Interlocking Concrete Blocks For Retaining Walls
It’s fair to say that Structural Engineers have a wide range of options available when designing a retaining wall. Over the last few years the UK construction industry has seen a huge rise in precast concrete retaining wall options including interlocking concrete blocks.
With so many retaining wall systems on offer, we wanted to share some of our knowledge to assist with this type of retaining wall design.
Types of Retaining Wall
For the retention of soil there are 4 main types which are most commonly used for this application:
- Gravity Retaining Wall – Interlocking concrete blocks
- Cantilever Retaining Wall – L-shape retaining walls
- King Post Retaining Wall – steel columns and prestressed concrete panels
- Mechanically Stabilised Earth (MSE) Retaining Wall – precast wall blocks & geogrid or geotextile
There are other types of walling available, but the above mentioned systems are based on precast concrete being the fundamental component of the retaining wall.
Choosing the most appropriate and cost-effective solution for your retaining wall, will largely depend on any additional challenges that you need to overcome. Some factors that may affect your wall selection include:
Wall Location – the proximity of the retaining wall to a water course or if it will be required to act as a sea defence.
Design Life – the location of the retaining wall will have an affect on the design-life required. Typically, as standard, a precast retaining wall will be designed for 50 years. However, if the retaining wall will be located close to a public highway, then 100 year design life will be required.
Retained Height – the retaining wall height will influence which precast products are suitable. As an example, the tallest unit in the bolt-down range is 3.75m.
Additional Surcharges – will there be any additional forces such as hydrostatic pressure or a vehicle surcharge that will affect the wall?
Retaining Wall Design
Once the retaining wall system has been selected, it is advisable to engage a qualified engineer who will be responsible for the overall design of the retaining wall.
As part of our services, we can provide a full precast retaining wall design. Our experience of the design, supply and installation of a wide range of precast retaining walls systems, enables us to value-engineer retaining walls to site specific criteria.
The majority of the design work for a gravity retaining wall, will be in the concrete foundation. Due to the mass and weight of the interlocking concrete blocks, it is usually necessary to have a foundation to take the load from the retaining wall blocks.
The load being applied to the wall and the ground bearing capacity, will dictate the thickness of the foundation and amount of reinforcement required. The blocks themselves have limited design information apart from the concrete mix design and lifting system.
The design loads and retained height will also affect the base width of the gravity retaining wall. Once the maximum height has been reached using a single row of concrete blocks, the bottom row(s) of blocks can be rotated through 90 degrees to provide greater stability.
This principal can be applied when designing for excessive surcharges. It is possible to design a gravity retaining wall, using the interlocking blocks for up to 30kN/m².
Interlocking concrete blocks are not reinforced. The main advantage of this, is that there is no steel inside the units which can corrode. On the other hand, the lack of reinforcement can be challenging from a design perspective.
An example of this is that we are not able to provide CE marking for the blocks. This could cause issues if the blocks are being used in a scheme that will need to be approved by the Highways Agency.
Having the largest range of precast retaining walls available in the UK, is clearly a huge advantage. We are able to provide our clients with a precast solution for a wide range of retaining wall applications.
From the construction of storage bays, using a king post system with tongue and groove prestressed panels, to bespoke retaining walls with RECKLI decorative patterns, we can design a precast retaining wall to suit even the most challenging situations.
The Benefits Of Interlocking Concrete Blocks
As the interlocking blocks are manufactured in fixed steel moulds and no reinforcement is required, we are able to cast units for stock. This enables us to keep good quantities of these precast units at the factory, ready for delivery.
Manufacturing in a factory controlled environment enables us to monitor the concrete quality and strength. The concrete mix design is typically C40 for the interlocking blocks, however this can be varied if required by the retaining wall design.
Retaining Wall Construction
The main advantage of the interlocking concrete blocks, has to be the speed of installation. Depending on the location of the wall and how close the delivery vehicle can get to the location of the wall, it is possible to install up to 90 blocks in a day; the equivalent of 115m².
Once the blocks have been installed they can be backfilled immediately. There are no delays on site for curing time with precast concrete, which helps to ensure that the project programme is kept on track.
Our product specialists work with our Consultant Engineers and our contracts team, to provide turn-key solutions.
Depending on what shape walling is required, we can also recommend alternative products which could be considered. Our aim is to offer our clients cost-effective solutions, based on the overall construction costs and construction duration.
If you would like more information about our range of interlocking concrete blocks or advice on the construction of precast retaining walls, please get in touch with our team.
We are happy to provide costings for the design, supply & installation of precast concrete products for your project.