DHARMSHALLOW FOUNDATIONS 617
15.4 Spread Footings
Spread footings are the most widely used type among all foundations be because they are
usually more economical than others. Least amount of equipment and skill are required for
the construction of spread footings. Further, the conditions of the footings and the supporting
soil can be readily examined.
Other types of foundations are more favourable when the soil has a very low bearing
capacity or when excessive settlements are expected to result due to the presence of compress-
ible strata within the active zone.
15.4.1Common Types of Spread Footings
A spread footing is a type of shallow foundation used to support a wall or a column. In the
former case, it is called a continuous or wall footing and in the latter, it is called an isolated or
individual footing. The commonly used variations of individual footings are illustrated in
Fig. 15.11.
(a) Plain or simple footing45° 45°(b) Mass concrete footing
for steel column45° 45°(c) Sloped footing (d) Stepped footing45° 45°Fig. 15.11 Common variations of individual footings
The base area of the footing is governed by the bearing capacity of the soil. The plain
footing is usually of reinforced concrete and is used to support a reinforced concrete column.
The mass concrete footing is used to support a steel column. Usually the sloped footing will be
of the same material as that for the column; alternatively, it can be of reinforced concrete. The
stepped footing is used either for a column or for a wall. All the steps may be of concrete or the
bottom most step alone may be of concrete, the others being of the same material as for the
column.
- Foundations should bear
directly on rock, since it is
relatively close to the sur-
face. If no basements are
required, piers may be used.
If basements are useful,
excavation is to be carried
to the rock and two base-
ment levels may be con-
structed.
(After McCarthy, 1977)2.5 m Miscellaneous soil fill2 m Loose sand and soft clayRockorBasementbasementSub-