Basics in Building Construction

Basics in Building Construction 4(2+2)

Lesson 02 : Shallow Foundations

Objectives Of Foundation

It is often misunderstood that the foundation is provided to support the load of the structure. In factfoundation is a device to transmit the load of the structure to the soil below. The main objectives of the foundation are to

1. distribute the weight of the structure over large area so as to avoid over loading of the soil beneath
2. load the sub- stratum evenly and thus prevent unequal settlement.
3. to provide a level surface for building operations.
4. take the structure deep into the ground and thus increase its stability , and prevent overturnin

All foundations settle under load. But if one part settles more than another, there will be differential settlement and cracks may appear many years after the completion of the building. Unequal settlement or differential settlement may cause due to

• Weak sub soils such as made up ground
• Shrinkable and expansive soil, such as clay
• Frost action
• Movement of ground water and uplift pressure
• Excessive vibrations due to traffic and machinery
• Slow consolidation of structured clay
• Slipping of strata on sloping sites.

The foundation is the most important part of a building as it provides an uniform base for the superstructure and transfers the load of the same down to the soil below it uniformly. Hence it should be laid on a firm and hard bed below the ground level so as to transfer the load of the structure safely on to the hard bed below and at the same time to provide good anchorage to the super structure.Utmost care should be exercised while fixing the foundation and its various dimensions, since foundation once laid if yields under load, little can be done to save the life of the structure.