Civil Engineering Reference
In-Depth Information
Figure 6.4
Suction in saturated soil.
diameter
d
t
. Resolving vertically on the column of water in the tube in Fig. 6.4(a)
d
t
4
γ
=−
π
T
π
d
t
w
h
w
(6.6)
where
T
is the surface tension force between water and glass. Hence the height of
water in the capillary tube is
4
T
γ
−
h
w
=
(6.7)
w
d
t
and, since
u
w
=
γ
w
h
w
the pore water suction at the top of the water column is
4
T
d
t
−
u
w
=
(6.8)
(Since the pore pressure in Eq. (6.8) is negative the pore water is in suction.) In the soil
in Fig. 6.4(b) the grain diameter is
d
s
, the specific volume is
v
and the mean pore space
diameter
d
v
is
d
v
=
(
v
−
1)
d
s
(6.9)
Hence, the height of saturated soil above the water table is
4
T
−
h
w
=
(6.10)
γ
w
(
v
−
1)
d
s
and the maximum pore water suction is
4
T
−
u
w
=
(6.11)
(
v
−
1)
d
s
