Soil Stiffness Parameters for Finite Element Simulation
Master thesis
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http://hdl.handle.net/11250/2614678Utgivelsesdato
2015Metadata
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Sammendrag
Numerical analyses are widely used in practical geotechnical engineering to assess the deformationbehaviour of deep excavations, in particular when the influence on existing infrastructure,such as buildings or adjacent tunnels, has to be evaluated. The key issue of numerical analysisis selecting a applicable constitutive model and determining the input parameters.Some commonly used constitutive models are studied, and the adaptabilities and limitationsof these models are also been analysed. It is found that the hardening soil model whichcan define the shear hardening, compression hardening and unloading-reloading characteristicsgives a very reasonable prediction in deformation analysis. But the models which can onlysimulate the shear hardening behaviour, such as Mohr- Coulomb model, are not suitable forthe deep excavation analysis. When the heave of the foundation after excavation of great interest,the hardening soil with small-strain gives a acceptable estimation, while the predictionfrom hardening soil has big errors. That may because the unloading-reloading modulus is notassociated with stress and strain level in hardening soil model, and can not define the nonlinearunloading-reloading characteristics.Then, the determination for parameters of hardening soil model, especially for stiffness parametersis discussed in detail. A selection scheme is proposed on the basis of empirical correlationsand back calculation for geotechnical engineering design with available soil data. Twocase study are performed to help determining the soil parameters. It is found that the initial estimationof soil parameters need to be calibrated for undrained simulation, while it can be useddirectly for the drained case in deep excavation.Finally, the foundation excavation of Shanghai Bank building has been analysed. Finite elementmethod software PLAXIS is employed to perform the numerical simulation. Three soilmodels are used in this study, and the soil parameters are determined by the selection schemeproposed before. The model results are compared with the on site measurements to prove thereasonableness of the parameters selecting scheme.