Geotechnical Engineering

DHARM

LATERAL EARTH PRESSURE AND STABILITY OF RETAINING WALLS 535

Eccentricity, e = (1.317 + 0.565 – 1.750) = 0.132 m

Since this is less than (1/6) b or (1/6) × 3.5 m, no tension occurs at the base.

Vertical pressure intensity at the base, σ =

W

b

e

b

1 6 345

35

1 6 0132

35

F ±

HG

I

KJ

=±F ×

HG

I

. KJ

.

.

or σmax = 120.88 kN/m^2 at the toe

and σmin = 76.26 kN/m, at the heel.

Example 13.27: A trapezoidal masonry retaining wall 1 m wide at top and 3 m wide at its

bottom is 4 m high. The vertical face is retaining soil (φ = 30°) at a surcharge angle of 20° with

the horizontal. Determine the maximum and minimum intensities of pressure at the base of

the retaining wall. Unit weights of soil and masonary are 20 kN/m^3 and 24 kN/m^3 respectively.

Assuming the coefficient of friction at the base of the wall as 0.45, determine the factor of

safety against sliding. Also determine the factor of safety against overturning.

(S.V.U.—B.E., (Part-time)—Dec.,1981)

Pai

Pah

1.33 m

b= 20°

1m

g= 24 kN/m^3

g

f

= 20 kN/m

= 30°

3

Toe x Heel

3m

W/R 2 W 1

Fig. 13.72 Retaining wall (Ex. 13.27)

For backfill,

γ = 20 kN/m^3 φ = 30° β = 20°

Kai = cos β.

(cos cos cos )

(cos cos cos )

ββφ

ββφ

−−

+−

22

22

= cos.

(cos cos cos )

(cos cos cos )

20

20 20 30

20 20 30

22

22

°

°− °− °

°+ °− °

= 0.414

Pai =

1

2

1

2

γHK^22 ..ai=× × ×20 4 0 414 66 24=.kN / m