Civil Engineering Reference
In-Depth Information
Figure 9.7
Normalized critical state and normal consolidation lines.
tests were drained so the pore pressure was zero and total and effective stresses were
equal. We also considered undrained tests in which pore pressures were not mea-
sured and the undrained strength was related to the constant voids ratio. A more
common and more useful test to examine soil behaviour is the triaxial test described
in Chapter 7. In the triaxial test a cylindrical sample is subjected to total axial and
radial stresses while the pore pressures and the sample volume can be controlled and
measured independently so that it is possible to determine the effective stresses and the
strains.
Relationships between stresses and strains in shear and triaxial tests were discussed
in Chapter 3. For shear tests the shear and normal stresses and strains are
τ
,
σ
,
γ
v
and for triaxial tests the equivalent parameters are
q
,
p
,
and
ε
ε
s
and
ε
v
; these can
be related through Mohr circle constructions, as described in Chapter 3.
All the features of soil behaviour in shear tests shown in Fig. 9.1 are seen in the
results of triaxial tests plotted as
q
against
s
. In triaxial tests soils
reach critical states where they continue to distort at a constant state (i.e. with constant
effective stresses and constant volume) and soils initially on the dry side of the critical
state line have peak states before the critical state is reached.
The critical state lines obtained from drained and undrained triaxial tests are shown
in Fig. 9.8, which may be compared with Fig. 9.4 which shows the critical state line
ε
s
and
ε
v
against
ε
