What is Driven Precast Concrete Piling?

Driven precast concrete piles are usually in square sections and produced in short lengths in 1-metre intervals between 3 and 15 metres. The specifications of precast concrete piles range from 200mm to 400mm. They can be installed in depths of up to 40m and used for the foundation of all sorts of ground engineering structures under most ground conditions. [1] Precast piles can be a single section, or several sections can be joined to provide longer piles for deeper ground conditions.

Larger pile sizes are used for large infrastructure projects such as wind turbines, pylons, river bridge foundations, bridge abutments, piers and marine construction. Smaller pile sizes can be used for the above projects but are also used in residential developments and areas with restricted access.

Determining the size of precast piles can also vary depending on the below factors:

• Type of soil and its properties
• Weight of load coming onto the pile

The process of installing driven precast concrete piles is relatively straightforward. Typically, precast concrete piles are installed in the following steps:

1. Machinery such as piling rigs and other equipment are transported to the site.
2. Setup processes, including permit signature, site inspection, platform inspection and internal induction, are carried out.
3. Precast piles are delivered to the site.
4. The piles are unloaded and laid on the ground near the pile pin positions. A rig is often used as a crane for this purpose. It may include methods of unloading on wages for edge protection.
5. Each pile is pitched, lifted from the ground with the hammer line, and then aligned over the pile position. A helmet is often attached to the pile to protect its head.
6. The pile is driven into the ground using a hydraulic hammer, air hammer, vibrator or hydraulic press.
7. Piles are tested to ensure structural capacity.
8. In some cases, a capping beam is placed on top to link the piles together. This helps spread the weight across the pile cap foundation.
9. In other cases, precast concrete ground beams or foundation beams are used to increase the support and stability of the structure.

For a visual explanation of the installation of driven precast concrete piles, watch our video below:

With the benefit of using pile joints, precast concrete piles can be driven to lengths longer than 30m. Often concrete precast piles can be driven down to 30m, however, in special circumstances, such as offshore projects, piles can be driven down to a maximum of 150m.

There is no established depth for foundations; nor is there a simple way of determining suitable depths. Instead, there is a very wide range of foundation types and depths suitable for different applications, depending on considerations, such as:

• The nature of the load requiring support
• Ground conditions
• The presence of water
• Space availability
• Accessibility
• Sensitivity to noise and vibration

Shallow foundations are suitable at a depth of around <2.5 m, any deeper and you would need to look at a suitable piling solution. If the foundations are to be in close proximity to an adjacent structure, care must be taken to ensure the excavation works do not undermine it, nor is additional pressure exerted upon it. The foundation may need to be at least the same depth as the adjacent building’s foundation base.

The fundamental difference between a driven pile foundation and bored pile foundation lies in their point of manufacture. A driven pile is formed off-site under factory-controlled conditions and a bored pile is manufactured on site and in place.

Bored pile foundations, also known as replacement piles, are typically poured in place and provide support for structures, transferring their load to layers of soil or rock that have sufficient bearing capacity and suitable settlement characteristics. Driven piles are sometimes referred to as displacement piles because in the process of driving the pile into the ground, soil is moved radially as the pile shaft enters the ground. There may also be a component of movement of the soil in the vertical direction.

The disadvantages of precast piles include:

• Advance planning is required for handling and driving, as well as the heavy equipment on site
• Withstand handling stresses during transportation and installation, pre-cast or pre-stressed concrete piles must be adequately reinforced
• Driven piles may not be suitable where the ground has poor drainage qualities
• Driven piles may not be suitable for compact sites, where the foundations of structures nearby may be affected by the vibrations caused by the installation