Types of Footing Foundations in Building construction works. What footing does work? The function of the footing foundation is to transmit the lord form the structure to the underlying soil. The foundation distributed the load over a large area. Pressure on the soil does not exceed its allowable bearing capacity and restricts the settlements of the structure within the permissible limits.
It helps to distribute the loads and minimizes distress against the foundation soil movement, thereby keeping them safe and stable. The selection of a suitable type of footing generally depends on the type of soil. Depending on the depth of the soil in which the foundation is made. basically, foundations are two types of Foundations are used in constructing a building. type of foundation is based on the type of the structure, calculate load, type of soil, depth of the soil which safe bearing strata exist and soil condition.
What is the Foundation ?
Foundation is defined as that part of the structure that transfers the load from the structure. foundation own weight over a large area of soil in such a way that the load does not exceed the ultimate bearing capacity of the soil and the settlement of the total structure remains within a tolerable limit.
Difference between Footings and Foundations:
The footing is a part of the foundation which is constructed with concrete or brickwork masonry and acts as a base to the floor columns and floor walls.
How Foundations Functioning:
- Load Distrubutions
- Stability Against overturning
- Safe against undermining
- Level Surface
- Minimize distress against soil movement
- Shallow Foundation
- Deep Foundation
Shallow Foundation: the shallow foundation is one which is placed on a firm soil near the ground, and beneath the lowest part of the superstructure. These are used for small and light buildings. They are commonly referred to as spread footings or open footings. If the depth of the footing is equal to or greater than its width, it is called deep footing, otherwise, it is called shallow footing.
Deep Foundation: the deep foundation is one which is placed on a soil that is not firm, and which is considerably below the lowest part of the superstructure. These are used for large structures. There are two main types of deep foundation Pile foundation and Drilled Shafts or caissons are the main deep foundation works. large-area footings are needed to spread the vertical load, improving the stability of the building. to much ultimate bearing capacity building, deep foundation works done. for example petrol pumps, motor drill plants types of industrial works deep foundation suitable perfect.
Choose shallow or Deep. construction structure Foundations may be shallow or deep foundations depending upon the load and type of foundation soil. in our Indian land many types of soil presented. If the load to be supported is very high and soil is of low bearing capacity, Deep foundations are provided. If the soil has adequate bearing capacity at reasonable depth then shallow footings are provided.
if soil bearing capacity is less than 24KN/m3 ->RAFT Footing
if soil bearing caparity is greater than 24KN/m3 -> Plain footings, isolated footings.
Shallow Foundation – 3m depth
Deep Foundation: 20 – 65m depth
Types of Foundation and their Uses
Following are different types of foundations used in construction:
Types Of Shallow Foundation
- Isolated Spread Footing
- Strip footing or Wall Footing
- Combined Footing
- Cantilever or Strap Footing
- Raft or Mat foundations
Types Of Deep Foundation
- Pile foundation
- Pier Foundation
- Caisson Foundation
Types Of Casson Foundation
- Box Caissons
- Floating Caissons
- Pneumatic Caissons
- Open Caissons
- Sheeted Caissons
- Excavated Caissons
Continuous Wall Footing:
The footing which supports a long masonry or RCC wall is known as a continuous footing. It runs throughout the length of the wall. Continuous wall footings are used to support the foundation walls and load-bearing walls.
Isolated Spread footing foundations are the most common and simplest type of foundation as this is the most economical type of foundation. They are generally used for ordinary buildings. The shape of individual footing is square or rectangle and is used when loads from the structure is carried by the columns. its mostly circular, square or rectangular slab of uniform thickness. Isolated footings are provided where the soil bearing capacity is generally high and it comprises of a thick slab that may be flat or stepped or sloped. Isolated footings are used as a shallow foundations in order to transfer concentrated loads to the ground. under the base of the foundation so that the load of the structure is distributed on a wide area of the soil in such a way that the safe bearing capacity of the soil is not exceeded.
A footing that supports two or more columns is known as a combined footing. It is used when two or more columns are close to each other or two or more individual footings of a column would overlap. This footing may be of rectangular or trapezoidal in plan. Soil having low bearing capacity and requires more area under the individual footing. For this is necessary to coincide the center of gravity of the footing area with the center of gravity of the total loads. When columns are close to each other and their individual footings overlap. Dimensions of one side of the footing are restricted to some lower value. By combining it with that of an interior column, the load is evenly distributed. A combined footing may be rectangular or trapezoidal in plan.
Strip & Strap Footing
Strap footings are similar to combined footings and reasons for considering or choosing strap footing is similar to the combined footing. Spread footings are those whose base is more wider than a typical load bearing wall foundations. he footings under the columns are built individually and connected by strap beam. Generally, when the edge of the footing cannot be extended beyond the property line the exterior footing is connected by strap beam with interior footing. Soil bearing capacity must be sufficient to support the weight of the structure over the base area of the structure.
Spread footings and wall footings are used for individual columns, walls and bridge piers where the bearing soil layer is within 3m (10 feet) from the ground surface.it is more economical to provide a strip footing than to provide a number of spread footings in one line. A strip footing is also known as continuous footing. The strap beam does not remain in contact with the soil and thus does not transfer any load to the soil.
Raft Footing Foundation:
MAT Foundation and Raft foundation covers the entire area under the structure. Raft or Mat foundations are used where other shallow foundation or pile foundation is not suitable. Raft or mat foundations are the types of foundation which are spread across the entire area of the building to support heavy structural loads from columns and walls. This is used to prevent differential settlement of individual footings, thus designed as a single mat (or combined footing) of all the load bearing elements of the structure. When the column loads are heavy or when the safe bearing capacity of soil is very low, The required footing area become very large raft footing using is best. A raft foundation is a solid reinforced concrete slab covering entire area beneath the structure and supporting all the columns. Such foundation due to its own rigidity minimizes differential settlements. It is widely used when soil has low load bearing capacity. It is provided in a places like seashore area, coastal area area where the water table is very high and soil bearing capacity is very weak. Mat foundations are useful in reducing the differential settlements on non-homogeneous soils or where there is large variation in the loads on the individual columns.
Pile Foundation Footing
Piles are used as deep foundation where the soil is very week and has higher groundwater table. it is desirable to transmit loads to soil strata which are beyond the reach of shallow foundations. A pile is a long vertical load transferring member made of timber, steel or concrete. In pile foundations, a number of piles are driven in the base of the structure.
When the soil has a low bearing capacity or the ground water level is high, pile footings are applied. It is used to transmit foundation loads to a deeper soil or rock strata when the bearing capacity of soil near the surface is relatively low. Piles are common while building foundation for bridges, dam etc. Pile foundation is a type of deep foundation which is used to transfer heavy loads from the structure to a hard rock strata much deep below the ground level. better to use if depth of hard rock strata may be 5m to 50m (15 feet to 150 feet) deep from the ground surface. Piles are hammered in to the ground till hard strata (in compressible) layer of earth is found.
Drilled shafts, also called as caissons, is a type of deep foundation and has action similar to pile foundations discussed above, but are high capacity cast-in-situ foundations. Caisson foundation is a watertight retaining structure used as a bridge pier, construction of dam etc. It is generally used in structures which requires foundation beneath a river or similar water bodies.
Reason for choosing caisson foundation is that it can be floated to the desired location and then sunk into place. It resists loads from structure through shaft resistance, toe resistance and / or combination of both of these. The construction of drilled shafts or caissons are done using an auger. Drilled shafts or caisson foundation is not suitable when deep deposits of soft clays and loose, water-bearing granular soils exists.