Civil Engineering Reference
In-Depth Information
Therefore,
For the strip footings:
q
ult
1
t
BN
1
2
(18.3 kN/m
3
) (1 m) (26)
238 kPa
2
q
ult
238
___
____
q
all
FS
5
48 kPa
For the spread footings [using Eq. (8.4)]:
q
ult
0.4
t
BN
0.4 (18.3 kN/m
3
) (1 m) (26)
190 kPa
q
all
q
ult
FS
190
___
____
5
38 kPa
Summary:
38 kPa for the 1-m
by 1-m spread footings. For the design of the footings, use the lower values calculated in
Prob. 8.5.
q
all
48 kPa for the 1-m-wide strip footings and
q
all
8.8
Total thickness of the unliquefiable soil layer minus footing embedment depth
T
3
0.3
2.7 m. Since
T
B
2.7
1.0
2.7,
N
c
5.5 per Fig. 8.8.
For the strip footings [using Eq. (8.6
a
)]:
q
ult
s
u
N
c
(20 kPa) (5.5)
110 kPa
q
all
q
ult
FS
110
___
____
5
22 kPa
For the spread footings [using Eq. (8.6
b
)]:
1
0.3
B
__
q
ult
s
u
N
c
L
1.3 (20 kPa) (5.5)
143 kPa
q
all
q
ult
FS
143
___
____
5
29 kPa
Use
q
all
30 kPa.
Summary:
q
all
22 kPa for the 1-m-wide strip footings, and
q
all
30 kPa for the 1-m by
1-m spread footings. For the design of the strip footings, use the value from Prob. 8.6 (
q
all
20 kPa). For the design of the spread footings, use the lower value calculated in this prob-
lem (
q
all
30 kPa).
8.9
Method from Sec. 8.2.2:
To calculate the allowable bearing pressure for the
spread footings, the following values are used:
FS
5.0
T
2.7 m
(total thickness of unliquefiable soil layer minus footing
embedment depth
3
0.3
2.7 m)
