Civil Engineering Reference
In-Depth Information
Figure 22.7
Bearing capacity factors for drained loading of foundations.
and these are equivalent to
tan
2
4
+
φ
exp
π
φ
N
q
=
tan
(22.11)
2
φ
in Fig. 22.7(b).
N
γ
is the contribution to the bearing capacity created by the self weight of the soil
beneath the foundation. There are no simple upper and lower bounds for this case.
The values of
N
γ
shown in Fig. 22.7(c) were found from a numerical method given by
Martin (2003).
The allowable bearing pressure is obtained by applying a load factor to the net
bearing pressure. Remember that the gross bearing pressure is the total stress at the
base of the foundation and it includes the applied load and the weight of the foundation,
so the allowable applied load
V
a
is
Values for
N
q
given by Eq. (22.11) are shown plotted against
L
f
2
(
1)
BD
w
)
B
2
N
γ
+
+
=
γ
−
γ
γ
−
γ
−
+
γ
V
a
W
(
w
)(
N
q
BD
(22.12)
If the soil is dry you should put
0 in Eq. (22.12). The term containing
N
γ
is the
contribution to the bearing capacity from the unit weight of the soil below foundation
γ
=
w
