Geoscience Reference
In-Depth Information
investigation of the mechanical behaviour of unsaturated soils are the suction,
s
=
u
a
- u
w
(where
u
a
and
u
w
are the air and water pressure respectively), and mean net stress,
p
net
=
p -
u
a
(where
p
is the total mean stress).
The loading paths followed during the oedometric tests are presented in Fig. 9. The
resulting compressibility curves in the [log
v
:
e
] diagrams are presented in Fig. 10, where
e
is the void ratio (
e = V
v
/V
s
, where
V
v
is the volume of void and
V
s
is the volume of solid
skeleton).
The testing program comprises four compression tests carried out as follows:
-
Test T1 (
e
i
= 0.575): dry compression (
s
30 MPa) up to 39.7 MPa, unload down to 0.44
MPa, water injection under 0.44 MPa, and subsequent loading up to 39.7 MPa.
-
Test T2 (
e
i
= 0.61): dry compression (
s
30 MPa) up to 22.41 MPa, unload down to 10.19
MPa, reload to 29.28 MPa, and water injection.
-
Test T3 (
e
i
= 0.602): suction controlled compression (
s
= 4.2 MPa) up to 39.7 MPa, unload
down to 8.82 MPa, and reload to 39.7 MPa.
-
Test T4: (
e
i
= 0.581): saturated compression up to 20.38 MPa, stress release at 0.26 MPa,
and reload at 40.76 MPa.
Dry, s = 30
MPa
T1
T2
T3
s = 4.2 MPa
s
a
t
ur
a
t
e
d, s =
0
MPa
T
4
100
1000
10000
100000
VERTICAL STRESS,
v
: kPa
Fig. 9. Loading paths
The compressibility curves in Fig. 10 show some responses typical of unsaturated soils:
-
increase in yield stress with increased suction
-
increase in compressibility with decreased suction
-
slight suction dependency of the pseudo-elastic compressibility module
-
slight swelling due to suction release in the elastic zone
-
significant collapse during water injection under high constant applied vertical load
(pore collapse). Interestingly, the void ratio of the collapsed sample (i.e., after water
injection) is close to the saturated compression curves of tests T1 and T4
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