Proctor Compaction Test


Soil compaction is a mechanical process by which the soil particles are constrained to be packed more closely together by reducing the air voids. Soil compaction causes decreases in air voids and consequently an increase in dry density. This may result in increase in shearing strength. Increase the dry density of a soil due to compaction.
Compaction depends on following three factors
  • The nature of soil
  • The compacting moisture content
  • The amount of compaction or compactive effort
At the laboratory, the dynamic compaction test call proctor compactions test is tested for determining the moisture-density relationship of soils. This relationship indicates that under a given compaction effort every soil has optimum moisture content at which the soil attains maximum dry density.
Through the compaction test, the maximum dry density (MDD) and optimum moisture content (OMC) of the soil found for the selected type and amount of compaction. The OMC of the soil indicates the particular moisture content at which the soil should be compacted to achieve MDD. The MDD in the proctor compaction test lower value indicating weaker soil.
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Proctor compaction test
Testing procedure:
The soil to be used in the test is first air dried and passed through a 20m test sieve.
It is mixed thoroughly with a small amount of water and compacted into the mould 5 equal layers.
Each layers being compacted by 27 blows of the 4.5Kg hammer dropped through a height of 450mm above the soil surface.
The soil is trimmed to the tope of the mould and weighted to determine it is dry density.
The test is repeated five times with gradually increasing water contents until the whale of the relevant range of water content has been covered.
Then, the moisture content and the dry density are determined and plot the dry density-moisture content graph. From this graph, the maximum dry density and optimum moisture content are read out the graph curve comes similar to following graph.
Calculation
image
a Dry density Vs moisture content

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