@meseretterefe543: CBR stands for California Bearing Ratio. It is a penetration test used to evaluate the mechanical strength and load-bearing capacity of subgrade soil, sub-base, and base course materials used in road construction and pavement design. Developed by the California Division of Highways in 1929, the test measures the resistance of a soil sample to penetration under controlled moisture and density conditions. How the Test Works Sample Preparation: Soil is compacted into a standard cylindrical mold at optimum moisture content (OMC) using standard or modified Proctor compaction. For wet-climate simulation, samples are often soaked in water for 96 hours to evaluate swelling and soaked strength. Penetration: A standard metal plunger (piston) with an area of 3 square inches (19.35\text{ cm}^2) is forced into the soil sample at a constant rate of 1.27 mm/min (0.05 inches/min). Load Measurement: The forces required to achieve penetrations of 2.5 mm (0.1 in) and 5.0 mm (0.2 in) are recorded. Mathematical Formula The CBR value is expressed as a percentage, comparing the test load to the standard load required to penetrate a high-quality crushed limestone material:
