Civil Engineering Reference
In-Depth Information
Table 9.1
Bearing capacity factors in common use.
φ
(°)
N
c
N
q
N
γ
0
5.14
1.00
0.00
5
6.49
1.57
0.1
10
8.34
2.47
0.52
15
10.98
3.94
1.58
20
14.83
6.40
3.93
25
20.72
10.66
9.01
30
30.14
18.40
20.09
35
46.12
33.30
45.23
40
75.31
64.20
106.05
45
133.87
134.87
267.75
50
266.88
319.06
758.09
9.6.2 Shape factors
These factors are intended to allow for the effect of the shape of the foundation on its bearing capacity.
The factors have largely been evaluated from laboratory tests and the values in present use are those
proposed by De Beer (
1970)
:
B
L
N
N
q
s
= + ⋅
1
c
c
B
L
s
q
= +
1
tan
φ
B
L
s
γ
=
1 0 4
.
9.6.3 Depth factors
These factors are intended to allow for the shear strength of the soil above the foundation. Hansen (
1970
)
proposed the following values:
z/B
≤
1.0
z/B
>
1.0
d
c
1
+
0.4(z/B)
1
+
0.4 arctan(z/B)
d
q
1
+
2 tan
φ
(1
−
sin
φ
)
2
(z/B)
1
+
2 tan
φ
(1
−
sin
φ
)
2
arctan(z/B)
1.0
1.0
d
γ
Note:
The arctan values must be expressed in radians, e.g. if z
=
1.5 and B
=
1.0 m then arctan
(z/B)
=
arctan (1.5)
=
56.3°
=
0.983 radians.
