Foundation, Concrete and Earthquake Engineering

Improving Performance of Expansive Soil

Expansive soils can be made to maintain volume changes within acceptable limits by controlling the soil water content and by reducing the potential of the soil to heave. Methods for improving the performance of foundations in expansive soil are illustrated in below:

Removal by excavation and replacement with non- expansive fill:

Removal of surface expansive soil to depths of from 4 to 8 ft and replacement with compacted nonexpansive fill usually eliminates most potential soil heave because the depth of mois ture change is often limited to about 8 ft.

Placement of vertical moisture barriers 
Vertical moisture barriers placed adjacent to pavements or around the perimeter of foundations down to the maximum depth of moisture changes is effective in maintaining uniform soil moisture within the barrier. Differential movements are minimized. Long-term soil wetting with uniform heave beneath impervious foundations may occur from lack of natural evapotranspiration.

Lime stabilization

Lime injected or mixed into expansive soil can reduce potential for heave by reducing the mass permeability thereby reducing amount of water seeping into the soil, by cementation, and by exchange of sodium for calcium ions. Fissures should exist in situ to promote penetration of lime injected slurry. Lime may be detrimental in soils containing sulfates.

Potassium injection

Potassium solutions injected into expansive soil can cause a base exchange, increase the soil permeability and effectively reduce the potential for swell.


Free water is added by ponding to bring soil to the estimated final water content prior to construction. Vertical sand drains may promote wetting of subsurface soil.


Placing 1 or 2 ft or more of permanent compacted fill on the surface of a level site prior to construction increases the overburden pressure on the underlying soil reducing the negative (suction) pore water pressure; therefore, the potential for swell is less and tends to be more uniform. This fill also increases elevation of the site providing positive drainage of water away from the structure.

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