Geotechnical Engineering

DHARM

LATERAL EARTH PRESSURE AND STABILITY OF RETAINING WALLS 517

φ = 45°

Ka =

145

145

−° 0172

+°

sin =

sin

.; Kp =^145

145

+°5 828

−°

sin =

sin

.

Active pressure at depth H m = 0.172 × 19.4H = 3.34 H kN/m^2

Passive pressure at depth H m = 5.828 × 19.4 H = 113.06 H kN/m^2

Ratio of active pressure in the dense state of that in the loose state =

0334

0609

.

.

= 0.55

Ratio of passive resistance in the dense state to that in the loose state =

11 306

4 314

.

.

= 2.62

Example 13.5: A smooth backed vertical wall is 6.3 m high and retains a soil with a bulk unit
weight of 18 kN/m^3 and φ = 18°. The top of the soil is level with the top of the wall and is
horizontal. If the soil surface carries a uniformly distributed load of 4.5 kN/m^2 , determine the
total active thrust on the wall per lineal metre of the wall and its point of application.
H = 6.3 m γ = 18 kN/m^3 φ = 18°
q = 45 kN/m^2

Ka =

118

118

−°0 528

+°

sin =

sin

.

Active pressure due to weight of soil at the base of wall = KaγH

= 0.528 × 18 × 6.3

= 59.9 kN/m^2

6.3 m

Wall

q = 45 kN/m^2 23.8 kN/m^2

2.56 m

Pa

23.8 59.9

(a) (b)

Fig. 13.54 Retaining wall and pressure distribution (Ex. 13.5)

Active pressure due to uniform surcharge = Ka.q

= 0.528 × 45

= 23.8 kN/m^2

The former will have triangular distribution while the later will have rectangular dis-

tribution with depth. The resultant pressure distribution diagram will be as shown in

Fig. 13.54 (b).