The CBR test is a soil ground bearing test that provides a strength parameter used to determine the thickness of road capping base. CBR values are also used to provide a general soil strength parameter when validating crane and piling mats.

In situ CBR tests can be carried out using the standard plunger method, or by the DCP (Dynamic Cone Penetrometer) method.

The plunger method gives a spot CBR test value at a specific depth. The plunger is pushed into the ground via a jacking device and load measured using a load measuring proving ring. The load required to push the plunger through successive 0.25mm increments is recorded and presented as a load versus settlement graph. The CBR is calculated by comparing the load required to push the plunger 2.5mm and 5mm toloads obtained from the standard CBR test as a percentage.

Generally an excavator bucket placed on the top of the testing frame provides counter weight for the test. Alternatively the test equipment may be fixed to the rear of a four by four.
CBR data can also be determined by using a DCP drop weight apparatus. A drop weight drives a small standard cone into the ground and the deflection in mm equates to a CBR value. With this test a profile of CBR versus depth is obtained up to one metre from ground surface.

CBR values can also be calculated from plate load testing. The method and calculation often used give a reasonable comparison where the ground is compact. Caution is required when using the plate test method to obtain CBR values on softer ground as unreasonably low values are often determined.