48 research outputs found
Mechanisms beneath rectangular shallow foundations on sands: vertical loading
No full textThis paper details analysis of deformation behaviour of silica and carbonate sands under a rectangular foundation subject to uniaxial vertical load based on results from a series of centrifuge model tests. A multiscale Particle Image Velocimetry/Digital Image Correlation (PIV/DIC) technique was used to record and analyse the foundation tests with high resolution and measurement precision. Cone penetrometer and pressuremeter tests provide in situ soil characterisation of the tested sand sample in the centrifuge environment. The soil behaviour is analysed through foundation load-settlement response and the observed soil deformation measurements. Different soil deformation mechanisms and strain behaviours were observed in the different sands tested, and particle shape effect is considered, with data from scanning electron microscopy, to explain the differences. The results and analyses contribute towards better understanding of different soil behaviours under shallow foundations in different sands
Shallow penetrometer tests - theoretical and experimental modelling of penetration and dissipation stages
No full textShallow penetrometers are devices that penetrate into and measure the properties of surficial offshore sediments via multi-phase tests involving penetration, dissipation and rotation stages. In fine grained soils such as silts and clays, these testing stages yield undrained strength, consolidation and friction properties relevant to subsea pipeline and shallow foundation design. This paper describes toroid and hemiball devices of the scale for use in box core samples, and associated interpretation methods for the penetration and dissipation stages. The aim of the paper is to provide all tools needed to design and interpret these tests. New large deformation finite element (LDFE) dissipation solutions are presented, which can be used for back-analysis of the dissipation stage. Results of an extensive laboratory proof testing exercise in kaolin clay, for both the hemiball and toroid penetrometer, are also reported. These results highlight the potential of the two devices to quickly and economically assess strength and consolidation characteristics of fine-grained sediments in box-core samples recovered to the deck of a site investigation vessel
Beyond Pain Scales: A Critical Phenomenology of the Expression of Pain
No full textThis is the final version. Available on open access from Frontiers Media via the DOI in this recordData Availability Statement:
The original contributions presented in the study are included in the article/supplementary materials. Further inquiries can be directed to the corresponding author/s.In this paper, we discuss the qualitative dimension of painful experiences by exploring the role of imagination and metaphorical association in the conceptualization and expression of pain. We employ an engaged critical-phenomenological approach to offer original analysis influenced by the perspectives of people in pain. The paper is organized into three parts. Part 1 reviews literature on the expression of pain, its communication, and its reception—attending in particular to the emphasis on verbalizing pain in healthcare contexts. We here discuss benefits and limitations of standard methods aimed at facilitating the meaningful expression of pain (such as “pain scales”) from the perspectives of patients and practitioners, respectively. We suggest that these methods might be importantly complemented by facilitating creative expression of painful lived experiences with respect to personal lifeworlds. Part 2 deals with the role of imagination and metaphorical association in making sense of pain. We explore how imagination is a cognitive and affective mode of experiencing the world which plays a crucial role in determining how pain is experienced, as well as helping to make sense of pain figuratively in relation to the lifeworld. In Part 3, we draw from principles of engaged phenomenology to foreground case studies in which projects have been able facilitate the intersubjective expression of pain. These examples demonstrate the value of attending to the contours of painful lifeworlds in their specificity, affording both agency and accessibility in their communication, while remaining mindful of the complex power relations which govern perceived legitimacy and testimony relating to the transformation of pain. The overall paper aims to contribute to literature on qualitative pain research on both theoretical and practical levels. By exploring the expression of pain through phenomenology, we aim to enrich current debate on the qualitative experience of pain. We also seek to critically highlight the socio-political dimensions which frame painful experiences, their expression, their lived significance, and their treatment.Israel Science FoundationWellcome Trus
Vermiculate artefacts in image analysis of granular materials
No full textSome reported analyses of images of deforming granular materials have generated surprising vermiculate strain features which are difficult to reconcile with the mechanics of deformation of granular matter. Detailed investigation using synthetic images and improved processing of images of laboratory experiments indicates that such features can emerge as a consequence of the image acquisition (sensor, contrast, resolution), the subsequent image correlation implementation, and the user’s choice of processing parameters. The two principal factors are: (i) the texture and resolution of the images and (ii) the algorithm used to achieve sub-pixel displacement resolution. Analysis of the images using a sub-pixel interpolation algorithm that is more robust than that used originally eliminates the vermiculate features for images with moderate resolution and texture. However, erroneous features persist in images with low resolution and poor texture. Guidance is provided on ways in which such artefacts can be avoided through improved experimental and image analysis techniques
Linking the installation response of screw piles to soil strength and ultimate capacity
No full textA perceived advantage of screw-type foundations is the ability infer aspects of foundation performance from quantities measured or observed during installation, especially the installation torque. A particular concept widely used in practice is to correlate installation torque to ultimate capacity. This notion has proven useful as a field verification technique despite the absence of validated models that relate key variables of interest, such as installation torque, axial (crowd) force, geometrical parameters, and soil strength. This paper considers previous work by the co-authors and collaborators on analytical, numerical, and physical modelling of screw piles to relate the quantities measured or controlled during installation (e.g., installation torque) to the ultimate capacity and soil strength. Attention is given to saturated clay as a particular soil type amenable to simplified analysis. An analytical model for a single-helix pile is considered as a means of directly relating the ultimate capacity and undrained shear strength to the installation torque, crowd force, plate pitch, plate diameter, shaft diameter, installation depth, and surface roughness. The connection between the installation variables and ultimate capacity—and the sensitivity to crowd force in particular, a quantity that is typically not measured during field installations—is also discussed. The theoretical predictions are compared against data obtained from small-scale laboratory experiments that suggest the installation torque relates to the remolded strength of the soil
Improved image-based deformation measurement for geotechnical applications
No full textThis paper describes and benchmarks a new implementation of image-based deformation measurement for geotechnical applications. The updated approach combines a range of advances in image analysis algorithms and techniques best suited to geotechnical applications. Performance benchmarking of the new approach has used a series of artificial images subjected to prescribed spatially-varying displacement fields. An improvement by at least a factor of ten in measurement precision is achieved relative to the most commonly used particle image velocimetry (PIV) approach for all deformation modes, including rigid body displacements, rotations and strains (compressive and shear). Lastly, an example analysis of a centrifuge model test is used to demonstrate the capabilities of the new approach. The strain field generated by penetration of a flat footing and an entrapped sand plug into an underlying clay layer is computed and compared for both the current and updated algorithms. This analysis demonstrates that the enhanced measurement precision improves the clarity of the interpretation.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author
Multiple congenital melanocytic nevi and neurocutaneous melanosis are caused by postzygotic mutations in codon 61 of NRAS
No full textCongenital melanocytic nevi (CMN) can be associated with neurological abnormalities and an increased risk of melanoma. Mutations in NRAS, BRAF, and Tp53 have been described in individual CMN samples; however, their role in the pathogenesis of multiple CMN within the same subject and development of associated features has not been clear. We hypothesized that a single postzygotic mutation in NRAS could be responsible for multiple CMN in the same individual, as well as for melanocytic and nonmelanocytic central nervous system (CNS) lesions. From 15 patients, 55 samples with multiple CMN were sequenced after site-directed mutagenesis and enzymatic digestion of the wild-type allele. Oncogenic missense mutations in codon 61 of NRAS were found in affected neurological and cutaneous tissues of 12 out of 15 patients, but were absent from unaffected tissues and blood, consistent with NRAS mutation mosaicism. In 10 patients, the mutation was consistently c.181C>A, p.Q61K, and in 2 patients c.182A>G, p.Q61R. All 11 non-melanocytic and melanocytic CNS samples from 5 patients were mutation positive, despite NRAS rarely being reported as mutated in CNS tumors. Loss of heterozygosity was associated with the onset of melanoma in two cases, implying a multistep progression to malignancy. These results suggest that single postzygotic NRAS mutations are responsible for multiple CMN and associated neurological lesions in the majority of cases
Calibration of a model to predict the Peak Punch-Through Penetration Resistance of a Spudcan on Sand Overlying Clay
No full textThis paper demonstrates the use of a geotechnical drum centrifuge in the calibration of a model to predict the peak punch-through penetration (qpeak) resistance of a spudcan on sand overlying clay. A series of loose sand overlying clay tests was performed and combined with an existing database of tests performed on dense sand overlying clay. The performance of the failure stress dependent model proposed by Lee (2009) and Lee et al. (2009) has then been assessed using this combined dataset which encompasses a wider range of soil properties and problem geometries than was used in the original calibration of the model. The single empirical stress distribution factor (DF) that is employed in the model was then optimised using a back calculation procedure for all tests. The scatter of the optimised DF values was then compared for the original bi-linear calibration proposed by Lee et al. (2009) and a new nonlinear power law calibration. The new non-linear relationship enables the model to better predict qpeak over a wider range of problem geometries and for conditions of both loose and dense sands overlying clay. The work demonstrates the importance of the geotechnical centrifuge in calibrating such models given that at present numerical methods are unable to reliably capture such punch-through behaviour and good quality field data of punch-through failure of spudcan foundations is unavailabl
Analysis of Failure Mechanisms in Silica and Carbonate Sands Beneath a Strip Foundation Under Vertical Loading
No full textThis paper reports the deformation behavior of silica and carbonate sands under a strip foundation subjected to uniaxial vertical load. Small-scale physical modelling tests of a strip surface foundation under vertical load were conducted in a geotechnical centrifuge and Particle Image Velocimetry/Digital Image Correlation (PIV/DIC) was used to analyze images of an exposed plane of the model beneath the foundation to visualize the failure mechanisms. The observed mechanisms are interpreted in conjunction with load-settlement response and cone penetrometer resistance profiles. The failure mechanisms are illustrated through normalized vertical and horizontal displacement fields and shear and volumetric strain fields derived from the PIV analysis. Different soil deformation mechanisms and load-settlement responses were observed in the different sands. Soil resistance profiles measured using a miniature cone penetrometer do not correlate with the measured foundation bearing resistance and an interpretation of particle shape effect is introduced to explain the differing behaviors. The results presented improve understanding of the different responses in carbonate sands and silica sand beneath a shallow foundation under vertical load.</jats:p
