Geotechnical Engineering

DHARM

STABILITY OF EARTH SLOPES 347

The following ru values obtained from a flow net and weights of slices are given:

Slice No. 12345

ru 0.360 0.420 0.375 0.300 0.075

W (kN) 42 114 150 162 75

a=

10°

1

1m

2

2.6

5°1.5

b = 2.5 m

3

13.6

20° 35°^4

3.9

5.6°

5

2

6m

11.7 m

r=9m

88°

Fig. 9.29 Stability analysis by the conventional approach (Ex. 9.9)
Conventional approach:
The calculations are best set out in a tabular form as shown below for the conventional
approach:

Table 9.2 Stability of downstream slope of an earth

dam–conventional approach

Slice z(m) b(m) W (kN) α° cos α sec α cos α– W(cos α– sin α W sin α

No. rusec α ru sec α)

tan φ

1 1.0 2.2 42 –10 0.985 1.015 0.620 13.27 –0.174 –7.31

2 2.6 2.2 114 5 0.996 1.004 0.574 33.34 0.087 9.92

3 3.6 2.2 150 20 0.940 1.063 0.541 41.35 0.342 51.30

4 3.9 2.2 162 35 0.819 1.208 0.457 37.72 0.574 92.99

5 2.2 2.2 75 56 0.559 1.788 0.425 16.24 0.829 62.18

Σ = 141.92 Σ = 209.08

θ = 88° ∴ c′rθ = 9 × 9 × 88π/180 = 124.41 kN

Factor of safety F =

(. .)

.

124 41 141 92

209 08

+

= 1.274