Numerical Modeling: An Efficient Tool for Analyzing the Behavior of Constructions - Multiscale Geomechanics: From Soil to Engineering Projects - page 268

Neutral loading

P

Softening

Hardening

f = F = 0

Unloading

ε ν

Figure 9.6. Five states of behavior

9.3.6.1. Capacity of the unsaturated model to simulate the collapse phenomenon
In unsaturated soils, the material sometimes contracts when the suction and effective
stress decrease. This is apparently the argument used to reject the use of effective stress
for describing the behavior of unsaturated soils. We demonstrate that these two aspects
are not contradictory and the developed constitutive model is capable of taking into
account this phenomenon, despite its formulation in terms of effective stress. In fact,
as we have seen in the previous subsection, a decrease in stress may be accompanied
by a generation of plastic strains.

The consistency condition ( f =0 )ofthe isotropic mechanism results in:
A λ iso =

B − C − D

[9.72]

where

A = K − ∂ r iso f iso · h iso − ∂ ε v f iso
B = K · ε v
C = ∂ π c f iso π c = −d · r iso · ∂ π c · π c

[9.73]