1,721,065 research outputs found
Failure of infrastructure embankments induced by flooding and seepage: A neglected source of hazard
No full textThe risk of failure of transportation embankments due to seepage induced by temporary and occasional impoundments taking place on the upstream side as a consequence of exceptional rainfalls is frequently underestimated. These failure events result from a combination of three main factors, i.e. the flooding event, the hydraulic weakness and the geotechnical weakness of the embankment. Based on the case study of a railway embankment in Southern Italy that collapsed in 2005 due to an upstream impoundment that occurred after few hours of a very intense rainfall, the paper describes a methodological approach aimed at assessing hazard of failure of transportation embankments induced by flooding and seepage. In particular, according to hydrological, hydraulic and geotechnical studies performed to define the factors affecting the process of the embankment failure, three subsequent activities are proposed: the historical analysis of flood damages at the watershed scale; and the assessment of the upstream peak impoundment based on hydrological analysis and the embankment stability analysis, these latter to be carried out at the site specific scale. The approach here proposed is planned to be further validated and improved by means of the application to other case studies, characterised by different contexts and embankment structures. © Author(s) 2011. CC Attribution 3.0 License
La valutazione delle condizioni di stabilità di cavità sotterranee: approcci semplificati e metodi avanzati di calcolo
No full textLa presenza di cavità sotterranee è di
frequente all’origine di fenomeni di sprofondamento,
derivanti dalla propagazione verso
l’alto di instabilità prodottesi all’interno degli
ambienti ipogei. Nel caso di cavità di origine
antropica, e specifi camente di cave sotterranee
(che presentano in genere notevole sviluppo
e complesse geometrie degli ambienti),
la conoscenza della presenza dei sistemi caveali
sotterranei e dell’interazione tra questi e
il sovrastante ambiente antropizzato, nonché
lo stato attuale delle proprietà fi sico-meccaniche
dei materiali, risultano imprescindibili
ai fi ni della valutazione della suscettibilità a
sprofondamenti. Per poter eseguire analisi
numeriche di stabilità in tali contesti, è quindi
fondamentale disporre di accurati rilievi topografi
ci delle gallerie sotterranee, di dati su
eventi di instabilità occorsi o in atto, e sui
caratteri geotecnici dei materiali interessati.
Il presente contributo descrive brevemente
i principali approcci, da quelli semplifi cati
ai metodi di calcolo più avanzato, utili alla
valutazione della stabilità di cave sotterranee,
e illustra brevemente alcune esperienze
condotte su cave ipogee in diversi contesti
dell’Italia meridionale, mediante l’applicazione
di codici di calcolo agli elementi fi niti,
sia in 2D che in 3D
A preliminary analysis of failure mechanisms in karst and man-made underground caves in Southern Italy
No full textNatural and anthropogenic caves may represent a potential hazard for the built environment, due to the occurrence of instability within caves, that may propagate upward and eventually reach the ground surface, inducing the occurrence of sinkholes. In particular, when caves are at shallow depth, the effects at the ground surface may be extremely severe. Apulia region (southern Italy) hosts many sites where hazard associated with sinkholes is very serious due to presence of both natural karst caves and anthropogenic cavities, the latter being mostly represented by underground quarries. The Pliocene-Pleistocene calcarenite (a typical soft rock) was extensively quarried underground, by digging long and complex networks of tunnels. With time, these underground activities have progressively been abandoned and their memory lost, so that many Apulian towns are nowadays located just above the caves, due to urban expansion in the last decades. Therefore, a remarkable risk exists for society, which should not be left uninvestigated.The present contribution deals with the analysis of the most representative failure mechanisms observed in the field for such underground instability processes and the factors that seem to influence the processes, as for example those causing weathering of the rock and the consequent degradation of its physical and mechanical properties. Aimed at exploring the progression of instability of the cavities, numerical analyses have been developed by using both the finite element method for geological settings represented by continuous soft rock mass, and the distinct element method for jointed rock mass conditions. Both the effects of local instability processes occurring underground and the effects of the progressive enlargement of the caves on the overall stability of the rock mass have been investigated, along with the consequent failure mechanisms. In particular, degradation processes of the rock mass, as a consequence of wetting and weathering phenomena in the areas surrounding the caves, have been simulated. The results obtained from the numerical simulations have then been compared with what has been observed during field surveys and a satisfactory agreement between the numerical simulations and the instability processes, as detected in situ, has been noticed. © 2011 Elsevier B.V
The interplay of erosion, instability processes and cultural heritage at San Nicola Island (Tremiti Archipelago, Southern Italy)
No full textThe cliffs of the Tremiti Islands, which are located in the Adriatic Sea in the north of the Apulian coastline (Southern Italy), are affected by severe instability processes. From the geological point of view, the Tremiti Islands are made of a sequence of bioclastic limestone, dolomitic limestone, calcilutite and calcarenite, with the age ranging from Paleocene to Middle Pliocene. These rocks are covered by a calcareous crust and loess deposits (Upper Pleistocene- Holocene). The structural set up of the major islands of the Tremiti (San Nicola and San Domino) is controlled by predominant NE-SW and E-W fault systems, which mark the coasdines of the islands. Along the cliffs, severe erosive processes are produced by different factors, as the climate and sea actions, and the effects of these processes are worsened by the seismic activity which affects the evolution of the cliff stability with time. Deeper instability processes are also observed at the Island of San Nicola as an effect of the presence of weak and low-cemented rock formations that are composed of dolomitic calcarenites, at the top of the island, and calcilutites. These processes are mainly represented by block topplings, slidings, rockfalls and roto-translative mass movements in some limited areas. These processes mainly threaten the cultural heritage buildings located on the island, as the Santa Maria Abbey, which have already suffered significant damages in the past. This study has represented the background for the engineering design of both the restoration works of the monumental area and the stabilization works of the cliffs below
Sinkhole hazard quantitative assessment: Insights from the application of numerical modelling techniques
No full textSinkholes generated by the failure of underground caves represent a major threat to structures and infrastructures. Therefore, methods aimed at increasing the capacity to assess failure susceptibility, or even failure prediction, are needed. Phenomenological or heuristical methods, based on geomorphological or geo-structural evidences, have been largely used in the last decades. However,
physically- or mechanically-based approaches allow to derive quantitative assessment of the equilibrium conditions of the rock mass and, as such, they allow to calculate proper safety margins against failure. Recently, the
available numerical modelling approaches have shown to represent reliable methods to explore the evolution of stress-strain state of the rock mass and to understand the possible failure mechanism, without the need to advance
a-priori assumptions on the failure mechanism. The contribution here proposed is aimed at presenting some insights into the recent advancements regarding
the application of numerical modelling techniques to investigate the stress-state conditions leading to failure of underground caves or the safety margins with respect to failure. Further, the paper is aimed at discussing the techniques
available to perform quantitative hazard assessment of underground caves, highlighting advantages and limitations of the different techniques, whose knowledge is necessary for a correct application of the methodologies.
The proposed work shows some examples of the application of the numerical methodologies with respect to Southern Italy case studies, where artificial caves excavated in soft rock are particularly frequent
Approccio integrato per lo studio delle cause del dissesto di un monumento in conci di calcarenite
No full textAn integrated study has been performed to investigate thè causes of thè damage occurred within thè Greek
monumentai fountain of Gallipoli (LE, Southern Italy). A detailed relief of thè cracks developed along thè
surfaces of thè fountain has initially been carried out, as well as both field tests on thè materials forming thè
monument and laboratory tests on thè foundation soils have been performed. The corresponding results bave
been used as input data of a distinct element analysis developed with UDEC 4.0 to investigate thè stress-strain
behaviour of thè structure interacting with thè foundation soils. The resulting strain behaviour is shown to be
consistent with thè crack System observable along thè external surfaces of thè fountain
Influence of stratigraphic factors on the failure mechanisms of sinkholes related to man-made underground caves at Cutrofiano (South-Eastern Italy)
Full text linkAn increasing number of areas in southern Italy are being interested by sinkholes related to the presence of
man-made cavities, with underground quarries representing the more problematic typology of anthropogenic
caves in terms of instability. The case of Cutrofiano (Apulia, SE Italy) is here presented as a representative case
study. This territory is well known for the underground quarrying activity of soft calcarenitic rocks that caused
in the last decades widespread phenomena of subsidence at the surface, with extensive damage and problems to
the main communication routes in the area. A very complex and intricate network of subterranean galleries is
present underground, for a total development on the order of several tens of kilometres. The Gravina Calcarenite
Formation, that is the object of the underground quarries, consists of whitish calcarenite with an upper greenish
clayey-sandy interval rich in fossils. This formation is overlain by grey sandy clays (Subapennine Clays) grading
upward to fossil-rich sands (Brindisi Sands). In recent years, clay mining has been resumed at the ground surface,
following the opening of a cement factory, and resulting in the realization of wide open-pit quarries. The local
sedimentary sequence is closed by terraced calcarenite deposits, that holds a phreatic groundwater body. The
results of detailed geological, geomorphological and geomechanical surveys, supported by laboratory tests, show
that in the Cutrofiano area the thickness of the stratigraphical succession, the depth of the underground galleries,
the structural conditions of the rock mass, and the failure mechanisms observed within the quarries are variable.
The geological model reconstructed represents the base for the implementation of numerical simulations, which
are aimed at defining the eventual mechanisms of rock failure, up to the formation of the sinkhole. Local changes
in the stratigraphy are very common in the area, due to the overall slight attitude of the strata, dipping toward
the SW, and to lateral variations in the geological succession. Thus, at least two different geological settings may
be recognized: the first is typical of those areas closest to the town, where the calcarenite rock mass is at low
depth, and appears to be covered by very thin deposits; in such a situation, the underground quarries develop at
depths ranging from 7 to 10 meters below the ground surface. The second setting, which typically characterizes
the sectors a few kilometres farther south, shows, on the other hand, the presence of thick cover of the clay-sandy
intervals, and has the galleries of underground quarries located at depth variable from 15 to 45 m. Starting from
these different situations, two-dimensional numerical analyses have been developed by using the finite element
method to investigate the stress-strain evolution of the rock mass surrounding the galleries due to long-term
degradation of the rock properties induced by weathering and water infiltration. The results obtained from the
numerical simulations point out a quite different behaviour between the two geological settings, since the presence
of the significant clay layer overlying the calcarenite substratum affects the geometry of the subsidence cone, and,
consequently, the real extent of the likely sinkholes at the surface.
These outcomes are of great importance to highlight the need to use detailed, site-specific, data in order to perform
numerical modelling, and warn about the common habit of extending a small number of borehole data, tens of
hundreds of meters apart, over large areas. Especially when carried out to define vulnerability and/or risk of
specific elements at risk, the researches should be performed having available on-site data, or, alternatively, the
end users should be properly warned in the use of the outcomes from the study
The Montaguto earthflow: A back-analysis of the process of landslide propagation
No full textEarthflow and mudflow processes represent a class of landslides that, owing to their typical long run-out, may generally induce huge damages to infrastructure lines, with negative economic impacts. Therefore, the analysis of the landslide propagation with time in such cases can provide useful information to mitigate landslide risk. The present paper discusses the case history of a huge earthflow developed in 2005-2006 in the area of Montaguto town (Southern Apennines, Italy), that produced significant damages to a national road and a national railway at the slope toe. The average displacement rate during the first critical stage of propagation was of some m/day. The aim of this contribution is the reconstruction of the propagation stage of this landslide during the first high-mobility stage. A detailed geomorphological analysis aimed at defining the main features of the in-situ landslide propagation is firstly described. Later on, a back-analysis of the kinematical features of the same landslide process, based on a simple infinite-slope sliding-consolidation model, is presented to investigate the role of different factors in the process of landslide propagation. The application of this analytical solution suggests that the development of high excess pore water pressures due to undrained loading processes and the consequent consolidation process can represent a reasonable way to explain the earthflow mobility. The application of the analytical model to the specific case study is also supported by the field evidence of the existence of excess pore water pressures in the landslide mass which have been measured in situ during the recent monitoring campaign and the corresponding data are also discussed in the work. © 2013 Elsevier B.V
A methodological approach to assess the hazard of underground cavities subjected to environmental weathering
No full textSoft highly porous carbonate rocks, such as calcarenites, and soluble sulphate rocks, such as gypsum, are very common in the Mediterranean region and, due to their microstructure and chemical composition, are prone to water induced weathering mechanisms. Cliffs, underground cavities and other morphological features in such formations are hence affected by intense erosion phenomena and weathering processes responsible for unexpected collapses and sinkholes. Just considering the Apulian region (Italy), 150 sinkholes have been recorded since 1925, with increasing frequency since 2000 (Fiore et al., 2018). The geosystem's failure is often the short- or long-term result of a very complex hydro-chemo-mechanical process taking place at the micro-scale which can be detected and analysed by means of field and laboratory experimental test campaigns. Therefore, stability problems are often related to changes of the mechanical properties of the rock forming the cave caused by environmental weathering processes, despite the external boundary conditions are not changing with time. The paper deals with the assessment of hazard associated with the stability of abandoned underground caves, which is nowadays frequently required for land and urban planning activities. A methodological approach for hazard assessment based on a step-by-step procedure is proposed. This includes in-situ surveys, laboratory experimental studies, theoretical analyses and finally numerical investigations. The approach derives from the experience developed from several case studies analysed by the authors. In this work, two of these are presented. The first one concerns the stability of an anthropic cavity in a calcarenite formation which is affected by a water induced short-term and long-term debonding processes. The second one regards the stability of a three-level abandoned gypsum mine, the lowest level being partially flooded by water. The methodological procedure aims to evaluate the factors controlling the change of the mechanical properties of the rock so that efficient remediation measures can be designed in order to avoid any further decay of the rock mass stability with time. The proposed methodological approach, validated on real case studies, shows the convenience of performing advanced experimental, theoretical and numerical studies to properly assess the hazard in space and time and to better design the mitigation measures if they are required. The adoption of the proposed approach reduced the remediation costs of the second case study of one order of magnitude
Comportamento di una diga in calcarenite e della sua fondazione in argille Pleistoceniche in base a dati di monitoraggio
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