Foundation
Shallow Foundation

According to Terzaghi, the foundation is shallow if its depth is equal to or less than its width.

Types of shallow foundation

1. Spread footing
2. Combined footing
3. Strap Footing
4. Mat Foundation
5. Raft Foundation
6. Grillage Foundation

Spread footing

• Spread footings are these which spread that super-imposed load of wall or column over a larger area.Spread footing helps either column about the wall.

Combined Footing

• Each spread footing that holds two or more columns is termed combined footing.

These combined footing someone of the following kinds.

• Rectangular combined footing:– The combined footings will be provided in rectangular shape if columns carry equal loads. The design of rectangular combined footing should be done in such a way that the centre of gravity of the column coincides with the centroid of the footing area.
• Trapezoidal combined footing:- If columns carry unequal loads the footing is of trapezoidal shape are provided.
• Combined column-wall footing: It may be required to provide a combined footing for columns and walls. A such combined footing is shown in Fig.

Strap Footing

• If an Independent footing of two columns is connected by a beam, it is called a strap footing.
• Each strap footing may be applied where the distance between this column is so great that the trapezoidal footing becomes very narrow.
• The strap gives not remain in contact with the soil and also does not transfer each pressure to the soil.

Raft foundation

• A raft foundation equals a combined footing that treats the entire area beneath a structure and also supports everything the walls and columns.
• They are used in areas where the soil masses contain compressible lenses or the soil is sufficiently erratic so that differential settlement would be difficult to control.
• Raft a foundation may be divided into three types based on their design and construction.

1. Solid slab system
2. Beam slab system
3. Cellular system

• All three types are basically the same, consisting of a large, generally unbroken area of slab covering the whole or large part of a structure.

Grillage Foundation

• It is a special type of isolated footing generally provided for heavily loaded steel columns and used in that locations where the bearing capacity of the soil is poor.
• The pitch of such a foundation is limited to 1 to 2 m.
• The load of steel, a column is distributed over a very large area utilizing two or more tiers of steel joints.
• Each layer is laid at a right angle to the layer below it.