Foundation failure can cause the building to collapse. Foundation is the first element of a building where the construction starts, but when it fails, it can cause many defects in the building including failure or collapse of the building. Repair of defects in foundations are most difficult and very costly, so it is most important to understand the types of foundation failure to avoid them by taking necessary steps before construction starts.
There are three main functions of a building foundation:
1. To sustain and safely transmit the loads from building / structure to the ground in such a way that it does not impair the stability or cause damage to the building or surrounding buildings.
2. The construction of foundations must safeguard the building against damage by physical forces generated in the subsoil.
3. Foundations must resist the chemical compounds present in soil to prevent corrosion to reinforcement.
The properties of soil have the major influence on the design, stability and sustainability of foundations to make it perform its functions.
Foundation failure due to Soil Movement:
When water present between soil particles is removed, the soil tend to move closer together. When water is absorbed by soil, the soil starts to swell. This movement of soil is based on the type of soil. Large movement is seen with clayey soils than sandy soils. These kind of movement of soil due to change in water content affects the foundation settlement. Foundation tends to settle to and excessive settlement of foundation may lead to differential settlement and damage to the structure.
Soil movement can occur due to following:
1. Presence of vegetation or remains of old cut tress
2. Presence of mining areas
3. Shrinkable soils
Remedies for foundation failure due to soil movement:
1. Use of pile foundations where the soil is shrinkable, so that forces are transferred to the hard strata or rock.
2. Taking the foundation levels down to avoid foundation on shrinkable soils.
3. The vegetation is removed from the construction site and its roots are removed. Any cavity due to roots of vegetation shall be compacted and filled with concrete.
4. Presence of any mining areas needs to be inspected and professional help shall be taken while construction new buildings in such areas.
Foundation failure due Settlement of Soil Fill
If the building is constructed on a newly developed land by soil filling, the foundation on such soils tend to settle more with time as long time is needed for such soil to settle and become compact to resist the loads from the building foundation.
It shall be ensured that such soils are adequately compacted before construction begins on them. The foundation depth shall be increased to the hard strata or rock below the filled soil or pile foundations shall be used to prevent subsidence of foundation.