Types of Shallow Foundations

Types of Shallow Foundations

 

1. Individual Footing or Isolated Footing

The individual or isolated footing is the simplest and most common type of foundation. They are constructed to support a single column. They are also known as a pad foundation, and their shape is typically square or rectangular, calculated based on column load and soil bearing capacity.

 Advantages:

·        Economical and straightforward in design

·        Ideal for supporting structures with a clear load path and predictable loads

 Disadvantages

·        Not suitable for heavy structures or when soil conditions are variable

·        Supports only a single column.

 2. Combined Footing

When columns are closely spaced such that their footings overlap, a combined footing is constructed. It shares attributes with isolated footings but differs in structural design, usually taking a rectangular shape. Specialised techniques like catavilier foundation footing may be employed in complex scenarios to mitigate issues and enhance performance.

 Advantages:

·        Efficiently supports multiple columns

·        Distributes loads evenly

·        Useful in confined spaces

 Disadvantages:

·        More complex and costly than individual footings

·        Requires detailed engineering to ensure load balance.

 3. Spread Footings or Strip Footings

 

Spread or strip footings feature a broader base than typical load-bearing walls, distributing the building's weight over a larger area. These are types of foundations used for walls, individual columns, and bridge piers where the soil layer is within 3 metres from the surface.

 

Advantages:

·        Provides better stability by spreading the load

·        Suitable for structures where the bearing soil layer is close to the surface

 Disadvantages:

·        Not applicable on soils at risk of water flow that might cause scour or liquefaction

·        Limiting their use to stable ground conditions.

 4. Raft or Mat Foundations

Raft or mat foundations cover the entire building area, supporting heavy loads from columns and walls. This type of foundation is chosen to prevent differential settlement of footings, acting as a single mat for all structural elements.

 Advantages:

·        Ideal for structures with high loads on columns and walls

·        Minimizes differential settlement across the foundation

 Disadvantages:

·        Complex and expensive to construct

·        Requires significant excavation and concrete work, making it suitable for select, heavily loaded structures