Geotechnical Engineering

DHARM

498 GEOTECHNICAL ENGINEERING

extended to meet the modified Culmann-curve in F 2 , the intercept G 2 F 2 equals GF. This im-
plies that if the line load is placed beyond C 2 , there is no effect on the lateral pressure, since
∆Pa = G 2 F 2 – GF = 0. For other positions of the line load between A and C 2 , ∆Pa may be obtained
as indicated in Fig. 13.38, and plotted as ordinates at the locations of the line load. It will be
observed that ∆Pa is maximum when the load is at the face of the wall, it remains constant
with positions of line load up to C 1 , and then decreased gradually to zero at C 2.

f

B

(+)fd

y-line

A

C 1 C

b f-line

C 2

DPa

Influence line for PD a

G 1 G

G¢

G 2

F 2

F¢

F 1 F

Modified

Culmann curve

Culmann

curve

Fig. 13.39 Influence line for thrust increment due to line load

This analysis is considered very useful in locating the position of railway line or a long

wall of a building on the backfill at a safe distance so that the thrust on the wall does not

increase.

Alternative Procedure

An alternative procedure may be adopted in case one is interested in obtaining not only the

total thrust, but also the distribution of pressure across the height of the wall (Taylor, 1948).

This is illustrated in Fig. 13.40.

a

A

C

C¢

q¢

A¢

E

F s 2

F¢

G

E

D

B

s 1

H

Approximate distribution

of additional thrust due

to the line load.

BA :

BE : H

BE : H

s

s

1

¢ 2

Hs

(a) Line load on backfill (b) Distribution of lateral

earth pressure

Fig. 13.40 Effect of line load on distribution of active earth pressure (After Taylor, 1948)