what is a cbr test
6. The CBR test is one of the most commonly used methods to evaluate the strength of a sub grade soil, sub base, and base course material for design of thickness for highways and airfield pavement. 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.t is the ratio of force per unit area required to penetrate a soil mass with standard circular piston at the rate of 1.25 mm/min. to that required for the corresponding penetration of a standard material.