The CBR laboratory test: What is it, and what is your procedure?

CBR Test

The test CBR (California Bearing Ratio: Test California Bearing Ratio) measures the resistance to shear of soil and to evaluate the quality of soil for subgrade, subbase, and base pavements. It is carried out under controlled humidity and density conditions. For the CBR Test this is an important deal.

Extended description

We differentiate different types of CBR according to soil quality, namely:

  • CBR undisturbed floors.
  • CBR remodeled floors.
  • CBR gravel and sandy soils.
  • CBR cohesive floors little or nothing plastic.
  • CBR plastic cohesive floors.

This procedure can be carried out in compacted soil.

This procedure measures the load necessary to penetrate a piston of determined dimensions at a previously fixed speed in a compacted sample of soil after it has been immersed in water for four days at the most unfavorable saturation and after having measured its swelling.

The sample is submerged to be able to foresee the hypothetical situation of moisture accumulation in the soil after construction. Therefore, after having compacted the soil and having submerged it, it is penetrated with a piston which is connected to a small “plotter” that generates a graph where the load is represented with respect to the depth to which the piston has penetrated inside. of the sample.

CBR Test

The graph obtained is usually a curve with the initial straight section and the final section concave downward; when the initial stretch is not straight, it is corrected.

With the graph, we observe the values ​​of the load that the ground supported when the piston had sunk 2.5 mm and 5mm, and we expressed them as a percentage (%), taking as the CBR index the highest of the calculated percentages.

The CBR test is used to evaluate the bearing capacity of compacted terrains such as embankments, pavement layers, esplanades as well as land classification.

The acronym CBR stands for Californian Bearing Ratio and comes from the fact that this essay was developed, before the Second World War, by the California Department of Transportation.

The CBR soil test basically consists of compacting soil in standardized molds, immersing them in water and applying a punching on the ground surface using a standardized piston.

It is governed by the ASTM 1883 standard or by the UNE 103502 standard, among others.

Next, the details of the CBR test are described.

CBR procedure floors

The CBR test consists of determining the load that must be applied to a 19.35 cm 2 circular piston to introduce it into a soil sample at a speed of 1.27 mm / min and until penetration of 2.54 mm is obtained. Through this procedure, what is called the CBR Index is determined, which is the relationship between the determined load and the one obtained by the same procedure for a sample type of crushed rock. It is expressed in percentage.

You need to be specific on the choice of these Tests. The more precise you are becoming, the better it is getting for you. This is what that makes the whole process perfect for you.