What is the meaning of 100% CBR?

What is the meaning of 100% CBR?

The California Bearing Ratio (CBR) test is a simple strength test that compares the bearing capacity of a material with that of a well-graded crushed stone (thus, a high quality crushed stone material should have a CBR @ 100%).

What do CBR values mean?

The CBR value is the stress at the 0.100in (2.54mm) penetration depth. Occasionally, the ratio at the 0.200in (5.08mm) penetration depth is higher than the 0.100in depth, and the test must be rerun. If the check test shows similar results, the stress from the 0.200in penetration depth is the reported CBR.

What is a good CBR test result?

What are the typical CBR values? The harder the material, the higher the CBR value. A CBR value of 2% is usually found for clay, high-quality sub-base will have CBR values between 80% and 100%, and some sands may have values around 10%. The CBR testing can be applied to soils with a maximum particle size of 20 mm.

What is a good CBR value for subgrade?

It is crucial for highway engineers to develop a subgrade with a California Bearing Ratio (CBR) value of at least 10. Research has shown that if a subgrade has a CBR value less than 10, the subbase material will deflect under traffic loadings in the same manner as the subgrade and cause pavement deterioration.

How do you read CBR values?

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.

Where is CBR value used?

The CBR value is used as a measure to indicate the stiffness of the subgrade natural soils. For CBR readings <2% a capping layer founding stratum might be required where the subgrade stiffness is not viable for the construction of roads and pavement.

What does 10% CBR mean?

The measured pressure is then divided by the pressure required to achieve an equal penetration on a standard crushed rock material. 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%.

Why CBR value is important?

CBR value is required to determine the thickness of those layers, especially for base and subgrade materials. For lower CBR, the thickness of layers will be higher and vice versa. If the CBR value of a material is too low, the layer thickness will be much higher.

Can CBR exceed 100%?

High quality crushed rock has a CBR over 80. The standard material for this test is crushed California limestone which has a value of 100, meaning that it is not unusual to see CBR values of over 100 in well compacted areas.

What is the minimum CBR value of soil?

The minimum CBR value of a sub-base soil should be 20% and 30% for traffic up to 2 msa and traffic exceeding 2 msa respectively. Also, the minimum CBR value for a subgrade soil is usually 6%, although subgrade characterization recommends 10% [4] .

What is CBR formula?

4. 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.

What is the maximum CBR?

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.

Does CBR relate to bearing capacity?

There is a strong linear correlation between the estimated ultimate bearing capacity and the corresponding CBR value. Rosenak (1968) equation underestimates significantly the ultimate bearing capacity especially for the higher CBR values.

What is the standard value of CBR?

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. If C.B.R. for 5 mm exceeds that for 2.5 mm, the test should be repeated.

Why do we use CBR test?

CBR Testing (California Bearing Ratio) is primarily undertaken to provide data for road pavement design. It was first developed by the California State Highway Department. It is a penetration test which is used to evaluate the subgrade strength primarily of roads, pavements and foundations.

How is CBR test calculated?

If the CBR value corresponding to a penetration of 5 mm exceeds that for 2.5 mm, the test shall be repeated.
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Calculation for California Bearing Ratio (CBR) Test.

What is the unit of CBR?

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 .