Numerical Modeling: An Efficient Tool for Analyzing the Behavior of Constructions - Multiscale Geomechanics: From Soil to Engineering Projects - page 244

248 Multiscale Geomechanics

now is quite considerable. This experience is manifold, from determining the model
parameters for sands [DAG 08, ELM 03, HUJ 85, KOR 95, LOP 03a, LOP 03b]; and
clays: [HAJ 84, LOP 03a, LAL 95, MIC 94] to its numerical integration or stability
conditions [HAM 06, HAM 08a, VOS 01] and [HAM 08b]. Moreover, the model has
been extended to unsaturated soils ([ABO 95, MOD 96]) and nonisothermal loading
[LAL 95, MOD 97, MOD 95]. The surface version [AUB 90] is possible to use for
modeling surfaces of kinematical discontinuity within a soil mass [LOP 03a] or rock
[MOD 89a] or between two different materials (soil-pile [DAG 08]).

Hence, the GEFDyn software has been used and validated for various applications,
and it is undoubtedly one of the most complete pieces of software in its field of
application. Since policy and decision-makers need to have calibrated and validated
numerical tools, it is essential to provide them with qualitative and quantitative
knowledge about the behavior of constructions, so that the optimal design can be
created out of testing different scenarios. With this in mind, a few examples of practical
problems related to design and geo-structures will be presented towards the end of this
chapter.

This chapter has been organized into four parts.

At first, in section 9.3, we will briefly describe the ECP elastoplastic model.
We will show how this simplified model can take into account the main features of
soil behavior observed in triaxial paths. In section 9.4, after generalizing this model
to a multimechanism formalism to describe anisotropy and intermediary stress, we
will discuss some aspects relative to the numerical integration of elastoplastic and
viscoplastic laws. In section 9.5, we will describe the strategy for identifying the
model parameters based on the concept of reference behavior , a notion highly valued
by Jean Biarez. The importance of properly identifying the model parameters cannot
be overstated. Special attention, therefore, will be paid to concepts such as critical
state and reference behavior. In section 9.6, we conclude this chapter by illustrating
the influence of the principal characteristics of soil behavior on the reaction of geo-
structures. In most cases, we are concerned with granular soils which do not present any
artificial or natural “glue”. With the illustration of several construction cases, we will
show how the constitutive law is important in analyzing the behavior of geo-structures.

9.3. Modeling soil behavior

9.3.1. Main characteristics of the soil's mechanical behavior

The study of the mechanical behavior of soil within the context of continuum
mechanics has been the subject of many publications in international literature. The
commonly termed Green Book [BIA 94] (the cover of the English edition is gray),