Fatin Altuhafi
Imperial College London, Materials, Post-Doc
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This research contributes to the debate on glacier dynamics, which have a significant effect on global climate change and sea-level changes. Glacier advances and retreats have great effects which can be viewed not only from their... more
This research contributes to the debate on glacier dynamics, which have a significant effect on global climate change and sea-level changes. Glacier advances and retreats have great effects which can be viewed not only from their influence upon human and habitats within their immediate locality but their much more pervasive influence on all global habitats due to the effect of modern ice masses on global climate and sea-level. One of the most fundamental characteristics of glaciers and ice sheets is their ability to move. In the early models adopted to simulate glacier flow, glaciers were thought to rest on clean bedrock. However, borehole studies in different glacial areas revealed the presence of a bed of deformable sediment underneath some glaciers. Although the old common model assumed that glacier movement is generated by sliding processes, recent research proved that a high percentage of glacier movement is attributed to the shearing process of the saturated bed sediment. In t...
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Research into the stress-strain behaviour of many stiff clays and weak rocks has demonstrated conclusively that it is highly nonlinear. Hence, to calculate ground movements it is necessary to define stiffness parameters at strains which... more
Research into the stress-strain behaviour of many stiff clays and weak rocks has demonstrated conclusively that it is highly nonlinear. Hence, to calculate ground movements it is necessary to define stiffness parameters at strains which correspond to the strains caused by the construction. In this paper the stiffness of five soils from various Greek construction sites was evaluated through improved equipment and test techniques. These included measurement of shear wave velocity and the use of local strain instrumentation. The latter comprised of miniature inclinometers and LVDTs. Tests were performed on natural (undisturbed) specimens trimmed from block samples. The specimens were isotropically and anisotropically consolidated and stiffness parameters were measured for each soil for a range of effective stress levels. Despite the wide variation of the deposits all soils contain less than 20% clay content and their Atterberg limits plot very close to the A line. The measured stiffnes...
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The large particle sizes of railway ballast and rock fill have meant that conventional techniques used to measure the small-strain stiffness of finer geomaterials have not been adopted, with the consequence that their stiffnesses are... more
The large particle sizes of railway ballast and rock fill have meant that conventional techniques used to measure the small-strain stiffness of finer geomaterials have not been adopted, with the consequence that their stiffnesses are poorly defined. In a series of tests on a UK railway ballast, simple adaptations were made to existing local strain measuring systems to account for the larger particle sizes. The study showed that the small-strain stiffnesses are different in second loading compared to virgin loading, but multiple cycles had little further effect on the stiffness. The large particle size was found rarely to have any detrimental effect on the quality of the strain measurements and the two independent measurements of axial strain taken at diametrically opposite locations were generally as consistent as for finer grained soils. As for other soils, the ‘external’ measurements of strain across the apparatus platens were of little use in determining stiffness. The presence o...
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Multi-axial compression of the mushy zone occurs in various pressurized casting processes. Here, we present a drained triaxial compression apparatus for semi-solid alloys that allow liquid to be drawn into or expelled from the sample in... more
Multi-axial compression of the mushy zone occurs in various pressurized casting processes. Here, we present a drained triaxial compression apparatus for semi-solid alloys that allow liquid to be drawn into or expelled from the sample in response to isotropic or triaxial compression. The rig is used to measure the pressure-dependent flow stress and volumetric response during isothermal triaxial compression of globular semi-solid Al-15 wt pct Cu at 70 to 85 vol pct solid. Analysis of the stress paths and the stress–volume data show that the combination of the solid fraction and mean effective pressure determines whether the material undergoes shear-induced dilation or contraction. The results are compared with the critical state soil mechanics (CSSM) framework and the similarities and differences in behavior between equiaxed semi-solid alloys and soils are discussed.
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ABSTRACT
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... Fatin Altuhafi a , E-mail The Corresponding Author and Béatrice A. Baudet b , low asterisk , E-mail The Corresponding Author. ... The dashed line showing a fractal dimension of 2.60 is shown here for comparison. View Within Article.... more
... Fatin Altuhafi a , E-mail The Corresponding Author and Béatrice A. Baudet b , low asterisk , E-mail The Corresponding Author. ... The dashed line showing a fractal dimension of 2.60 is shown here for comparison. View Within Article. 3.3. ...
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A series of isotropic compression tests and drained and undrained triaxial compression tests have been performed on glacial sediment from Iceland. Langjökull sediment, which is well graded, is thought to have reached a critical grading... more
A series of isotropic compression tests and drained and undrained triaxial compression tests have been performed on glacial sediment from Iceland. Langjökull sediment, which is well graded, is thought to have reached a critical grading during deposition and transportation. Multiple parallel normal compression lines (NCLs) were found, but a unique critical state line (CSL) could be identified. This is unlike other so-called “transitional” soils, whose grading varies between reasonably well graded to gap graded, which tend to have distinct NCLs and critical state lines depending on the specimen density. It is thought that in the case of the Langjökull sediment studied, its particular strain history that involved incessant shearing during deposition accounts for the difference in behaviour. This provides the interesting case of a soil that has been crushed to a critical grading in situ, which depends on the mineralogy of the grains, which was then sampled and tested. Despite the unique...