Essay on CBR Test and its Result Analysis

Analysis of the CBR results:
CBR value that is obtained from the sample helps to provide the strength of the soil, sub-grades of the road and the capacity of bearing load by the soil. The value that is obtained in the CBR test helps to determine the quality of pavements beneath the soil and this helps in evaluating the need of creating pavements below it. The soils with high CBR indicate that the pavement that would be required to be developed beneath it would not require excessive strength because high CBR of the soil indicates that the soil has high capacity to absorb load and resist penetration by the load (Asmani, Hafez, & Shakri, 2013).
It also involves considering the content of lime, fly ash and a mixture of lime and fly ash in the soil. All the specimens that were tested on the top and the bottom layer was done by using a standard proctor test. The quality of soil involves untreated compacted soils as well as treated stabilized one. It is observed that the soil which has higher lime content will have higher CBR as compared to that with low content of lime.
In this test, we have carried a penetration test through a plunger, that is, a compression machine that will be operated manually. It also involves considering the value of the corrected CBR as shown in the calculations above. The value which would be having higher CBR needs to be considered and the respective value of the penetration should either be 2.5 or 5 mm. it is found that when the value of CBR for the soil is found to be greater than 65%, then only the sample is going to be approved. The results are obtained at the top and the bottom layer with a penetration of up to 2.5 to 5 mm.
The graph that is plotted is for the values of load vs. penetration for the surfaces at the bottom as well as on the top at every 0.04 mm of penetration.
When the values for the bottom layer are considered, the following graph is obtained for load vs. penetration:

Here, it is found that for the bottom layer, the increment in the penetration layer is found to be from 0.02- 0.04 mm. the curve is steep in the beginning and then becomes consistent and follows a smooth curve afterwards. This shows the impurities and other factors present in the bottom layer of soil. The value of the CBR for the bottom layer helps to estimate the quality of the foundation that should be obtained in the base of the pavement and it also recommends various techniques of constructing the pavement depending on the strength of the soil in the bottom layer.
However, for the top the increment in the penetration is about .08 to .10 mm of the soil. The total penetration is measured and each individual curve for the top surface and the bottom surface is obtained. We have the curve for load vs. penetration for the top surface as follows:

It is observed that the curve increase steeply due to the irregularities that exist on the top surface and the unevenness in its texture. Thus, this values of CBR for the top layer will help to estimate the quantity and content of the filling that is required to be made under it to create pavements and provide support to the upper layer (Bandyopadhyay & Bhattacharjee, 2010). The top layer has to be finished smoothly and hence requires high value of CBR to ensure that the heavy rollers and other very heavy equipments can be rolled and moved over it without any problem.

With the advancement in technology and increase in the transport facilities, the development of infrastructure in terms of roads and highways has boosted on a large scale. At the same time, the loads on the construction companies to complete the construction of the roads within a specified short time and also provide the desired quality that is required by the Government and other customers has resulted into the automation in the construction industry.
The test that we have carried out provides the estimation of the pavements that is to be constructed while laying the foundation for the roads for both bottom as well as the top layer of the soil. This pavement strives to play a critical role in determining and guessing the life of the road when it will be exposed to different climatic conditions and wear due to the usage of the roads. The pavement that is to be constructed will take very less time if the sub grade of the soil on which it is to be created has high level of CBR on the top side and comparatively high level at the bottom too (Blakeley, 1965).
The bottom layer with the foundation and the top layer as the pavement on the surface above can be constructed quite speedily when the pavement required to be constructed beneath does not require much of the fillings to be made in it. However executing the CBR test on the field could cost more than carrying it on the same sample of soil. But the cost can be covered in terms of savings that can be made in the cost, time and man power, that is, labour that will be used in the construction of the roads and its pavements to ensure that the construction is of prescribed standards and quality as specified by the government.
Thus in order to meet the increasing demand of constructing highly efficient and strong roads that would sustain for a long time without any maintenance by the government, this test will help tremendously.
Asmani, D., Hafez, & Shakri. (2013). Comparison between Static and Dynamic Compaction for California Bearing Ratio (CBR).
Bandyopadhyay, K., & Bhattacharjee, S. (2010). Comparative Study Between Laboratory and Field CBR by DCP and IS Method. Indian Geotechnical Conference. Bombay: GEOtrendz.
Blakeley, J. (1965). The California bearing ratio test on loess. .: . Road Research Unit, National Roads Board. Wellington, N.Z.


Posted on

March 10, 2018

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