California Bearing Ratio Trial

The California bearing ratio ( Engl. Engl. As "Californian viability ratio" shortly CBR test ) is a test method, the carrying capacity of that help soils and hydraulically bound layers can be (rarely) studied. The process was originally developed for fastening airfield surfaces and is now also used in road construction . Basically, the experiment indicates how much force a punch has to be pressed into a soil sample in order to reach a certain depth at a defined penetration speed. The greater the required stamp pressure, the higher the load-bearing capacity of the soil sample.

In addition to assessing the strength, the test result can also be used to make statements regarding the frost sensitivity of a soil and the effect of soil consolidation with lime.

Test procedure

The experiment is carried out on a disturbed soil sample in the laboratory. The sample is normally "hammered" in a container with the ideal water content using the Proctor method, or the modified method, and can then be tested under consideration of any storage conditions (see above). The test stamp, with a circular cross-sectional area of ​​1963 mm², is pressed into the soil sample at a constant speed of 1.27 ± 0.02 mm / min. The maximum penetration depth is usually 10 mm. The test result is compared with a standard soil, a mixture of California limestone, and a ratio is established. This percentage ratio gives the CBR value:

${\displaystyle CBR={\frac {p}{p_{s}}}\cdot 100\quad }$

${\displaystyle CBR\quad }$	= CBR value [%]
${\displaystyle p\quad }$	= Pressure under the stamp for the soil sample [N / mm²]
${\displaystyle p_{s}\quad }$	= Pressure under the punch with the standard floor [N / mm²]

See also

• Proctor trial
• Plate load test

Norms and standards

• DIN EN 13286-47 - Test method for determining the CBR value
• Technical test regulations for soil and rock in road construction (TP BF-StB, Part B 7.1)