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A brief explanation about CBR (California Bearing Ratio)
A brief explanation about CBR (California Bearing Ratio)
CBR (California Bearing Ratio) is an experimental carrying capacity developed by the California State Highway Department. The principle of this test is penetration testing by sticking an object into a test object. In this way can be assessed the strength of the base soil or other materials used to make pavement. Soil strength was tested by CBR test in accordance with SNI-1744-1989. The soil strength value is used as a reference to whether or not it is stabilized after being compared to that specified in the specification.
CBR testing is the ratio between the burden of penetration of a material to a standard material with the same depth and penetration speed. The CBR value is calculated at 0.1-inch penetration and penetration of 0.2 inches and then the results of both calculations are compared in accordance with SNI 03-1744-1989 are taken the greatest result.
The CBR value is the ratio (in percent) between the pressure required to penetrate the ground with a 3 inch2 round piston with a velocity of 0.05 inch/min against the pressure required to penetrate a certain standard material. The purpose of this CBR test is to know the value of CBR on the variation of the water content of compaction. To determine the strength of the basecoat by means of a CBR experiment, a value is then used to determine the required pavement thickness above a layer with a specific CBR value (Wesley, 1977). In testing the CBR value of soil can be performed in the laboratory. The subgrade on new road construction is the original soil, pile ground, or compacted soil until it reaches a density of 95% of the maximum density. Thus the carrying capacity of the soil is the value of the ability of the soil layer to bear the load after the soil is compacted. This CBR is called CBR plan point and because it is prepared in the laboratory, it is called CBR laboratories. The higher the soil CBR value (subgrade) then the pavement layer will be thinner and smaller the CBR value (low soil bearing capacity), the thicker layer of pavement on top will be loaded.
There are two kinds of CBR measurements:
1. CBR value for penetration pressure at 0.254 cm (0.1 ") against penetration
the standard is 70.37 kg / cm2 (1000 psi).
Value of CBR = (PI / 70,37) x 100% (PI in kg / cm2)
2. CBR value for penetration pressure at 0,508 cm (0.2 ") penetration
against standard penetration of 105.56 kg / cm2 (1500 psi)
Value of CBR = PI / 105.56) x 100% (PI in kg / cm2)
Of the two counts are used the greatest value.
CBR laboratories can be divided into two kinds:
a. CBR Soaking Laboratory (CBR)
b. CBR laboratory without immersion (Unsoaked Design CBR)
In the CBR laboratory testing the exertion is more difficult because it requires relatively greater time and cost than laboratory CBR without immersion.
While the results of laboratory CBR testing soaked up so far have always resulted in greater soil bearing capacity compared to CBR of immersion laboratory.
That's it for the info about CBR that we may share with you. We really hope this info can be useful for you and so you will understand more about soil.
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