Civil Engineering Reference
In-Depth Information
Moment due to passive force
1.35
10
6
resisting moment
destabilizing moment
1.35
10
6
_________
8.90
__________________
FS
10
5
1.52
A
p
P
A
P
E
P
p
FS
27,500
8690
32,600
___
______
1.52
14,700 lb
ft
For a 10-ft spacing, therefore,
A
p
10 (14,700)
147,000 lb
147 kips
Earthquake Analysis, Liquefaction of Active Wedge.
For the third earthquake analysis,
assume that the sand located in front of the retaining wall has a factor of safety against lique-
faction greater than 2.0. However, assume that the submerged sand located behind the
retaining will liquefy during the earthquake. Further assume that the tieback anchor will be
unaffected by the liquefaction. Calculate the factor of safety for toe kick-out.
As indicated in Sec. 10.3.2, when the water levels are approximately the same on both
sides of the retaining wall, use Eq. (10.1) with
k
A
1 [i.e., for
0,
k
A
1, see Eq. (10.2)]
and use
b
(buoyant unit weight) in place of
t
.
As an approximation, assume that the entire 50 ft of soil behind the sheet pile wall will
liquefy during the earthquake. Using Eq. (10.1), with
k
A
1 and
b
64 lb
ft
3
,
P
L
1
2
k
A
b
(
H
D
)
2
1
2
(1.0)(64)(50)
2
80,000 lb
ft
Moment due to liquefied soil
80,000[
2
3
(50)
4]
2.35
10
6
Moment due to passive force
1.71
10
6
resisting moment
destabilizing moment
1.71
10
6
__________________
__________
2.35
FS
10
6
0.73
Summary of Values
Factor of safety
A
p
,
Example problem
for toe kick-out
kips
Static analysis
2.19
76.8
Pseudostatic method [Eq. (10.7)]
1.92
136
Partial passive wedge liquefaction
*
Earthquake
1.52
147
Liquefaction of soil behind wall
0.73
—
*
Pseudostatic force included for the active wedge.
As indicated by the values in this summary table, the sheet pile wall would not fail for
partial liquefaction of the passive wedge. However, liquefaction of the soil behind the
retaining wall would cause failure of the wall.
