Geotechnical Engineering

DHARM

SOIL STABILISATION 719

Load versus penetration curve is drawn as shown in Fig. 17.7.

9.6

7.4

01 234 567 8

Penetration, mm

Load, kN

12

11

10

9 8 7 6 5 4 3 2 1

Fig. 17.7 Load versus penetration curve (Example 17.1)

Standard Load:

At 2.5 mm ... 13.44 kN

At 5.0 mm ... 20.16 kN

CBR at 2.5 mm penetration =

Test load at 2.5 mm

Standard load at 2.5 mm

× 100

=

74

13 44

.

.

× 100 = 55%

CBR at 5.0 mm penetration = Test load at 5.0 mm

Standard load at 5.0 mm

× 100

=^96

20 16

.

.

× 100 = 47.6

Since, the CBR is greater at 2.5 mm penetration, it is to be taken.

∴ CBR = 55%.

Example 17.2: The following observations are made in a standard CBR test. Plot the values
and evaluate the CBR value of the soil.

Penetration (mm) 2.5 5.0 7.5 10.0 12.5

Load on piston (kg/cm^2 )1028496063

(S.V.U.—B.E., (Part-time)—Dec., 1981)

Standard Load:

At 2.5 mm penetration ... 70 kg/cm^2

At 5.0 mm penetration ... 105 kg/cm^2

The observations are plotted as shown in Fig. 17.8.