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CBR LAB REPORT
Introduction
The California Bearing Ratio(CBR) test was developed by the California Division of Highways as a method of classifying and evaluating soil- subgrade and base course materials for flexible pavements. CBR is a measure of resistance of a material to penetration of standard plunger under under controlled density and moisture conditions. CBR test may be conducted in remoulded or undisturbed sample. Test consists of causing a cylindrical plunger of 50mm diameter to penetrate a pavement component material at 1.25mm/minute. The loads for 2.5mm and 5mm are recorded. This load is expressed as a percentage of standard load value at a respective deformation level to obtain CBR value.
Objectives
To determine the California Bearing Ratio value of the subgrade soil.
Apparatus
-CBR mould -Filter paper -Water -Soil -Weighing scale -Rammer -Loading machine -Metal weight -Spacer disk
Procedure
1.
Weight the mould with the plate.
2.
Sieve soil for 6 kg. Put in large container.
3.
Add 10% of water into the soil. Combine well.
4.
Lubricate the mould and put filter paper in the mould,on the top of plate. Attache collar to the mould.
5.
Put soil into the mould,for five layers and every layers have 62 blows.
6.
After done five layers, remove the collar and weight the mould with plate and compacted soil.
7.
Reattached mould invertedly to plate wtihout the spacer disk at bottom.
8.
Put filter paper and load with metal weight on top of the compacted soil.
9.
Turn on the machine for the test.
10. Some soil from the compacted soil are taken for the determination of moisture content.
Result
Results - Top
Penetration
2.50
5.00
mm
Load
1.15
2.05
kN
Standard Load
13.20
20.00
kN
California Bearing Ratio
8.70
10.26
%
Results - Bottom Penetration
2.50
5.00
mm
Load
1.90
2.87
kN
Standard Load
13.20
20.00
kN
California Bearing Ratio
14.41
14.36
%
Discussion
In this test, each group are given about 6kg of soil to complete the test. The test every step has been taken as the procedure. The result we obtained is the result of top and bottom for penetration 2.50mm and 5.00mm.
From the result we see that the CBR value for 2.50mm penetration for the bottom is higher than the top which the bottom is 14.41% while the top is 8.70%. The result happen the same for 5.00 mm penetration.
Throughout the test there are few precaution need to be taken such as align the surcharged weight with the plunger so that the plunger penetrates freely to the soil and ensure doing the compaction with 62 blows every layer so that the result of the t est is true and to avoid any errror that may arise.
Conclusion As the conclusion,the repeated load CBR test is a simple and quick test to get a good estimate of the effective modulus of fine grained materials and, most probably, of coarser grained unbound base and subbase materials too. Although not discussed in detail, it can be stated that the repeated load CBR test is a useful tool to evaluate the influence of example gradation, degree of compaction and moisture content on the resilient modulus and resistance to permanent deformation of soils and unbound materials.
