Structural Concrete - Hassoun

506 Chapter 14 Retaining Walls
1′0″
330 psf
16′6″
18′0″
Frost line
1′6″
1′6″
3′6″
1′6″
10′6″
5´6″
Figure 14.11
Example 14.2: Trial configuration of retaining wall.
b. The overturning moment is 1.755 × 9.75 + 5.665 × 6.5 = 53.93 K⋅ft.
c. Calculate the balancing moment against overturning (see Fig. 14.12):
Force (lb) Arm (ft) Moment (K⋅ft)
w 1 = 1 × 18 × 150 = 2,700 4.50 12.15
w 2 = 1 × 18 × 1 × 150 = 675 3.83 2.59
2 2
w 3 = 10.5 × 1.5 × 150 = 2,363 5.25 12.41
w 4 = 5.5 × 21 × 110 = 12,705 7.75 98.46
∑
w = R = 18.44 K
∑
M = 125.61 K ⋅ ft
Factor of safety against overturning = 125.61
53.93
= 2.33 > 2.0
4. Calculate the base soil pressure. Take moments about the toe end 0 (Fig. 14.12) to determine the
location of the resultant R of the vertical forces.
∑ ∑ M − Hy balancing M − overturning M
x =
=
R
R
125.61 − 53.93
= = 3.89 ft > 10.5 or 3.5ft
18.44
3
The eccentricity is e = 10.5/2 − 3.89 = 1.36 ft. The resultant R acts within the middle third of
the base and has an eccentricity of e = 1.36 ft from the center of the base. For a 1-ft length of the