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Misure mitigatorie dei fenomeni erosivi localizzati attorno a pile dei ponti esistenti
No full textThe functionality of a river crossing must be ensured not only under normal conditions but especially during hazardous events, e.g. floods, when the efficiency of the infrastructure becomes fundamental to ensure the mobility of the rescue teams and the evacuation of the inhabitants. However, this is not currently accomplished, so that hydraulic phenomena account for over of bridge failures. Among the hydraulic causes, the localized erosion at bridge piers that mainly develops during flood events plays a relevant role, also because it cannot be recognized or detected through a simple visual inspection.
In the present work, the localized erosive phenomena around in-river structures of bridges have been extensively investigated in an effort to clarify the unclear aspects of the phenomena coming from literature analysis.
The focus has been mainly devoted on the scour around piers of different geometry, considering circular piers, elongated piers also supported by the foundation, and twin circular pier supported by the foundation.
Attention has been posed on the time evolution of maximum depth and volume (or area) of the scouring, as well as on the influence of the flow depth respect to the width of the pier. Additionally, the other concurrent parameters influencing the scour depth in laboratory experiments have been specifically considered.
The knowledge acquired in this initial phase was instrumental in preliminarily defining the geometric characteristics required for an anti-erosion mattress.
Both past and current rip-rap protection methods have been considered, including launchable stones (developed in the past) and rip-rap mattresses (currently adopted).
As an empirical maintenance technique, old bridges are still working thanks to the ancient custom of filling any recognized scour around piers with launchable stones after each relevant flood event.
Currently, rip-rap mattresses of appropriate thickness are often suggested as scour countermeasures for existing bridges, as an alternative to structural reinforcements such as foundation deepening.
Both the techniques (launchable stones and rip-rap mattress) have been studied through laboratory experiments considering piers of different geometries, suggesting for the mattresses some improvements respect to the technical solution reported in literature.
At the end, the performance of monitoring techniques has been investigated, exploring the ability of sonar sensors to continuously monitor the scour evolution, and investigating sensor measurements in several locations around piers comparing them with maximum scour depths. If effective, these monitoring techniques can provide valuable insights to prevent dangerous conditions, even during the progression of flood events.
The experimental activities were primarily conducted under clear water conditions, although some rip-rap linings were tested with flow velocities exceeding the critical threshold.
The following are the main findings derived from the conducted tests and their critical analysis in the context of existing literature:
- new insights into the temporal evolution of maximum scour around shallow and narrow piers have been gained;
- enhancements to current rip-rap mattress configurations have been developed, proposed, and subjected to experimental testing;
- radar monitoring techniques have been evaluated on complex pier geometries under clear water conditions, demonstrating how the effectiveness in critical scour recognition varies depending on sensor placement
Safety assessment of historical barrages and hazard cascades following their failure: the Roggia Morlana case study
Full text linkBarrages are low-head dams, used to realize diversion works for irrigation, hydroelectric or human consumption purposes. These in-river structures control the river bed elevation and maintain a prescribed water level upstream, affecting the levees’ elevation too if present. Often, they have been present for a long time (in the examined case centuries) and act as an inherent element of the surrounding environment, representing a constraint for the human activities growing through the years along the river.
The Roggia Morlana barrage, which is located across the Serio River in the Province of Bergamo, northern Italy, has for centuries been a fundamental part of the economic life in the area, thanks to the several artificial canals that supply water for irrigation purposes. In the mid-twentieth century, a maximum capacity of 4500 l/s was derived and distributed in an extensive area of about 4200 hectares, while nowadays this barrage keeps an important role also for hydroelectric power production.
In October 2020, an event led to the collapse of a part of the barrage and to the subsequent lowering of the river bed and destabilization of the banks. In addition to the stop of the hydropower production and the lack in satisfying the irrigation demand, the retrogressive erosion threatened various fundamental infrastructures crossing the river upstream (a gas pipeline, a water main and a bridge), hence a rapid rehabilitation of the barrage was required.
The stability of the restored barrage depends on the flood discharges and on the related scouring phenomena that could take place immediately downstream. With the aim to assess the exposure and vulnerability of this critical infrastructure to the natural hazard, the effects of different riverbed protection configurations are analysed through physical modelling, testing each configuration against flood events.
The area downstream the barrage is subdivided in frames delimited by bottom sills, filled with material. The physical model allowed to evaluate the effectiveness in scouring mitigation using different size of natural stones, put in place as loose boulders or wired in groups. To reduce the amount of damages and increase the resilience of the riverbed protection boulders have been substituted by concrete blocks in some frames. By this way, the goal to shift the scouring phenomena downstream, localizing the maximum scour depth far from the barrage foundations, is fulfilled.
The cost of the restoration obtained via different riverbed protections, increasing with the resilience of the barrage, is compared with the cost of their failure that can cause complex hazard cascades. This is because a failure of the Roggia Morlana barrage does not have consequences only to the hydropower production and irrigation service, but also on the safety of the infrastructures crossing the river upstream, potentially affected by backward erosion phenomena
Cascading Events Following the Roggia Morlana Barrage Failure and Multi-Risk Assessment
Full text linkBarrages are low-head dams built to divert a prefixed amount of flow rate from the river. They set the water level upstream, for instance to ensure the diversion of water toward a hydroelectric plant or for irrigation purposes, affecting the riverbed elevation and the topography of the surrounding area. The Roggia Morlana barrage is an ancient structure located along the Serio river in the province of Bergamo, northern Italy. Since 1200, it was used for irrigation purposes thanks to the several artificial canals that derive water from it. Nowadays, it has an important role also for hydroelectric power production. Furthermore, various fundamental infrastructures are located 200 m upstream of the barrage, that are a gas pipeline, a water main and a bridge.
In October 2020, a flood event led to the collapse of a part of the barrage and to the subsequent lowering of the river bed and destabilization of the banks. In addition to the stop of the hydropower production and the lack in satisfying the irrigation demand, the retrogressive erosion threatened the upstream infrastructures, which possible failure induces remarkable issues to surrounding villages. Hence, to ensure the safety condition of all the infrastructures, a proper rehabilitation of the barrage was needed.
The stability of the restored barrage depends on the magnitude of the flood event and on the scouring phenomena that develop downstream of it. To analyse the physical processes involved, a physical model was developed reproducing several riverbed protection configurations and different flood events. By this way, the exposure and vulnerability of the critical infrastructures are assessed.
The multi-risk of failure of the infrastructures and the subsequent impact is evaluated through a combination of probabilities and consequences, according to a combination of the exceedance probability of the flood event and the vulnerability of the infrastructures. The consequences, instead, are defined according to the importance of each infrastructure for the society and the impact caused by its failure. The application of the multi-risk concept aims to highlight how the interaction among hazards increases the risk respect to that for independent events. Other possible flood risk management strategies for these interrelated critical infrastructures are also described
Mitigation strategies against seawater intrusion in the context of climate change
Full text linkIn coastal regions, where about 40% of world population is settled, freshwater aquifers are affected by a saltwater intrusion. The presence of elevate salt concentrations, among the most common pollutants in groundwater aquifers, represents a world-wide spread problem for coastal areas, such as Mediterranean coasts, both East and West coasts in the U. S., Gulf of Mexico and Middle East coasts. The seriousness of the situation is enhanced by the high demand of water supply, especially in the drier periods, and by the mean sea-level rise due to climate change. So that seawater will encroach farther inland and will threaten the available fresh groundwater supply, affecting not only human livelihood, but also coastal ecosystems. The form and transformation of the seaward hydraulic gradient of the aquifer and a constant freshwater discharge into the sea are fundamental in order to control the rate of intrusion.
To maintain the seaward gradient in the system the aquifer may be artificially recharged by freshwater by increasing the inland piezometric heads. The purpose of this solution is to create a hydraulic barrier against the inland flow of saline water by injecting freshwater in the vicinity of the shoreline. For phreatic aquifers both injection wells and surface spreading of water, such as irrigation, may be applied. Surface reservoirs, lakes and canals can be used as recharge systems for unconfined aquifers through freshwater infiltration (Hussain et al., 2019).
To assess the effectiveness of this mitigation approach and the amount of volumes of freshwater required, physical experiments are developed in a laboratory canal developed to reproduce a controlled heterogeneous porous media.
The sandbox measures 500 cm long by 30 cm wide by 60 cm high, with 3 cm thick plexiglass walls. Two tanks are located upstream and downstream from the sandbox, with volumes of about 0.5 m3 and 2.0 m3, respectively. The upstream tank is filled with fresh-water and is continuously supplied by a small pump, providing fresh-water recharge. The downstream tank is filled with salt-water, previously prepared by adding salt to fresh-water till a proper density is reached, and it represents the sea. This canal has been used in previous works (Bouzaglou et al., 2018, Crestani et al., 2022), but in the present the homogeneous porous media has been substituted by three different nominal size ranges of glass beads, equal to 0.3-0.4, 0.4-0.8 and 1.0-1.3 mm respectively, organized in 250 cells, each of size 20x30x5 cm3 to reproduce a prescribed statistical anisotropic structure.
The evidences deduced from the physical experiments developed simulating the seawater intrusion-retreat phenomenon due to drought periods are discussed in comparison with the results of a numerical model
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
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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