Determination of California Bearing Ratio of Soil using Dynamic Cone Penetrometer

Published on 04 Mar 2021. Written by Reddy Shekar

California Bearing Ratio (CBR) is a key parameter to ensure the strength of soil. Indian Road Congress (IRC) is also recommended the CBR values as an indicator of subgrade soil strength.

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The CBR values also used to design the base thickness of flexible pavements. Cost-expensive, tedious and fewer chances of repeatability are the few demerits of this conventional laboratory CBR test. Dynamic cone penetrometer test is an alternative solution for the conventional CBR test to minimize these demerits.

About California Bearing Ratio

The California bearing ratio is a penetration test for determining the strength of subgrade and base courses beneath the pavements. The CBR test is also used to find the load-bearing capacity of soils under paved airstrips. In the CBR test, the resistance of a material against penetration of standard plunger measured under the standard density and moisture conditions.

The CBR test developed by the California Division of highways to test and classify the sub-grade and base course materials for flexible pavements. The design of new flexible pavements and improving the strength of existing pavements needs more accurate CBR values. The conventional CBR test is not provided these required values at a much faster pace. So that, reason researchers developed dynamic core penetrometer to overcome these problems.

Apparatus required:

Dynamic Cone Penetrometer (DCP) :- The penetrometer should have 20mm base diameter and a 60 degree point angle. It consists of 8kg hammer used to driven into the soil with a free fall of 575mm.

Experimental Procedure:

1. Dynamic cone penetrometer carried on the existing subgrade or base courses to determine the DCP based CBR values at field moisture content and in-situ density.
2. The first step in this test is, placing the dynamic cone penetrometer on the subgrade properly.
3. The test starts with penetrating the hammer into the subgrade soil.
4. The soil resistant measured penetration (mm) per blows.
5. At least three trial reading should taken at different points on the location.
6. To determine the average CBR value.
7. Remaining field and laboratory tests should conducted as per the IRC recommendations.
8. To determine the different properties of subgrade soil.

Field and laboratory tests to be performed:

1. Sieve Analysis
2. Atterberg’s limit test
3. Compaction test
4. CBR test

Benefits:

1. Gives more accurate and efficient results
2. Less expensive
3. Less tedious method
4. Safer and less complicated.

Conclusion:

With the use of dynamic cone penetrometer, we can get more accurate CBR results compared to conventional laboratory CBR test. DCP test is the best method to find the mechanical strength of soil.

Kit required to develop Determination of California Bearing Ratio of Soil using Dynamic Cone Penetrometer:

• Dynamic cone penetrometer

Technologies you will learn by working on Determination of California Bearing Ratio of Soil using Dynamic Cone Penetrometer:

• CBR
• Dynamic cone pentrometer test

Any Questions?