1,720,958 research outputs found
Multi-physical modeling of climate-driven elasto-plastic deformation, stress redistribution, and water potential in desiccation-cracked soils of arid regions
No full textpeer reviewedThis study presents a multi-physical modeling approach to analyze the dynamics of moisture potential and stress-deformation features near deep desiccation cracks in clayey soils under three consecutive years’ climate variability in an arid region. A triple research approach of statistical analysis, analytical framework, and numerical modeling was used to investigate the complex thermo-hydro-mechanical behavior of desiccation-cracked soil, incorporating realistic climatic data of Qom, Iran. The results revealed the interplay between stress, strain, and pore water pressure over time, demonstrating that soil experiences significant swelling and shrinkage due to cyclic wetting and drying. The horizontal stress distribution shows compressive stress concentration at crack tips during wetting, transitioning to tensile stresses uniformly across the soil surface during drying paths. Similarly, vertical stress distributions exhibit localized compressive stresses along crack boundaries during wetting and tensile stresses during drying, highlighting the critical stress conditions at crack tips. The model differentiates between microstructural and macrostructural changes in porosity. Annual trends in micro-porosity revealed cyclic-dependent behavior, with significant volumetric changes occurring in the first year, stabilizing with successive cycles. The results also indicated that part of the volumetric changes are irreversible, with volumetric plastic strain increasing exponentially but at a decreasing rate over three years. Principal stress analysis indicates a shift from compressive to tensile stress states around cracks, driven by climate-induced wetting and drying cycles. These findings underscore the critical role of climate variability in shaping cracked soil behavior in arid regions, providing insights into the heterogeneous behavior of cracked soil surficial layers
3D DEM-based analysis of cylindrical rock specimen failure and micro-fracturing: impact of stiffness and tensile strength
Get PDFpeer reviewedRock failure triggering with micro-fracturing poses significant challenges in engineering practices. In this study, the failure mechanism of the rock specimens was investigated focusing on the impact of stiffness and tensile strength on rock fracturing. To achieve this, uniaxial compression tests were simulated using the discrete element method for three rock types including granite, sandstone, and limestone. To enable elastic interactions at particle contacts for diverse rock material responses under stress, a linear parallel bond model was utilized. This model allows for elastic interactions while permitting slip, effectively simulating the complex behavior of rock materials under stress. The results revealed distinct mechanical behaviors among the three rock types, with granite exhibiting the highest peak stress and a steep stress–strain curve, indicative of its superior compressive strength. In contrast, sandstone shows lower peak stress and earlier failure due to its higher porosity and lower cohesion, while limestone demonstrates significant plastic deformation before failure, resulting in a more ductile response. Increased stiffness correlates with higher final strain values across all rock types, with limestone showing the greatest sensitivity to stiffness changes. The study demonstrates that increased tensile strength leads to higher peak stress and strain values, significantly delaying failure mechanisms, with a threefold increase in tensile strength resulting in a 1.47-fold increase in final stress for granite and a 2.46-fold increase for limestone. The analysis of crack development indicates that both stiffness and tensile strength substantially influence crack formation and distribution, particularly in sandstone
Coupled multi-physics modeling of spatio-temporal behavior of embankment subjected to freeze-thaw cycles considering layered construction phases
No full textpeer reviewedClimate change and the increasing frequency of extreme climatic conditions have profound implications for geostructures, significantly altering their stability, durability, and long-term performance. Therefore, this study is focused on a fully coupled multi-physics modeling of a layered embankment subjected to freeze-thaw (FT) cycles. The model incorporates a thermo-elasto-plastic constitutive framework to effectively capture the irreversible deformations of the embankment, leading to its progressive failure. The embankment was modeled to investigate deformation, pore water pressure dynamics, and pore structure evolution during construction and FT cycles. The results reveal critical mechanisms governing the long-term performance of earth structures in cold regions. Notably, heterogeneous deformation patterns, stress redistribution, and localized accumulation of ice pressure lead to progressive instability risks. During FT cycles, frost heave and thaw settlement resulted in the greatest vertical deformation occurring at the crest edge and the center of the slope. Subsurface layers exhibited delayed responses with reduced magnitudes, driven by indirect thermal effects and stress redistribution due to the expansion in the freezing front. Pore water pressure dynamics demonstrated spatial variability, with pronounced fluctuations in upper layers and significant negative pressures in subsurface layers due to water migration and dissipation. The findings further highlight that hysteresis in permeability-ice saturation loops indicated irreversible structural changes, posing long-term stability risks. In particular, the permeability in the centre of the slope was found to increase by more than 1.5 times during successive FT cycles. These findings contribute to the broader understanding of climate-resilient geotechnical infrastructure design and maintenance strategies in seasonally frozen regions
Thermo-hydro-mechanical modeling of stress redistribution around deep desiccation-induced cracks in arid and semi-arid regions
No full textpeer reviewedSoil cracking primarily results from the development of tensile stresses among soil particles, caused by the shrinkage of surface soil layers during desiccation. Climate change and global warming intensify cracking in soils with high plasticity, potentially leading to irreversible damage to infrastructure and both surface and subsurface structures. Additionally, soil cracking exacerbates desiccation in the unsaturated zone, contributing to land subsidence, a major global and national issue in Iran. During the desiccation process, the stress state in cracked soils constantly changes, altering stress distribution among particles. Therefore, understanding stress redistribution in the unsaturated zone is essential as a fundamental mechanism in desiccation-induced soil cracking. In this study, thermo-hydro-mechanical modeling was employed to simulate the impact of climate changes in Qom city on a cracked soil, to investigate the transition of stresses from compressive to tensile near the cracks. Governing equations for the problem, including water and gas flow in the soil, energy transfer, and soil-atmosphere interaction, were defined in the numerical model. The results indicated that the initial compressive stress distribution in cracked soil was heterogeneous, with different stress patterns at the ground surface and crack tips. As desiccation progressed, tensile stresses emerged at the surface, crack walls, and tips, potentially leading to the propagation of existing cracks in both width and depth, as well as the initiation of new surface cracks
Thermo-hydro-mechanical modelling of the heterogeneous subsidence and swelling in the desiccation cracked clayey strata
No full textpeer reviewedSoil desiccation cracking as a consequence of severe environmental changes alters soil deformation mechanisms significantly. Therefore, this study aims to explore the effect of crack characteristics and environmental conditions on the heterogeneous deformation of desiccation-cracked soils using thermo-hydro-mechanical analyses. The model framework consists of balance equations, thermal, hydraulic, and mechanical constitutive equations, while the model scenarios were determined based on statistical analyses. The meteorological record of Qom city was used for three years, from 2015 to 2017, to capture long-term behaviour under wetting-drying cycles. Findings revealed that cracks extend the deformation range, potentially up to six times, with variation based on crack dimensions and spacing. Notably, narrower cracks experienced more pronounced deformation than wider ones. The cracked soil with a crack depth of 2.5 m showed 1.5 times higher swelling and subsidence than crack depth of 1 m. Furthermore, the wider cracks indicated a lower rate of increase in their dimensions compared to the initial state during drying. The investigation also highlights the mechanisms of soil surface shape due to swelling and shrinkage, resulting in concave and convex surfaces, respectively. The results provide new perspectives on the behaviour of fine-grained deposits in arid to semi-arid climates with deep groundwater levels
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe 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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