Geoscience Reference
In-Depth Information
0.8
0.8
D
r
= 0.6
0.6
0.6
D
r
= 0.6
0.4
0.4
0.5
0.5
0.4
0.2
0.2
0.4
0.2
0.05
0.2
0.05
0.0
0.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0
5
10
15
20
25
p = (
σ
1
+σ
2
+σ
3
)/3
(MPa)
ε
1
(%)
(a)
(b)
Figure 7.9.
Numerical simulations of undrained triaxial tests:
(a) stress
−
strain relation; and (b) effective stress path
These different evolutions can be related to the stress paths followed in a
p', q
plane: continuous decrease of the mean effective stress for strongly contractive
materials, with a decrease followed by an increase up to the critical state for dilative
materials. These results indicate that, in undrained condition, the model is capable of
capturing the general trend observed for contractive and dilative sands [HIC 98].
7.4. Model extension to clayey materials
The representative scale of the constitutive elements that affect the mechanical
behavior of the equivalent continuous medium is less evident in this case. Several
scales coexist in a clayey material:
- the elementary clay layer, consisting of the basic element of a clay particle;
- the clay particle made up of an assembly of layers, usually organized in stacks;
- the aggregate made up of particles whose size and internal arrangement depend
on the history of the material. The size of the aggregates can be measured by
sedimentation.
A research study has been undertaken to relate the mechanical behavior of
saturated remolded clays to their structural organization [HIC 00]. Two clays were
studied: a kaolinite and a bentonite. The evolution of the shape, the size, and the
concentration and the orientation of the elements that constitute the clay structure
were examined by means of scanning and transmission electron microscopes, thanks
to techniques that obviate possible disturbances of the micro-structure during
observation. The results of this study show the main role played by the aggregates,
similar to the role played by the grains in the mechanical behavior of granular
materials. This explains the similar behavior of the equivalent continuous medium
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