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an example, we can consider an earth dam during its life cycle which, after construction,
traverses several cycles of water impounding and drainage.
As we shall see in section 9.5.2, the objective is to identify the parameters using
a minimum amount of laboratory and field data, and to make the most of existing
correlations. We thus seek a set of consistent parameters for sandy and clayey soils
using parameters such as Atterberg limits for clays and relative density and the grain-
size distribution for sand.
The model parameters can be classified differently depending on the objective. As
the model is a plastic one, a preliminary classification of obvious parameters gives:
−
elastic parameters:
E,ν,n
e
,P
ref
−
plastic and critical state parameters:
φ
pp
,β,b,d
−
hardening parameters:
ψ,a
1
,a
2
,n
p
,c,c
cyc
r
ela
,r
hys
,r
mbl
,r
iso
,m
p
,n
p
−
initial state parameters:
p
c0
to these parameters we should add those which govern the unsaturated behavior:
- non-saturation parameters:
p
sat
,κ
ns
,d
10
We classify model parameters according to the role they play in soil behavior.
The parameters can be divided into three categories: those that contribute directly to
the stiffness (stress strain), those which are associated to a state independent of the
loading history (
τ/σ
n
,
q/p
or
q
k
/p
k
for instance) and, finally, those which govern the
evolution of hardening variables. For the identification process, we suggest a third type
of classification, according to the method of their determination (see Table 9.2).
There are parameters that are directly measured from the quantitative analysis of
observed results, such as parameters of elasticity and perfect plasticity. There are thus
parameters which are not directly measurable and which must be obtained through
calibration. Let us note that the equivalent parameters (
r
ela
,
r
hys
) and (
γ
ela
,γ
hys
)
because of the parameters (
a
1
,
a
2
) belong to the not directly measurable and directly
measurable categories, respectively. Parameter
p
c0
defining the initial state, depending
on the initial density for sands and the degree of overconsolidation for clays is directly
measurable. There are correlations in the literature which permit all the directly
measurableparameterstobequantified.BiarezandHicher[BIA 94]provideasummary
of the major directly measurable soil parameters. They have classified parameters
governing the behavior of soils into two categories:
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