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| Titel |
Small sinkhole-like features in alluvial plains: the example of Paganico (Lucca Plain, Italy) |
| VerfasserIn |
M. Dell'Aringa, R. Giannecchini, A. Puccinelli |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1561-8633
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| Digitales Dokument |
URL |
| Erschienen |
In: Natural Hazards and Earth System Sciences ; 14, no. 1 ; Nr. 14, no. 1 (2014-01-06), S.41-51 |
| Datensatznummer |
250118229
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| Publikation (Nr.) |
 copernicus.org/nhess-14-41-2014.pdf |
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| Zusammenfassung |
Paganico is a little village located in the southeastern portion of the
Lucca Plain (northwestern Tuscany, Italy). Since the seventies, a few square
kilometers' area around Paganico has been involved in the opening of small
cavities (sinkhole-like) on the land surface. At the beginning they were very
small and sporadic. Later on the phenomena were characterized by a
significant extension, increasing in frequency and size (up to 2 m in
diameter and depth), causing inconvenience to local people, agricultural
operations and occasionally a little damage (cracks to buildings, fencing walls
and outside floorings).
The cavities prevalently occur at the end of the dry season, during or
immediately after the first intense rainy events, that is, between the end of
summer and early autumn. Even so, the predisposition and triggering causes at present are not
completely clarified. Therefore this study is aimed at
individuating the triggering and evolution mechanism of the Paganico
sinkhole-like features, particularly referring to the stratigraphic,
hydrogeological and geotechnical features of the involved materials.
Another important issue made clear with this research is represented by the
overexploitation of the local aquifer, characterized by particular
hydro-structural conditions. In fact, the Paganico underground shows three
horizons with different lithologic, hydrogeological and geotechnical
properties: a superficial silty-sandy horizon (2–3 m thick), which is
particularly involved in collapses; an intermediate silty-clayey horizon
(2–4 m thick); and a lower and thick gravel-pebbly horizon, characterized by
important water resources and heavy pumping. Since the seventies, such water
pumping rose considerably due to the local demographic (well field),
industrial (paper manufacture) and agricultural development.
From a hydrogeological point of view, this area is consequently characterized
by two water tables: a temporary one, housed in the superficial silty-sandy
horizon (perched aquifer), and a second one, confined, associated with the
lower gravel-pebbly horizon (aquifer). The perched aquifer and confined
aquifer are separated by an impermeable silty-clayey horizon. According to
the observations resulting from this study, the latter probably tends to
fracture by desiccation during the dry season, originating water exchange
between the two water tables during the first important autumnal rainfall,
depending on the pumping conditions, which lower the piezometric surface of
the confined aquifer. Cracking would also characterize the superficial
horizon. Thus, the water exchange would produce erosional phenomena in the
superficial material, with removal of the fine fraction and collapse. This
process could be at the origin of the cavities opening. |
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