California bearing test is a test conducted both in institute as well as lab to find out the stability and strength of the soil sample. The outcomes of the test are showed in percentage and are relative outcomes. It was developed by the California Department of Transportation in the 1930s. The CBR test is used to measuring the load-bearing ability for new road, pathways, and airstrips or soils already under paved places. The California Bearing Ratio is a measure of resistance of material to penetration of a plunger under controlled moisture and density conditions.
The advantages of the CBR testing with STS
- The test can be done by personnel with relatively pretty experience and training
- The CBR technique adapts more rapidly to airfield pavement design for quick use than any other technique.
- The test is correlated to behavior service and construction techniques and has been successfully used for many years.
- You can run tests in either the laboratory or the field for design, evaluation of existing construction, or construction control.
- You can test soil with portable, simple equipment.
- Testing can be performed on samples representatives of future water situations.
- The test is initially intended for sub-grades but applicable to a big range of different materials.
- At least 3 samples should be tested on each soil sample at same moisture and density content. If the highest variation in the CBR values of 3 samples exceeds the specified restrictions, the CDR design should be the average of at least 6 samples.
- A guess of road traffic to be carried out by the road pavement at the end of guessed life should be made keeping in view the growth rate of traffic and existing traffic. Pavements of big roads should be designed for a period of 10 years.
- The perfect design curve should be picked from the table given in design chart after guessing the design traffic.
Factors affecting CBR
The general soil factors affecting the CBR are moisture, soil texture, and density. The STS testing procedure employed depends mainly upon the kind of stuff being tested. Granular soils are largely affected by swelling during the soaking period. In contrast, claylike soils, which are largely affected by swelling forces, yield CBR values depending upon the weight of the sub-charges applied during the soaking period. Sub-charges weights are very vital during the penetration portion of the granular test stuffs but not too important for the very well grained soils.