What should be the CBR value for subgrade?

CBR value for subgrade in road construction in India : CBR value is taken at 2.5mm & 5 mm penitration. in subgrade material CBR value should be nearly 15-19% .

What does CBR mean in soil?

California Bearing Ratio
The California Bearing Ratio or CBR test is performed in construction materials laboratories to evaluate the strength of soil subgrades and base course materials.

What is CBR subgrade?

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 the CBR value for subbase?

The harder the surface, the higher the CBR value. 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). The CBR test is carried out on soils with a maximum particle size of 20mm.

Which soil is best for subgrade?

A clayey soil generally has a low CBR value (less than 8). Sands are more granular and drain better and will generally have CBR values between 15 and 35. Gravel will have the best CBR values, generally 25 and up. That is why it is suggested to save the best material to cap the subgrade.

How is subgrade prepared?

The foundation of the pavement structure is known as subgrade. Preparation of subgrade consists of all operations before the pavement structure could be placed over it and compacted. The subgrade may be situated on an embankment or excavation or at the existing ground surface.

What is the minimum value of CBR of subgrade in flexible pavement?

➢The sub-base material should have minimum CBR of 20% for cumulative traffic up to 2 msa and 30% for traffic exceeding 2 msa. ➢The material should be tested for CBR at the dry density and moisture content expected in the field.

What is a good CBR test result?

C.B.R. values are usually calculated for penetration of 2.5 mm and 5 mm. If C.B.R. for 5 mm exceeds that for 2.5 mm, the test should be repeated. If identical results follow, the C.B.R. corresponding to 5 mm penetration should be taken for design.