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News & Press: 2017 News Items

Information sheet on the classification of soil compaction

Friday, 01 September 2017  
Posted by: Bert vd Heever
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The objective of this information sheet is to provide clarity regarding soil compaction classification and to broaden the readers’ understanding of process and the terminology used within the industry.

Compaction is the process whereby particles within a soil sample are pressed closer together to increase the interlocking properties between this, a force (impact, rolling, vibration) is needed to overcome particle resistance and densify the material.

The efficiency of this process is dependent upon the compacting effort applied to the soil, as well as the inherent friction between the various size particles within the soil sample. To increase compaction efficiency and reduce friction of particle resistance, water is added as a lubricant. The amount of water required is determined from laboratory tests and is referred to as the optimum moisture content (OMC), which is a percentage of the soil’s mass.

In general the following relationships can be found between compaction effort and moisture:

  • Using a large force requires less moisture
  • Using a small force requires more moisture
  • Coarse material requires less moisture
  • Fine material requires more moisture
    Density is one of the key measures used when analysing compaction efforts and efficiency in the field, thus it is important to understand what density refers to.
    What is meant by the density of soils?

Density is a measure of the degree of the togetherness of particles within soil and highlights the interlocking capability of the soil. It is defined as dry density when only the mass of the solid particles per unit volume of the soil is measured and wet density when the mass of the water is also taken into account.

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