CALIFORNIA BEARING RATIO TEST

(As per IS: 2720, Part-16)

Apparatus:

1. Moulds with base plates and collar.

2. Spacer disc, expansion measuring apparatus, annular weights and dial gauges. Loading machine of capacity 5000kg and penetration plunger.

Procedure:

1.     The material shall pass a 19mm sieve, replacement of 19mm pass and 4.75mm retained shall be done for larger material.

2.     The mass of wet soil at required OMC to give the desired density shall be calculated and soil shall be thoroughly mixed with water to give the required water content.

3.     The correct mass of soil shall be placed in the mould and compaction obtained by pressing in the displacer disc. A filter paper should place between disc and the soil. The mould with the soil should be kept in water for 4days soaking.

4.     Water Content should be determined before compaction  and after soaking as per IS:2720 part-2

5.     The tripod for expansion measuring device shall be mounted on the edge of the mould and the initial & final dial gauge reading shall be noted for swelling.

6.     After 4 days soaking the mould with the soil shall be placed on the lower plate of the testing machine and the surcharge weights shall be placed on the specimen.

7.     The plunger shall be seated and load applied to the plunger into the soil at the rate of 1.25mm per minute. Reading of load shall be taken at penetrations of 0.5, 1.0, 1.5, 2.0, 2.5, 4.0, 5.0, 7.5, 10.0 and 12.5mm.

8.     About 50gm of soil should be collected from the top 30mm layer for water content determination as per IS: 2720, Part2.

RESULT: The CBR values shall be calculated for penetrations of 2.5 and 5.0mm from the load penetration curve. Generally CBR value at 2.5mm penetration is higher and this value is adopted. However if CBR value at 5.0mm is high, test is to be repeated and is higher again CBR at 5.0mm value is reported as CBR value