Environmental Engineering Reference
In-Depth Information
Figure 3.10.
Slope with non-saturated zone and the primary effects of desaturation
Insofar as resistance is concerned, Fredlund [FRE 93] proposes a modification of
Mohr-Coulomb's law in the form:
b
(
)
(
)
τ
=+ −
c
'
σ
u
tg
ϕ
'
+ −
u
u
tg
ϕ
[3.9]
f
a
a
w
where
u
a
is the pore-air pressure,
s = u
a
−
u
w
is the matrix suction and
c'
,
φ'
,
φ
b
material constants.
Thus the increase in suction contributes to the increase in cohesion through the
last term of equation [3.9]
.
Within the framework of the elastoplasticity, there are
now constitutive laws for non-saturated soils that incorporate the majority of the
above-mentioned characteristics. Alonso
et al.
[ALO 90] proposed a formulation
that consists of an extension of the Cam Clay elastoplastic law, while Geiser [GEI
99] based his formulation on the family of hierarchical HISS models developed by
Desai
et al
.
3.4.2.
Types of modeling
Modeling of the effect of non-saturation on the stability of soil masses can be
performed with various degrees of complexity, depending on the desired result, as
developed below.
The simplest approach consists of again taking up the developments made for
perfectly plastic, rigid masses (the methods of slices, for example), postulating or
