Civil Engineering Reference
In-Depth Information
Factor of safety for sliding:
2
3
2
3
(30°)
20°
FS
N
tan
P
p
___________
Eq. (10.11)
P
A
450 tan 20°
7.3
_______________
103
1.66
Factor of safety for overturning:
Wa
______
1
FS
3
P
A
H
Eq. (10.12)
450 (5
2)
__________
1
3
(103) (8)
4.1
Earthquake analysis:
To find
P
L
,
we do as follows: From Prob. 6.15,
a
max
g
0.16, and
the soil will liquefy from a depth of 1.2 to 6.7 m behind the retaining wall. To simplify the
calculations, assume that the entire active wedge will liquefy during the earthquake.
For the passive wedge and the soil beneath the bottom of the wall, the factor of safety
against liquefaction is very high up to a depth of 13 m.
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
.
Using Eq. (10.1) with
k
A
1 and
b
9.7 kN/m
3
gives
2
k
A
b
H
2
1
2
(1.0) (9.7) (8
2
)
310 kN/m
P
L
1
Resultant value of
N
and distance of
N
from the toe of footing:
Take moments about
the toe of the wall to determine location of
N.
8
__
Nx
P
L
3
W
(moment arm)
8
5
__
__
450
x
310
3
450
2
298
____
x
450
0.66 m
Middle third of the foundation,
x
1.67 to 3.33 m. Therefore,
N
is not within the middle
third of the foundation.
Factor of safety for sliding:
FS
N
tan
P
p
___________
P
L
450 tan 20°
7.3
_______________
310
0.55
