When the soil beneath a building site is too weak (or too easily compressed) to offer the level of support that the building needs, a standard foundation is not going to work. Something sturdier is required. In this case, that ‘something’ often ends up being what’s known as a deep foundation.
Deep foundations are also known as pile foundations. They are constructed through a sophisticated system of piles driven deep into the earth, combined with a support structure that works in harmony to create a much more solid surface on which to build. Because of pile foundations, construction of all the following becomes possible:
- Large megastructures
We could add many other structures to the list, but the examples given above sufficiently illustrate the situation. In short, without pile foundations, we wouldn’t have many of the structures that are now seen as commonplace in modern society.
While pile foundations are most often used in conjunction with grand-scale construction projects, they also have their place at smaller build sites. In fact, there are situations in which a private homebuilder may find the need to drive a pile or two in order to shore up the site.
The Components of Deep Foundations
There are two basic components to a pile foundation – the pile cap and the pile itself (or group of piles). Piles are usually made of steel, especially for large construction projects. However, they can also be constructed of concrete (often steel reinforced) or timber. Regardless, these piles are driven into the ground with considerable force. They’re often jacked or drilled with heavy duty equipment. Once they are secure in the ground, the pile cap is applied.
A pile cap is essentially a concrete mat that is laid over the top of the piles. The cap is, in a sense, a lid that closes of the pile structure. It forms the foundation on which the actual building will be constructed. Once the cap has been applied, you have the beginnings of a buildable foundation on what was previously unsuitable land.
A Short Background of Piling
Pile systems were first used as load bearing and load transferring systems, and they date back several centuries. The earliest examples would have been timber houses built on stilts. In this case, the stilt is a type of pile, though it wasn’t always used to build in unsuitable soil. Instead, stilts were more often used to protect against flooding and to keep vermin out.
In the 19th century, builders began using steel pilings for more sophisticated construction projects. This is the point at which we begin to see larger structures being built – which was really only possible due to the elaborate foundation systems that were being devised.
Finally, in the 20th century, concrete piles were developed and became ubiquitous in construction. Today, the use of pile foundations is more common than ever – due in large part to the unavailability of suitable land for building. In short, all of the best land (especially close to major metropolitan areas) has already been developed. That which remains only becomes accessible through the application of a deep foundation.
When Are Deep Foundations Necessary?
A pile foundation is going to be necessary when the load-bearing capacity of the soil is insufficient for the structure that is going to be built there. This could have to do with the soil itself, or with the layers that are found underneath. The need for a deep foundation could also be attributed to the type of building being constructed.
Sometimes, the need for piles is obvious. For example, this type of support structure makes it possible to support a bridge’s heavy load by driving the piles through the water and deep into the bed of the underlying soil. This process of driving the piles is known as ‘piling’.
In reality, there are myriad reasons that a pile foundation may be necessary. For inexperienced or DIY builders, it’s best to call out an expert for an on-site consultation, as determining the need for piles requires significant insight and, at times, complex calculations.
More specifically, here are four specific reasons that pile foundations are sometimes deemed necessary:
- The soil is unsettled (unpacked) and therefore unsuitable for laying a strong foundation.
- The structure has a high centre of gravity (because it’s extremely tall), and the piles serve to anchor and counterbalance its weight more deeply in the soil.
- The load from the structure needs to be transferred to a greater depth, because the soil near the surface is not capable of bearing the load.
- The soil conditions otherwise limit the size and scope of construction that could take place at the building site.
Of course, all of the above are related, but this offers a bit of insight into why piles are used in certain situations. You’ll find in every case that the underlying reason has to do with either the size of the building, the quality of the soil – or some mix of the two.
The Nuances of Pile Foundations
It’s worth noting that developing a safe and sufficient deep foundation requires a substantial degree of expertise. To begin with, there are several different types of foundations that can be developed. It’s not enough to simply say, ‘This job requires a deep foundation’. Instead, it’s necessary to determine which type of pile structure is going to be most beneficial given the ground conditions.
This is when it becomes necessary to call out the experts for a consultation. Ideally, you’ll want to notify a piling contractor in your area who can come out for a site survey. This allows them to get a first-hand look at the situation so that they can then advise you about the best way to proceed. They’ll also be able to offer you an estimate.
If you suspect that a potential construction site may require a deep foundation, there is no harm in calling a contractor out for a look. The most reputable are happy to offer free consultations to this end.