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Thermal Improvement of Normally Consolidated Clay
Full text linkConstruction on soft clay deposits poses challenges to geotechnical engineers due to low shear strength, high compressibility, and complex dynamic response. The main soil improvement technique used in practice requires the placement of a surcharge load in conjunction with vertical drains, which is time consuming, requires transporting significant amount of surcharge material, and can only be used in onshore applications. As an alternative, this study investigates the improvement of soft clays using in-situ heating with geothermal heat exchangers. Heating of soft clays leads to differential expansion of the pore water and soil solids, causing pressurization and drainage of the pore water resulting in permanent volumetric contraction. While the impact of temperature on soft soils has been widely investigated, a key missing piece of information is the effect of initial mean effective stress of the soft clay on thermal volume change and corresponding increase in undrained shear strength. To address this limitation, the overall objective of this study is to understand the effects of subjecting saturated normally consolidated clays with different initial mean effective stresses to drained heating. Innovative testing approaches include glass thermal triaxial tests which permits use of image analysis to track thermal volume changes, and a thermal triaxial cell with embedded bender elements to measure the shear wave velocity of clay specimens. The magnitude of thermal volumetric strain increased with increasing initial mean effective stress, which is a departure from expected trends in established constitutive models. A corresponding increase in undrained shear strength with both temperature and initial mean effective stress was observed. Further, an increase in the shear wave velocity was observed during heating and no significant change was observed during cooling, indicating permanent hardening of the clay.
Experimental results were useful in calibrating a new constitutive model for the thermal volume change of normally consolidated clays, which was implemented into numerical simulations of heat transfer and water flow around a vertical drain containing a geothermal heat exchanger. Overall, this study provides the technology behind an exciting new thermal soil improvement technique that can have positive long-term energy savings for civil infrastructure in soft soil regions
Computational Code for Optimization of Thermal Treatment of Fine Grained Soils as a Method of Expediting their Load Induced Consolidation
Full text linkConstruction in soft soils has been a challenging task for engineers due to the excessive time taken for dissipation of construction induced pore water pressure and the ensuing postconstruction settlement. Use of vertical drains has proven to be an effective and economical method for soft ground improvement and hence extensive research has been carried out to further improve its efficiency. Effect of temperature on radial consolidation is one aspect of such research among many others that have been pursued.
Elevated temperature certainly has a pronounced effect on the hydraulic conductivity due to the reduction it causes in the viscosity of water. Furthermore, temperature also generates excess pore water pressure due to the tendency for differential volumetric expansion between the soil grains and pore water. Thermally induced volumetric strains can have an effect on the magnitude of settlement as well. A numerical methodology based on the NavierStokes equations of flow and thermoelasto-plastic soil compressibility relationships was developed to model transient fluid flow in a clay under thermal treatment. Experimentally verified soil compressibility relationships coupling the loading and thermal effects obtained from literature were employed in this model. The transient temperature distribution within the consolidation soil was modeled using the Fourier’s equation of heat transfer.
The effect of temperature on consolidation of clay was investigated by a parametric study involving different maximum temperatures, surcharge loads and initial porosities of clay. It was concluded that the improvement in the magnitude and rate of settlement at elevated temperature is more significant at relatively smaller surcharges and low initial porosities. Since there is a possibility for thermally induced volumetric expansion even in normally consolidated clays, an optimum combination of surcharge and thermal treatment should be employed for given initial conditions of the soil, in order to achieve the maximum improvement in settlement. The developed numerical model will provide the framework to carry out further investigations and determine the viability of the practical implementation of coupled thermomechanical consolidation using prefabricated vertical drains
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
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
Impact of Drained Heating and Cooling on Undrained Shear Strength of Normally Consolidated Clay
No full textEffect of Drained Heating and Cooling on the Preconsolidation Stress of Saturated Normally Consolidated Clays
No full textSimulation of thermal drains using a new constitutive model for thermal volume change of normally consolidated clays
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Impact of Drained Heating and Cooling on Undrained Shear Strength of Normally Consolidated Clay
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