In construction, you can see different types of foundations. And, each caters to different load-bearing needs.
A building’s foundation is without a doubt a huge deal. It’s what supports the entire building above the ground. But did you know that the foundation of a house can vary from that of a massive structure? Well, yeah.
Here, we are going to look into each type of foundation. Keep reading to learn about them.
What is a Foundation in Construction?
A foundation is the lowest structural element of a building that transfers the loads from the superstructure—walls, columns, floors, roof—safely to the ground. It distributes the weight over a sufficient soil area or transfers it to deeper, stable strata, ensuring stability, preventing uneven settlement, and resisting lateral forces.
Types of Foundations in Construction
Type #1: Shallow Foundations
Shallow foundations are ideal when the soil near the surface has enough strength and stiffness to support the loads of the structure.
In this type of foundation, the depth is generally less than the width.
Shallow foundations are widely used in residential, light commercial, and some low-rise industrial structures.
Spread footings or open footings are some of the other names of Shallow Foundations.
Advantages of Shallow Foundations
- Less complex, easier to construct.
- More economical (lower cost in material and labour) than deep foundations.
- Faster construction time.
- Suitable for light to moderate load structures (houses, small buildings).
Limitations
- Unsuitable if soil near surface is weak or unstable.
- Not ideal for heavy structures or tall buildings with high load.
- Greater risk of differential settlement if soil conditions are variable.
Type #2: Deep Foundations
Foundations that transfer structural loads to deeper, more stable layers of soil or rock, often used when surface soils are weak or when the load from the structure is large. Deep foundations extend deeper into the earth compared to shallow foundations.
Ideal when: the building is heavy/high, soil near surface is poor, load-bearing layers are deeper, or there is a high water table.
Advantages
- They provide greater stability for structures built on poor soils or areas with high water tables.
- They can resist uplift forces from wind or seismic activity better than shallow foundations.
Disadvantages
- They are complex.
- They are expensive.
- Their installation requires special equipment and techniques.
- Mistakes in installation can be costly to repair.
Type #3: Pile Foundations
A Pile foundation is a deep foundation.
Wondering where they are used? Their typical applications include large structures and buildings constructed over water bodies.
They consist of long, slender, columnar elements driven deep into the ground to transfer loads through weak soils to stronger ones below.
Steel, concrete, or timber can be used to create piles.
Advantages
- Their load-bearing capacity is impressive.
- They are good at resisting uplift forces effectively.
- They are suitable for areas with challenging soil conditions or high water tables.
Disadvantages
- Pile foundation construction is time-consuming and requires substantial investment.
- It also demands skilled labour and precise engineering calculations.
Type #4: Raft or Mat Foundations
Raft foundations, also known as mat foundations, are a type of shallow foundation that spreads the load from the building over a large area.
These types of foundations are like a raft floating on the soil, hence the name.
They are typically used when the soil has low bearing capacity, or when the structure’s load is distributed over a large area, such as in high-rise buildings.
Advantages
- They provide excellent stability and evenly distribute the load across the entire footprint of the building, reducing the risk of differential settlement.
- They also require less excavation depth than deep foundations.
Disadvantages
- They can be expensive due to the large amount of concrete required.
- They’re not suitable in areas with high groundwater levels or aggressive soil conditions.
Type #5: Strip Foundations: One of the Common Types of Foundations
Strip foundations are also known as wall footings.
This is a variation of a shallow foundation, which supports a line of loads, such as a load-bearing wall.
This foundation is usually a strip of concrete spread along the length of the wall, making it suitable for light-loaded structures like residential buildings.
Advantages
- They are simple to construct and require less concrete than other types, making them cost-effective.
- They are suitable for stable ground conditions and buildings with relatively light loads.
Disadvantages
- They aren’t suitable for heavy structures or areas with poor soil conditions.
- Any differential settlement could lead to cracks in the walls supported by the strip foundation.
Type #6: Pad Foundations
Pad foundations, also known as isolated or individual footings, are a type of shallow foundation used to support individual points of load, such as columns.
They are typically square or rectangular slabs of concrete.
Planning to construct residential or low-rise commercial buildings, this foundation would be perfect.
Advantages
- This is a cost-effective option.
- You can easily design and build this foundation.
- They are suitable for light to medium-loaded structures built on strong and stable soils.
Disadvantages
- They are not suitable for heavy structures or those built on weak soils.
- They are susceptible to differential settlement issues.
Type #7: Grillage Foundations
Grillage foundations are a special kind of shallow foundation composed of one or more layers of beams, called grillage beams, laid perpendicular to each other.
They are suitable for heavy structures built on soft soils as they distribute the load over a large area.
Grillage foundations are often used for bridges, piers, and heavy column loads.
Advantages
- They are advantageous due to their high load-bearing capacity and ability to distribute loads evenly.
- They can be constructed quickly and require less excavation than deep foundations.
Disadvantages
- They can be expensive due to the high cost of steel beams.
- They may not work at their best in areas with high water tables or corrosive soil conditions.
Type #8: Combined Footing Foundations
Combined footing foundations are a type of shallow foundation that supports two or more columns, typically when they are close to each other or near a property boundary.
These footings can be rectangular or trapezoidal in shape.
This works best for row houses, bridges, and multi-storey buildings.
Advantages
- Firstly, they provide excellent support for multiple columns and help prevent differential settlement.
- What’s more, they can also save space and decrease excavation costs.
Disadvantages
- Its design part can be difficult and require careful calculations and expertise.
- They can be expensive because they require more concrete and reinforcement.
Type #9: Floating Foundations
Floating foundations, as the name suggests, are designed to ‘float’ on the soil, like a boat on water.
They are used when the soil has a low bearing capacity, and the building’s weight is less than the weight of the soil it displaces.
Floating foundations are typically used for lightweight structures or in areas with expansive clay soils.
Advantages
- They can significantly reduce settlement and are effective in areas with problematic soil conditions.
- They distribute the load evenly, reducing stress on the soil.
Disadvantages
- They are complex to design and construct, requiring skilled engineering.
- They may not be suitable for heavy structures or areas with high groundwater levels.
How to Choose the Right Foundation Type
Selecting an appropriate foundation involves evaluating:
- Soil conditions: Strength, bearing capacity, depth to bearing strata, water table, soil type.
- Load from the structure: Building weight, number of floors, concentrated loads (columns) vs distributed loads (walls).
- Spacing of structural elements: Columns close together may require combined or raft footing.
- Budget and timeline: Shallow foundations are cheaper and faster; deep foundations cost more and take longer.
- Groundwater/water table level: High water table or soft soil may necessitate deep foundation.
- Risk of settlement / uneven settlement: Structures on weak or variable soil may need raft or deep foundations.
Winding Up
From shallow to deep foundations, from pile to raft, and strip to pad, there are different types of foundations that cater to different needs. We hope that now it’s clear to you about each type and where to use them.