What is the purpose of a California Bearing Ratio (CBR) test?

The California Bearing Ratio (CBR) test is specifically designed to evaluate the strength of subgrade soil, which is crucial for the design and construction of roadways and other paved surfaces. The test measures the penetration resistance of the soil when subjected to a standard load, allowing engineers to determine the relative strength of the soil compared to a standard crushed rock material.

By assessing the CBR value, engineers can gauge how well the soil will support traffic loads, which directly affects the thickness and type of pavement necessary for a given roadway. Ensuring that the subgrade soil is adequately evaluated helps in preventing future structural issues related to inadequate support, thus maintaining the integrity and durability of road constructions.

The other options do not align with the primary purpose of the CBR test, which focuses on the strength aspect rather than saturation, groundwater levels, or permeability. The test does not measure saturation levels of the soil, which are more suitably assessed by other methods; groundwater assessment requires different testing methodologies; and soil permeability is evaluated through separate tests designed to measure water movement through soil.