3) Soil compaction

3) Soil compaction

1. Process of obtaining higher density of soil by reduction of its pore space through forced expulsion of air

   • Unit weight increases
   • Air voids are reduced to a minimum
   • Denser soils support more load
   • Expressed in terms of dry unit weight γd
   • Reduction in void ratio
   • Increase in soil strength
   • Reduces settlement
   • Decreases permeability
   • Prevents liquefaction during earthquakes

2. Compaction process

   • Loose soils are densified using equipment that apples compressive mechanical energy on the soil
   • Instantaneous, carried out on partially saturated soil

3. Factors affecting compaction

   • Water content
   • Gradation
     • Granular soils - compacted by vibration Fine grained soils - compaction by static pressure
   • Amount of compactive energy used

4. Labatory compaction Proctor Test

   • Determination of total energy and water content
     • ρ=Mt/Vt
     • ρd=ρ/1+w
       • Is only a maximum for a specific compactive effort
   • 1000cm3 mould 2.5kg hammer 300mm drop

5. Relative density

   • For cohesionless soils alternative specifications for compaction are used
     • Achieving relative density Id
       • Id=(emax-e)/(emax-emin)
       • Id=1, e=emin
         • Soil is at its densest state
       • Id=0, e=emax
         • Soil is at its loosest state
   • Id ranges
     • 0.000<Id,0.333 - loose soil
     • 0.333<Id<0.667 - medium soil
     • 0.667<Id<1.00 - dense soil

6. Field compaction

   • Properties of a good compaction
     • Adequate strength
     • Incompressibility
       • Minimizes settlement
     • Stability against volume changes with varying conditions
     • Appropiate permeability

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