BASIC PROCEDURE OF CALIFORNIA BEARING RATIO (CBR) TEST

California Bearing Ration is the test which is carried out, in a very indirect way, to find out the thickness of pavements and layers in road construction. The principle lies in using a penetration equipment on a prepared soil sample and then taking ratios of it with a standard value; this results in an empirical curve which is then analysed to work out the thickness of pavements. In this blogpost, you will get to know the basic procedure of California Bearing Ratio (CBR) test.

Procedure:

  • ·         Weigh the empty mould for accurate results.
  • ·         Assemble the mould and attach the collar over it.
  • ·         Add water to the specimen and start compaction as per the Standard Proctor or the Modified Proctor test.
  • ·         When compaction is complete, remove the collar and use a cutting edge to level off the surface of specimen.
  • ·         Weigh the mould and compacted specimen, and work out the bulk density of the specimen.
  • ·         Take a sample for moisture content test; work out dry density of sample.
  • ·         Place the mould upside down on the base plate covered with filter paper to perform un-soaked penetration test.
  • ·         Calibrate the load and deformation gauges to show zero.
  • ·         The plunger should load the soil at a rate of 1.25mm per minute. Take readings at 0.5, 1.0, 1.5, 2.0, 2.5, 4.0, 5.0, 7.5, 10.0 and 12.5 mm.
  • ·         Remove the plunger and take moisture content of the specimen.
  • ·         Plot the load-deformation curve using the readings thus obtained.

Follow the steps above to make sure you perform CBR test accurately.


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