Foundations

Foundations form an important part of building construction. The forces and moments acting on a structure have to be ultimately transmitted to the ground and this is achieved by means of foundations. The loads on a building are transmitted downwards, floor by floor by means of columns and or walls. If these are directly set on the ground, the pressures under them would be so much that either the soil will give way or large and uneven settlements would take place. In order to prevent this, the load is spread over a wider area by means of foundations such as footings, strips, rafts etc. At the same time, we have to ensure that the stresses in the elements of foundation like concrete, steel masonry etc. are within the specified limits. 

The crust of the earth over which the foundation rests, consists of various types of soils androcks having widely different characteristics and properties. Further, the presence of sub oil water affects some of these properties. Before foundations are designed, we should know the details of the soil characteristics. 

Generally, one is confronted with a situation where the desired land has been acquired and the foundation for the proposed building has to be designed taking into consideration the soil characteristics at the site. For important and heavily loaded structures, it may be worthwhile to take into consideration the necessary soil properties and other features at the site, before acquiring the land. 

In earlier days, the design of foundations was based mote on experience and intuition, but modem developments in Soil Mechanics have enabled us to understand in greater detail, the properties of soil and the mechanism of load transfer from the building to the ground. 

In this unit, you will learn about the various types of building foundations, where they used and their constructional details. 

Objectives 

After studying this unit, you should be able to 

• classify the various types of building foundations, 
• describe the tests used for site investigation, 
• establish the criteria for selecting the type of foundations, and 
• describe the constructional details of the commonly used foundations.