1,720,993 research outputs found
A methodological approach to assess the hazard of underground cavities subjected to environmental weathering
No full textSoft highly porous carbonate rocks, such as calcarenites, and soluble sulphate rocks, such as gypsum, are very common in the Mediterranean region and, due to their microstructure and chemical composition, are prone to water induced weathering mechanisms. Cliffs, underground cavities and other morphological features in such formations are hence affected by intense erosion phenomena and weathering processes responsible for unexpected collapses and sinkholes. Just considering the Apulian region (Italy), 150 sinkholes have been recorded since 1925, with increasing frequency since 2000 (Fiore et al., 2018). The geosystem's failure is often the short- or long-term result of a very complex hydro-chemo-mechanical process taking place at the micro-scale which can be detected and analysed by means of field and laboratory experimental test campaigns. Therefore, stability problems are often related to changes of the mechanical properties of the rock forming the cave caused by environmental weathering processes, despite the external boundary conditions are not changing with time. The paper deals with the assessment of hazard associated with the stability of abandoned underground caves, which is nowadays frequently required for land and urban planning activities. A methodological approach for hazard assessment based on a step-by-step procedure is proposed. This includes in-situ surveys, laboratory experimental studies, theoretical analyses and finally numerical investigations. The approach derives from the experience developed from several case studies analysed by the authors. In this work, two of these are presented. The first one concerns the stability of an anthropic cavity in a calcarenite formation which is affected by a water induced short-term and long-term debonding processes. The second one regards the stability of a three-level abandoned gypsum mine, the lowest level being partially flooded by water. The methodological procedure aims to evaluate the factors controlling the change of the mechanical properties of the rock so that efficient remediation measures can be designed in order to avoid any further decay of the rock mass stability with time. The proposed methodological approach, validated on real case studies, shows the convenience of performing advanced experimental, theoretical and numerical studies to properly assess the hazard in space and time and to better design the mitigation measures if they are required. The adoption of the proposed approach reduced the remediation costs of the second case study of one order of magnitude
PFEM Modeling of Strain Localization Processes in Non-local Multiplicative Plasticity
No full textA fully non-linear PFEM platform developed for coupled flow and deformation processes in saturated structured soils is employed in this work to explore the possibility of modeling the occurrence of strain localization and the evolution of the displacement field in the post-localization regime without the pathological mesh-dependence typically observed in conventional non-linear FEM simulation. The proposed formulation adopts an isotropic hardening elastoplastic model for bonded geomaterials, developed in the framework of multiplicative plasticity, equipped with non-local hardening laws of the integral type for both density- and bonding-related internal variables. These hardening laws provide the material with an internal length scale based on the size of the neighborhood where the non-local averaging is performed. A number of PFEM simulations of plane strain compression tests on ideal calcarenite specimens have been performed to explore the convergence of the numerical solution in the post-localization regime as the element size is reduced. The convergence study is focused on simulations with non-uniform, adaptive discretizations, exploring the convergence of the solution as the adopted minimum element size of the mesh is reduced. The results of the convergence study demonstrate the effectiveness of the adopted non-local approach in eliminating the pathological mesh-dependence in presence of strain localization, in the context of h-adaptive PFEM simulations
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
Micromechanical investigation of grouting in soils
Full text linkGrouting and jet grouting are geotechnical consolidation techniques commonly employed to improve the mechanical behaviour of soils. Although these techniques are common, the micromechanical processes taking place at the local level are not yet totally understood and modelled. In this work, such a problem has been approached from a micromechanical perspective via the discrete element method by considering the local interaction among soil grains and pseudo-fluid particles. Homogeneous representative elementary volumes of a virtual analogue of silica sand have been first generated and tiny rigid frictionless particles have been subsequently injected through them, to simulate the grouting in granular materials. Various injection pressures, initial soil pressures and initial soil densities have been considered. The different diffusion patterns, the flow rate, the consequent increase in local stresses and the consequent reduction in local porosity have been discussed. To overcome the DEM computational restrictions and to speed up the injection simulations, a novel procedure based on the replication of pre-equilibrated cells has been adapted for both the initialization and injection phase. Finally, a qualitative laboratory-scale pressure grouting test has been reproduced to validate the results
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
Visual programming for the structural assessment of historic masonry structures
No full textThe objective of this work is to formulate a new methodology the assessment of masonry structures that is using a fully digital procedure to automatically build up a reliable structural model, limiting expensive destructive tests. Data arising from laser scanning surveys and digital photogrammetry techniques are employed to generate a detailed 3D model that can be automatically imported in a Finite Element (FE) software environment. This is used to perform a non-linear static analysis aiming at investigating on possible collapse modes of the structure. As the focus is not on the actual structural capacity of the structure, such results are not strongly dependent on material parameters employed, which are set based on engineering judgement only. This preliminary structural analysis is employed to generate a possible configuration of failure surfaces through the Control Surface Method (CSM), which is here proposed for the first time. These are associated to the 3D models and implemented into a visual coding which embeds an upper bound limit analysis of the problem assuming a no-tension material hypothesis. Based on such failure surfaces, Genetic Algorithms are used to generate other possible collapse mechanism and search for the actual failure mode corresponding to the minimum value of the loads multiplier. The work-flow is all integrated into a computational tool implemented in the visual programming environment offered by Grasshopper and Rhino3D. The procedure is validated by the analysis of one benchmark case, whose results are presented and discussed
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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