Geoscience Reference
In-Depth Information
22.8 Compression capacity of rock for splitting failure
•
A splitting failure condition applies for widely spaced and near vertically oriented
joints.
•
Joint spacing (S)
>
Footing width (B). The joint extends below the below footing
for a depth H.
•
The ratio of the joint depth to the footing width (H/B) is used to provide a joint
correction factor for the bearing capacity equation.
Table 22.8
Ultimate bearing capacity with failure in splitting (Bishnoi, 1968; Kulhawy and Goodman,
1980).
Foundation
Ultimate bearing
Correction factor (J) based
type
capacity (q
ult
)
on discontinuity spacing (H/B)
Circular
1.0JcN
cr
Square
0.85JcN
cr
/B
0
1
2
3
4
5
6
7
8
Continuous
1.0JcN
cr
/
J
0.41
0.52
0.67
0.77
0.85
0.91
0.97
1.0
1.0
strip
(2.2
0.18 L/B)
+
-J
Joint Correction Factor.
-N
cr
=
=
Bearing Capacity Factor.
-L
Length of footing.
-B
=
=
Width of footing.
22.9 Rock bearing capacity factor for discontinuity spacing
•
The bearing capacity factor in Table 22.7 for the wedge failure does not allow for
discontinuity spacing.
•
This table is to be used with Table 22.8, and applies when the joints are more
widely spaced than the foundation width.
Table 22.9
Bearing capacity factors (from graphs in Bishnoi, 1968; Kulhawy and Goodman, 1980).
Friction angle
Bearing capacity factors
(N
cr
)
with discontinuity spacing (S/B)
φ
◦
Previously tabulated N
c
(Table 22.7)
0.5
1.0
2
5
10
20
0
4
4
4
4
4
4
4
10
6
4
4
4
6
6
6
20
8
4
4
5
9
9
8
30
15
4
4
6
15
15
15
40
25
4
4
8
20
25
25
50
50
4
6
10
25
40
50
60
110
4
8
15
35
50
110
22.10 Compression capacity of rock for flexure and
punching failure modes
•
This table applies for a rigid layer over weaker layers. The top layer is considered
rigid for S
>
B while the layer is thin for S
<
B.
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