At optimum water content, the reduction in air void is null approximately. With this constant air void, when water content is increased further the total void is increased as void consists of air and water. With the increase in total void dry density is reduced.
Dear reader in previous post we have learnt about difference between compaction and consolidation of soil. Our concern is compaction here. In both process water plays important role; our aim is here to co-relate water content with compaction.
Where water content in soil is low, it shows stiffness which means more compaction effort is required as soil provide more resistance. In normal foundation compaction, we use water to have better compatibility, sometimes on backfilled soil or natural weak deposit.
When we add water, soil particles become lubricated. The lubricated soil mass have better workability and particles can be compacted into close packing. With the increase of water content the dry density of compacted soil is increased.
But after reaching an optimum water content, the dry density have tendency to decline. This can be explained as follows:
As after optimum water content it is very difficult to expel out air, the purpose of further water adding is not served as higher total void (air plus water) result less dense soil mass.