1,721,149 research outputs found
The shaft capacity of small displacement piles in chalk
No full textMulti-pile foundation systems are used to support offshore infrastructure in areas of Northern Europe underlain by Chalk. During installation, the tip of the tubular open-ended ‘small displacement’ pile crushes and destructures the Chalk forming a ‘putty’ interface or ‘annulus’ around it. Pile resistance to uplift (i.e. shaft capacity) results from sliding friction between the pile shaft and this putty chalk annulus. The limited knowledge of the characteristics of this interface is associated with pile design guidelines that may be overconservative, which could result in unnecessary increases in economic costs for the offshore renewable energy industry.The present Thesis investigates the prospect of using soil mechanics to describe shaft friction in small displacement piles in Chalk as function of the critical state strength of the chalk putty that composes the annulus. To this end, oedometer and triaxial tests were conducted on low and medium density destructured White Chalk samples to determine the suitability of a critical state framework to characterise the mechanical behaviour of the material. Monotonic and cyclic simple shear tests were then used to simulate load transfer through the chalk-pile interface and examine the compatibility of interface performance with the prospective critical state framework. Thereafter, model piles of different geometries were installed in intact chalk cores and micro-focus X-ray computed tomography (XCT) was applied to measure the density of the chalk putty annulus. The piles were then tested in tension.Oedometer and triaxial results demonstrate that a unique one-dimensional normal compression line and a unique critical state line (CSL) exist for the tested materials, regardless of their origin and the varied preparation methods used. This ‘uniqueness’ is associated with comparable grain shapes and size distributions, and to grain breakage processes that resemble those reported for sands. Simple shear experiments show that interface failure states comply with the CSL, although strain localisation precludes the attainment of critical state strengths when shearing initiates in significantly dense of critical conditions. A CSL-based framework defining interface strength as a function of void ratio was produced and found to compare well with the small number of early-life shaft capacity measurements of piles available in the literature. Yet, this framework could not predict the shaft capacity of the model pile experiments, due to heavily dense of critical states at the end of installation. XCT further revealed that pile penetration processes in chalk and sand are generally comparable, and that design approaches based on the cone penetration test might successfully estimate early-life shaft capacity. Though pile set-up was found to possibly result from annulus consolidation, its prediction may need to rely on empiricism for the foreseeable future
Mechanical behaviour of low–medium density destructured White Chalk
No full textLow- and medium-density White Chalk often destructures during civil engineering works, forming a putty that exhibits problematic low strengths in the short term but may build-up strength with time. The underlying mechanisms that control the mechanical performance of the material are not well understood. This paper explores the prospect of developing a framework to characterise the behaviour of chalk putty. To this end, triaxial tests were carried out using low- and medium-density reconstituted chalks produced by different methods. Using void ratio against mean effective stress results, a unique critical state line (CSL) is proposed, regardless of parent rock origin or the crushing process used to generate the putty material. The CSL was also found to satisfactorily fit independent test data by various authors, even though each independent sample material may have had different ‘intrinsic’ CSLs. This was suggested to stem from the similar particle characteristics of the chalks used. An assessment of the ageing effect indicates increases in strength as a result of densification due to consolidation and secondary compression, however, the end-of-test state could still be described using the CSL
Laboratory Investigation of Shaft Friction in Displacement Piles Installed in Chalk
No full textThis dataset supports the thesis entitled 'The Shaft Capacity of Small Displacement Piles in Chalk' by Alvarez Borges and includes results from soil mechanics tests and computed tomography analysis.</span
Tomography data for interparticle contact detection analysis in spheroidal granular packings
No full textThis collection contains a series of synchrotron XCT scans on a hexagonal close-packed arrangement of soda-glass pellets. The field of view (FOV) diameter is 68.9 mm in diameter, approximately, and the nominal individual pellet diameter is 10 mm. The detector pixel size is 21 microns for all scans. The pellets were arranged in three horizontal lattices (layers). The middle and top lattices were separated by a layer of polyethylene film (cling film), while the bottom and middle layer were fully-contacting. Each file corresponds to a scan of either the bottom contacting or top non-contacting lattice pair. Thus, each filename includes a 'top' and 'bot' identifier. Acquisition parameters (number of projections, exposure time per projection, rotation range and sample position) were varied to achieve different image qualities and are included in 'README.txt'. All but scan A5 were local scans; scan A5 is a full-field scan acquired using the 'half-acquisition' method. Tomographic reconstruction was carried out using filtered back-projection in Savu. After reconstruction, a 3D median filter (kernel size = 2) and an anisotropic diffusion filter (diffusion threshold = 100; iterations = 2) were used to reduce noise. Data was acquired using Beamline I12-JEEP at Diamond Light Source (proposal NT26307-1). Please read README.txt Copyright 2021 Diamond Light Source Ltd. Licensed under the Apache License, Version 2.0.</span
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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