What is a CBR value?
The California Bearing Ratio (CBR) is a measure of the strength of the subgrade of a road or other paved area, and of the materials used in its construction. The ratio is measured using a standardized penetration test first developed by the California Division of Highways for highway engineering.
What is a good CBR test result?
The CBR test is performed by measuring the pressure required to penetrate a soil sample with a plunger of standard area. Typically, a value of 2% equates to clay, while some sands may have a CBR value of 10%. High quality sub-base will have a value of between 80-100% (maximum).
What is the meaning of CBR in soil?
CBR is the ratio expressed in percentage of force per unit area required to penetrate a soil mass with a standard circular plunger of 50 mm diameter at the rate of 1.25 mm/min to that required for corresponding penetration in a standard material. The ratio is usually determined for penetration of 2.5 and 5 mm .
Why CBR test is done?
The california bearing ratio test is penetration test meant for the evaluation of subgrade strength of roads and pavements. The results obtained by these tests are used with the empirical curves to determine the thickness of pavement and its component layers.
Why CBR test is important?
The purpose of doing a CBR test is to find out the California Bearing Ratio (CBR) of a material which has to be used for the subgrade of flexible pavements. We can read the required thickness for which we need to design the subgrade layer if we know the CBR of our material and the design traffic.
What is the main drawback of CBR method?
Main drawback of CBR method is that it. Does not consider the strength characteristics of sub-grade soil. Is a complex method. Gives the total thickness which remains the same irrespective of the quality of materials used in the component layers.
How do you calculate CBR?
C.B.R. = (PT/PS) X 100 The C.B.R. values are usually calculated for penetration of 2.5 mm and 5 mm. Generally the C.B.R. value at 2.5 mm will be greater than at 5 mm and in such a case/the former shall be taken as C.B.R. for design purpose.
