Synthesis and Physical-Chemical characterization of Metallic Nanoparticles

The stabilization of nanoparticles against their irreversible particle aggregation and oxidation reactions. is a requirement for further advancement in nanoparticle science and technology. For this reason the research aim on this topic focuses on the synthesis of various metal nanoparticles protected with monolayers containing different reactive head groups and functional tail groups. In this work cuprous bromide nanocrystals haave been synthetized with a diameter of about 20 nanometers according to a new sybthetic method adding dropwise ascorbic acid to a water solution of lithium bromide and cupric chloride under continuous stirring and nitrogen flux. Butane thiolate Cu protected nanoparticles have been synthetized according to three different syntesys methods. Their morphologies appear related to the physicochemical conditions during the synthesis and to the dispersing medium used to prepare the sample. Synthesis method II allows to obtain stable nanoparticles of 1-2 nm in size both isolated and forming clusters. Nanoparticle cluster formation was enhanced as water was used as dispersing medium probably due to the idrophobic nature of the butanethiolate layers coating the nanoparticle surface. Synthesis methods I and III lead to large unstable spherical nanoparticles with size ranging between 20 to 50 nm. These nanoparticles appeared in the TEM micrograph with the same morphology independently on the dispersing medium used in the sample preparation. The stability and dimensions of the copper nanoparticles appear inversely related. Using the same methods above described for the butanethiolate protected copper nanoparticles 4-methylbenzenethiol protected copper nanoparticles have been prepared. Diffractometric and spectroscopic data reveal that decomposition processes didn’t occur in both the 4-methylbenzenethiol copper protected nanoparticles precipitates from formic acid and from water in a period of time six month long. Se anticarcinogenic effects by multiple mechanisms have been extensively investigated and documented and Se is defined a genuine nutritional cancer-protecting element and a significant protective effect of Se against major forms of cancer. Furthermore phloroglucinol was found to possess cytoprotective effects against oxidative stress, thanks to reactive oxygen species (ROS) which are associated with cells and tissue damages and are the contributing factors for inflammation, aging, cancer, arteriosclerosis, hypertension and diabetes. The goal of our work has been to set up a new method to synthesize in mild conditions amorphous Se nanopaticles surface capped with phloroglucinol, which is used during synthesis as reducing agent to obtain stable Se nanoparticles in ethanol, performing the synergies offered by the specific anticarcinogenic properties of Se and the antioxiding ones of phloroalucinol. We have synthesized selenium nanoparticles protected by phenolic molecules chemically bonded to their surface. The phenol molecules coating the nanoparticles surfaces form low ordered arrays as can be seen from the wider shape of the absorptions in the FT-IR spectrum with respect to those appearing in that of crystalline phenol. On the other hand, metallic nanoparticles with unique optical properties, facile surface chemistry and appropriate size scale are generating much enthusiasm in nanomedicine. In fact Au nanoparticles has immense potential for both cancer diagnosis and therapy. Especially Au nanoparticles efficiently convert the strongly adsorbed light into localized heat, which can be exploited for the selective laser photothermal therapy of cancer. According to the about, metal nanoparticles-HA nanocrystals composites should have tremendous potential in novel methods for therapy of cancer. 11 mercaptoundecanoic surface protected Au4Ag1 nanoparticles adsorbed on nanometric apathyte crystals we have successfully prepared like an anticancer nanoparticles deliver system utilizing biomimetic hydroxyapatyte nanocrystals as deliver agents. Furthermore natural chrysotile, formed by densely packed bundles of multiwalled hollow nanotubes, is a mineral very suitable for nanowires preparation when their inner nanometer-sized cavity is filled with a proper material. Bundles of chrysotile nanotubes can then behave as host systems, where their large interchannel separation is actually expected to prevent the interaction between individual guest metallic nanoparticles and act as a confining barrier. Chrysotile nanotubes have been filled with molten metals such as Hg, Pb, Sn, semimetals, Bi, Te, Se, and with semiconductor materials such as InSb, CdSe, GaAs, and InP using both high-pressure techniques and metal-organic chemical vapor deposition. Under hydrothermal conditions chrysotile nanocrystals have been synthesized as a single phase and can be utilized as a very suitable for nanowires preparation filling their inner nanometer-sized cavity with metallic nanoparticles. In this research work we have synthesized and characterized Stoichiometric synthetic chrysotile nanotubes have been partially filled with bi and monometallic highly monodispersed nanoparticles with diameters ranging from 1,7 to 5,5 nm depending on the core composition (Au, Au4Ag1, Au1Ag4, Ag). In the case of 4 methylbenzenethiol protected silver nanoparticles, the filling was carried out by convection and capillarity effect at room temperature and pressure using a suitable organic solvent. We have obtained new interesting nanowires constituted of metallic nanoparticles filled in inorganic nanotubes with a inner cavity of 7 nm and an isolating wall with a thick ranging from 7 to 21 nm.

Chemical and kinematical properties of Blue Straggler stars in Galactic globular clusters

Blue straggler stars (BSSs) are brighter and bluer (hotter) than the main-sequence (MS) turnoff and they are known to be more massive than MS stars.Two main scenarios for their formation have been proposed:collision-induced stellar mergers (COL-BSSs),or mass-transfer in binary systems (MT-BSSs).Depleted surface abundances of C and O are expected for MT-BSSs,whereas no chemical anomalies are predicted for COL-BSSs.Both MT- and COL-BSSs should rotate fast, but braking mechanisms may intervene with efficiencies and time-scales not well known yet,thus preventing a clear prediction of the expected rotational velocities.Within this context,an extensive survey is ongoing by using the multi-object spectrograph FLAMES@VLT,with the aim to obtain abundance patterns and rotational velocities for representative samples of BSSs in several Galactic GCs.A sub-population of CO-depleted BSSs has been identified in 47 Tuc,with only one fast rotating star detected.For this PhD Thesis work I analyzed FLAMES spectra of more than 130 BSSs in four GCs:M4,NGC 6397,M30 and ω Centauri.This is the largest sample of BSSs spectroscopically investigated so far.Hints of CO depletion have been observed in only 4-5 cases (in M30 and ω Centauri),suggesting either that the majority of BSSs have a collisional origin,or that the CO-depletion is a transient phenomenon.Unfortunately,no conclusions in terms of formation mechanism could be drawn in a large number of cases,because of the effects of radiative levitation. Remarkably,however,this is the first time that evidence of radiative levitation is found in BSSs hotter than 8200 K.Finally, we also discovered the largest fractions of fast rotating BSSs ever observed in any GCs:40% in M4 and 30% in ω Centauri.While not solving the problem of BSS formation,these results provide invaluable information about the BSS physical properties,which is crucial to build realistic models of their evolution.

Physico-chemical and microstructural properties of food dispersions

The macroscopic properties of oily food dispersions, such as rheology, mechanical strength, sensory attributes (e.g. mouth feel, texture and even flavour release) and as well as engineering properties are strongly determined by their microstructure, that is considered a key parameter in the understanding of the foods behaviour . In particular the rheological properties of these matrices are largely influenced by their processing techniques, particle size distribution and composition of ingredients. During chocolate manufacturing, mixtures of sugar, cocoa and fat are heated, cooled, pressurized and refined. These steps not only affect particle size reduction, but also break agglomerates and distribute lipid and lecithin-coated particles through the continuous phase, this considerably modify the microstructure of final chocolate. The interactions between the suspended particles and the continuous phase provide information about the existing network and consequently can be associated to the properties and characteristics of the final dispersions. Moreover since the macroscopic properties of food materials, are strongly determined by their microstructure, the evaluation and study of the microstructural characteristics, can be very important for a through understanding of the food matrices characteristics and to get detailed information on their complexity. The aim of this study was investigate the influence of formulation and each process step on the microstructural properties of: chocolate type model systems, dark milk and white chocolate types, and cocoa creams. At the same time the relationships between microstructural changes and the resulting physico-chemical properties of: chocolate type dispersions model systems dark milk and white chocolate were investigated.

Structural and biochemical studies of Sporosarcina pasteurii UreE: a nickel-chaperone involved in the urease activation process

Urease is a nickel-dependent enzyme that catalyzes hydrolysis of urea in the last step of organic nitrogen mineralization. Its active site contains a dinuclear center for Ni(II) ions that must be inserted into the apo-enzyme through the action of four accessory proteins (UreD, UreE, UreF, UreG) leading to activation of urease. UreE, acting as a metallo-chaperone, delivers Ni(II) to the preformed complex of apo-urease-UreDFG and has the capability to enhance the GTPase activity of UreG. This study, focused on characterization of UreE from Sporosarcina pasteurii (SpUreE), represents a piece of information on the structure/mobility-function relationships that control nickel binding by SpUreE and its interaction with SpUreG. A calorimetric analysis revealed the occurrence of a binding event between these proteins with positive cooperativity and a stoichiometry consistent with the formation of the (UreE)2-(UreG)2 hetero-oligomer complex. Chemical Shift Perturbations induced by the protein-protein interaction were analyzed using high-resolution NMR spectroscopy, which allowed to characterize the molecular details of the protein surface of SpUreE involved in the complex formation with SpUreG. Moreover, backbone dynamic properties of SpUreE, determined using 15N relaxation analysis, revealed a general mobility in the nanoseconds time-scale, with the fastest motions observed at the C-termini. The latter analysis made it possible for the first time to characterize of the C-terminal portions, known to contain key residues for metal ion binding, that were not observed in the crystal structure of UreE because of disorder. The residues belonging to this portion of SpUreE feature large CSPs upon addition of SpUreG, showing that their chemical environment is directly affected by protein-protein interaction. Metal ion selectivity and affinity of SpUreE for cognate Ni(II) and non cognate Zn(II) metal ions were determined, and the ability of the protein to select Ni(II) over Zn(II), in consistency with the proposed role in Ni(II) cations transport, was established.

Impact of metal and metal oxide engineered nanoparticles in soil and plant systems

Nanotechnology promises huge benefits for society and capital invested in this new technology is steadily increasing, therefore there is a growing number of nanotechnology products on the market and inevitably engineered nanomaterials will be released in the atmosphere with potential risks to humans and environment. This study set out to extend the comprehension of the impact of metal (Ag, Co, Ni) and metal oxide (CeO2, Fe3O4, SnO2, TiO2) nanoparticles (NPs) on one of the most important environmental compartments potentially contaminated by NPs, the soil system, through the use of chemical and biological tools. For this purpose experiments were carried out to simulate realistic environmental conditions of wet and dry deposition of NPs, considering ecologically relevant endpoints. In detail, this thesis involved the study of three model systems and the evaluation of related issues: (i) NPs and bare soil, to assess the influence of NPs on the functions of soil microbial communities; (ii) NPs and plants, to evaluate the chronic toxicity and accumulation of NPs in edible tissues; (iii) NPs and invertebrates, to verify the effects of NPs on earthworms and the damaging of their functionality. The study highlighted that NP toxicity is generally influenced by NP core elements and the impact of NPs on organisms is specie-specific; moreover experiments conducted in media closer to real conditions showed a decrease in toxicity with respect to in vitro test or hydroponic tests. However, only a multidisciplinary approach, involving physical, chemical and biological skills, together with the use of advanced techniques, such as X-ray absorption fine structure spectroscopy, could pave the way to draw the right conclusions and accomplish a deeper comprehension of the effects of NPs on soil and soil inhabitants.

Soil enzyme activities and biochemical indexes to assess soil quality in agronomic and forested ecosystems

The soil carries out a wide range of functions and it is important study the effects of land use on soil quality in order to provide most sustainable practices. Three fields trial have been considered to assess soil quality and functionality after human alteration, and to determine the power of soil enzymatic activities, biochemical indexes and mathematical model in the evaluation of soil status. The first field was characterized by conventional and organic management in which were tested also tillage effects. The second was characterized by conventional, organic and agro-ecological management. Finally, the third was a beech forest where was tested the effects of N deposition on soil organic carbon sequestration. Results highlight that both enzyme activities and biochemical indexes could be valid parameters for soil quality evaluation. Conventional management and plowing negatively affected soil quality and functionality with intensive tillage that lead to the downturn of microbial biomass and activity. Both organic and agro-ecological management revealed to be good practices for the maintenance of soil functionality with better microbial activity and metabolic efficiency. This positively affected also soil organic carbon content. At the eutrophic forest, enzyme activities and biochemical indexes positively respond to the treatments but one year of experimentation resulted to be not enough to observe variation in soil organic carbon content. Mathematical models and biochemical indicators resulted to be valid tools for assess soil quality, nonetheless it would be better including the microbial component in the mathematical model and consider more than one index if the aim of the work is to evaluate the overall soil quality and functionality. Concluding, the forest site is the richest one in terms of organic carbon, microbial biomass and activity while, the organic and the agro-ecological management seem to be the more sustainable but without taking in consideration the yield.

Ocean-Atmosphere Interactions: Linking Oceanic Biological Activity to Marine Aerosol Physico-Chemical and Cloud Properties

In this work, in-situ measurements of aerosol chemical composition, particle number size distribution, cloud-relevant properties and ground-based cloud observations were combined with high-resolution satellite sea surface chlorophyll-a concentration and air mass back-trajectory data to investigate the impact of the marine biota on aerosol physico-chemical and cloud properties. Studies were performed over the North-Eastern Atlantic Ocean, the central Mediterranean Sea, and the Arctic Ocean, by deploying both multi-year datasets and short-time scale observations. All the data were chosen to be representative of the marine atmosphere, reducing to a minimum any anthropogenic input. A relationship between the patterns of marine biological activity and the time evolution of marine aerosol properties was observed, under a variety of aspects, from chemical composition to number concentration and size distribution, up to the most cloud‐relevant properties. At short-time scales (1-2 months), the aerosol properties tend to respond to biological activity variations with a delay of about one to three weeks. This delay should be considered in model applications that make use of Chlorophyll-a to predict marine aerosol properties at high temporal resolution. The impact of oceanic biological activity on the microphysical properties of marine stratiform clouds is also evidenced by our analysis, over the Eastern North Atlantic Ocean. Such clouds tend to have a higher number of smaller cloud droplets in periods of high biological activity with respect to quiescent periods. This confirms the possibility of feedback interactions within the biota-aerosol-cloud climate system. Achieving a better characterization of the time and space relationships linking oceanic biological activity to marine aerosol composition and properties may significantly impact our future capability of predicting the chemical composition of the marine atmosphere, potentially contributing to reducing the uncertainty of future climate predictions, through a better understanding of the natural climate system.

Physical modeling and numerical simulations of degradation mechanisms in devices and insulators for power applications

In this thesis, a TCAD approach for the investigation of charge transport in amorphous silicon dioxide is presented for the first time. The proposed approach is used to investigate high-voltage silicon oxide thick TEOS capacitors embedded in the back-end inter-level dielectric layers for galvanic insulation applications. In the first part of this thesis, a detailed review of the main physical and chemical properties of silicon dioxide and the main physical models for the description of charge transport in insulators are presented. In the second part, the characterization of high-voltage MIM structures at different high-field stress conditions up to the breakdown is presented. The main physical mechanisms responsible of the observed results are then discussed in details. The third part is dedicated to the implementation of a TCAD approach capable of describing charge transport in silicon dioxide layers in order to gain insight into the microscopic physical mechanisms responsible of the leakage current in MIM structures. In particular, I investigated and modeled the role of charge injection at contacts and charge build-up due to trapping and de-trapping mechanisms in the oxide layer to the purpose of understanding its behavior under DC and AC stress conditions. In addition, oxide breakdown due to impact-ionization of carriers has been taken into account in order to have a complete representation of the oxide behavior at very high fields. Numerical simulations have been compared against experiments to quantitatively validate the proposed approach. In the last part of the thesis, the proposed approach has been applied to simulate the breakdown in realistic structures under different stress conditions. The TCAD tool has been used to carry out a detailed analysis of the most relevant physical quantities, in order to gain a detailed understanding on the main mechanisms responsible for breakdown and guide design optimization.

Bio-physical interactions and feedbacks in a global climate model

This PhD thesis addresses the topic of large-scale interactions between climate and marine biogeochemistry. To this end, centennial simulations are performed under present and projected future climate conditions with a coupled ocean-atmosphere model containing a complex marine biogeochemistry model. The role of marine biogeochemistry in the climate system is first investigated. Phytoplankton solar radiation absorption in the upper ocean enhances sea surface temperatures and upper ocean stratification. The associated increase in ocean latent heat losses raises atmospheric temperatures and water vapor. Atmospheric circulation is modified at tropical and extratropical latitudes with impacts on precipitation, incoming solar radiation, and ocean circulation which cause upper-ocean heat content to decrease at tropical latitudes and to increase at middle latitudes. Marine biogeochemistry is tightly related to physical climate variability, which may vary in response to internal natural dynamics or to external forcing such as anthropogenic carbon emissions. Wind changes associated with the North Atlantic Oscillation (NAO), the dominant mode of climate variability in the North Atlantic, affect ocean properties by means of momentum, heat, and freshwater fluxes. Changes in upper ocean temperature and mixing impact the spatial structure and seasonality of North Atlantic phytoplankton through light and nutrient limitations. These changes affect the capability of the North Atlantic Ocean of absorbing atmospheric CO2 and of fixing it inside sinking particulate organic matter. Low-frequency NAO phases determine a delayed response of ocean circulation, temperature and salinity, which in turn affects stratification and marine biogeochemistry. In 20th and 21st century simulations natural wind fluctuations in the North Pacific, related to the two dominant modes of atmospheric variability, affect the spatial structure and the magnitude of the phytoplankton spring bloom through changes in upper-ocean temperature and mixing. The impacts of human-induced emissions in the 21st century are generally larger than natural climate fluctuations, with the phytoplankton spring bloom starting one month earlier than in the 20th century and with ~50% lower magnitude. This PhD thesis advances the knowledge of bio-physical interactions within the global climate, highlighting the intrinsic coupling between physical climate and biosphere, and providing a framework on which future studies of Earth System change can be built on.

Physiological and Biochemical Aspects of Iron Nutrition in Grapevine

The objective of this thesis was to study the response mechanisms of grapevine to Fe-deficiency and to potential Fe chlorosis prevention strategies. The results show that the presence of bicarbonate in the nutrient solution shifted the activity of PEPC and TCA cycle enzymes and the accumulation/translocation of organic acids in roots of Fe-deprived plants. The rootstock 140 Ruggeri displayed a typical behavior of calcicole plants under bicarbonate stress. The Fe chlorosis susceptible rootstock 101-14 reacted to a prolonged Fe-deficiency reducing the root activity of PEPC and MDH. Noteworthy, it accumulates high levels of citric acid in roots, indicating a low capacity to utilizing, transporting and/or exudating organic acids into the rhizosfere. In contrast, 110 Richter rootstock is capable to maintain an active metabolism of organic acids in roots, accumulating them to a lesser extent than 101-14. Similarly to 101-14, SO4 genotype displays a strong decrease of mechanisms associated to Fe chlorosis tolerance (PEPC and MDH enzymes). Nevertheless it is able to avoid excessive accumulation of citric acid in roots, similar as 110 Richter rootstock. Intercropping with Festuca rubra increased leaf chlorophyll content and net photosynthesis. In addition, intercropping reduces the activity of PEPC in roots, similary to Fe-chelate supply. Applications of NH4+ with nitrification inhibitor prevents efficiently Fe-deficiency, increases chlorophyll content, and induces similar root biochemical responses as Fe-EDDHA. Without the addition of nitrification inhibitors, the effectiveness of NH4+ supply on Fe chlorosis prevention resulted significantly lower. The aspects intertwined in this investigation highlight the complexity of Fe physiology and the fine metabolic tuning of grapevine genotypes to Fe availability and soil-related environmental factors. The experimental evidences reveal the need to carry out future researches on Fe nutrition maintaining a continous flow of knowledge between theoretical and agronomical perspectives for fully supporting the efforts devoted to convert science into practice.

Fish quality assessment through the application of chemico-physical, sensory and microbiological analyses

The quality of fish products is indispensably linked to the freshness of the raw material modulated by appropriate manipulation and storage conditions, specially the storage temperature after catch. The purpose of the research presented in this thesis, which was largely conducted in the context of a research project funded by Italian Ministry of Agricultural, Food and Forestry Policies (MIPAAF), concerned the evaluation of the freshness of farmed and wild fish species, in relation to different storage conditions, under ice (0°C) or at refrigeration temperature (4°C). Several specimens of different species, bogue (Boops boops), red mullet (Mullus barbatus), sea bream (Sparus aurata) and sea bass (Dicentrarchus labrax), during storage, under the different temperature conditions adopted, have been examined. The assessed control parameters were physical (texture, through the use of a dynamometer; visual quality using a computer vision system (CVS)), chemical (through footprint metabolomics 1H-NMR) and sensory (Quality Index Method (QIM). Microbiological determinations were also carried out on the species of hake (Merluccius merluccius). In general obtained results confirmed that the temperature of manipulation/conservation is a key factor in maintaining fish freshness. NMR spectroscopy showed to be able to quantify and evaluate the kinetics for unselected compounds during fish degradation, even a posteriori. This can be suitable for the development of new parameters related to quality and freshness. The development of physical methods, particularly the image analysis performed by computer vision system (CVS), for the evaluation of fish degradation, is very promising. Among CVS parameters, skin colour, presence and distribution of gill mucus, and eye shape modification evidenced a high sensibility for the estimation of fish quality loss, as a function of the adopted storage conditions. Particularly the eye concavity index detected on fish eye showed a high positive correlation with total QIM score.

Land use change to perennial energy crops in Northern Italy: Effects on soil organic carbon sequestration and distribution, soil enzyme activities and microbial communities.

Studies on soil organic carbon (SOC) sequestration in perennial energy crops are available for North-Central Europe, while there is insufficient information for Southern Europe. This research was conducted in the Po Valley, a Mediterranean-temperate zone characterised by low SOC levels, due to intensive management. The aim was to assess the factors influencing SOC sequestration and its distribution through depth and within soil fractions, after a 9-year old conversion from two annual systems to Miscanthus (Miscanthus × giganteus) and giant reed (Arundo donax). The 13C natural abundance was used to evaluate the amount of SOC in annual and perennial species, and determine the percentage of carbon derived from perennial crops. SOC was significantly higher under perennial species, especially in the topsoil (0-0.15 m). After 9 years, the amount of C derived from Miscanthus was 18.7 Mg ha-1, mostly stored at 0-0.15 m, whereas the amount of C derived from giant reed was 34.7 Mg ha-1, evenly distributed through layers. Physical soil fractionation was combined with 13C abundance analysis. C derived from perennial crops was mainly found in macroaggregates. Under giant reed, more newly derived-carbon was stored in microaggregates and mineral fraction than under Miscanthus. A molecular approach based on denaturing gradient gel electrophoresis (DGGE) allowed to evaluate changes on microbial community, after the introduction of perennial crops. Functional aspects were investigated by determining relevant soil enzymes (β-glucosidase, urease, alkaline phosphatase). Perennial crops positively stimulated these enzymes, especially in the topsoil. DGGE profiles revealed that community richness was higher in perennial crops; Shannon index of diversity was influenced only by depth. In conclusion, Miscanthus and giant reed represent a sustainable choice for the recovery of soils exhausted by intensive management, also in Mediterranean conditions and this is relevant mainly because this geographical area is notoriously characterised by a rapid turnover of SOC.

Physiological and biochemical adaptation to salinity in wild halophytes suitable for Mediterranean agriculture

Due to the accelerating processes of soil salinization and shortage of fresh water, the practice of saline agriculture is gaining momentum in many areas of the world. However, there are some concerns that using saline water for irrigation may be non-environmentally sustainable, with potential to cause irreversible soil degradation. In addition, there is a lack of information on the morphological, physiological, and biochemical changes that can occur in plants when irrigated with saline water. In light of the above, the major aim of this work was to investigate the effects of a range of water salinity levels and irrigation regimes on the performances of salt tolerant species promising as future crop plants for saline agriculture. The following objectives were addressed: To determine the effects of different water regimes (leaching irrigation vs. no leaching irrigation) with water at increasing salinity concentrations on the growth, ion accumulation and water relations of Sorghum bicolor plants grown under saline soil conditions. To describe the germination response of Salicornia europaea seeds across a wide range of water salinity levels through six reliable indices for screening salinity tolerance at the seed germination stage. To explore the different physiological responses of six wild halophytes commonly found in the Mediterranean area (Artemisia absinthium, Artemisia vulgaris, Atriplex halimus, Chenopodium album, Salsola komarovii, and Sanguisorba minor), and rank their tolerance after exposure to growing levels of water salinity. To identify the main adaptation mechanisms that distinguish C3 from C4 halophytes when exposed to increasing salinity in the growth media, through a comparative study between the C3 species Atriplex hortensis and the C4 species Atriplex halimus. To identify the main adaptation mechanisms that distinguish annual from perennial halophytes when exposed to severe conditions of salinity and drought, through a comparative analysis between two annual Salicornia spp. and the perennial Sarcocornia fruticosa.

A comprehensive experimental and numerical approach for assessing the hydro-mechanical behaviour of river embankments

In this doctoral dissertation, a comprehensive methodological approach for the assessment of river embankments safety conditions, based on the integrated use of laboratory testing, physical modelling and finite element (FE) numerical simulations, is proposed, with the aim of contributing to a better understanding of the effect of time-dependent hydraulic boundary conditions on the hydro-mechanical response of river embankments. The case study and materials selected for the present research project are representative for the riverbank systems of Alpine and Apennine tributaries of the main river Po (Northern Italy), which have recently experienced various sudden overall collapses. The outcomes of a centrifuge test carried out under the enhanced gravity field of 50-g, on a riverbank model, made of a compacted silty sand mixture, overlying a homogeneous clayey silt foundation layer and subjected to a simulated flood event, have been considered for the definition of a robust and realistic experimental benchmark. In order to reproduce the observed experimental behaviour, a first set of numerical simulations has been carried out by assuming, for both the embankments and the foundation unit, rigid soil porous media, under partially saturated conditions. Mechanical and hydraulic soil properties adopted in the numerical analyses have been carefully estimated based on standard saturated triaxial, oedometer and constant head permeability tests. Afterwards, advanced suction-controlled laboratory tests, have been carried out to investigate the effect of suction and confining stresses on the shear strength and compressibility characteristics of the filling material and a second set of numerical simulations has been run, taking into account the soil parameters updated based on the most recent tests. The final aim of the study is the quantitative estimation of the predictive capabilities of the calibrated numerical tools, by systematically comparing the results of the FE simulations to the experimental benchmark.