of different landslide types. The two susceptibility zonation maps were used to define landslide hazard using information about landslide reactivation and the return periods of precipitation that triggered the respective landslide types. A risk matrix was then used to qualitatively analyze the landslide risk to selected assets. The monetary value of these assets, according to actual market prices, was calculated and analyzed with respect to the risk classification. Since the study area is an important residential and recreational area, the practical application of the derived results was checked through a series of interviews conducted with personnel of the local government planning and construction office. This demonstrated a willingness to apply the landslide hazard maps as well as restraints of its successful application. The main one is the absence of legally binding regulations to enforce the spatial planers to use this information.
A multidisciplinary geophysical survey, consisting of electrical resistivity tomography (ERT), ground penetrating radar (GPR), shallow seismic refraction (SSR) and gravity survey (GS), was used to ...investigate the counter-slope scarps, one of the typical manifestations of the relaxed zones of rock massifs, and the possible initial stages of deep-seated landslides (DSLs). Two upper parts of the extensive DSLs within the Moravskoslezské Beskydy Mountains (Outer Western Carpathians – OWC) built by the sedimentary flysch rock were chosen as the testing sites. A combined geophysical survey on the flysch rocks was performed on both localities to enhance our present findings. The survey revealed that the ERT is able to reliably detect underground discontinuities, which are manifested at the ground surface by one of the typical landforms (tension cracks, trenches, pseudokarst sinkholes, double-crested ridges and counter-slope scarps). Previous studies suggested that bedrock discontinuities should be depicted by high-resistivity features within ERT surveying. According to SSR and GS, expected zones of weakened rock massif were not confirmed directly underneath the superficial landforms, but they were shifted. Based on the SSR and GS measurements, the depicted high-contrast transitions between high- and low-resistivity domains within the ERT profiles were newly identified as possible manifestation of bedrock discontinuities. The results of GPR measurements give only limited information on the sedimentary flysch rocks, due to shallow penetrating depth and locally strong signal attenuation. The combined results of multidisciplinary geophysical surveying confirmed an importance of employing more than one geophysical technique for integrated interpretations of measured data. Integrated interpretations of the measured geophysical data provided a new insight into massif disintegration and the geomorphic origin of the landforms related to the DSL.
•A multidisciplinary geophysical survey firstly used in the counter-slope scarps study•Integrated interpretations used to enhance overall model of the landscape development•Various geophysical fields were compared indirectly within integrated interpretations.•A new approach, improving accuracy of the ERT interpretations, was introduced.
Terrestrial laser scanning (TLS) was performed in tectonically undisturbed flysch in the Elerji quarry (south-west Slovenia), which represents heterogeneous rock mass with alternation of marlstone ...and sandstone beds. A 9.3-m-thick lithological profile was measured in detail and then compared to TLS values of reflected intensity and mineralogical composition of general marlstones and sandstones. The results showed distinguishable differences between the intensity values of marlstones and sandstones, as these two groups were found to be statistically different. It was also possible to discriminate these units with regard to their moisture content, as different values were observed for combinations of lithology and moisture content. Correlations of intensity and RGB (red, green, blue) values for the mineralogical composition of marlstones and sandstones revealed a good correlation of intensity with combined calcite and quartz content; however, such correlation is valid only for sandstones due to their bigger grain size. Larger quartz grains can scatter the laser beam and lower the correlation. The results showed that acquiring data from heterogeneous rock mass using TLS could be used for the geotechnical engineering classification of distant, inaccessible outcrops and excavated faces, based on the well-established RMR (Rock Mass Rating) and GSI (Geological Strength Index) rock mass classification systems. Both RMR and GSI classification systems classify rock mass based on rock composition, structure and surface conditions of discontinuities. Lithological segmentation of heterogeneous rocks presents, therefore, an important input parameter for their further classification.
Weathering processes cause significant changes in the engineering properties of rocks. Slope instability in flysch rock formations along the northern Adriatic coast of Croatia is related to the ...effects of weathering on the shear strength of siltstones from the flysch rock mass. Therefore, changes in geotechnical properties according to weathering grade are of immense importance in relation to instability processes. In this work, we investigated siltstones from flysch rock masses in the study area, and evaluated changes in engineering properties due to weathering. The research began with field observations and determination of the strength of different weathering grades of siltstones in the area. Mineralogical and laboratory studies were subsequently conducted, and mineral content was determined for siltstones of different weathering grades. We also performed a series of drying–wetting cycles to simulate natural conditions of the weathering process involved in the disintegration of the rock material into sand-sized and smaller particles. This weathering process resulted in disintegration of the siltstone rock mass into smaller particles that were not a unique rock block, with the soil-like material consisting of unbound particles of rock. Laboratory tests were also carried out on the soil-like material to determine the specific gravity, grain size distribution, Atterberg limits and residual shear strength for the different weathering grades of siltstones. Based on this research, we determined the changes in engineering properties for different weathering grades. Our results underscore the significant influence of the weathering process on mineral content, cation exchange capacity, liquid limit and residual shear strength, thus affecting slope stability in siltstones in flysch rock masses.
The Krbavčići landslide occurred in January 1979 near the town of Buzet, Croatia, after a long period of heavy rainfall. It is located in Northern Istria in the area built of flysch rock mass where ...numerous mass movements in the past and recent history have been recorded. A flysch rock mass is highly susceptible to weathering, which leads to material disintegration, changes in geotechnical properties, and shear strength decrease, finally resulting in instability processes in flysch slopes. This paper describes existing information about the Krbavčići landslide occurrence, laboratory testing of siltstone samples from a flysch rock mass, and numerical slope stability analyses of a possible landslide reactivation caused by possible long rainy periods and further weathering of the flysch rock mass. Slope stability analysis using the Rocscience, Slide software, as well as landslide numerical simulations using the LS-Rapid simulation software were performed on the basis of the digital elevation model (DEM) and laboratory test results of siltstones with different weathering grades. A DEM of the Krbavčići landslide was obtained on the basis of the unmanned aerial vehicle (UAV) survey conducted in March 2016. The residual shear strength of siltstones to predict a reactivation of landslides is of highest importance and was determined by ring shear and direct shear tests on siltstone samples with different weathering grades. The results of the numerical simulations show that an increase of the groundwater level in the landslide body in combination with the further weathering of the flysch rock material at the sliding surface would have the main influence on a possible landslide reactivation and the further development of the landslide displacement.
Opisuje se metodologija projektiranja i izvedbe sustava za osiguranje stabilnosti zasjeka u flišnoj stijenskoj masi na riječkom području. Na temelju rezultata istražnih radova, iskustva tijekom ...izvedbe zahvata na osiguranju stabilnosti stijenskih zasjeka u naslagama fliša te mjerenja i promatranja tijekom izvođenja i provedbom povratnih analiza o stanju naprezanja i deformacija utvrđene su značajke stijenske mase s opisom realne veličine parametara čvrstoće i deformabilnosti.
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