What is the California Bearing Ratio a measurement of?

The California Bearing Ratio (CBR) is a measurement that specifically evaluates the soil's resistance to penetration by a standard cylindrical rod, which reflects the soil's ability to support loads. This test is particularly used in the field of civil engineering and geotechnics to assess the strength of subgrade soils for road construction and other pavement designs.

The CBR value is derived from the ratio of the pressure required to penetrate the soil to that required to penetrate a standard crushed rock material. A higher CBR value indicates a stronger soil that can better withstand traffic loads, which is critical for planning and construction in areas subject to vehicular traffic.

The other options relate to different soil characteristics but not directly to the CBR. For instance, soil's moisture level pertains to the water content in the soil, which is measured differently than by CBR. Compaction level reflects how densely the soil is packed, and contamination levels indicate the presence of pollutants or harmful materials but do not evaluate the soil's load-bearing abilities. The accurate focus of the CBR measurement makes it a vital parameter in determining the suitability of soil for foundational and pavement design.