Civil Engineering Reference
In-Depth Information
φ
=
As before,
W
=
γ
BD
. From Fig. 22.7(b), for
25,
N
γ
=
8 and
N
q
=
11 and
1
10)2.5
2
V
c
=
2
(20
−
×
8
+
(20
−
10)(11
−
1)2.5
×
2
=
750 kN/m
If the applied load is
V
a
=
300 kN/m the load factor is 2.5.
Example 22.3: Settlement of an embankment
The embankment in Fig. 22.17 is suf-
ficiently wide so that the strains and seepage in the soil can be assumed to
be one-dimensional. From Eq.
(22.25) the magnitude of the final consolidation
settlement is
σ
z
=
10
−
4
ρ
=
m
v
z
5
×
×
8
×
100
=
0.40m
c
=
(a) From Fig. 22.15(a) the time when the settlement is complete (i.e. when
U
t
1.0)
corresponds to
T
v
=
1.0. Hence, from Eq. (22.27),
T
v
H
2
c
v
8
2
1.0
×
t
=
=
=
32 years
2
(b) After 5 years the time factor is
c
v
t
H
2
2
×
5
T
v
=
=
=
0.16
8
2
From Fig. 22.15(a) this corresponds to a degree of consolidation
U
t
≈
0.50 and
the settlement after 5 years is
ρ
=
U
t
ρ
∞
=
0.50
×
0.40
=
0.20m
t
Example 22.4: Settlement with drains
In order to speed up the settlement of the
embankment in Example 22.3 sand drains are installed in the clay. The drains are
200 mm in diameter (
r
=
100mm) and they are spaced 2 m apart (
R
=
1.0m).
Figure 22.17
Embankment settlement - Examples 22.3 and 22.4.
