Some studies have shown that the typical cost of foundations can be 20% of a project – and that’s for just the simple cases. In other words, once you start getting into high-rise buildings, the cost can suddenly shoot up, and that’s before surpassing ground level.
Of course, high-rise buildings and other large developments are in a breed of their own. V. Reddy Kancharla is one of a few experts in the industry who knows how crucial this stage of development is and particularly, selecting a suitable foundation. While from the outside it may appear as though the important decisions come towards the top of a building, in actual fact it’s beneath ground level where the crucial calculations are made.
As this piece will be looking at large-scale developments, we’ll only be concentrating on deep foundations. The simple definition for this is a foundation which goes lower than 3m – meaning that the vast majority of domestic buildings are immediately discounted.
If a building does fall into this category though, what are the foundation options?
Arguably one of the most common types of deep foundation involves one that uses piles.
As the name may suggest, these are long pieces of material that are driven down to the required level. A slight deviation is when tubes are drilled into the ground, before then being filled with concrete. In some cases the engineer may decide that the piles should be formed out of other materials, with timber and steel being viable alternatives.
Pile foundations are regarded as one of the most versatile around. If the site happens to be one with a high water table, the nature of piles means that they are preferred over other types of foundations. This also means that they are used in docks and piers, although they are not necessarily the only option for these developments as we’ll look into later down the page.
While piles are seen as one of the most versatile and comprehensive solutions around, there are occasions where they won’t be used. The method in which piles are driven into the ground isn’t always easy – particularly if the ground is hard and rocky.
It’s in circumstances like the above where a pier foundation might be turned to. In some ways, these are very similar. They are comprised of a large column, with this constructed from either concrete or masonry depending on the approach which is taken.
A slightly less common type of foundation comes in the form of the caisson. These are constructed as either a circle or rectangle shape, before being sunk into the ground. They are much bigger in size than pier foundations, which mean that they tend to be used for large developments. Examples of suitable developments include bridges, quay walls or any large device which is going to be based on water.
Caisson foundations are unique in the way that they are hollow inside, with sand usually being used to fill this gap.