As urban spaces become more and more densely compacted, new solutions are needed to accommodate the increase in people and traffic, one of the most common of which is the underground car park.
Sheet piles are a common method used in the construction of basement car parks and can be used both to provide temporary excavation support and as a permanent and effective structure in itself. But how exactly does it work?
In any underground construction, a retaining wall is required to prevent walls from deflecting inwards and causing settlement behind the walls, which can also cause damage to other nearby structures.
Sheet piling is a common method in which large sheets of materials (often steel) with interlocking edges are driven into the ground, with the purpose of holding back the earth and are used for multiple purposes such as retaining walls, land reclamation and, of course, basements.
It’s a very efficient and cost-effective solution and is used in the construction of many underground car parks.
The benefits of using sheet piling for this purpose include:
- Provides watertight containment for the excavation pit
- Can serve as the permanent outer structural wall
- Can serve as a retaining wall during the excavation process to help support horizontal pressures
- Maximise the available space in the car park, which is especially useful in dense urban areas
- Make the overall construction time quicker
- Reduce the overall costs of the project
- Comply with fire safety regulations
You can read more about exactly what sheet piling is and the multiple benefits of it in this post from Designing Buildings Wiki.
However, one negative to using sheet piling for basements is that the piles have a tendency to deviate from a vertical plane while being driven, so that they lean sideways, although this can be rectified with guide controls.
The whole process is a relatively quick one and once the work is complete, the sheet piling can easily be made to fit in with the overall construction of the building by being painted for an aesthetic finish.
As mentioned, the piles which are used are usually made from steel, although in some situations, concrete and timber can also be used and the piles are usually delivered and used as welded double piles.
Steel is used because it provides good resistance to high driving stresses, water-tightness and can easily be increased in length through welding or bolting.
The piles are also still very lightweight and easy to handle, while still being able to handle high compressive loads.
The piles are usually installed using vibratory hammers, although if the soil proves to be heard or dense, impact hammers are sometimes used instead, or they can also be hydraulically driven into the ground if vibrations are a concern in the nearby area.
Fire safety is always an important consideration, although it’s even more important for an underground car park
For a real life example of how sheet piling is used in the construction of basement car parks, check out this case study from Sheet Piling UK Ltd.