It 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 . When the ratio at 5 mm is consistently higher than that at 2.5 mm, the ratio at 5 mm
The following table gives the standard loads adopted for different penetrations for the standard material with a C.B.R. value of 100%.
|Penetration of Plunger (mm)||Standard Load (kg)|
Table 1 : Standard Load Values at Penetration
For Railway Formation purpose, the test is performed on remoulded specimens which are compacted dynamically.
The methodology covers the laboratory method for the determination of C.B.R. of remoulded /compacted soil specimens in soaked state.
IS 2720(Part 16):1987 Methods of test for soils: Laboratory determination of CBR (second revision). Reaffirmed- Dec 2016.
RDSO report No. RDSO/2009/GE: G-0014 - Guidelines and Specification for Design of Formation for Heavy Axle Load.
|Penetration(mm)||Applied Load (kg)|
Table 2 : Recordings during CBR Test