Procedure of California Bearing Ratio Test:
1. Take a given soil; sample and add water equal to OMC of soil to prepare wet mix soil.
2. Take the CBR mould of 150 mm diameter and 175 mm height. Keep it inverted fashion and put the spacer disc of 50 mm thick at its bottom.
3. Fill the prepared wet soil in it within number of layers by properly compacting with rammer. Fill it completely and trim excess soil if any.
4. Now make the CBR mould in regular fashion and remove the space disc. Put the one or two surcharge weights of 2.5 kg each on the soil.
5. Keep it over loading platform of CBR test apparatus as shown in figure 6(c) below.
6. Insert the plunger of 5 cm dia. In the slotted weight and apply the compressive load at a rate of 1.25 mm per minute constantly.
7. Note down the load at each 0.5 mm penetration. Continue the loading till failure of soil or 12.5 mm maximum penetration.
8. Draw the graph i.e. load penetration curve to find the test load.
The load values corresponding to 2.5 and 5.0 mm penetration values from the corrected graph are noted as Test load. Normally the CBR value at 2.5 mm penetration which is higher than that at 5.0 mm penetration recorded.
9. Calculate the California Bearing Ratio of given soil as
% CBR = (Test load / Standard load ) X 100.