Geotechnical Engineering

DHARM

LATERAL EARTH PRESSURE AND STABILITY OF RETAINING WALLS 493

Pp

y

(+)qf

(180° –yqf– – )R

W

H

l 1

l 2

l 3

l 4

l 5

l 6

b

H 1

C 1

C 3

C 2

C C

4 C^5

C 6

t

t

2 ¢

F¢

3 ¢ 4 ¢ 5 ¢ 6 ¢

Culmann

curve

l 1

l 2

l 3

l 4

l 5

l 6

(+)fd

(–)f

1

2

y

(^3) y
4
5
6
1 ¢
(a) Culmann curve (b) Force triangle
P=Pmin
p
Fig. 13.34 Culmann’s graphical method for passive resistance
13.7.6 Break in the Backfill Surface
Sometimes the surface of the backfill may consist of a combination of two different slopes. The
treatment of such a situation is illustrated in Fig. 13.35.
(i) Let the surface of the backfill be ADE with a break at D. Let AB represent the backface
of the wall. First, ignore the line DE and locate the failure plane BC and obtain the pressure
distribution AK 1 B, by means of a Poncelet construction.
If P 1 is the total thrust on the wall obtained from this construction σ 1 =
2 P 1
Hs
, repre-
sented by BK 1.
(ii) Draw DG parallel to BC to meet the wall face in G. If AG is considered to be the wall,
the pressure distribution is AJG; the break in the backfill will have no effect for this since it is
to the right of the failure plane GD. However, below G the break will result in smaller pres-
sures than those represented by the line JK 1.