Geotechnical Engineering

DHARM

LATERAL EARTH PRESSURE AND STABILITY OF RETAINING WALLS 465

If the backfill is submerged, the lateral pressure due to the submerged unit weight of

the backfill soil acts parallel to the surface of the backfill, while the lateral pressure due to

pore water acts horizontally.

For the passive case, the right-hand sides of Eqs. 13.14 and 13.15 will represents σl and

σv respectively.

The conjugate ratio, K, is given by

K =

cos cos cos

cos cos cos

ββφ

ββφ

+−

−−

22

22 ...(Eq. 13.19)

and the passive pressure coefficient Kp is given by

Kp = cos

cos cos cos

cos cos cos

β

ββφ

ββφ

+−

−−

F

H

GG

I

K

JJ

22

22 ...(Eq. 13.20)

The total thrust or passive resistance per unit length of wall Pp is given by^12 Kpγ.H^2 ,

acting at 31 H above the base of the wall, parallel to the backfill surface.
It is interesting to note that if β = 0 is substituted in Eqs. 13.18 and 13.20, we obtain
Eqs. 13.8 and 13.9, respectively, for the case with the backfill surface horizontal.

13.6.7 Effect of Inclined Back of Wall

The back of a retaining wall may not always be vertical, but may occasinally be battered or

inclined. In such a case, the total lateral earth pressure on an imaginary vertical surface pass-

ing through the heel of the wall is found and is combined vectorially with the weight of the soil

wedge between the imaginary face and the back of the wall, to given the resultant thrust on

the wall.

The procedure is applicable whether the backfill surface is horizontal or inclined, as

illustrated in Fig. 13.13.

W

H/3

Pa

Pav

H

W

H/3

Pa

Pav

H

b

b

(a) Inclined back of wall—

Horizontal backfill

(b) Inclined back of wall—

Inclined backfill

Fig. 13.13 Effect of inclined back of wall on lateral earth pressure