Thesis

Development and implementation of advanced soft soil models in finite elements

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Awarding institution
  • University of Strathclyde
Date of award
  • 2012
Thesis identifier
  • T13093
Qualification Level
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Department, School or Faculty
Abstract
  • Numerical algorithms to implement an advanced nonlinear constitutive model, S-CLAY1S, for natural soft clay into PLAXIS are studied in order to reduce the numerical instability. Simulations performed using several triaxial tests and a benchmark test indicate that the use of an automatic substepping modied Newton-Raphson (MNR) algorithm can eliminate or minimize the problem. Therefore, this algorithm is adopted to implement S-CLAY1S into PLAXIS as a user dened soil model. The modified S-CLAY1S model was proposed by incorporating Lode angle dependency failure criterion. This has improved the model predictions in failure condition especially in extension. A hybrid implicit numerical algorithm for the Sekiguchi-Ohta (SO) in-viscid/viscid models capable of robustly overcoming the vertex singu-larity is presented. The proposed hybrid algorithm consists of modified Newton-Raphson algorithm and Stolle's algorithm, used to implement the SO models into PLAXIS. Numerical simulations and benchmark test demonstrate the algorithm's accuracy and numerical stability even for large strains. The main part of this thesis is the development and implementation into FE code of a new constitutive model to represent the cyclic behaviour of natural soft clays. The S-CLAY1S model has been extended to the bubble surface plasticity in which smooth transitions between elastic and plastic behaviour can be modelled. The model developed in this research is named 'B-SCLAY1S' and requires thirteen parameters. Numerical examples show that the implementation into PLAXIS of the present model is successful. Finally, applications of the B-SCLAY1S model are made in two levels. First, simulations and comparison with laboratory tests including kaolin, Swiss lacustrine clay and Bothkennar clay test data. Second, the nite element benchmark analysis of an embankment and a pile driving problem subjected to cyclic loading were presented. At both levels the B-SCLAY1S is shown to be superior to the S-CLAY1S models, mainly because it captures the small strain behaviour.
Advisor / supervisor
  • Karstunen, Minna
  • Kenny, Michael
Resource Type
Note
  • THIS THESIS WAS PREVIOUSLY HELD UNDER MORATORIUM FROM 24TH JULY 2012 UNTIL 24th JULY 2016.
DOI
Date Created
  • 2012
Former identifier
  • 999437293402996

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