Geoscience Reference
In-Depth Information
Table 19.11
Use of wall friction.
Consideration
Value of wall
Comment
friction,
δ
Active state
0.67
φ
maximum
0.5
φ
for small movements
Passive state
0.5
maximum
0.33
for small movements
φ
φ
Vibration
Adjacent to machinery, railways, vehicular traffic causing
vibration
δ =
0
Anchored walls
Negligible movement to mobilise wall friction
δ =
0
Wall has tendency to
δ =
0
Uncertainty on the effects of wall friction
settle
Wall supported on
Example, cantilever reinforced concrete wall, where
δ =
0
foundation slab
virtually no movement of soil relative to back of wall
•
The magnitude of
does not often significantly affect the value of the active force.
However the direction is affected and can significantly affect the size of the wall
bases.
δ
•
Avoid Coulomb values for
δ
>
0.5
.
φ
19.12 Values of active earth pressures
•
The log spiral surface approximates the active and passive failure surfaces rather
than the straight line.
•
The value of the active earth pressure coefficient (K
a
) is dependent on the soil,
friction angle and the slope behind the wall.
Table 19.12
Active earth pressure coefficients (after Caquot and
Kerisel, 1948).
Angle of friction
Active earth pressure coefficient for
various slope (i) behind wall
Soil (
)
Wall (
)
i
0
◦
i
15
◦
i
20
◦
φ
δ
=
=
=
20
0
0.49
0.65
0.99
2/3
φ
0.45
0.59
0.91
20
◦
0.44
0.58
0.89
φ =
25
0
0.41
0.51
0.58
2/3
0.36
0.46
0.56
φ
25
◦
0.35
0.40
0.50
φ =
30
0
0.33
0.41
0.46
2/3
0.29
0.35
0.39
φ
30
◦
0.28
0.33
0.37
φ =
35
0
0.27
0.32
0.35
2/3
φ
0.23
0.28
0.30
35
◦
0.22
0.27
0.28
φ =
40
0
0.22
0.25
0.30
2/3
0.18
0.22
0.23
φ
40
◦
0.17
0.19
0.21
φ =
Search WWH ::
Custom Search