Technical Data – In-situ Testing: CBR & Plate Bearing

In-situ CBR Testing The California Bearing Ratio test, or CBR test, is an in-situ testing method which is used to estimate the bearing value and the mechanical strength of highway subbases and subgrades. In the test, a cylindrical plunger which has an area of 1935mm2 is forced into the soil at a uniform rate of 1 mm per minute. This requires the use of a reaction load, (usually a 4WD drive vehicle), to provide the force to the plunger and CBR press. The CBR is the ratio of the force required to cause a standard penetration divided by the force required to cause the same penetration in a standard material, expressed as a percentage.

Plate Bearing Test The plate bearing test is carried out in accordance with BS 1377 Part 9: 1990 Standards. In this test, a plate of known dimensions is jacked against a reaction load, usually the underside of a tracked excavator and deformation readings are taken. The results can be used then to determine whether the ground has sufficient bearing capacity to support temporary structures such as cranes or piling rigs. A prediction of settlement can also be made.