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Title: Numerical modelling of strain localization in dense sands
Author: Karstunen, M. K.
Awarding Body: University of Wales Swansea
Current Institution: Swansea University
Date of Award: 1998
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This study concentrates on modelling strain localization in dense sands. Strain localization is a phenomenon in which the nearly homogenous deformation of a body is abruptly changed into a highly concentrated deformation mode. Failures of slopes and embankments are examples of strain localization problems in geotechnical engineering practice. In finite element context, the onset of localization causes severe numerical problems: the governing rate equations change type and the problem becomes ill conditioned. To overcome this homogenisation technique has been adopted. At the onset of localization different constitutive models are adopted for the shear band and the surrounding material in proportion to their relative volumes, and the governing equations become regularised with a measure of internal length. More insight into the physical conditions causing localization has been attained by adopting the multilaminate framework. A plane strain approach enables the use of a large number of planes for the numerical integration of the constitutive model. To model the typical behaviour of dense sand, a deviatoric hardening model has been implemented. The mobilisation of shear strains on different planes is monitored, and a criterion for strain localization has been defined based on shear strain concentration. Numerical simulations have been performed at constitutive and finite element level. The results have been compared with test data on dense sand. At constitutive level, a very realistic presentation of the material behaviour can be attained. Parametric studies have been conducted to establish the sensitivity of the solution to changes in various material parameters. Two types of plane strain problems, a biaxial test and a passive wall test, have been analysed with finite elements. The homogenisation technique can overcome some of the numerical problems associated with localization, like severe mesh dependence and non-convergence. Similarly, features in biaxial tests such as the size effect can be realistically modelled.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available