Foundation | Shallow Foundation

Shallow Foundation

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

The two most typical varieties are mat foundations, which are enormous continuous slabs that cover the whole building area, and spread footings, which support individual columns or walls through larger pads. Lightweight structures with relatively modest loads, such as those seen in homes and smaller commercial structures, are best suited for shallow foundations. For constructions with shallow foundations to be stable and safe, proper design is essential.

To disperse the weight of a building or structure to the underpinning soil or rock, a shallow foundation is a sort of structural support system used in construction. It is distinguished by having a shallow depth in relation to the breadth or load-bearing area of the structure.

When the soil close to the surface provides enough bearing ability to support the load without requiring substantial excavation, shallow foundations are frequently employed. Spread footings and mat foundations are the most typical forms of shallow foundations.

Mat foundations are continuous slabs that cover the whole building footprint, whereas spread footings are expanded pads placed beneath load-bearing columns or walls.

When the weights are modest and the soil conditions are good, shallow foundations are frequently used for residential and light commercial constructions. The stability and safety of structures supported by shallow foundations depend on proper design and engineering.

Types of shallow 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 trapezoidal 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.

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