Different Types Of Shallow Foundations

A shallow foundation is a type of foundation used in building construction that is designed to transfer a load of a structure to the underlying soil near the surface. 

Shallow foundations are typically used for low-rise structures or where the soil has the adequate bearing capacity to support the load of the building.

Types of Shallow foundations

There are several types of shallow foundations, including:

1. Spread footing
2. Strip footing
3. Mat foundation
4. Combined footing
5. Pad foundation
6. Stepped footing

Brief introduction about types of shallow foundations

1. Spread footing: This is the most common type of shallow foundation. It consists of a concrete pad or footing that spreads the load from the structure over a larger area of soil. 

The footing may be rectangular, circular, or square in shape, depending on the design requirements.

Uses

1. Spread footings are used to transfer a load of a structure to the underlying soil near the surface.
2. They are typically used for low-rise structures, where the soil has the adequate bearing capacity to support the load of the building.
3. They provide a stable base for the structure, preventing settling or shifting over time.

Functions

1. Spread footings distribute the weight of the structure over a larger area, reducing the load per unit area on the soil.
2. They are designed to withstand the loads and forces of the structure, including dead loads, live loads, and environmental loads such as wind and earthquakes.
3. They can be reinforced with steel bars to increase their strength and durability.
4. They are usually made of concrete, which is strong, durable, and resistant to wear and tear.
5. Spread footings may be rectangular, circular, or square in shape, depending on the design requirements.

2. Strip footing: A strip footing is a type of spread footing that is long and narrow, typically used to support a load-bearing wall. It may be continuous or segmented.

Uses

1. Strip footings are used to support a load-bearing wall or column.
2. They are typically used when the load of the structure is concentrated in a narrow area or when the soil has adequate bearing capacity for the load.

Functions

1. Strip footings distribute the weight of the structure over a larger area, reducing the load per unit area on the soil.
2. They provide a stable base for the load-bearing wall or column, preventing settling or shifting over time.
3. Strip footings may be continuous or segmented, depending on the design requirements.
4. They can be reinforced with steel bars to increase their strength and durability.
5. Strip footings are designed to withstand the loads and forces of the structure, including dead loads, live loads, and environmental loads such as wind and earthquakes.

3. Mat foundation: A mat foundation, also known as a raft foundation, is a large, thick concrete slab that supports the entire structure. 

It is used when the soil is weak or when the loads on the structure are too heavy for individual footings.

Uses

1. Supports heavy structures like high-rise buildings and bridge piers
2. Ideal for soft soil, sloping sites, and shallow water table
3. Cost-effective compared to deep foundations
4. Designed to resist seismic loads and prevent differential settlement
5. Can be reinforced with steel bars for added strength and stability
6. Reduces the impact of vibrations on the building in industrial or laboratory settings.

Functions

1. Provides a wide base to distribute the load of the structure over a large area of soil
2. Increases the bearing capacity of the soil and reduces the stress on the soil
3. Prevents differential settlement between different parts of the building
4. Resists seismic loads and provides stability during earthquakes
5. Can be designed to provide vibration control, reducing the impact of vibrations on the building.

4. Combined footing: A combined footing is used when two or more columns or walls are close together and a spread footing for each would overlap. In this case, a combined footing is used to support both columns or walls.

Uses

1. Used to support two or more closely spaced columns in residential, commercial, and industrial buildings
2. Can be used in bridge construction to support piers holding up the bridge deck
3. Ideal for supporting underground structures such as tunnels, subways, or parking garages
4. Used to support the base of a staircase in a building
5. Reinforced with steel bars to provide strength and stability
6. Designed to prevent differential settlement between the columns

Functions

1. Transfers the load of two or more closely spaced columns to the soil
2. Provides a wider base for the columns to distribute the load over a larger area of soil
3. Increases the bearing capacity of the soil and reduces the stress on the soil
4. Prevents differential settlement between the columns, ensuring the structure remains stable

5. Pad foundation: A pad foundation is a small, isolated footing used to support a single column or post.

Uses

1. Used to support individual columns, walls, and piers in small to medium-sized structures
2. Ideal for structures with light loads and on firm or stiff soil

Functions

1. Transfers the load of the column, wall, or pier to the soil
2. Provides a wider base for the load to distribute the load over a larger area of soil
3. Increases the bearing capacity of the soil and reduces the stress on the soil
4. Prevents differential settlement between the column, wall, or pier, ensuring the structure remains stable

6. Stepped footing: A stepped footing is used when the soil is not uniform and requires the foundation to be stepped to follow the slope of the soil.

Uses

1. Used when the soil is not uniform and has varying bearing capacity
2. Ideal for sloping sites, hillsides, and areas with steep gradients
3. Provides a level base for the structure on uneven terrain

Functions

1. Transfers the load of the structure to the soil
2. Provides a level base for the structure on uneven terrain
3. Increases the bearing capacity of the soil and reduces the stress on the soil
4. Prevents differential settlement between different parts of the structure

A quick comparison between types of shallow foundations

Types of Footing	Shape	Function	Use	Soil Bearing Capacity	Suitability
Spread Footing	Rectangular or circular	Distributes the load of the structure over a wide area of soil	Used to support individual columns or walls in small to medium-sized structures	Medium to good	Ideal for structures with light to moderate loads and in areas with firm soil
Strip Footing	Rectangular	Distributes the load of the structure over a long, narrow strip of soil	Used to support load-bearing walls and to create a continuous foundation for the entire structure	Medium to good	Ideal for structures with heavy loads and in areas with uniform soil
Mat Foundation	Rectangular	Distributes the load of the structure over a large area of soil	Used to support entire building structures or heavy equipment	Medium to poor	Ideal for structures with heavy loads, uneven soil, or seismic loads
Combined Footing	Rectangular or trapezoidal	Distributes the load of two or more closely spaced columns over a wider area of soil	Used to support two or more closely spaced columns in residential, commercial, and industrial buildings	Medium to good	Ideal for supporting closely spaced columns with varying loads
Pad Foundation	Square or circular	Distributes a load of individual columns or equipment over a small area of soil	Used to support individual columns or equipment in small to medium-sized structures	Medium to good	Ideal for structures with light to moderate loads and in areas with firm soil
Stepped Footing	Rectangular with varying heights	Provides a level base for the structure on sloping terrain	Used in areas with varying soil bearing capacity or on sloping sites	Poor to good	Ideal for sites with sloping terrain or areas with varying soil-bearing capacity