Civil Engineering Reference
In-Depth Information
6. For wide foundations on relatively thin beds of soil the strains during consolidation
are one-dimensional. The magnitude of the settlement is given by
δσ
z
δρ
=
zm
v
(22.25)
c
The rate of settlement is given by the relationship between the degree of
consolidation and the time factor, which are given by
=
ρ
t
ρ
∞
U
t
(22.26)
c
v
t
H
2
T
v
=
(22.27)
A reasonable approximation is
T
v
=
1 when
U
t
=
1.
Worked examples
Example 22.1: Undrained bearing capacity of a foundation
For the foundation in
Fig. 22.16 the ultimate load for undrained loading is found from Eq. (22.6)
+
=
+
γ
V
c
W
s
u
N
c
B
DB
If the unit weights of soil and concrete are the same,
W
=
γ
DB
. From Fig. 22.6(b),
for a long foundation with
D
/
B
≈
1 we have
N
c
=
6 and
V
c
=
30
×
6
×
2.5
=
450 kN/m
If the applied load is
V
a
=
300 kN/m the load factor is 1.5.
Example 22.2: Drained bearing capacity of a foundation
For the foundation in Fig. 22.16
the ultimate load for drained loading is found from Eq. (22.10)
)
N
q
1
BD
1
2
B
2
N
γ
+
(
γ
−
γ
+
=
(
γ
−
γ
−
+
γ
V
c
W
)
BD
w
w
Figure 22.16
Loading of a foundation - Examples 22.1 and 22.2.
