What are Piled Foundations?
Piled foundations for houses and basements are columns of concrete extending deep into the ground to transmit building loads to lower levels. Piles can transmit the loads via friction on the sides, end bearing, or a combination of the two.
Piling can be used in a variety of ways to form foundations.
- Individual bored piles connected to a ground beam for a foundation.
- Individual bored piles in the base of pad foundations.
- Individual bored friction piles to prevent uplift in basements.
- As precast-driven piles in steel or concrete.
- To form a basement wall with contiguous piles.
- To form a basement wall with secant or interlocking piles.
- As mini-piling where there is limited access.
- With steel screw piles drilled into the ground
More information on piling can be found at the Federation of Piling Contractors
What is CFA Piling?
This is continuous flighted auger piling and can be used in conditions where the ground is not stable for open bore. The auger is driven deep into the ground and then concrete is pumped through the hollow stem of the auger. As the concrete is pumped the auger is withdrawn leaving a column of wet concrete. A circular reinforcement cage is then dropped into the wet concrete to make a reinforced concrete column. CFA piling can support individual loads or be drilled in a continuous line to form basement walls such as contiguous piling or secant piling. An example project in Blackheath can be seen here.
What is open-bore piling?
Open bore piling can be used in subsoils such as clay where the ground is capable of remaining open after the hole is bored. The auger is usually in short sections that are added on while the hole is bored to depth. The auger is then withdrawn and each section of the auger is removed to leave a completely open hole. The hole is checked to make sure it is clear of debris and then a steel reinforcement cage is dropped into the hole. Finally, the hole is filled with grout or concrete.
What is Mini-piling?
Mini piling is commonly used where there is limited access in width or headroom. Mini piling contractors can use small mini-piling rigs that can fit through the doorway of a house. Mini piling installation can be achieved in low headroom environments down to 2.3m. Piling can be an open bore or cased in short connecting steel sections to support poor ground conditions. As the pile bores, deeper sectional auger flights between 100mm and 300mm diameter are added.
The mini piling contractors will then pour grout or concrete into the hollow stem to form the pile. Reinforcement can also be connected in short sections. The advantages of being light and inexpensive with low vibration and noise make it a good choice for piling in urban environments. Any mini piling contractor should give you an outline design and costs free of charge based on the Project Engineers drawings.
What is screw piling?
Screw piling is usually formed of a hollow circular steel tube piled foundation with a pointed end. Steel auger flights will have been welded to the outside of the tube so that the pile screws itself into the ground as it is twisted. Large screw piles will be augured into the ground with a hydraulic screwing attachment on an excavator. Small screw piles can be driven by hand held petrol or electric auguring machines.
Screw piles can be used on projects where the loading is low. Shorter and lighter piles mean they are cost effective and will be installed quickly. House piled foundations can be constructed of screw piles but it is not very common. Ground stabilization, tension ties and foundations for lightweight structures like decks and sheds are the most common uses for screw piles. Lots of different types of screw piles are made by Helix UK.