Geotechnical Engineering

DHARM

568 GEOTECHNICAL ENGINEERING

14.5.9Balla’s Method

Balla has proposed a theory for the bearing capacity of continuous footings (Balla 1962). The
theory appears to give values which are in good agreement with field test results for footings
founded in cohesionless soils.

The form of the bearing capacity equation is the same as that of Terzaghi:

qult = c. Nc + γDf Nq +

1

2

γ b Nγ
But the equations for the bearing capacity factors are cumbersome to solve without the
aid of a digital computer. Therefore, it is generally recommended that Balla’s charts be used
for the determination of these factors.

The charts are shown in Figs. 14.12 and 14.13:

5.5

4.5

3.5

2.5

1.5

0.5

r

D/b=0f

10° 30° 50°

c/b = 3.5g

2.5

1

0.5

0

f

5.5

4.5

3.5

2.5

1.5

0.5

D /b = 1.5f

10° 30° 50°

0

f

c/b = 3.5g

5.5

4.5

3.5

2.5

1.5

0.5

D/b=1f

10° 30° 50°

0

f

c/b = 3.5g

5.5

4.5

3.5

2.5

1.5

0.5

D /b = 0.5f

10° 30° 50°

0

f

c/b = 3.5g

r r r

Fig. 14.12 Balla’s charts for the parameter ρ

600

(^0) 10° 20° 30° 40° 50°
Nq
Nq
f
0.5
r=4
600
(^0) 10° 20° 30° 40° 50°
Ng
Ng
f
0.5
rf=
400
300
200
100
(^0) 10° 20° 30° 40° 50°
Nc
Nc
3
2.5
2
1.5
1
0.5
f
r=4
0°
Fig. 14.13 Balla’s charts for the bearing capacity factors