1,720,996 research outputs found
Investigation and preservation of historic foundations
No full textItalian experiences provide a long list of successful engineering solutions for the preservation of historic sites and, in particular, of tall structures like medieval and bell towers. Among them, Pisa Tower and Frari Bell Tower in Venice can demonstrate that innovative approaches and methodologies for the strengthening of historic foundations can be devised without any direct intervention on the structures and with the main aim of preserving their full integrity. Through purposely implemented and extensive real-time monitoring systems, it has been possible to minimize the impact of stabilization measures on the existing structures, including the historic foundations. The technologies used in the case studies described in this paper have proved to be especially gradual and flexible. Together with a number of other well described and successful examples of preservation activities currently available in the literature, such case studies will be hopefully used as a source of inspiration for future strengthening interventions aimed at preserving the integrity and the authenticity of historic foundations
A novel medium-scale experimental setup to investigate backward erosion piping
No full textBackward erosion piping (BEP) is a phenomenon that can develop in the subsoils of river embankments
during intense flood events, manifesting at the ground level as emerging sand boils. This process affects more than 130
sections of the Po river main embankments and many major streams in Europe and worldwide. This contribution aims to
illustrate the experimental setup recently developed at the University of Bologna, for the medium-scale physical
modelling of the BEP process. The experimental layout and testing procedures are briefly presented, along with some
preliminary results from the ongoing laboratory activities
Impact of cumulated land subsidence on the preservation of the Santa Croce historic site in Ravenna, Italy
No full textThe historic church of Santa Croce, dated 5th century AD and located in the city centre of Ravenna
(Italy), was originally connected to the Mausoleum of Galla Placidia, contiguous to the Basilica of San
Vitale, both Unesco World Heritage sites.
A widespread land subsidence process, of both natural and anthropogenic origin, has always affected
territories around Ravenna and its city centre, including Santa Croce and the surrounding ruins. This
phenomenon has been extensively investigated over the last century. Land settlement, initially of the
order of few mm/year, dramatically increased up to 110 mm/year after World War II, primarily due to
groundwater pumping and, subordinately, gas production from a number of deep onshore and offshore
reservoirs. A significant deterioration to the urban as well as to the natural environments became evident
in the late 1970s. In the city centre the crypt of monumental churches, such as S. Francesco’s, and the
basement of old buildings were permanently flooded. Cumulative land subsidence nowadays approaches
almost 1 m over more than one third of the municipality area including the city and a significant fraction
of the coastland, with peaks larger than 1.5 m over a 10 km2
zone located between the historic centre and
the coastline. Most recent records, however, show that at present the mainland appears to be substantially
stable.
In the investigated site of Santa Croce, considering the limited size of the structures in the area and, at
the same time, the reduction trend of the phenomenon, subsidence progression does no longer represent
a major critical issue. Nonetheless, the cumulative land settlement has reached more than about 3 m with
respect to the surrounding areas, well above the typical position of the ground water level, making the
site especially sensitive to recurrent flooding, despite continuous dewatering is currently carried out.
Main impacts on the investigated site of present conditions, which could be seriously aggravated in the
long term by climate change effects (e.g. sea level rise, increased storm surges and changes in
precipitation rate), have been identified. First, an increase of flood risk (frequency, severity and duration
of inundation) and of rainfall induced floods could make ineffective the drainage systems and/or increase
the need for pumping. At the same time, damage to building foundations and subsurface structures could
be also generated by progressive loss of functionality of the drainage system, which has been in operation
for many decades by now.
Within such context, the contribution aims at describing a recent geotechnical investigation campaign
carried out to improve the definition of the stratigraphic soil profile and to install a piezometric
monitoring system for the control of the shallowest aquifer dynamics. The monitoring system includes
not only the Santa Croce site, but also the surrounding San Vitale and Galla Placidia area. The
investigation campaign has been carried out in the framework of the EU H2020 SHELTER project, that
works towards a heritage-led resilience enhancement of historic areas
ANALISI A RITROSO DELLA RIATTIVAZIONE DEI FONTANAZZI PRESSO GLI ARGINI MAESTRI DEL FIUME PO
No full textL’erosione retrogressiva nei terreni di fondazione (o backward erosion piping in inglese) degli argini maestri del
fiume Po è un fenomeno che si sviluppa periodicamente in occasione dei principali eventi di piena e che si
manifesta esternamente con la formazione dei cosiddetti fontanazzi. Tale fenomeno, legato al particolare assetto
stratigrafico che caratterizza numerosi tratti degli argini maestri del Po, può svilupparsi a partire a partire dal
punto di uscita dei fontanazzi e progredire sotto la base dell’argine, all’interfaccia con l’acquifero, con la
formazione di piccoli canali (pipes) fino a causare il collasso della struttura. Questo lavoro presenta il caso di
studio di una sezione situata nella provincia di Reggio Emilia, selezionata per l’elevata vulnerabilità nei
confronti dei fenomeni di piping osservati durante l’evento di piena del novembre del 2014. A partire dei dati di
input per la definizione di un accurato modello geotecnico e delle condizioni idrauliche locali, è stato messo a
punto un modello numerico tridimensionale che permette di cogliere l’innesco dei fontanazzi
Field measurements on a large natural sand boil along the river Po, Italy
Full text linkSand boils are the surface manifestation of an erosion process, known as backward erosion piping, which may take place beneath river embankments during high-water events. The risk of embankment failure greatly increases in locations affected by sand boils. Numerous studies have been carried out, mainly at the laboratory scale, providing significant advancements in this field. Nonetheless, there is still a gap between research and practice that needs to be filled. This study presents a set of field measurements carried out on a large sand boil reactivated near the toe of an embankment along the river Po, Italy. Hydraulic heads, velocity and discharge, concentration and pipe geometry were measured as a function of the water level in the river during the November 2018 flood. The collected data are compared with predictions of a theoretical model that provides the head loss in the vertical pipe. Furthermore, the local exit gradients, as deduced from measurements, are discussed, together with the operational critical gradients adopted in current design practice. The collected data provide important input parameters for the calibration of analytical and numerical models, typically implemented to investigate the sand boil evolution and then to assess the backward erosion piping risk at real scale
Progettazione degli apparati sperimentali per la modellazione fisica alla scala di laboratorio dei fenomeni di sottofiltrazione nei rilevati arginali
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Probability of Reactivation of a Sand Boil near a River Embankment of the Po River (Italy)
No full textThis paper presents a reliability analysis referred to backward erosion piping phenomena. The study is carried out
on a cross-section of the major Italian watercourse, the Po River, where evidence of piping effects, namely a sand boil of
remarkable size, has been periodically detected during past high-water events. The initiation of the process has been analysed
by means of a two-dimensional (2D) finite element (FE) model of the groundwater flow beneath the river embankment, to
obtain an effective description of the hydraulic gradient variation close to the sand boil due to the rise of the river water level,
and thus capture the conditions triggering piping. Detailed stratigraphic soil profiling, as well as careful geotechnical
characterization of the riverbank sediments and the foundation subsoil, have been carried out. In particular, representative
mean values of the saturated permeability, and the relevant standard deviation, have been obtained from statistical analysis of
the estimates provided by empirical correlations applied to cone penetration tests (CPT) profiles. The methodology adopted
for reliability analysis relies on the use of fragility curves. The probability of backward erosion piping initiation as a function
of the floodwater elevation has been therefore calculated assuming that hydraulic conductivity and a few geometrical
parameters affecting the problem could be considered as random variables in the FE model. Then, the probability of
reactivation has been estimated using the Taylor’s Series first-order second moment (FOSM) method. The same procedure
has been developed by applying the well-known blanket theory. Both analyses result in a high probability of reactivation of
the sand boil, also for moderate river levels. In addition, fragility curves have been interpreted in the light of the available
field observations. The interpretation indicates that, despite the significant variability of the water levels recorded at the on set of reactivations, the blanket theory tends to overestimate the probability of sand boil initiation, while the FE analysis
results are closer to the field observations collected in the last 20 year
Sustainable levee construction along the Danube River
No full textNowadays changing weather conditions and the resulting increasing flood levels make flood protection improvement essential. In Hungary, in the Szigetköz floodplain area, a complex water resources management unit of the Upper part of the Danube River, the rehabilitation of the water levels, and the setting back of the settled low and middle water levels had become necessary. It has been achieved by relocating the estuary of the Mosoni-Danube River and constructing a complex water control structure. A new ~1.5 km long levee connects to the structure. Due to a large volume of fine-grained blanket material on the site, the possibility arose to build a section of the levee using the blanket material without applying a cut-off wall to prevent water flow through the levee. The geotechnical parameters of the available local material were based on a complex site investigation program. According to the results of the field and laboratory tests, the blanket layer was suitable as fill material and could be compacted to the required 90% degree of compaction using standard machinery and procedures. Plaxis 2D software using fully coupled flow-deformation analysis, imitating the previously registered flood waves, modeled seepage and stability behaviour to evaluate the ultimate limit states of the levee constructed from the blanket material. The analysis proved the adequacy of the blanket material, avoiding the necessity for a barrier within the embankment. The use of local blanket material as fill eliminated the need to excavate and transport additional material, reducing environmental impact, shortening construction time, and saving costs on the project
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