In this lesson, we will explore the two primary types of foundations used in construction: shallow foundations and deep foundations. Foundations are critical to the stability of any structure, as they transfer the load from the building to the ground. Understanding the differences between these foundation types is essential for ensuring that the appropriate foundation is selected based on the soil conditions and the building’s design.
Learning Objectives
By the end of this lesson, you will:
Understand the purpose of foundations in construction.
Identify the differences between shallow and deep foundations.
Learn when to use each type of foundation based on soil and structural conditions.
What are Foundations?
Foundations are the structural elements that provide support to buildings and other structures. Their primary function is to transfer the load of the building to the ground, ensuring stability and preventing settlement or collapse. Foundations also help resist forces such as wind and seismic activity, ensuring the building remains safe over time. The type of foundation chosen depends on factors like the building’s size, the load it will carry, and the characteristics of the soil at the site.
Shallow Foundations
Shallow foundations, also known as spread or open foundations, are used when the load from the structure can be easily transferred to the ground at a shallow depth. These foundations are typically used in situations where the soil near the surface has sufficient bearing capacity to support the building’s load. Shallow foundations are economical and relatively easy to construct, making them common in residential and small commercial buildings.
Types of Shallow Foundations:
Strip Foundations: These foundations consist of a continuous strip of concrete that supports walls. They are commonly used for load-bearing walls in small buildings.
Pad Foundations: Used to support individual columns or posts, pad foundations are isolated sections of concrete that spread the load of the column to the ground.
Raft Foundations: Also known as mat foundations, these consist of a large slab of concrete that supports the entire building. They are used when the soil has low bearing capacity or when the building loads are spread over a large area.
When to Use Shallow Foundations:
When the soil near the surface has good load-bearing capacity.
For lighter structures like homes, small offices, and low-rise buildings.
In areas where the ground conditions are stable and the risk of ground movement is low.
Deep Foundations
Deep foundations are used when the soil near the surface is not strong enough to support the building’s load. In such cases, the foundation needs to be placed deeper into the ground to reach stronger soil layers or bedrock. Deep foundations transfer the building's load to these deeper, more stable layers, making them suitable for larger and heavier structures, or for sites with poor surface soil.
Types of Deep Foundations:
Pile Foundations: Piles are long, slender columns driven deep into the ground. They transfer the load of the building to deeper, more stable soil or rock layers. Pile foundations are used in soft or waterlogged soils.
Drilled Shafts (Caissons): These are large, deep, cylindrical shafts drilled into the ground and filled with concrete. They are used to support heavy loads in areas where the soil near the surface is unstable.
Pier Foundations: Similar to pile foundations, piers are large columns that extend deep into the ground, but they are typically constructed in-situ (on-site) rather than driven.
When to Use Deep Foundations:
When surface soil is weak or unstable.
For large, heavy structures like high-rise buildings, bridges, and industrial facilities.
In areas where ground movement, such as soil settling or erosion, poses a risk to building stability.
Key Differences Between Shallow and Deep Foundations
Depth: Shallow foundations are placed at depths of about 1-3 meters, while deep foundations can reach depths of 10 meters or more.
Cost: Shallow foundations are generally less expensive and faster to build than deep foundations, which require specialized equipment and more labor.
Soil Conditions: Shallow foundations are used in areas where the upper layers of soil have sufficient load-bearing capacity, while deep foundations are used when stronger soil layers or bedrock are located deeper below the surface.
Building Type: Shallow foundations are typically used for smaller, lighter buildings, whereas deep foundations are required for taller, heavier structures.
Conclusion
Foundations are essential to the stability and safety of any structure, and selecting the correct type of foundation is critical to the success of a construction project. Shallow foundations are used for lighter buildings with strong surface soils, while deep foundations are necessary for heavier structures in areas with weak or unstable soil. Understanding these foundation types and their appropriate uses will help ensure the durability and safety of construction projects.
