To understand the impact of CBR (subgrade strength) on the pavement, let's look at some typical CBR values. 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.
Is a higher CBR value better?
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.
What is the typical range of CBR value for subgrade?
CBR values for common soil subgrades can be estimated according to the USC soil types, for example: clay around 2%, sand from 7% (poorly graded) to 10% (well graded), well graded sandy gravel 15%, clayey sand 5-20%, silty gravel 20-60%, gravel from 30-60% poorly-graded to 40-80% if well-graded.
What is a low CBR?
Crude birth rates of more than 30 per 1,000 are considered high, and rates of less than 18 per 1,000 are considered low. The global crude birth rate in 2016 was 19 per 1,000. Countries with a low fertility rate (and low crude birth rate of 10 to 12 in 2016) include European nations, the United States, and China.19 Jan 2019
Can CBR be more than 100 %?
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. (Note: For material greater than 20mm please see Plate Bearing Tests).
What does CBR percentage mean?
Definition. The CBR is the ratio of the bearing load that penetrates a material to a specific depth compared with the load giving the same penetration into crushed stone. The CBR is expressed as a percentage of the actual load causing the penetrations of 2.5 mm or 5.0 mm to the standard loads on crushed stone.
What is a good CBR result?
A good quality laboratory load frame with a capacity of 10,000lbf (44.5kN) or more that can operate at a strain rate of 0.05in (1.3mm) per minute is suitable for CBR penetration testing.
What is a high CBR?
Crude birth rates of more than 30 per 1,000 are considered high, and rates of less than 18 per 1,000 are considered low. The CBR in the United States continued trending down, as it did for the entire world since peaking in 1963, coming in at 12 per 1,000.19 Jan 2019
How is CBR calculated?
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.
What is CBR value?
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 .