Wall footings are pad or spread and strip footings which are used to support structural or nonstructural walls to transmit and distribute the loads to the soil in such a manner that the load-bearing capacity of the soil is not surpassed. In addition to avoiding excessive settlement and rotation and maintain sufficient safety against sliding and overturning.
Wall footing runs along the direction of the wall. The size of the footing and the thickness of the foundation wall are specified on the basis of the type of soil at the site. The width of the wall footing is generally 2-3 times the width of the wall.
The wall footing can be constructed from stone, brick, plain concrete, or reinforced concrete. Economical wall footing can be constructed provided that the imposed load needed to be transmitted are of small magnitude and the underlying soil layer is of dense sand and gravels. Therefore, wall footing is best suited for small buildings.
Construction of Wall Footings
1. Brick Wall Footing
- In the case of brick walls, the footing consists of several courses of bricks, the lowest course being usually twice the breadth of the wall above.
- The increased base width of the wall footing is obtained through the provision of 5cm offsets on either side of the wall.
- The depth of each course can be one brick or multiples of brick thicknesses.
- The base of the footing wall rests on a plain concrete footing which projects 10 to 15 cm beyond the last brick offset as shown in Fig. 1.
- The width at the base shall not be less than the width of the supported wall plus 30 cm.
2. Stone Masonry Wall Footing
- In the case of stone masonry walls, the offsets could be 15 cm with the heights of the course as 30 cm. Therefore, the size of offsets is slightly more than that of the brick wall footings.
- The depth of the concrete should not be less than 15 cm.
- By and large, the lean concrete mix proportions is 1:4:8 (1 Cement : 4 Fine aggregate : 8 Coarse aggregate) or 1 : 5 : 10 ( 1 Cement : 5 Fine aggregate : 10 Coarse aggregate) mix
- The angular spread of load from the wall should not be more than 1 vertical to 112 horizontals in masonry and 1 vertical to 1 horizontal for cement concrete.
3. Reinforced Concrete Wall Footing
If the load on the wall is heavy or the soil is of low bearing capacity, reinforced concrete strip footing can be provided.
The thickness of the strip can be reduced towards the edge to effect economy.