Geotechnical Engineering

DHARM

SOIL STABILISATION 715

17.5.2Use of CBR

Design curves have been developed by different authorities for determining the appropriate
thickness of construction above subgrade materials of known CBR for different wheel loads
and traffic conditions. This approach is one of the popular ones for the design of flexible pave-
ments.

Typical design charts developed by the Road Research Laboratory, London, which are
also used in India, are shown in Fig. 17.4 and 17.5.

0

10

20

30

40

50

60

70

80

90

100

Thickness of construction, cm

2 3 4 5678910 15 20 30 40 50 6070 80 100

C.B.R.

Curve

A B C D E F G

No. of vehicles day (> 3t)

0–15

15–45

45 – 150

150 – 450

450 – 1500

1500 – 4500

Over 4500

AA

BBCC

DDEE

FFGG

Fig. 17.4 Design charts for flexible pavements—CBR method

(After R.R.L., London & Alam Singh, 1967)

0

10

20

30

40

50

60

70

Thickness of construction, cm

2345689101520 30 40 50 607080

C.B.R

Medium traffic

(40 kN wheel load)

Light traffic

(30 kN wheel load)

Heavy traffic

(50 kN wheel load)

Fig. 17.5 Use of CBR in the design of flexible pavements