To determine the California bearing ratio by conducting a load penetration test in the laboratory.
The california bearing ratio test is penetration test meant for the evaluation of subgrade strength of roads and pavements. The results obtained by these tests are used with the empirical curves to determine the thickness of pavement and its component layers. This is the most widely used method for the design of flexible pavement.
This instruction sheet covers the laboratory method for the determination of C.B.R. of undisturbed and remoulded /compacted soil specimens, both in soaked as well as unsoaked state.
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 . When the ratio at 5 mm is consistently higher than that at 2.5 mm, the ratio at 5 mm is used.
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) |
|---|---|
| 2.5 | 1370 |
| 5.0 | 2055 |
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.