Civil Engineering Reference
In-Depth Information
FIGURE 10.5b
Example problem (
continued
). Calculation of the factor of safety for overturning and the
location of the resultant force
N.
(
From Lambe and Whitman 1969; reproduced with permission of John
Wiley & Sons.
)
●
Friction between the back face of the wall and the soil backfill:
w
30
●
Friction angle of backfill sand:
30
Inputting the above values into Coulomb's equation (Fig. 10.3), the value of the active
earth pressure coefficient
k
A
0.297.
By using Eq. (10.1) with
k
A
0.297, total unit weight
t
110 lb
ft
3
(17.3 kN
m
3
), and
the height of the retaining wall
H
20 ft (see Fig. 10.5
a
), the active earth pressure resultant
force
P
A
6540 lb per linear foot of wall (95.4 kN per linear meter of wall). As indicated in
Fig. 10.5
a,
the active earth pressure resultant force
P
A
6540 lb
ft is inclined at an angle
of 30
due to the wall friction assumptions. The vertical (
P
v
3270 lb
ft) and horizontal
(
P
H
5660 lb
ft) resultants of
P
A
are also shown in Fig. 10.5
a.
Note in Fig. 10.3 that even
