Civil Engineering Reference
In-Depth Information
8.4
Use the following values:
FS
5.0
T
2.5 m
f
10 kPa
10 kN/m
2
B
L
2 m
Inserting the above values into Eq. (8.1
b
) (spread footing) gives
FS
2 (
B
L
)
T
f
___________
P
5.0
2 (2
2) (2.5 m) (10 kN/m
2
)
________________________
P
P
40 kN
8.5
The first step is to check the two requirements in Table 8.3. Since the footings will
be located within the upper unliquefiable cohesionless soil, the first requirement is met. As
indicated in Fig. 7.6, the surface unliquefiable soil layer must be at least 3 m thick to pre-
vent liquefaction-induced ground damage. Since a fill layer equal to 1.5 m is pro posed for
the site, the final thickness of the unliquefiable soil will be 3 m. Thus the second require-
ment is met.
To calculate the allowable bearing pressure for the strip and spread footings, the fol-
lowing 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)
v
0
v
u
0. Use a total unit
weight of 18.3 kN/m
3
(Prob. 6.12) and an average depth of 1.65 m [that is, (0.3
Since the soil is above the groundwater table, assume
u
3.0)
2
1.65 m] or
v
0
18.3
1.65
30 kPa
f
k
0
v
0
tan
0.5 (30 kPa) (tan 33°)
9.8 kPa
9.8 kN/m
2
[Eq. (8.2
c
)]
B
L
1 m
Using Eqs. (8.1
a
) and (8.1
b
) and the above values, we have the following:
For the strip footings:
P
q
all
B
2
T
f
____
FS
2
T
f
(FS) (
B
)
2 (2.7 m) (9.8 kPa)
_______
________________
q
all
5 (1 m)
10 kPa
For the spread footings:
P
q
all
B
2
2 (
B
L
)
T
f
___________
FS
