Why is a California Bearing Ratio (CBR) test performed?

The California Bearing Ratio (CBR) test is specifically performed to evaluate the strength of subgrade soils and is critical for pavement design. This test measures the bearing capacity of the soil, which is crucial in determining how well the soil can support loads from vehicular traffic and structures. A higher CBR value indicates better load-bearing properties of the subgrade, which directly influences the thickness and material selection for pavement layers.

The CBR test provides a numerical value that helps engineers design pavement that can adequately withstand the expected traffic loads and environmental conditions. By understanding the strength of the soil through the CBR assessment, engineers can make informed decisions on the design and construction of roads, ensuring durability and safety.

Other options focus on different aspects of soil properties. Assessing soil shrinkage limits relates to moisture movement and volume changes but does not directly determine strength for pavement design. Soil permeability pertains to how water flows through the soil, which is not the primary focus of the CBR test. Measuring soil density involves determining mass per unit volume, which is important for various engineering calculations but does not provide direct insight into structural capacity as evaluated by the CBR. Thus, the CBR test stands out because it directly assesses the essential strength properties relevant to subgrade soils in