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I fenomeni d'instabilità nell'evoluzione della costa alta delle Cinque Terre (Liguria Orientale)
No full textRelationships between some geotechnical properties of the Genoese area's clayey rock formations and the instability problems that affected the historic tunnels between Polcevera and Scrivia Valleys (Ligurian Appennines) [Relazioni fra alcune caratteristiche geomeccaniche delle formazioni argillose del genovesato e le problematiche evidenziate in gallerie storiche fra le valli Polcevera e Scrivia (Appennino ligure)]
No full textThe results obtained during the first part of a study focussed on the geomechanical characterization of the clayey rock masses outcropping in the Polcevera Valley, in the Genoese area, are presented in this paper. Since 1852 a great number of railway and highway tunnels have been bored inside them. Many of these tunnels have been affected by serious instability problems both during the tunnelling and afterwards, caused by the pressure acting on the lining.
The study, so far, includes mineralogic/petrographic analysis and Point Load Tests on both surface and underground rock samples. The results of the mineralogic and petrographic analysis suggest that the studied formations would be characterized by a visco-plastic behaviour (squeezing rocks) rather than, as previously believed, by a swelling behaviour (swelling rocks). The Pont Load Test’s results allows to estimate the uniaxial compressive strength’s characteristic range of the different
types of rocks forming the clayey formations.
The carried out analysis constitute only the first step of a series of investigations that could lead to a geotechnical zoning of the area
Lago della Nava (Northern Apennines): hypothesis for the recent drying of an ancient DGSD trench
No full textMogge di Ertola peat bog (Northern Apennines, Italy): geological investigation's results
No full textI promontori di Punta Baffe - Punta Moneglia e del Mesco nell'evoluzione del tratto costiero ligure di levante
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Ricostruzione dell’evoluzione di una complessa deformazione di versante presso Ventimiglia (Liguria di Ponente).
No full textThe coastal tract to the immediate west of Ventimiglia, to the orographic right of the Roia River and to the south of its tributary the Bevera, shows strong evidence of slope deformations. Relict remains of delta-fan deposits, referable to the Lower Pliocene, crop out; these lie discordantly above a substratum of Ventimiglia Flysch (Eocene). The Pliocene deposits, which have a thickness up to 300 m in this sector, are situated along a ridge that extends from Mt. Magliocca (515 m) to the sea. The study is of major interest for the morphological and stratigraphic features of the slope deformation and for the events that most probably caused it. The first are represented by various trenches, scarps and terraces at different altitudes along the slope and by superficial landslides. In at least two cases the trenches affected the ridge near the summit of Mt. Magliocca, causing evident splitting phenomena. The causes can be found in the Plio- Quaternary uplifting of the area, which caused notable valley deepening and a height variation of a good 500 m between Mt. Magliocca and the bed of the Roia; in the geomorphological configuration that developed during the Quaternary and that is now characterised by a real relief inversion; in the disjunctive Plio-Quaternary tectonics, which caused the development of the fault system that is clearly visible in the drainage pattern; in the seismicity caused by tectonic activity in the sector, which is the most notable in Liguria, having its origin in hypocentres on the continental shelf and in the Maritime Alps; in the peculiar stratigraphic-structural features, characterised by the superimposition of rock masses with different mechanical characteristics and inclinations. The Pliocene succession prevalently consists of marly clays often up to 180 m thick and overlain by conglomeratic bodies up to 150 m thick. The basal erosive surface, which dips 7° towards SE, cuts the Flysch of Ventimiglia whose strata dip towards the E (Roia River valley) with an inclination of 30-50°. It is possible to hypothesise the chronological collocation of the landslides bearing in mind the probable sedimentation depth of the Pliocene clays, their age and their actual altitude. The velocity of the uplifting so calculable allows us to determine when the reliefs of an altitude able to initiate the observed gravitative phenomena were formed. Given the notable anthropisation of the area involved in the deep-seated gravitational deformation, which includes the slope and valley floor, and the regional seismicity, a risk assessment of the area is highly recommended
Shallow landslides triggered by intense rainfall and land use setting: an example from Cinque Terre (eastern Liguria)
No full textOn 25 October 2011 very intense rainfall affected an area of ca. 1000 km2 between eastern Liguria and northern Tuscany (northwest Italy). The storm rainfall caused thousands of shallow landslides, widespread erosive and depositional processes, several floods, 13 casualties, evacuation of thousand of people, interruption of highways and railways, closure of many provincial
roads and destruction of some bridges. Along the coast, the western sector of the Cinque Terre was affected by floods at Monterosso and Vernazza, causing four casualties and severe structural and economic damage. Cinque Terre are worldwide known because of their environmental value related to the presence of an historical terraced coastal agricultural landscape. Hence, this area was included in the Cinque Terre National Park and recognized as a world heritage site by UNESCO. Changes of social and economic conditions since the early 1900’s caused a progressive abandonment of cultivation on terraces, with negative consequences for the maintenance of dry stone walls leading to disruption of many sectors of terraced areas. The Vernazza basin, which slopes were terraced for about 50%, was the most affected by shallow landslides triggered by rainfall. A great amount of shallow landsliding materials (soils and debris from colluvial and anthropically reworked deposits and stones derived by dry walls of terraces), reaching the drainage network, increased density and energy of stream flows. A disastrous debris flood originated at the valley floor affecting the Vernazza village with mud and debris heights rising up to 4 meters in the centre of the village and, locally, up to 5-6 m. Geomorphological features of the basin such as small area, very steep slopes and short streams, with considerable erosive power and capacity to transport sediment, played a role in favouring geo-hydrological processes but also other factors are involved. This study deal with the analysis of the distribution of shallow landslides triggered by rainfall in relation to land-use in order to define the influence of this factor in landslide occurrence. The study highlights the high vulnerability of agricultural terraces, which were identified as the main landslide-prone areas. The lack of maintenance of the dry-stone walls could be a primary factor favouring shallow landslides. The study also confirms the positive role of vegetation cover for increasing the rainfall threshold for triggering shallow landslides. The obtained results, providing basic information for landslide susceptibility assessment, could be useful for identifying proper strategies for risk mitigation and land management
Signs and causes of a complex slope deformation near Ventimiglia (Western Liguria, Italy)
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