1,721,045 research outputs found
Progettazione e costruzione di un sito di caratterizzazione geologico-tecnica per un deposito di scorie nucleari in Finlandia
No full textThe problem of the nuclear waste is continuously rising, due to the increase of energy request. Their management requires accurate procedures, because of the radioactivity potentially harmful for the environment and the human health. Its dangerousness decreases during a long interval, and the best repository is represented by the subsoil, isolating the waste in canisters confined in the rock mass. ONKALO represents a facility for the geological and geotechnical characterization in order to define the characteristics of the rock mass of the future site for the Finnish nuclear waste. Moreover, during the construction of this facility, the possibility of using effectively the prescriptions requested for the realization of the final site is investigate
Mechanical behaviour of conditioned material for EPBS tunnelling
Get PDFThe rapid growth of the development of the cities all over the World, brought the necessity of bringing deeper the services and all the activities which are not strictly necessary above the ground like houses. This sudden demand of new tunnels obliged to push the excavation industry towards mechanized methods which allow to avoid settlements on the surface, where other structures and infrastructures are located. In this context EPB shield machines play a crucial role, as with a good control of this technology, a tunnel can be excavated basically everywhere, also below important structures. This implies the perfect knowledge of the geology but especially requires a precise study of the soil conditioning, in order to allow an effective counterpressure to the front. The development of preliminary laboratory tests, which means before the tunnel project starts, allows to assess the best conditioning set for each lithotype which can be encountered during the excavation. These tests are performed at room pressure, nevertheless recently the main goal is to study the conditioned mass at pressure conditions which can be found in an excavating chamber, which might influence the state of the mass itself. The aim of this work is the development of new techniques which can exactly reproduce this state, through the use and modification of techniques proper of the geotechnical engineering (shear and triaxial tests) and the design of new devices able to underline these aspects in detail. The new approach includes, as well as the consideration of a certain pressure condition, also the definition of an undrained condition used for testing, which allows to keep the conditioned mass in its original state for its stud
Functional and structural MRI signature of the induced migraine attack
Get PDFMagnetic resonance imaging (MRI) studies have consistently shown a distributed pattern of static and dynamic functional brain alterations in migraine patients. Up to now, it is elusive whether these alterations may represent a migraine-specific or phase-specific modification occurring along the migraine cyclical experience.
This study aims to assess the functional and microstructural alteration of the grey matter which characterizes the brain of people living with migraine compared with a matched group of healthy subjects, particularly during the activation derived from an attack induced by nitroglycerin (NTG) administration.
Ten subjects suffering from episodic migraine without aura (EM, 5 female, 28,9 years old, 4.4 migraine days per month) underwent 3T MRI examinations consisting of four task-free functional MRI (fMRI) and T13D scan repetitions during subsequent phases of a nitroglycerin-induced migraine attack (baseline, prodrome, full-blown attack, recovery). Ten healthy subjects (HS, 4 female, 26.9 yo) were enrolled for reference as control and underwent the same pharmacological protocol. A non-parametric permutation test was run to detect significant functional connectivity (FC) changes between EM and HS subjects in the different attack phases. Secondly, a seed-based correlation analysis (SCA) and a wavelet component analysis (WCA) were performed to focus the attention on the static and dynamic altered relationship between the thalamus and the rest of the brain, during the different phases of the migraine attack. Moreover, 3D-T1 images were processed to obtain subject-specific GM density (GMd) maps. A non-parametric permutation test was run to detect significant GMd differences in EM compared to HS during the attack phases. Finally, fMRI data were tested for correlations with the clinical variables collected.
At baseline, EM subjects showed a significantly altered FC within the posterior cerebellum, frontal/prefrontal cortex, and cingulate cortex. The thalamus, instead, expressed its pivotal role from the prodromal phase, exhibiting an altered coupling with the brainstem, the cingulate cortex, and the cerebellum's posterior part over the migraine cycle. Moreover, WCA proved a loss of synchronisation between the thalami and the salience network, observed mainly during the prodrome and full-blown phases. These findings further support the idea that a temporal change in thalamic function occurs over the experimentally induced phases of NTG-induced headache in migraine patients.
From a structural point of view, EM subjects showed significantly reduced GMd in the insula, inferior parietal lobe, and superior and middle temporal gyrus, compared to healthy subjects. An increased density was instead observed in the cingulate cortex, middle frontal gyrus and the limbic system, but it did not significantly change during the different phases of the attack.
Migraine-like pain induction caused a profound alteration of the FC, which persisted over recovery. The results point to the involvement of the cerebellum - a multiple effector system integrator and a ruler of pain perception modulation – and the frontal/prefrontal cortex. The changes observed in these areas may also explain the cognitive impairment associated with the migraine ictal phase. Finally, the microstructural modification here discussed suggests that migraine is associated with significant GM volume loss in key areas for pain processing, possibly reflecting alterations in the local dendritic complexity caused by the disease.Magnetic resonance imaging (MRI) studies have consistently shown a distributed pattern of static and dynamic functional brain alterations in migraine patients. Up to now, it is elusive whether these alterations may represent a migraine-specific or phase-specific modification occurring along the migraine cyclical experience.
This study aims to assess the functional and microstructural alteration of the grey matter which characterize the brain of people living with migraine compared with a matched group of healthy subjects, particularly during the activation derived from an induced attack by nitroglycerin (NTG) administration.
Ten subjects suffering from episodic migraine without aura (EM, 5 female, 28,9 yo, 4,4 migraine days per month) underwent 3T MRI examinations consisting of four task-free functional MRI (fMRI) and T13D scan repetitions during the subsequent phases of a nitroglycerin-induced migraine attack (baseline, prodrome, full-blown attack, recovery). Ten healthy subjects (HS, 4 female, 26.9 yo) were enrolled for reference as control and underwent the same pharmacological protocol. A non-parametric permutation test was run to detect significant functional connectivity (FC) changes between EM and HS subjects in the different attack phases. Secondly, a seed-based analysis (SCA) and a wavelet component analysis (WCA) were performed to focus the attention on the static and dynamic altered relationship between the thalamus and the rest of the brain, over the migraine experience. Moreover, 3D-T1 images were processed to obtain subject-specific GM density (GMd) maps. A non-parametric permutation test was run to detect significant GMd differences in EM compared to HS during the attack phases. Finally, fMRI data were tested for correlations with the clinical variables collected.
At baseline, EM subjects showed a constitutively significantly altered FC within the posterior cerebellum, frontal/prefrontal cortex and cingulate cortex. The thalamus instead, express its pivotal role since the prodromal phase, exhibiting an altered coupling with the brainstem, the cingulate cortex and the posterior part of the cerebellum over the course of the migraine cycle. WCA showed instead a loss of synchronisation between the thalami and the salience network, mainly occurring during the prodrome and full-blown phases. These findings further support the idea that a temporal change in thalamic function occurs over the experimentally induced phases of NTG-induced headache in migraine patients.
From a structural point of view, EM subjects showed significantly reduced GMd in the insula, inferior parietal lobe, and superior and middle temporal gyrus, compared to healthy subjects. An increased density is instead observed in the cingulate cortex, middle frontal gyrus and the limbic system, but it does not significantly vary along the migraine attack experience.
The findings observed suggest a baseline alteration in descending modulation pain processing in migraine. Migraine-like pain induction caused a profound alteration of the FC, which persisted over recovery. The results also point to the involvement of the cerebellum - a multiple effector system integrator and a ruler of pain perception modulation – and the frontal/prefrontal cortex. These involvements are not only correlated with pain intensity and migraine frequency but are also suggestive of the cognitive impairment associated with the migraine ictal phase. Finally, the microstructural modification here discussed suggests that migraine is associated with significant GM volume loss in key areas for pain processing, possibly reflecting alterations in the local dendritic complexity caused by the disease
Uso delle gallerie per la stabilizzione di versanti in frana
Get PDFL'uso del sottosuolo per la gestione idrogeologica del territorio e per la bonifica delle frane è una so-luzione efficace ed ampiamente utilizzata nel mondo. Nel lavoro dopo un inquadramento generale dell'argomento vengono illustrati alcuni casi studio di particolare interesse
Extensive sensitivity analysis of the Kivenlahti metro center using DEM
Get PDFThe Kivenlahti metro center is a combined residential and commercial building complex designed on top of a metro station in Espoo, Finland. Rock mechanical modelling was carried out using 3DEC to ensure the integrity of the metro station. A detailed sensitivity analysis was conducted consisting of simulating the effects of reduced horizontal in-situ stress, increased loading and weaker rock mass. Whilst the base case scenario confirmed that the proposed design should not lead to critical deformations within the metro station, the results of the sensitivity analysis indicated vulnerable locations if the loading is increased from the current design. An in-situ stress significantly lower than expected could lead to critical deformations within the metro station. Whilst the sensitivity analysis was conducted using extreme values, it successfully demonstrated areas for concern and thus aided in designing measures for mitigating the risks for the metro statio
Industrial Explosives and their Applications for Rock Excavation
No full textIndustrial Explosives and their Applications for Rock Excavation focuses on applications of industrial explosives in civil and mining engineering works. Explosives and their actions are explained in terms of basics, principles, and related chemistry. Explosives and initiation devices are described, including their characteristics, geometry, and timing aspects of the blast design. Designing blasts for rock excavation works is explained, including devices for obtaining large-sized blocks, construction of yards, and excavation of big foundations. Finally, criteria for the mitigation of the associated seismic disturbances are summarized.
The book:
provides an updated vision of industrial explosives, including the best technical advice for rock excavation;
contains harmonized preliminary modules aimed at introducing basic concepts of chemistry and physics applied to the drilling and blasting technique;
defines balanced mix of theory capable of providing skills to design an efficient blasting;
covers excavation problems from different points of view and in different contexts; and
addresses issues of drilling and loading blast-holes.
Industrial Explosives and their Applications for Rock Excavation is aimed at graduate students, researchers, and professionals in mining engineering and explosives technology
Comparison of Mud Pressures Predicted with Different Constitutive Models in Anisotropic Shale Rocks
No full textDepleted oil and gas fields are good targets for gas storage both in offshore and onshore environments. Carbon capture and sequestration (CCS) must repurpose existing rigs to drill new wells cost-effectively. The integrity of the well is crucial for successful carbon dioxide sequestration. During the drilling phase, well integrity involves preventing not uniform wellbore wall geometry induced by local rock failures and ensuring that cave-ins and washouts do not occur. The post-drilling experience in depleted fields can undoubtedly help selecting mud pressures to avoid instability when drilling new wells. The cap of most depleted fields is composed of shale rock that often exhibits variation in strength properties along and across the lamination planes and has been responsible for the major source of instability [Carey & Torsæter, 2019; Mehrabian et al., 2019]. The mechanical properties of shale at significant depths are hard to ascertain [Steiger & Leung, 1992]. Although laboratory tests provide accurate assessments, retrieving cores from deep wells is challenging due to potential alterations during retrieval and specimen preparation. Shale cores can undergo changes in pressure, temperature, and oxidation state as they are brought to the surface, which can affect their properties [Basu et al., 2020]. Cores retrieved from wells may be limited and damaged, making it difficult to obtain reliable mechanical property data directly from them [Josh et al., 2012]. Alternatively, mechanical properties can be obtained from laboratory tests conducted on outcropping formations similar to those found in the subsurface [Risnes, 2001]. Mechanical properties at depth are often inferred indirectly using correlations with log data and microscopic models [Abousleiman et al., 2007, Woehrl et al., 2010]. These correlations are empirical equations used to establish continuous profiles of elastic constants and strength parameters (Mandal et al. 2021]. Empirical relationships derived from log data are typically valid within specific geological settings, reflecting the conditions of the region where they were established. Additionally, the transverse isotropy of shale, a common characteristic in many formations, is often not specifically addressed in indirect approaches. This can lead to challenges in accurately characterizing the mechanical behavior of shale formations, particularly in situations where transverse isotropy significantly influences rock behavior. The low permeability of saturated shale rock indeed has implications for wellbore stability, especially immediately after drilling. When drilling through shale formations, the drilling process can disturb the equilibrium of pore fluid pressure within the rock, leading to undrained conditions in the short term. The undrained pore fluid pressure evolution can enhance plasticity around the wellbore [Asaka & Holt 2021; Vales et al. 2004; Aoki et al., 1993; Holt et al. 2014; Detournay & Atkinson, 2000; Deangeli & Marchelli, 2022; Tran et al., 2022].
All the previous considerations evidenced the difficulty and uncertainties related to the prediction of mud pressures in wellbore drilled in transversely isotropic shales. To reduce uncertainties on mud pressure prediction, there is the need of properly investigate the mechanical response of anisotropic shales during drilling operations.
By integrating multiple models, engineers can gain a deeper understanding of the complex interactions between different factors influencing shale behavior. This enables them to anticipate potential challenges and hazards during drilling and wellbore operations, leading to more proactive risk mitigation strategies
Application of a Finite-Discrete Element Method Code for Modelling Rock Spalling in Tunnels: The Case of the Lyon-Turin Base Tunnel
Get PDFBrittle failure, or spalling, occurs around openings excavated in hard rock masses with high in situ stresses. It takes place due to the nucleation and growth of cracks around the excavation boundary, induced by the redistribution of stresses following the excavation. Modelling this failure process is a tough challenge. The hybrid finite-discrete element method (FDEM) can overcome the boundary between continuum and discontinuum, capturing emergent discontinuities associated with brittle fracturing processes. In this study, FDEM is applied using a commercial code to show its applicability to model brittle behaviour around deep underground excavations in the case of the Torino-Lyon Base tunnel in three different stress conditions. Except for the hydrostatic condition, cracking is triggered immediately after the excavation. Spalling occurring around the tunnel is quite extended; therefore, an accurately designed support must be installed to prevent blocks from falling from the tunnel boundary. The obtained results are aligned with previous results existing in the literature. However, in this case, a deeper spalling is caused by the shape change due to the gradual stress redistribution. Such a phenomenon underlines the importance of using a code able to identify crack propagation, opening, and the formation of loose blocks that progressively modify the tunnel contour
Effect of soil conditioning on tool wear in soft ground tunnelling using shield machines تاثير فرآيري خاک ت سًظ آب ي ف مً برريي ميسان سایش ابسارحفاري با ماشيى اُي
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