Civil Engineering Reference
In-Depth Information
The surcharge adds weight to the active wedge, where
L
top length of the active wedge,
so
W
s
QL
(200 lb/ft
2
) (20 tan 30°)
2300 lb/ft
P
E
k
h
W
0.20 (2300)
460 lb/ft
Eq. (10.5)
Total
P
E
2540
460
3000 lb/ft
Factor of safety for sliding:
FS
N
tan
P
p
___________
P
H
Eq. (10.13) where
cv
30°
P
E
15,870 tan 30°
750
__________________
6690
3000
1.02
Factor of safety for overturning:
Overturning moment
21,030
2
3
(20) (3,000)
61,030 ft
lb/ft
Moment of weight
55,500 ft
lb/ft
FS
55,500
______
61,030
0.91
Location of
N:
x
55,500
61,030
______________
15,870
0.35 ft
Middle third of the foundation:
x
2.33 to 4.67 ft, therefore
N
is not within the middle
third of the foundation.
10.6
Static analysis:
w
30°
30°
0°
18.4°
Inserting the above values into Coulomb's equation (Fig. 10.3) gives
k
A
0.4065. From
Eq. (10.1),
P
A
1
2
k
A
t
H
2
1
2
(0.4065) (110) (20
2
)
8940 lb/ft
P
v
P
A
sin 30°
8940 sin 30°
4470 lb/ft
P
H
P
A
cos 30°
8940 cos 30°
7740 lb/ft
N
12,000
4470
16,470 lb/ft
