1,721,015 research outputs found
Rockfall hazard and risk management: an example of a comprehensive approach in northern italy
No full textIn the context of slope instability phenomena, the detachment of blocks from steep walls account for 40% of landslides occurences in Alpine areas (Cooco,1991).
This phenomenon, also known as rockfall, occours in densely populated area such as the Italian Alps, where the hazard is quite high due to the presence of several buildings and house.
We have chosen to assess the risk posed by potential rockfalls in an area hosting a small industrial complex close to a steep limestone slope. To this aim, a comprehensive set o geological, geomorphological and geomechanical surveys were conducted both in detachment and transit zones.
The study area is located in the Carnic Alps, in proximity of a small stream - torrent vajont - at a height of 800-1300 m
Recognition and classification of evaporite karst phenomena: examples of outstanding sinkholes from Sauris (NE Italy)
No full textSinkholes are one of the most hazardous phenomena due to their occurrence and
unpredictability. In the Friuli Venezia Giulia Region (northeast Italy), the presence of
outcropping, mantled or capped evaporites is the main predisposing factor for these
phenomena. Even if evaporites do not exceed 1% of the entire regional territory, their
presence causes catastrophic events mainly in the Carnian alpine valleys. Chalks are
included in the Bellerophon Formation (Late Permian) and in the Raibl one (Upper Carnian).
These weak rocks are mainly located in the valley bottoms and not at the top of the
mountains. Even if, in correspondence of the northern ridges of Sauris municipality, several
sinkholes have been observed. In detail, north of Sauris, quartz sandstones and mica-
siltstones belonging to the Werfen Formation (Triassic) are widely present. These rocks,
capping evaporitic ones, belonging to the Bellerophon Formation, are jointed and
characterized by a secondary permeability. Over time, water infiltration and weathering led to
the solution of the Permian evaporites and to
the progressive failure of the overlying
terrigenous rocks, less soluble but more plastic. The result is the genesis and evolution of
depressed landforms classifiable as sinkhol
es. On the grassy meadows stretching from
Sauris di Sopra to Sella Festons at 1800 m a.s.l., outstanding sinkholes can be observed at
the top as well as on the slope. Since now, almost 80 sinkhole phenomena were recognized
and classified in the Sauris Municipality; mo
st of them are aligned along approximately E-W
oriented faults. All the data were added and stored in a GIS, which represents the first
sinkhole inventory related to the evaporite karst environment in Friuli Venezia Giulia Region
Factors triggering sea cliff instability along the Slovenian coasts
No full textCoastal cliff behaviour in five sites along the Slovenian coast, in the North-eastern Adriatic Sea, has been studied through the comparison of 2515 images collected at the sites and more than 4500 additional pictures collected since 1998. Moreover, a detailed characterization of the geomechanical properties and the quality of rock masses, the susceptibility to rockfalls have been used in order to determine the geomechanical properties of the studied sites.
Significant modifications of the cliff face are located in particular in correspondence of the sites showing poor or very poor rock mass quality. Moreover, photographic surveying suggests that cliffs are affected by a complex behaviour with respect to coastal retreat: during long stable-weather periods, cliff modifications are very low, while major changes in the cliff face occur after great storm events owing to the interaction of both marine and non-marine factors
EVAPORITE SINKHOLE INVESTIGATIONS IN THE OVARO VILLAGE (NE ITALY)
No full textSinkhole are ephemeral karst feature linked to karstifiable rocks. These phenomena are very common in the Carnian Alps (NE Italy) and represent a severe geo-hazard for locals and human facilities.
Few papers regarding NE Italian sinkhole integrate geomorphological investigations and geo-hazard assessment. Zini et al. (2015) and Calligaris et al. (2015) recently recognized and classified tens of sinkholes proximate to Tagliamento River Valley analyzing their evolution with the contribution of geophysical and hydrogeological techniques. But already in 2009 Calligaris et al., proceeded to a preliminary reconnaissance and identification of these features based also on previous papers by Burelli et al. (2004), by Cucchi and Piano (2002) and Gortani back in 1965.
Since then, only few very detailed investigations were realized on specific areas. At now, the knowledge has been developed after an extensive work done overall regional territory. The study, funded by the Geological Survey of the Friuli Venezia Giulia Region brought out that more than 30 municipalities (among the 221 that make up the Region) are affected by sinkholes. Through this extensive analysis, more than 600 phenomena were identified, georeferenced and classified according to Gutiérrez et al. (2014). One of the areas most affected by this geo-hazard is the Ovaro Village (Fig. 1).
Ovaro is set on an alluvial fan were moraine deposits are also present, in a N-S oriented valley where the Degano River flows. In a territory of about 58 km2 with an elevation between 456 and 2.076 m a.s.l., 90 subsiding areas were identified. The municipality, in the past had some geo-hazard problems linked to sinking features. This is not surprising seen that, in Entrampo, a small hamlet of Ovaro sited in its NW side, close to Degano River, is located an historical and still active gypsum quarry. The evaporitic bedrock is not well exposed in the area, but it is widely present in the subsurface.
Geotechnical and geophysical investigations highlighted its presence at variable depths: from few meters below the surface, until 50 m. Several have been the drilled boreholes and some of them were investigated also using a camera that clearly gave the possibility to identify the presence of cavities in the bedrock. The number of identified voids allowed to understand that the karstification degree is particularly high explaining in this way the presence of a karst surface landscape. From a lithological point of view, the area is characterized by the presence of an evaporitic bedrock (Bellerophon Fm. – Permian in age) mantled by fan deposits mixed with moraine ones. The chalks are saccharoidal and whitish, microcrystalline, poorly cemented where the hypogean karstic features are present. A bedrock with the just described characteristics highlight its poor geotechnical properties, which favor the occurrence of collapse or sagging phenomena that caused and could cause new future instabilities to the existing infrastructures.
Acknowledgements The research activities have been funded by the Regional Geological Survey.
References
Burelli, G., Cleva, S., Cucchi, F., Oberti di Valnera, S. (2004). Stato di evoluzione di sinkholes in alcune aree montane del Friuli Venezia Giulia. 1° Seminario "Stato dell'arte sullo studio dei fenomeni di sinkholes", APAT, Roma, 159-170.
Calligaris, C., Devoto S., Zini, L., Cucchi F. (2015). Evaporite geo-hazard in the Sauris area (Friuli Venezia Giulia Region – Northeast Italy). 14th Sinkhole Conference, NCKRI Symposium, 5-9 October 2015, 465-470, ISBN 978-0-9910009-5-1.
Calligaris, C., Zini, L., Cucchi, F., Stefanelli, S. (2009). Gypsum’s role in the Friuli Venezia Giulia Sinkholes. Proceedings of the 2°Seminario “I sinkholes: gli sprofondamenti catastrofici nell’ambiente naturale ed in quello antropizzato”, ISPRA. Roma, 213-221.
Cucchi, F., Piano, C. (2002). Ipercarsismo superficiale e sepolto nelle evaporiti del Friuli-Venezia-Giulia. Proceedings of Le voragini catastrofiche, un nuovo problema per la Toscana. Edizioni Regione Toscana, Grosseto, 35-41.
Gortani M. (1965). Le doline alluvionali. Natura e Montagna, 3, 120-128.
Gutiérrez F., Parise M., De Waele J., Jourde H. (2014). A review on natural and human-induced geohazards and impacts in karst. Earth-Science Reviews, 138, 61-88.
Venturini C. (2009). Note illustrative della Carta Geologica d’Italia in scala 1:50.000, Foglio 031 Ampezzo. Serv. Geol. D’It., pp. 232.
Venturini C. (2001). Geological Map of the Carnic Alps, western sheet. 1:25.000 scale. SEdizioni del Museo Friulano di Storia Naturale, Pubblicazione no.48, 2006.
Zini L., Calligaris C., Forte E., Petronio L., Zavagno E., Boccali C., Cucchi F. (2015). A multidisciplinary approach in sinkhole analysis: The Quinis village case study (NE-Italy). Engineering Geology, 197, 132-144
Recognition and strength characterization of platy limestone layers in the Classical Karst quarries (NE Italy)
No full textThis paper shows the results of research investigations carried out along the karst plateau located in the Trieste and Gorizia counties (NE Italy), with special emphasis on limestone quarries. Field surveys allowed the recognition, identification and mapping of quarries characterized by the
presence of Platy Limestone (PL). The latter is characterized by a single discontinuity set with spacing not exceeding 10 cm. For this reason, the
geometry of PL rock masses provided, for a long time, slabs easy to be excavated. PL was widely used by locals for roofs of buildings situated
mainly in the rural surroundings of Trieste.
The research envisaged a multidisciplinary approach, which also included the definition of the main geometrical features of PL quarries, the
state of activity and the geotechnical properties of PL rock mass. Particular attention was devoted to the definition of PL intact rock strength, which is major rock property. Intact rock strength determines the strength of the rock slab and therefore its geomechanical quality. The outputs of this paper can motivate local authority to protect PL and promote its use for the restoration of historical buildings
Evaporite sinkholes of the Friuli Venezia Giulia region (NE Italy)
No full textSinkholes are common in the Friuli Venezia Giulia (FVG) Region (NE Italy), where the presence of karstifiable rocks favours their occurrence accelerated by intense rainfalls. Their existence has been reported since the end of the 1800s along the Tagliamento Valley, in correspondence
with the mantled evaporites (gypsum). Furthermore, tens of evaporite sinkholes have been documented on the reliefs adjacent to the village of Sauris and along the narrow W–Eoriented valleys, where regional faults have played a major role in their spatial distribution.
This paper reports for the first time an inventory of the sinkholes affecting the evaporites of the FVG Region. These phenomena were mapped and categorised using a genetic classification. The main output is an A0-format map, which incorporates a 1:50,000 scale
Sinkhole Inventory Map (SIM). The SIM encompasses 552 sinkholes. The cover suffosion sinkholes are the most abundant, followed by bedrock collapses. There is a clear prevalence of the circular shape (65%) over other shapes. Diameters are 1–140 m, with depths ranging 0.1–40 m with a mean value of 4.5 m. The SIM can motivate regional planning authorities to perform further investigations aimed to understand the geomorphological evolutions of these phenomena
Multi-disciplinary surveys for the new geologicla maps of the low Friuli plain (Italy)
No full textThe study site is located in the central area of the Friuli Venezia Giulia (Italy) and is covered by geological map sheets 087 Palmanova and 108 Lignano Sabbiadoro. The area under consideration extends between the spring horizon to the north and Marano lagoon to the south. It covers a total area of 760 km2. The zone under consideration is characterised above all by the presence of alluvial deposits dating back to the Last Glacial Maximum (LGM; 30,000-17,000 b.C.) and by the presence of deposits originated by the activity of resurgent rivers including Stella, Zellina, Corno and Aussa. The western sector of the Lignano sheet also includes deposits that can be ascribed to the post-LGM activity of river Tagliamento (last 17,000 years). Along the coastline post-LGM deposits reach a thickness of 10 m. Along the lagoon fringe there are territories that were reclaimed in the Twentieth century where lagoon deposits outcrop.
The project was conducted within the framework of the GEO-CGT by the Regional Geological Survey – DG Environment and Public Works of the autonomous region of Friuli Venezia Giulia and the University of Trieste and Udine. It involved the preparation of 1:10,000 geological maps of Friuli Venezia Giulia which integrated new geological data (surveyed and processed to this very aim) into already existing information. Reference criteria for the cartographic representation and digitalisation are those set by the Italian Government for the preparation of the new national geological cartography at a scale of 1:50,000 (CARG project).
The Technical Geological Map (CGT) has been the primary source of grain-size and geotechnical information as far as the soil and the immediate subsoil of the areas taken into consideration. The bibliography collected has been integrated with the most recent studies and data on the geology and pedology of the areas involved. Also archaeological aspects have been taken into consideration to better define the history ad evolution of more recent deposits.
The map representing microrelief, together with the observation of aerial photographs taken in different years and satellite images, has proven a useful tool to analyse and define the area of the most frequent morphologies connected with river erosion and deposition phenomena.
This information has been subsequently cross-checked during surveying campaigns. More in detail, historic maps helped identify natural and/or man-made modifications of the hydrographic network ad of the use of soil in recent past. Some information on the age of the deposits were also taken from the numerous Roman archaeological sites present in the study areas.
Field surveys were aimed at identifying geomorphological landforms and sedimentologic characteristics and at defining the age of deposits. As the areas observed are plain ones and no deep natural outcrops are present, particular attention was given to the stratigraphy of the deposits that outcrop along the walls of artificial excavations. In the areas with no significant outcrops and in the most interesting ones, borehole logging was performed by means of a manual Edelmann probe. These boreholes reached a depth of 2-3 m and sometimes 6 m. The sediment samples collected were tested for grain-size distribution and carbon-14 dating.
Simultaneously, mechanical surveys were performed on the whole area reaching a depth of 10 m plus approximately a hundred static penetrometer probes reaching a 30 m depth.
The comprehensive geomorphological, sedimentological and geotechnical data collected permitted to define stratigraphic units, sedimentation environments, texture of surface deposits and the main landforms that characterise the western low Friuli plain.
The last surveying phase consisted in organising and processing the data collected thanks to the special functions of GIS. The entire project was conducted using a comprehensive set of hardware and software tools which permitted to maintain a close relation between the data collected on the field (database) and their digital geo-referenced map representation (geo-database). Data could therefore be viewed and interpreted according the standards set within the framework of the CARG project
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