How can expansive clay be used as compacted fill under foundation?

This is obvious that swelling clay should not be permitted to fill beneath floors that support on soil or foundations. The placement moisture content and the moisture content after foundation construction are not supposed to be same or the moisture content after construction cannot be predicted accurately to compare. When soil dries, it becomes shrunk differentially resulting irregular subsidence which is very detrimental to health of structure. When moisture content in the soil is increased, the structure with floors, supported on soil, subjected to heave resulting cracks. The basement walls/foundation walls are subjected to serious lateral pressure which may sometimes lead to failure.Now question is, where there has no alternatives, what to do?

Lime treated expansive soil

From the behavior of shrinkage and swelling failure it is clear that impact of swelling are more harmful than that of shrinkage. So to have less impact of expansive soils to be used as fill, there should have moisture content above optimum moisture content not to give chance to swell.

In the previous post-“low cost foundation solution foe expansive soils.”, it has been discussed how moisture content in foundation soil can be kept constant all over the year. If the home owner failed to prevent alternate decrease and increase of moisture content, serious damage from both shrinkage and swelling can be happened.

The plasticity of expansive soils can be lowered or swelling potential can be lowered applying small percentage of hydrated lime, Ca(OH)2. Suitable investigation regarding degree of benefit, amount of lime required to be treated and durability of treated soil are conducted carefully. Lime hydrated to arrest free water and it reduces plasticity too. The compaction of treated soil gains strength and stiffness with time. Sometimes Portland cement is used to treat soil. Though the reduction in free water is less, it renders longtime strength greater than that from lime. For economy, cement addition after lime treatment can be used to have longtime additional strength.

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