Ever wondered how tall buildings are built on soft soil like clay or loose sand? It’s amazing to witness how far humans have come in terms of construction… starting with grass and mud huts, and moving all the way up to 800m skyscrapers!
To lay the foundation of any building, you need some strong screw piles or bored piers that are installed deep into the ground.
If you’re working in particularly soft foundations, bored concrete piers may be deemed as preferable over helical screw piles. And with this decision will come the use of casing for the pile construction or alternatively they may call for continuous flight Auger methodology.
What is this casing and why is it used?
Casing retains collapsible soil material while piers are constructed
Casing is an essential part of installing bored concrete piers in collapsible materials.
Example: building a sandcastle
Everybody loves warm summer days down at the beach. As a kid, they were probably some of your fondest memories – but also some of your most educational experiences. Building sandcastles, for example, was likely your first encounter with construction. When you ‘excavated’ a hole for your sandcastle moat, little bits of sand kept falling back into the moat, requiring you to keep digging it out until you hit solid-enough ground.
Applying this concept to bored piers
Now, imagine if you were trying to fill a bored pier with concrete, but the same thing kept happening: soil collapsing into the hole you’re boring, and mixing in with the concrete. This would be catastrophic for your foundation and, therefore, your entire home or building as a whole – the foundation would be weak, and would shift very easily.
Casing prevents the soil from collapsing
In situations where the soil material is particularly loose and collapsible, foundation specialists use casing to retain the material while the concrete is installed. This temporary casing prevents the soil from collapsing into the hole, allowing the pier to be kept in perfect shape. Then, concrete is poured into the hole and the casing is removed when the concrete has reached the appropriate depth.
Risks of not using casing
Without casing, a number of negative outcomes would occur:
- Weak concrete bored piers
- Ineffective foundation which would shift very easily
- Serious structural problems with the building, and correlating danger to inhabitants
Building foundations on loose soil is a specialty and a structural Engineer should be consulted.