The California Bearing Ratio (CBR) test is used in evalutating subgrade, subbase and base materials as an aid to the design of pavements. The laboratory test uses a circular piston to penetrate material compacted in a mold at a constant rate of penetration. The CBR is expressed as the ratio of the unit load on the piston required to penetrate 0.1 in. (2.5mm) and 0.2 in. (5.1 mm) of the test material to the unit load required to penetrate a standard material of well-graded crushed stone.