A simple non-associated flow model for sand |
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Authors: | G R McDowell |
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Affiliation: | (1) School of Civil Engineering, University of Nottingham, University Park, Nottingham NG7 2RD, UK e-mail: Glenn.McDowell@nottingham.ac.uk Tel: +44-(0)115-951-4603 Fax: +44-(0)115-951-3898 [6pt] $$Lecturer, University of Nottingham, UK, GB |
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Abstract: | This paper proposes a simple non-associated plasticity model for sand. The yield surface is taken to be a member of a recently
derived family of yield loci, requiring the specification of a single parameter in addition to the stress ratio at the peak
value of deviatoric stress on the yield surface in deviatoric:mean effective stress space. This simple equation, can easily
be fitted to given sand data. The flow rule also has a simple equation, such that the critical state is not at the top of
the yield locus in stress space. The equation of the flow rule requires the specification of the critical state dissipation
constant, plus one additional parameter. This permits realistic modelling of the undrained behaviour of sand in states looser
and denser than critical. The parameter controlling the flow rule can, for convenience, be taken to be equal to the parameter
governing the shape of the yield surface. However, since the two parameters are not required to be equal, the flow rule can
easily be adjusted to model more accurately the rate of change of direction of the plastic strain increment vector with changing
stress ratio around the yield surface. The model resembles more complex models based on the mathematical theory of envelopes,
but the equations of the yield loci and flow rules are much simpler. The contribution in this paper is therefore to provide
a model similar to those derived based on micro mechanical considerations, but which is more useful to geotechnical engineers,
in that the number of parameters is kept to a minimum, the constitutive equations are simple, and the flow rule can easily
be controlled. The model is easy to apply in geotechnical analysis, and would be easy to implement in a finite element program.
Received: 11 January 2002 |
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Keywords: | Non-associated flow Plasticity Sand Yield surface |
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