Retaining wall design


Retaining wall design principles

Retaining wall design – Retaining walls can fail in many ways. The diagram above and the explanation below describes the failure types.

Overturning – The material being retained creates a force (moment) that causes the toppling of the wall.  The weight of a gravity retaining wall resists this moment.

Bearing capacity – The weight of the wall and earth is supported by the ground beneath. The ground bearing capacity needs to be checked to ensure any settlement is within limits.

Sliding – The retaining earth creates a horizontal force that can cause the retaining wall to slide. This is resisted by the friction between the wall and the earth beneath, and the embedment of the wall.

Stability – The earth around the wall requires adequate strength to avoid an overall slip failure.

Shear – The blocks can shear at the base or on courses. We introduce a kicker at the base and interlocking buttons to resist these forces.

Retaining wall design

Now we know how retaining walls fail we can design them so they don’t fail. The types of retaining walls we build use interlocking concrete blocks. They deliver a fast and economical solution to many civil engineering retaining wall problems. The types we design and build are:

Gravity retaining walls : Use the mass of the blocks to resist the forces

Reinforced block retaining walls : Use the reinforced block wall together with the foundation to act as a cantilever to resist the forces

Inclined retaining walls  : Use the mass and gravity acting on the inclined blocks to resist the forces

Reinforced earth retaining walls : Use the reinforced earth as the retaining structure

The concrete interlocking blocks come in three sizes 300, 600 and 800mm wide. The blocks interlock so they cannot slide from the horizontal joints. The walls are designed to resist the failure modes above. A soil investigation has to be carried out to check the ground bearing capacity and to make sure the wall is stable within the ground. We highly recommend that a structural engineer reviews all design to make sure they work. We can do this work for you using our structural engineering service.

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Retaining wall design guide

Download our free design and price guide to learn how to design and build fast and economical retaining walls. The guide is essential reading for civil engineering contractors, self-builders and structural engineers. It will give you some great design ideas for your project.



Retaining wall failure


Retaining wall failure

You can see in the image above what happens when a retaining wall fails.

Retaining wall failure can create huge accidents, claims and upset the local residence.

To see how a retaining wall can fail watch the video below.

The video above shows a great example of what happens when a retaining wall is too light to do the job. You can see a few types of failure happening in front of your eyes. The main types of failure you can see are slippage and overturning.

Retaining wall modes of failure

You can also see how the sand falls away giving its angle of propose. The angle of propose in this example is quite steep. This angle can be much shallower in some soils putting greater pressure on the wall.

The small building is applying a surcharge load and you can how this falls into the ground as the wall fails.

As the wall slips and the sand begins to fall into the gap, you can see the wall overturn.

This is a great visual example of why retaining walls need to be designed. It also shows why it is vital to obtain good ground information.

The one condition you cannot see in this example is the ground-bearing reactions. Ground bearing capacity is also important as it can cause similar failure.

There are two important soil investigations needed for the design of a retaining wall. The soil being retained and the soil the wall is sitting on. Sometimes they are the same and some times they are different.

Another important factor is the height of the water table. Water behind the wall adds more pressure. This pressure can be reduced by introducing a drainage system at the back of the wall.

If a retaining wall is being constructed to fill land, you have greater control of what you can place behind the wall. In cases where the wall is being cut into the side of bank, you do not have as much control and it is important to understand the material.

British Standards

It is vital to understand retaining wall failure to understand how you can design the failure out. There are British Standard codes for this purpose. The main standards are BS 8002, BS 5628 : 2005 and BS 8110 : 1997

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Retaining wall design and price guide

We have a free design and price guide to support contractors and engineers with different types of retaining wall types and designs. Click on the link below and download your copy. It’s essential reading and may give you some ideas for your next project.

Download the design and price guide

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