CBR laboratory test

The method was developed by the California Road Service in the 1930s and has since been adopted by many administrations/organisations around the world. The original test method has been slightly modified by some organisations. The modifications were mainly concerned on the moisture at compaction and on the compaction effort. The procedure, however, in determining the CBR value remained unchanged. 

The test determines the soil s bearing capacity from laboratory-compacted specimen, expressed as CBR. 

CBR is defined as the ratio of the load required to cause a certain penetration of the plunger into the soil material to the load required to obtain the same penetration on a specimen of standard material. 

The CBR laboratory test can be carried out by ASTM D 1883 (2007), AASHTO T 193 (2013) or CEN EN 13286-47 (2012) other equivalent national specifications may have been developed. 

The soil material, after being pulverised so as no aggregations (lumps) exist, passed through a 19.0 mm sieve. In case there are remaining aggregates on the 19.0 mm sieve, an equivalent mass is replaced from the same soil material passing through the 19.0 mm sieve but was retained on the 4.75 mm sieve. This replacement is necessary for the validity of the result when coarse soil material is tested. 

---