The Foundations in Expansive Soils

Greetings! Here are the lecture notes for the next lecture of Advanced Foundation Engineering.

The following methods can be used for the construction of foundations on expansive soils:

• A) Designing the structure as a solid structure to withstand the effects of swelling & shrinkage of strata.
• B) Eliminating the swelling by:
• i) stabilizing the moisture.
• ii) Loading the soil more than the swelling pressure.
• iii) Treating the soil, so that its behavior changes.
• iv) Replacing the soil by non-swelling soil.
• C) Isolating the structure by taking down the foundation to a stratum, which is not affected by swelling.

A) Strengthening the structure beyond a certain limit is not economic, however, reinforcement bands can be provided at different levels, such as plinth, lintel and beams.

 Heavily reinforced rafts can also be provided, but the flexible structures are not practical.

B) Taking down the foundation to a level where no volume changes or water content change occur, pre-wetting techniques may also be required. For isolated structures it may not be possible.

• Loading the foundation with more than swelling pressure has shown better performance, but quantification of suitable load is not practical, as the factors affecting are many.
• Stabilization of an expansive soil by lime is well known but mixing of soil and compacting it in layers is problematic and sometimes un-economical too. Usually 2 to 8% lime decreases the liquid limit(LL) and Swelling; increases the OMC and strength of expansive soil. This method is more practical for roads. For deeper treatments lime slurry may be injected, but it is not a common practice.

Thank you!