Compaction of Soils

Compaction refers to increasing the density of soils and to decrease the percentage of air voids. 

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What is compaction of soil? 

Compaction is densification of soil by application of mechanical energy. It refers to increasing the density of soils and to decrease the air voids.

To increase the shear strength it is necessary to decrease the air voids, if air voids are there then water may enter into the voids leads to swelling and volume change hence compaction is necessary

How is it different from consolidation? 

Compaction is instantaneous where as consolidation is a time taking phenomena.

Compaction results in reduction in the volume of air voids. Consolidation leads to pore water expulsion

Lab compaction tests

Standard proctor test
• It is a dynamic impact test
• Mould is filled with soil and compacted by the hammer
• Soil is compacted in 3 layers with 25 blows in each layer

Modified Proctor Test
• Standard proctor test is modified
• Increased weight of hammer and height of fall
• Compacted in 5 layers with 25 blows each layer

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Methods of compaction

• Different rollers are used in the field for compaction
• Sheepsfoot rollers are used for clayey soils and plastic soils
• Vibratory rollers are used for cohesion less soils
• Results from the lab and field would always be different

Summary Points

• Compaction is densification of soil. Air voids decreased
• It increases shear strength of soils
• Compaction is different from consolidation
• Compaction is instantaneous
• Lab tests for compaction are Standard proctor test and Modified proctor test
• Field methods for compaction: Sheepfoot rollers, Vibratory Rollers

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