Considering
(i) Number of layers
(ii) Weight of hammer
(iii) Height of fall
(iv) Number of blows
The key parameters in dynamic compaction for California Bearing Ratio (CBR) Test mold are

Explanation:

California Bearing Ratio (CBR) Test is used to evaluate the strength of subgrade soil for roads and pavements. The test involves compacting soil into a mold and then penetrating it with a plunger to measure resistance.

The quality of compaction affects the test results, and these factors are key:

Number of Layers 

• The soil is placed in the mold in layers to ensure uniform density throughout the specimen.

• Typical CBR procedures use 3 layers for compaction.

• Uniform layering avoids zones of weakness or excessive density variation in the specimen.

Number of Blows 

• Compaction is achieved by giving a certain number of hammer blows per layer.

• The number of blows ensures consistent energy input for each layer and is crucial for achieving repeatable and accurate test results.

• For example: Standard CBR uses 56 blows per layer with light compaction; Modified CBR uses more blows or heavier compaction.

 Additional InformationStandard CBR Test (Used for evaluating subgrade for flexible pavements like roads)

Soil Compaction:

• Soil is compacted in 3 layers inside a standard mold.

• Each layer receives 56 blows using a 2.6 kg hammer.

• The hammer falls from a height of 310 mm.

• The purpose is to achieve light compaction, simulating ordinary subgrade conditions.

Modified CBR Test (Used where higher pavement loads or airfield pavements are expected)

• Soil Compaction:

  • Soil is compacted in 5 layers.

  • Each layer is compacted with 56 blows using a heavier 4.9 kg hammer.

  • Hammer falls from a greater height of 450 mm.

  • This provides higher compaction energy, simulating more heavily loaded conditions (e.g., airports).