California Bearing Ratio (CBR) of Soil

The CBR test measures the resistance of a compacted soil sample to penetration by a standard plunger, and expresses it as a percentage of the resistance offered by a standard crushed-stone material. It can be run on remoulded samples at the design moisture/density, either unsoaked or after four days of soaking to simulate the worst-case saturated condition.

CBR value is the key input to flexible pavement thickness design (as used for roads and airfields) — a lower CBR means a thicker pavement structure is needed to spread the traffic load.