Un modello di danno fragile per mezzi porosi: esempi di applicazione

Si presenta un approccio accoppiato per modellare il danneggiamento indotto da sollecitazioni idrauliche e meccaniche in ammassi rocciosi. Il danneggiamento del materiale è legato alla formazione a scala microstrutturale di diverse famiglie di fratture parallele, annidate una nell’altra, ciascuna caratterizzata da una propria orientazione e spaziatura. La semplicità della geometria delle fratture permette di esprimere analiticamente la variazione di porosità e di permeabilità causate dal progressivo danneggiamento del materiale. Si illustrano alcune simulazioni, sia a livello di punto di volume sia come problema al contorno, per mettere in evidenza i potenziali campi di applicazione del modello, tra i quali si individuano la stabilità di perforazioni in roccia e l’ottimizzazione di processi di fratturazione idraulica

A water retention model for compacted clays subjected to salinization and desalinization processes

Environmental actions are known to induce relevant effects on the fabric of compacted active clays, which are successfully described by adopting a double porosity framework. In particular, the role of aggregate deformation has been recognized as fundamental to interpret the water retention behavior and the transport properties. These aspects are particularly relevant in the context of clay liners, being the material cast in place in unsaturated conditions and subjected to wetting process by pore fluids characterized by a chemical composition that is different from the one of compaction. Experimental data evidence that the water retention properties of active clays evolve as a function of pore water chemistry, since for a given matric suction the mass of stored water changes with water salinity. In this paper, a double porosity water retention model is proposed, capable of reproducing the variation of matric suction with water content accounting for the salinity of pore fluid. The role of salinity changes is accounted for by a suitable evolution law for aggregate deformation, which in turn affects the inter-aggregate porosity and thus the storage properties of the material

Elasto – plastic modelling of the behaviour of non - active clays under chemo – mechanical actions

Environmental variables such as temperature, matric suction and pore fluid composition are well known to influence the hydro-mechanical behavior of clays and shales. The type and the relevance of this influence depends on the mineralogical composition and on the fabric of the material. Soil activity is an engineering proxy for mineralogical composition which can be used for a preliminary characterization of the expected type of behaviour under chemical actions, if those do not imply very significant cation exchange or pH variations. Very large chemo-mechanical effects occur in highly active soils used in engineering works such as barriers for nuclear waste or landfills, however concentration changes also impact on the mechanical behavior of non – active soils and rocks, such as illitic or natural blends of clays. Such materials are widely distributed in nature and their mechanical response upon chemical changes can be problematic in many cases. Examples of engineering relevance include vast slope instabilities promoted by fabric changes due to desalinization in Scandinavian quick clays, and instability or convergence issues for boreholes drilled in shales exposed to muds with a different chemical composition from the one of the pore fluid. An elastoplastic model is formulated to simulate the volumetric behaviour of such materials along chemical and mechanical loads. In addition to the parameters of the Modified Cam Clay, it requires defining the dependency of the elasto-plastic compliance and reference void ratio on pore fluid salinity. The model performs well against experiments from literature where complex chemo-mechanical histories were imposed

Modelling the role of pore water salinity on the water retention behaviour of compacted active clays

Compacted active clays are used as construction material for engineering barriers in many geotechnical and geo-environmental applications. Their very low permeability makes them particularly suitable as liners for the containment of both municipal and radioactive waste, since it allows very limited fluxes of contaminants. Experimental data show that the water retention behaviour of active clays is very dependent on pore water chemistry, since for a given matric suction the mass of stored water decreases with water salinity. This issue can have relevant effects on the performance of clay liners, considering that active clays are usually cast in place in unsaturated conditions and that the chemical composition of their pore water after compaction may be different from the one of the surrounding environment. In this paper, the effects of water content and water salinity on compacted clay fabric are firstly reviewed, through existing formulations which consider them separately. An enhancement of the existing formulations is then proposed, by merging both contributions. The model is finally validated against experimental water retention data from the literature, showing good prediction capabilities. In the case of the active clays considered, at given water ratios, the model predicts that the matric suction can vary between one and two orders of magnitude with salt concentration. As a counter fact, at a given matric suction and initial dry density, the model predicts that the water retained by samples inundated with distilled water is more than twice with respect to the water retained by samples saturated with a concentrated solution

Modelling the behaviour of unsaturated non-active clays in saline environment

Funding Information: The first author acknowledges the financial support provided by the Erasmus+ programme for her stay at Aalto University. Publisher Copyright: © 2021 The AuthorsThe chemical composition of pore fluid and matric suction rule the mechanical behaviour of soils. In case of clays, their fabric changes in line with those variables. Since both the increase in matric suction and salinity cause a transition from an open to a close microstructure of low and medium activity clayey materials, a unique framework could tackle problems where salinity and saturation changes are expected. This paper presents a simple elasto-plastic model capable of reproducing the behaviour of unsaturated clayey soils in saline environments. Changes in the pore fluid composition are addressed through the use of osmotic suction as a variable. The proposed model extends the Barcelona Basic Model for partially saturated soils to consider the effect of osmotic suction. The model, implemented in the Thebes code, is calibrated for Boom Clay. The reproduced tests include mechanical loading at different matric and osmotic suctions in oedometric conditions, as well as more complex chemo-mechanical stress paths. Despite the simplicity of the formulation, the agreement between the experimental results and the simulations is encouraging. It seems that the modelling approach addresses the most important features of partially saturated soils with saline pore fluid which are slightly or moderately expansive.Peer reviewe

The paradox of pulmonary arterial hypertension in Italy in the COVID-19 era: is risk of disease progression around the corner?

36noObjective The coronavirus disease-2019 (COVID-19) oubreak has led to significant restrictions on routine medical care. We conducted a multicenter nationwide survey of PAH patients aiming at determining the consequences of the Governance measures on PAH management and risk of poor outcome in patients with COVID-19. Meterials and Methods Demographic data, number of in-person visits, 6-min walk and echocardiographic tests, BNP/NT-proBNP tests, WHO functional class assessment, presence of elective and non-elective hospitalisation, need for treatment escalation/initiation, newly diagnosed PAH, incidence of COVID-19 and mortality rates were considered in the present study including 25 Italian centers. Data were collected, double checked and tracked by institutional records, between the 1st March and 1st May 2020 to coincide with the first peak of COVID-19 and compared with the same time-period in 2019. Results Among 1922 PAH patients the incidence of SARS- CoV-2 infection and COVID-19 was 1.0% and 0.46%, respectively, the latter comparable to the overall Italian population (0.34%), but associated with 100% mortality. Less systematic activities were converted into more effective remote interfacing between clinicians and PAH patients allowing lower rates of hospitalisation and related death compared with 2019 (1.2% and 0.3% versus 1.9% and 0.5%, respectively; p<0.001). High level of attention is needed to avoid the potential risk of disease progression related to less aggressive escalation of treatment and the reduction in new PAH diagnosis compared with 2019. Conclusion Cohesive partnership of health care providers with regional public health officials is needed to prioritise PAH patients for remote monitoring by dedicated tools.noneopenRoberto Badagliacca, Silvia Papa, Michele D'Alto, Stefano Ghio, Piergiuseppe Agostoni, Pietro Ameri, Paola Argiento, Natale Daniele Brunetti, Vito Casamassima, Gavino Casu, Nadia Cedrone, Marco Confalonieri, Marco Corda, Michele Correale, Carlo D'Agostino, Lucrezia De Michele, Giulia Famoso, Giuseppe Galgano, Alessandra Greco, Carlo Mario Lombardi, Giovanna Manzi, Rosalinda Madonna, Valentina Mercurio, Massimiliano Mulè, Giuseppe Paciocco, Antonella Romaniello, Emanuele Romeo, Laura Scelsi, Walter Serra, Davide Stolfo, Matteo Toma, Marco Vatrano, Patrizio Vitulo, Pietro Geri, Paola Confalonieri, Carmine Dario VizzaBadagliacca, Roberto; Papa, Silvia; D'Alto, Michele; Ghio, Stefano; Agostoni, Piergiuseppe; Ameri, Pietro; Argiento, Paola; Daniele Brunetti, Natale; Casamassima, Vito; Casu, Gavino; Cedrone, Nadia; Confalonieri, Marco; Corda, Marco; Correale, Michele; D'Agostino, Carlo; De Michele, Lucrezia; Famoso, Giulia; Galgano, Giuseppe; Greco, Alessandra; Mario Lombardi, Carlo; Manzi, Giovanna; Madonna, Rosalinda; Mercurio, Valentina; Mulè, Massimiliano; Paciocco, Giuseppe; Romaniello, Antonella; Romeo, Emanuele; Scelsi, Laura; Serra, Walter; Stolfo, Davide; Toma, Matteo; Vatrano, Marco; Vitulo, Patrizio; Geri, Pietro; Confalonieri, Paola; Dario Vizza, Carmin