This guide page is intended as a basic introduction to screw piling in general with a specific focus on our own piling system called QuadraPile.
We class this as a helical pile rather than a screw pile but the terms are generally used interchangeably within the industry
How about 'Helical Piles?'
The terms ‘screw pile’, ‘screw anchor’, ‘ground screw’, ‘helical anchor’ and ‘helical pile’ are often used interchangeably.
Whilst technically the products that these terms refer to differ, in general terms they are all foundations with a part or fully helical shape.
The QuadraPile system is a true helical pile as it is helical along its entire length whereas most other piling systems in this group only have the helical shape for small sections of their length.
How are Screw Piles Installed?
There are two main methods for installing helical piles:
- Percussion – in simple terms, driving the pile by hitting it. This is usually achieved using an electric, hydraulic or pneumatic driver. This looks similar to a road breaker but is usually higher powered. The pile will rotate as it is driven simply because of its shape. The QuadraPile system is installed in this way using pneumatic post drivers imported from the US.
- Screwing – driving by applying torque (or a rotational force) to the pile. This is usually achieved using a “torque head” which is fitted to an excavator or a smaller electric driver more similar to an electric drill (usually with an anchor arm to try to prevent it spinning out of control).
Installation of a QuadraPile helical pile
How do Screw Piles Work?
Screw piles transfer load from a structure to the ground through a number of means.
These include “skin friction”, “mechanical effect” and “end bearing”:
This is the effect of friction between the sides of the pile itself and the surrounding ground. The effect will vary depending on the surface area of the pile and the type of ground.
This is the physical effect similar to a nut-and-bolt and a timber screw whereby the shape of the pile locks it into the surrounding ground. This is the main difference between screw piles and more traditional piles which are a consistent shape over their length and therefore don’t exhibit this effect.
This is the effect of the end of the pile bearing onto the ground below. The effect will vary depending on the type of ground and sectional area of the pile. In harder graound such as gravel this will be much more than in softer clay for example. Some systems, such as our QuadraPile, will increase the effective end bearing by using the surounding ground via the mechanical effect and thus operate as a larger diameter pile.