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Validation of geotechnical finite element analysis
Validation d'analyse par éléments finis pour la géotechnique
Brinkgreve R.B.J.
Delft University of Technology & Plaxis bv, Delft, The Netherlands
Engin E.
Plaxis bv, Delft, The Netherlands
ABSTRACT: The use of the Finite Element Method for geotechnical analysis and design has become quite popular. It is often the
younger generation of engineers who operate easy-to-use finite element programs and produce colourful results, whilst the responsible
senior engineers find it difficult to validate the outcome. The NAFEMS Geotechnical Committee has concluded that there is a need
for guidelines on validation of geotechnical finite element calculations. The first author is a member of this committee and the main
author of a reference document on validation of numerical modelling in geotechnical engineering. This paper contains the highlights
of the aforementioned document. After defining the term
Validation
, sources of discrepancies between a real project and its
corresponding finite element model are described. In addition, the paper presents various methods to validate geotechnical finite
element calculations. The paper ends with some conclusions and a list of references for further reading.
RÉSUMÉ : L'utilisation de la méthode des éléments finis pour l'analyse et la conception en géotechnique s'est généralisée. C'est
souvent la plus jeune génération d'ingénieurs qui utilise des programmes d'éléments finis et produit des résultats avec des figures
pleines de couleurs, quand les ingénieurs seniors trouvent difficile la validation de ces résultats. Le comité géotechnique NAFEMS a
conclu que des recommandations pour la validation des calculs géotechniques utilisant les éléments finis sont nécessaires. Le premier
auteur est un membre de ce comité et l'auteur principal d'un document de référence sur la validation des modélisations numériques en
géotechnique. Cet article contient les points principaux de ce document. Après la description du terme Validation, les sources de
divergence entre un projet concret et le modèle élément fini correspondant sont décrites. De plus, cet article présente des méthodes
variées pour valider des calculs éléments finis en géotechnique. L'article se termine par les conclusions et une liste de références pour
une lecture approfondie.
KEYWORDS: Finite element method (FEM), validation, verification, benchmark, numerical modelling, discrepancies.
1 INTRODUCTION
In the past decennia the Finite Element Method (FEM) has been
used increasingly for the analysis of geotechnical engineering
applications. Besides developments related to the method itself
the role of the FEM has evolved from a research tool into a
daily engineering tool. It has obtained a position next to
conventional design methods, and offers significant advantages
in complex situations. However, as with every other method, the
FEM also has its limitations. These limitations are not always
recognized by users of finite element software, which can lead
to unreliable designs.
Despite the development of easy-to-use finite element
programs, it is difficult to create a good model that enables a
realistic analysis of the physical processes involved in a real
project and that provides a realistic prediction of design
quantities (i.e. displacements, stresses, pore pressures, structural
forces, bearing capacity, safety factor, drainage capacity,
pumping capacity, etc.). This is particularly true for
geotechnical applications, because the highly non-linear and
heterogeneous character of the soil material is difficult to
capture in numerical models. When using the finite element
method, soil is modelled by means of a constitutive model
(stress-strain relationship) which is formulated in a continuum
framework. The choice of the constitutive model and the
corresponding set of model parameters are the most important
issues to consider when creating a finite element model for a
geotechnical project. It forms the main limitation in the
numerical modelling process, since the model (no matter how
complex) will always be a simplification of the real soil
behaviour. Hence, some features of soil behaviour will not be
captured by the model.
Considering the use of geotechnical finite element software,
it is often the younger generation of engineers who perform the
numerical modelling and produce colourful results; sometimes
without fully understanding the backgrounds and limitations of
the constitutive models and the numerical methods used in the
software. Supervisors, i.e. project managers or senior engineers,
often find it difficult to validate the outcome, especially when
these do not match with what they would expect based on their
experience. This leads to the conclusion that there is a need for
guidelines on validation of geotechnical finite element
calculations, which was the primary motivation for the
NAFEMS Geotechnical Committee to write a publication on
validation of finite element models for geotechnical engineering
applications. This paper summarizes the main issues addressed
in the NAFEMS publication.
The next chapter 2 starts with a definition of the term
Validation
and other related terms. Before elaborating various
methods of validating finite element models for geotechnical
applications in Chapter 4, an overview of possible discrepancies
between a real project and the corresponding finite element
model is presented in Chapter 3. The last chapter contains the
main conclusions of this paper.
2 WHAT IS VALIDATION?
Validation
is concerned with the accuracy at which a model
represents reality. In order to use the results from a model
reliably in the design process, a proper validation of the model
is required. Another term that is often used in relation to
validation is
Verification
. To give more insight in the meaning
