Civil Engineering Reference
In-Depth Information
Example 14.4:
CBR test
A CBR test on a sample of subgrade gave the following results:
Plunger penetration (mm)
0.25
0.5
0.75
1.0
1.25
1.5
1.75
2.0
Plunger load (kN)
1.0
1.6
2.4
3.6
4.5
5.3
6.0
6.8
Plunger penetration (mm)
2.25
2.5
2.75
3.0
3.25
3.5
3.75
4.0
Plunger load (kN)
7.5
8.3
9.0
9.4
10.1
10.7
11.2
11.7
Plunger penetration (mm)
4.25
4.5
4.75
5.0
5.25
5.5
5.75
6.0
Plunger load (kN)
12.2
12.7
13.0
13.5
14.1
14.4
14.6
14.9
The standard force penetration curve, corresponding to 100% CBR has the following
values:
Plunger penetration (mm)
2
4
6
8
Plunger load (kN)
11.5 17.6 22.2 26.3
Determine the CBR value of the subgrade.
Solution:
The standard penetration curve is shown drawn in Fig.
14.12.
The test points are plotted and a smooth curve drawn through them. In this case there
is no need for the correction procedure as the curve is concave upwards in its initial
stages.
From the test curve it is seen that at 2.5 mm the plunger load is 8.3 kN and at 5.0 mm
the penetration is 13.5 kN.
Fig. 14.12
Example
14.4.
