Civil Engineering Reference
In-Depth Information
As indicated in the previous table, each domain corresponds to a behavior type,
the characterization of which involves measuring specific parameters.
4.2.1.
An experimental description of elastic soil behavior (
JdJ
s
)
For strains lower than 10
-6
to 10
-5
, soil behavior is typically linear elastic. Some
saturated materials can present a slight damping of viscous origin (a few percent), in
which case soil behavior can be characterized by an elastic or possibly visco-elastic,
linear type of behavior law. In the case of an isotropic material, the modulus of shear
elasticity G (similar to Lame's modulus P in continuous medium mechanics) and a
volumic bulk modulus B allow the complete characterization of the behavior.
Alternately, it is possible to use the propagation rate of the elastic waves V
s
(shear
waves) and V
p
(compression waves) linked to the previous values by:
4
G = ȡ V B = ȡ VV
3
§
·
2
2
2
[4.2]
¨
¸
s
p
s
©
¹
where U is the density of the material.
Measuring these values can be either done
in situ
(V
s
, V
p
) or under laboratory
conditions on intact samples (G, B).
The measurements correspond to very specific techniques. Among the
in situ
techniques used, we include the logging suspension test, spectral analysis of SASW
surface waves, or any other drilling measure technique (crosshole or downhole test)
as examples; in the laboratory, the most appropriate test is the resonant column test.
The study of soil behavior within its elastic field is important, and a whole range
of problems exist for which the models are valid: cases of vibrations of well
conditioned machine blocks, low amplitude seismic stresses like those caused by
geophysical tests are examples.
4.2.2.
Linear visco-elastic models for medium strain domains where
J
s
dJdJ
v
In this strain field, more or less marked non-linearities appear in the stress-strain
curve.
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