Civil Engineering Reference
In-Depth Information
Therefore,
(50 kPa) (20) (10)
_________________
v
16)
10.7 kPa
(10
16) (20
Or, in terms of a percentage increase in
v
0
,
10.7
____
Percent increase in
v
0
178
6%
This is a very low percentage increase in vertical stress due to the foundation load. Thus
the shear stress caused by the building load should not induce any significant additional set-
tlement of the liquefied soil. Using the data from Prob. 7.11 at a depth of 15 to 20 m, we
find the results shown on the next page.
7.17
Since the tank is in the middle of a liquefied soil layer, it is expected that the
empty tank will not settle, but rather will float to the ground surface.
7.18
The thickness of the liquefiable sand layer
H
2
is equal to 4 m. Entering Fig. 7.6
with
H
2
0.4
g
curve, the minimum thickness of the sur-
face layer
H
1
needed to prevent surface damage is 8.3 m. Since the surface layer of unliq-
uefiable soil is only 6 m thick, there will be liquefaction-induced ground damage.
4 m and intersecting the
a
max
7.19
Problem 6.12 was solved based on a peak ground acceleration
a
max
0.16
g.
For
a peak ground acceleration
a
max
0.2
g,
the factor of safety against liquefaction at a depth
of 1.5 m is as follows:
0.20
____
CSR
0.16
(0.10)
0.13
Therefore,
FS
CRR
CSR
0.12
_____
____
0.13
0.92
For a peak ground acceleration of 0.2
g,
the zone of liquefaction will extend from a depth
of 1.5 to 11 m. The thickness of the liquefiable sand layer
H
2
is equal to 9.5 m. Entering
Fig. 7.6 with
H
2
9.5 m and extending the
a
max
0.2
g
curve, the minimum thickness of
the surface layer
H
1
needed to prevent surface damage is 3 m. Since the surface layer of
unliquefiable soil is only 1.5 m thick, there will be liquefaction-induced ground damage.
7.20
Since the zone of liquefaction extends from a depth of 0.85 to 8 m, the thickness
of the liquefiable sand layer
H
2
is equal to 7.2 m. Entering Fig. 7.6 with
H
2
7.2 m and
intersecting the
a
max
0.2
g
curve, the minimum thickness of the surface layer
H
1
needed
to prevent surface damage is 3 m. Since the surface layer of unliquefiable soil is only 0.85
m thick, the minimum thickness of the surface fill layer is equal to 3
0.85
2.2 m.
7.21
For a peak ground acceleration of 0.2
g,
the zone of liquefaction will extend from
a depth of 2.5 to 3.5 m. The thickness of the liquefiable sand layer
H
2
is equal to 1 m.
Entering Fig. 7.6 with
H
2
1 m and intersecting the
a
max
0.2
g
curve, the minimum thick-
ness of the surface layer
H
1
needed to prevent surface damage is 0.9 m. Since the surface
layer of unliquefiable soil is 2.5 m thick, there will not be liquefaction-induced ground
damage.
