scholarly journals Magnetic fabric of sheared till: A strain indicator for evaluating the bed deformation model of glacier flow

2008 ◽  
Vol 113 (F2) ◽  
Author(s):  
Thomas S. Hooyer ◽  
Neal R. Iverson ◽  
France Lagroix ◽  
Jason F. Thomason
Keyword(s):  
Magnetic Fabric ◽  
Deformation Model ◽  
Bed Deformation ◽  
Glacier Flow ◽  
Strain Indicator

Anisotropy of magnetic susceptibility as strain indicator in a fold-and-thrust belt sandbox model above décollements with frictional contrast

2020 ◽  
Author(s):  
Thorben Schöfisch ◽  
Hemin Koyi ◽  
Bjarne Almqvist
Keyword(s):  
Magnetic Susceptibility ◽  
Complex Structure ◽  
Anisotropy Of Magnetic Susceptibility ◽  
Magnetic Fabric ◽  
Low Friction ◽  
Thrust Belts ◽  
Fold And Thrust Belt ◽  
Analogue Models ◽  
The Individual ◽  
Strain Indicator

<p>Magnetic fabric is used as strain indicator to provide further insights into different tectonic settings. Applying anisotropy of magnetic susceptibility (AMS) analysis on analogue models has shown to be a useful approach to understand details of deformation. Here we use this technique on shortened sandbox models to illustrate the relationship between rotation of grains and the influence of décollement friction in fold-and-thrust belts. Layers of sand were scraped to a thickness of 2.5 cm on top of high-friction sandpaper on one side and on low-friction fibreglass on the other side of the sandbox model. After shortening the model by 26%, samples were taken at the surface and at depth for measuring AMS. During shortening, above the high-friction décollement, a stack of imbricates was formed, which shows distinct clustering of the main principal magnetic susceptibility axes (k1 ≥ k2 ≥ k3) around the dip of the forethrusts. In contrast, AMS data above the low-friction décollement show a more heterogeneous AMS pattern due to complex structure development with box folds and fault bending. In general, the magnetic fabric can be differentiated between the initial model fabric in the foreland and a tectonic overprint within the hinterland. The AMS analysis show that strain increases with the development of structures towards the hinterland and additionally with depth, but differs between the two frictional décollements. At the transition zone between the two different frictional environments, a deflection zone developed where the trace of thrusts change trend causing additional rotation of sand grains within this zone perpendicular to main shortening direction, as reflected by the orientation of the k1 and k3 axes. Overall, the orientation of the AMS axes and shape of anisotropy depend on the structure geometry and movement, which are determined by the friction of the individual décollement beneath. Consequently, AMS in models indicates and describes the development of structures and reflects strain above different basal friction.</p>

Prediction of Overtopping Dike Failure: Sediment Transport and Dynamic Granular Bed Deformation Model

2019 ◽  
Vol 145 (6) ◽  
pp. 04019021 ◽  
Author(s):  
Francisco Nicolás Cantero-Chinchilla ◽  
Oscar Castro-Orgaz ◽  
Subhasish Dey
Keyword(s):  
Sediment Transport ◽  
Deformation Model ◽  
Granular Bed ◽  
Bed Deformation ◽  
Dike Failure

Two dimensional bed deformation model in turbulent streams

2019 ◽  
Vol 17 (2) ◽  
pp. 73-84
Author(s):  
Amin Gharehbaghi ◽  
Birol Kaya ◽  
Gökmen Tayfur
Keyword(s):  
Deformation Model ◽  
Two Dimensional ◽  
Bed Deformation

scholarly journals Diffusive mixing between shearing granular layers: constraints on bed deformation from till contacts

2000 ◽  
Vol 46 (155) ◽  
pp. 641-651 ◽  
Author(s):  
Thomas S. Hooyer ◽  
Neal R. Iverson
Keyword(s):  
Shear Strain ◽  
Deformation Model ◽  
Maximum Shear Strain ◽  
Bed Deformation ◽  
Mixing Coefficient ◽  
Minimum Value ◽  
Order Of Magnitude ◽  
Geologic Record ◽  
Granular Layers ◽  
Kinetic Gas Theory

AbstractShearing of subglacial till has been invoked widely as a mechanism of glacier motion and sediment transport, but standard indicators for determining shear strain from the geologic record are not adequate for estimating the very high strains required of the bed-deformation model. Here we describe a laboratory study of mixing between shearing granular layers that allows an upper limit to be placed on bed shear strain in the vicinity of till contacts. Owing to random vertical motions of particles induced by shearing, mixing can be modeled as a linearly diffusive process, and so can be characterized with a single mixing coefficient, D. Ring-shear experiments with equigranular beads and lithologically distinct tills provide the value of D, although in experiments with till D decreases systematically with strain to a minimum value of 0.0045 mm2. Kinetic gas theory provides an estimate of the dimensionless mixing coefficient which is within an order of magnitude of laboratory values. Knowing the minimum value of D, the distribution of index lithologies measured across till contacts in the geologic record can be used to estimate the maximum shear strain that has occurred across till contacts. Application of this technique to the contact between the Des Moines and Superior Lobe tills in east-central Minnesota, U.S.A., indicates that shear strain did not exceed 15 000 at the depth of the contact.

Improvement Of Curvilinear Diagrams Of Concrete Deformation

2019 ◽  
pp. 99-104
Keyword(s):  
Reinforced Concrete ◽  
Peak Load ◽  
Experimental Studies ◽  
Concrete Structures ◽  
Deformation Model ◽  
Reinforced Concrete Structures ◽  
Significant Difference ◽  
Deformation Diagrams

Problems when calculating reinforced concrete structures based on the concrete deformation under compression diagram, which is presented both in Russian and foreign regulatory documents on the design of concrete and reinforced concrete structures are considered. The correctness of their compliance for all classes of concrete remains very approximate, especially a significant difference occurs when using Euronorm due to the different shape and sizes of the samples. At present, there are no methodical recommendations for determining the ultimate relative deformations of concrete under axial compression and the construction of curvilinear deformation diagrams, which leads to limited experimental data and, as a result, does not make it possible to enter more detailed ultimate strain values into domestic standards. The results of experimental studies to determine the ultimate relative deformations of concrete under compression for different classes of concrete, which allowed to make analytical dependences for the evaluation of the ultimate relative deformations and description of curvilinear deformation diagrams, are presented. The article discusses various options for using the deformation model to assess the stress-strain state of the structure, it is concluded that it is necessary to use not only the finite values of the ultimate deformations, but also their intermediate values. This requires reliable diagrams "s–e” for all classes of concrete. The difficulties of measuring deformations in concrete subjected to peak load, corresponding to the prismatic strength, as well as main cracks that appeared under conditions of long-term step loading are highlighted. Variants of more accurate measurements are proposed. Development and implementation of the new standard GOST "Concretes. Methods for determination of complete diagrams" on the basis of the developed method for obtaining complete diagrams of concrete deformation under compression for the evaluation of ultimate deformability of concrete under compression are necessary.

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