field compaction

 

General

Granular soil is compacted with a standard amount of energy over a range of moisture contents to identify the optimum moisture content for maximum compaction.

Fills for highways and buildings must be compacted to attain appropriate strength and minimize settlement.  The most common method of specifying compaction is to require a certain percent of the maximum that can be attained in proctor compaction tests.

The original moisture-density test was developed by R.R. Proctor and is commonly referred to as the Standard Proctor Test, Proctor Test, or Standard Moisture-Density Test.   The Modified Proctor or Modified Moisture-Density Test is performed the same way but in a larger mold with higher compactive energy. Each of the approximately 8 different variations of standard and modified proctor se can produce different results, so contract documents must specify which  procedure is to be used.

Apparatus

 
Standard Proctor (5.5 lb, 12-in. drop) Hammer
Standard Procotor (1/30 ft3=944cm3) Mold
Moisture cups
Straight Edge
Spatula
Sprinkler Bottle
Paint Brush
Large Mixing Pan
#4 sieve Scale accurate to 0.01g for water content samples
Scale accurate to 0.01 lb. or 1 g for weighing mold
 

Procedure


 

Procedure 

  1. Take 2kg of sample and add 2% of water by weight and mix thoroughly.

  2. Record the empty weight of mold.

  3. Place the extension collar on the mold and put the sample to approximately half of the mold height. This is to ensure that the sample will reach one third of the height of the mold after compaction.

  4. Compact the sample in three layers at the rate of 25 blows per layer

  5. Remove the extension collar and trim the sample even with the top of the mold using the straight edge.

  6. Record the weight of mold with sample.

  7. Remove the entire sample and place it in a can whose weight has been recorded. Take the weight of can with sample. Then, place it in a n oven to determine the moisture content.

  8. Repeat the above steps with increasing water contents of 4,6,8,10 and 12 percentages.

  9. Calculate the dry unit weight and plot it with water content. Find the optimum water content from the plotted graph.

NOTE:

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Final compacted sample height should not be less than the mold height.

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Make sure to remove the collar before taking weight.

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A minimum of 4 tests on dry side of optimum and two on wet side of optimum should be performed.

Data Sheets [right-click | "save target as" Excel 2000]

References

Al-Khafaji & Andersland (1992), pages 530-539.

Lambe (1951), 43-51.