| المستخلص: |
This thesis investigates the effect of cyclic loading on the behaviour of granular materials used in railway platforms. Rate-dependency, non-associated flow and ratcheting are used within a constitutive model to simulate the granular materials.Cyclic loading has been introduced in the constitutive model by using logarithmic Chicago law.Return mapping is presented to predict a trial elastic stress. A consistency factor and a consistent modulus are calculated by using Newton’s method approach.A finite element model is developed to predict the response of a typical railway cross-section. The results prove that this method is reliable to simulate the behaviour of granular materials under the effect of cyclic loading. A parametric study is conducted to investigate the effect of granular materials behaviour under different conditions. The parameters varied in this thesis are: fluidity coefficient, mixing hardening parameter, Poisson’s ratio, and the internal friction and dilation angles.Those parameters reflect the physical characteristics of the material. The analysis shows that increasing the fluidity of the material that affects the rate-dependency of granular materials, produces anisotropic settlements. The combinedeffect of isotropic and kinematic behaviour is studied by varying the mixing parameter. The analysis shows how the selection of the mixing parameter governs the contribution of non-linear plastic behaviour as well as ratcheting. The results also reveal that Poisson’s ratio affects considerably the level of settlement in an inversely proportional manner. Finally, the study covers the effect of internal friction anglesand dilation angles. The analysis showsthat the higher the friction and dilation angles are, the larger the settlement observed. However the last result for the friction angles is contradictory to the expected behaviour. This is due to,the modelboundary condition as the volumetric deformation issmallafter the analysis reaches the plastic stage for a small number of cycles.
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