1,721,032 research outputs found
Advanced constitutive modelling for soft rocks
Full text linkThe investigation of the soft rocks macro-behaviour through both standard and dedicated laboratory tests has become more and more important and has triggered the interest towards the formulation of constitutive models specifically dedicated to them. However, in some cases, the analysis of the macro-structural features of a soft rock has been combined with the analysis of changes occurring at the micro-scale, highlighting many similarities between soft rocks and natural clays, and therefore, opening for the possibility to explore the applicability of constitutive models formulated for structured clays to the case of soft rocks.
In this research, two soft rocks have been taken into consideration, since they have been both studied at the micro- and macro-scale: a soft rock from Abu Dhabi and a soft rock extracted in Malta. Both rocks are characterised by bonding and cementation that progressively degrade with the applied load already at rather small strains. This indicates the necessity of adopting a constitutive model that accounts for at least two surfaces, i.e. a small elastic nucleus and a larger surface representing the locus of gross yield points. These features are common to many multi-surface constitutive models with mixed kinematic and isotropic hardening rules and destructuration, proposed mainly for natural clays rather than soft rocks. Constitutive models for soft rocks are often characterised by a single large surface representing the effect of structure, within which the behaviour is purely elastic.
The constitutive model chosen for simulating the behaviour of both soft rocks presented in this research is the RMW model, by Rouainia and Muir Wood (2000), whose features have been extended to account for an increased stiffness of the natural material and different amplification factors for the contribution of plastic volumetric and deviatoric strains to destructuration. It is necessary to distinguish between the model parameters that can be rigorously determined based on experimental results, and the ones that cannot be associated with a specific measurable quantity of the material behaviour, but that have a clear meaning in the model equations.
One of the purposes of this research is to provide a clear and comprehensive methodology for calibrating the model specific parameters, with a direct application to the case of soft rocks, but that could be easily extended to the case of other materials and, even more generally, other constitutive models. In addition, this research investigates the capabilities and limitations of a model commonly used to simulate the behaviour of natural clays, to capture the distinctive features of these soft rocks
The mechanical behaviour of a pyroclastic rock: Yield strength and "destructuration" effects
No full textA research programme on the mechanical behaviour of a homogenous volcanic tuff found in the centre of the city of Naples (Italy) was carried out at the University of Naples a few years ago. Isotropic and drained triaxial tests were performed in a very wide range of confining pressures (up to 60 MPa). After presenting the stress-strain curve pattern and the mean stress influence on the shear behaviour, the paper focuses on the definition of a strength criterion and of the yield surface for this material. Some tuff samples were subjected to isotropic compression tests up to a confining pressure approximately twice as high as the isotropic yield stress; they were subsequently unloaded and subjected to drained triaxial tests. Partial loosening of the interparticle bonds ("destructuration") was observed. The paper also compares the mechanical behaviour of intact and "destructured" samples, emphasising the effects of the structure on strength and yield
Thermal-expansion of Neapolitan Yellow Tuff
No full textIn saturated rocks and soils it is possible to define different coefficients of thermal expansion depending on the drainage conditions. This topic is first examined from the theoretical point of view with regard to an ideal isotropic thermo-elastic porous medium. Some special features of the behaviour of natural soils and rocks during thermal expansion tests are subsequently discussed. An experimental evaluation of some of these coefficients is presented in the second part of the paper. The material investigated is a pyroclastic rock, the so-called Neapolitan Yellow Tuff. Thermal expansion coefficient in drained conditions has been evaluated, when this material is saturated with water. The pore pressure increase induced by heating has been measured in undrained tests. The temperatures investigated range between room temperature up to 225 degrees. Different types of apparatus have been used and, when possible, a comparison between the results has been proposed. The results obtained in undrained thermal expansion tests are in agreement with theoretical predictions. This research is part of an on-going study of the complex phenomena known as Bradyseism, which is occurring in a volcanic area a few kilometers from Naples (Italy). Some considerations on this phenomenon are drawn in the last paragraph of the paper
Comportamento meccanico di una pozzolana parzialmente satura: messa a punto delle apparecchiature di laboratorio e primi risultati sperimentali
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L'attività del TC19 - Preservation of monuments and historic sites - della International Society of Soil Mechanics and Geotechnical Engineering
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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
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