Civil Engineering Reference
In-Depth Information
sand. Determine the lateral resistance of the anchor block for static conditions and for earth-
quake conditions, assuming that all the soil behind the retaining wall will liquefy during the
earthquake.
Answer:
Static condition: lateral resistance
26.6 kips; earthquake conditions:
lateral resistance
0.
Braced Excavations
10.14
A braced excavation will be used to support the vertical sides of a 20-ft-deep
excavation (i.e.,
H
20 ft in Fig. 10.10). If the site consists of a sand with a friction angle
h
and the resul-
tant earth pressure force acting on the braced excavation for the static condition and the
earthquake condition [using Eq. (10.7)] if
a
max
32
and a total unit weight
t
120 lb
ft
3
, calculate the earth pressure
0.20
g.
Assume the groundwater table is
well below the bottom of the excavation.
Answer:
Static condition:
h
480 lb
ft
2
and the
resultant force
9600 lb per linear foot of wall length. Earthquake condition:
P
E
2700 lb
per linear foot of wall length.
10.15
Solve Prob. 10.14, but assume the site consists of a soft clay having an
undrained shear strength
s
u
300 lb
ft
2
(i.e.,
c
s
u
300 lb
ft
2
) and use Eq. (10.8).
Answer:
Static condition:
21,000 lb per linear
foot of wall length. Earthquake condition:
P
E
3600 lb per linear foot of wall length.
10.16
Solve Prob. 10.15, but assume the site consists of a stiff clay having an
undrained shear strength
s
u
1200 lb
ft
2
and use the higher earth pressure condition (i.e.,
h
2
).
Answer:
Static condition:
h
2
960 lb
ft
2
, and resultant force
14,400 lb per linear
foot of wall length. Earthquake condition:
P
E
3600 lb per linear foot of wall length.
h
1200 lb
ft
2
, and the resultant force
Subsoil Profiles
10.17
Use the data from Prob. 6.15 and Fig. 6.15 (i.e., sewage site at Niigata). Assume
the subsoil profile represents conditions behind a retaining wall. Also assume that the type
of retaining wall installed at the site is a concrete box structure, having height
8 m, width
5 m, and total weight of the concrete box structure
823 kilonewtons per linear meter
of wall length. The soil behind the retaining wall is flush with the top of the concrete box
structure. The water level in front of the retaining wall is at the same elevation as the
groundwater table behind the wall. The effective friction angle
of the soil can be
assumed to be equal to 30
, wall friction along the back face of the wall can be neglected,
and the coefficient of friction along the bottom of the wall
2
3
. In addition, the ground
in front of the wall is located 1 m above the bottom of the wall, and the subsoil profile in
Fig. 6.15 starting at a depth of 7 m can be assumed to be applicable for the soil in front of
the wall. For the static conditions and earthquake conditions, determine the resultant normal
force
N
and the distance of
N
from the toe of the wall, the maximum bearing pressure
q
and
the minimum bearing pressure
q
exerted by the retaining wall foundation, factor of safety for
sliding, and factor of safety for overturning.
Answer:
Static conditions:
N
450 kN
m and
location
1.89 m from toe,
q
156 kPa and
q
24 kPa, FS for sliding
1.66, and FS for
overturning
4.1. Earthquake conditions:
N
450 kN
m,
N
is not within the middle third of
the footings, FS for sliding
0.55, FS for overturning
1.36.
Submerged Backfill Condition
10.18
A cantilevered retaining wall (3 m in height) has a granular backfill with
30
and
t
20 kN
m
3
. Neglect wall friction, and assume the drainage system fails and the water
level rises 3 m above the bottom of the retaining wall (i.e., the water table rises to the top of the
retaining wall). Determine the initial active earth pressure resultant force
P
A
and the resultant
force (due to earth plus water pressure) on the wall due to the rise in water level. For the
