Residential Precast Concrete Retaining Walls
It’s no secret that there is a shortage of skilled trade-persons in the UK. When you add to this the mounting pressures on housebuilders and construction companies to reduce build costs, minimise delays and maximise profitability in a hugely competitive market, now is the time to utilise modern building products and construction techniques.
This article will explore the options and benefits of using precast concrete retaining walls in residential construction projects.
The UK Government and media have both highlighted the benefits of off-site construction, to help increase productivity in the construction industry. This is not a case of reducing the number of people required in the construction industry, more that our current workforce requires new skills to prepare them for a digital construction age.
Data below from the Office for National Statistics show a steady increase in the value of new orders in the construction industry between 2007 – 2017; with house building accounting for a large percentage of this.
They have also calculated the estimated labour productivity levels over the same period for a variety of sectors, of which, construction fairs the worst.
If we assume that the increase in order values, is an indication of growth in the housing sector and compare this to the fairly stagnant productivity levels, it would seem that the current working practises are not sustainable.
With this in mind, how can precast concrete benefit the UK housebuilding industry and enable it to become more efficient and productive? Read on to find out more.
Retaining Wall Design
The design phase of a construction project, specifically retaining wall design can be simplified and sped up if precast elements are included in the design phase.
Precast retaining walls are pre-designed, manufactured in standard moulds, with the reinforcement design already completed. This information can be shared with a project engineer to enable them to carry out their design checks and incorporate a finished precast unit into the overall scheme.
The list below highlights the common characteristics that can be found in a precast retaining wall design:
- Design – to BS EN 1992-1-1:2004
- Manufactured – to BS EN 13369:2013.
- Reinforcement – to BS4449 (500B or C)
- Reinforcement Cover – Typically 30mm minimum
- Concrete Strength – C50
- Design Life – 50 years
- Exposure Classes – XC3/4, XD3, XF4
- Maximum retained material density – 18kN/m³
- Maximum Surcharge Capacity – 10kN/m²
The precast wall units also come with the added benefits of structural calculations, CAD drawings and CE marking. If your project will be designed and managed using BIM methodology and associated technology and you require BIM object models and CObie information exchange specification, please get in touch. We have experience of delivering BIM Level 2 designs for bespoke precast retaining wall systems and are working towards creating a product library for our standard precast products.
Retaining Wall Foundation Design
Depending on the precast retaining wall system used and ground conditions on-site, there are options available for the foundation design to suit a variety of situations.
To enable a structural engineer to complete their design, they will typically require some site information. This can include a ground investigation or site investigation (SI) report and a topographical survey.
The exact dimensions of the foundation, concrete strength and amount of reinforcement required will vary from project to project. The main factors that will affect the design are:
- Ground bearing capacity
- Retained material density
- Retained Height
- Angle of Repose
- Surcharge capacity
Types of Precast Retaining Wall Foundation
Bolt Down L Shape Retaining Wall – These units require a reinforced concrete foundation for the units to be anchored with steel bars. Holes are drilled into the foundation and the bars are secured using a fast curing polyester anchoring adhesive – Such as Sika AnchorFix®-1
King Post Retaining Wall – The panel and post system works in conjunction with our prestressed concrete panels. The Foundations for the steels are formed by boring a hole with a continuous flight auger (CFA) piling rig, then lowering the steel column into position before filling the hole with concrete. It is also possible to secure steels to pad foundations using a similar anchor system to the bolt-down units.
Modular Retaining Wall – These L shape retaining walls have a longer toe than you typically find in a cantilever retaining wall. This helps with the stability of the wall unit and the ability to better resist the overturning moment. If the ground bearing capacity is sufficient, the walls can be installed onto a compacted Type1 base and sand/cement dry blinding layer.
Cast In Retaining Wall – These units are installed onto a small strip foundation and then cast into a reinforced concrete (RC) floor, or poured footing. The units have reinforcement bars protruding from the base of the units, which is ties into the reinforcement for the floor.
Benefits of Precast Retaining Walls
As we mentioned at the beginning of this article, the UK construction industry is facing a number of challenges to keep up with the volume and scale of residential house building projects. Let’s look at a selection of challenges that housebuilders face and how incorporating precast concrete can help to overcome these.
There’s rarely enough time to complete a construction project, It’s estimated that 60% of UK Construction projects fail to finish on time. Progress on-site can often be hampered by the weather, long lead time on building products and lack of available labour.
Precast products are manufactured in factories and therefore are not exposed to the elements. Lead times vary depending on the current demand, but in many cases, the precast elements can be in stock.
The simplicity of the installation process means that precast retaining walls can be installed quickly and safely. There is no need for specialist trades and often the units can be off-loaded manoeuvred into position using the existing plant on site.
In the majority of projects, where a precast retaining wall is appropriate and it fulfils the design criteria, it will be the most cost-effective option.
Unlike other forms of retaining wall construction, the cost of the precast wall will not fluctuate, making the pricing of a retaining wall more accurate.
UK construction media suggests that 70% of projects go over budget. Precast concrete could enable contractors better control on their budgets and avoid additional costs to themselves or their clients.
Manufacturing the concrete blocks in a factory-controlled environment means that the quality of every individual precast unit can be checked before delivery.
We are committed to providing quality products and services. To demonstrate our ability to consistently provide products and services that meet customer and regulatory requirements we are ISO 9001 certified.
Residential Retaining Wall Case Study
As you can see below, incorporating a precast retaining wall into your residential project will help you achieve a contemporary look, without compromising the overall design aesthetics.
This new house build in Hertfordshire, made full use of the features of our range of modular retaining walls, satisfying the needs of the client, engineer and architect. Some of the benefits of this precast system include:
- Wide range of unit heights, from 500mm to 6m
- Unit lengths of 2m & 4m
- Internal 90º corner units for all unit heights
- Sloping top units for a smooth transition between wall heights
- Tongue & groove interlocking for easy alignment
- Chamfered edges on top of wall and edges
- Type1 foundation
- Fast installation – up to 100m per day
To find out more on this project and to see additional project photos, please see the Green Banks – Residential Retaining Wall projects page.
No matter what stage you are currently at with your residential construction project, we’re here to help.
Our retaining wall product specialists will give you free advice on the most appropriate and cost-effective precast system and provide costs for these.
Our design & technical teams can provide CAD product drawings, product data sheets and structural calculations.
We can also offer turn-key solutions and full construction services, our contracts team can provide costings for:
- Site Surveys
- Structural Design
- Technical Drawings
- Foundation Construction
- Precast Installation
- Mastic Application
Get In Touch
If you would like more information about our precast retaining wall systems or discuss a project – call 01158 220 282 or email [email protected]