Shallow Foundations Versus Deep Foundations

A foundation is the lowest load-bearing part of a building. It is typically out of sight below ground level, and acts as the structure’s point of connection with the earth; in other words, it transfers the structure’s load to the ground.

Foundations can be divided loosely into two types – deep and shallow. In this article, Piling Experts will discuss the difference between shallow and deep foundations, list examples of each kind, and explore the benefits of deeper foundations in a residential context.

Defining deep and shallow foundations

A shallow foundation transfers the load of the structure close to the surface, rather than at a greater depth. It is typically wider than it is deep. Sometimes, a depth of 3 metres is used to separate a shallow from a deep foundation. Types of shallow foundations may include:

• Isolated footing or single column footing – a square slab supporting parts of the structure (such as a column or pole) independently
• Combined or strap footing – when a number of single column footings are connected together.
• Mat, raft, or slab foundation – a single, unbroken slab under the building’s base. For example, this is used for some homes, where the builder digs a trench and pours in the concrete slab.

Conversely, a deep foundation transfers the structure’s load deep within the earth, penetrating the subsurface layers to a greater depth. The prime example is prefabricated piles being placed into the ground, in situ, by a pile driver. A quality piling rig, matched with the appropriate piles, can go up to 30 metres deep.

There are various different types of piles including screw piling, bored piles, and underpinning. Browse our website for more information on these types.

What’s better – shallow foundations or deep foundations?

The correct solution depends on the project and is something to be determined by a professional with an engineering background, who has worked within screw piling Wollongong.

Shallow foundations may be appropriate when building a small, light structure, that requires less technical complexity. For example, a shelter, or a home on a perfect earth. In this context, they may be an affordable option.

Deep foundations may be appropriate when:

• Working with softer or less predictable soil. Deep foundations go past any poor soil at shallow depths, enabling the building to be founded on better soil or firmer earth deeper down. This may include into rock, to the point of ‘refusal’, where they cannot be driven further. This benefit is especially true when working on various soil types, such as sandy or loamy soils, as can be found near the beach and in new developments. In this context, a shallow foundation may be prone to settlement due to poor soil, be unable to cope with lateral loads, and so forth – whereas a deeper foundation can overcome these challenges.
• Deep foundations are more capable of handling very heavy and large structures, compared to shallow loads; therefore, they are often used for projects such as apartments and skyscrapers. A shallow foundation would never be considered for a structure over a certain size.
• Deep foundations may be preferred where there is limited space due to property restrictions because they allow an engineer to create a firm foundation for the structure, whereas, with shallower foundations, this may not be as possible due to limitations in space.
• Deep foundations are more versatile, creating a solid structure in more ways than shallow foundations – for example, not just end bearing, but also greater friction.

Shallow or deep foundations in the residential setting

Both types of pile types have their application. Shallow foundations may be considered for light applications, whereas pile-driven, deep foundations offered by your local screw piling expert will be used for all heavy jobs beyond a certain point.

However, there can be an interesting grey area around residential settings. Builders or owner-builders can be uncertain about which path to go down and should always seek advice from a technical expert in screw piling Newcastle.

However, there may be a number of arguments in favour of the deep foundation method screw piles, compared to a concrete slab foundation for the residential setting, when building a home. These arguments include:

• Access – screw piling Wollongong rigs are able to work in very limited spaces and with limited head heights.
• Low cost – screw piles are often the most affordable type of deep foundation.
• Versatile – screw piles can work with various soil types, whichever is encountered on the site. They will be able to be used more reliably across all contexts, compared to shallow foundations.
• Speed – screw piles don’t require digging and can be installed in situ. Time does not always have to be allowed for concrete to set.

For more information, browse our website, or contact us.