Concrete Sleeper Retaining Walls

 

What Are Concrete Sleeper Retaining Walls?

You'll notice a lot of new Brisbane and Gold Coast houses with concrete sleeper retaining walls, whereas homes built in the 60s through to 90s would have most likely had timber, now in need of replacement.

Concrete sleeper retaining walls are a popular choice for modern Brisbane and Gold Coast homes due to their low maintenance and durability.

Concrete sleepers are usually 200mm high, and 75-80mm thick with either 2 or 3 pieces of rebar inside, designed to withstand the force of the soil acting behind it. They are designed to be stacked vertically in between steel posts. The steel posts are concreted into the ground, usually at slightly more than the amount visible, ie if the wall is 1m high, usually the posts are buried at least 1m deep, depending on the soil type.

Many suppliers stock the posts and concrete sleepers, so it's worthwhile shopping around to find the best supplier.

These walls also come in a variety of textures too, which cost slightly more but add value to your project as many people prefer the look of the timber grain style, for example.

Key Benefits of Concrete Sleeper Retaining Walls

1. Durability

The sleepers themselves are designed to last 40-50 plus years, whereas the galvanised steel posts are up to 10mm thick, so even though they'll eventually rust, it will take many decades. You can expect basically a lifetime out of a well constructed wall. The issue most of the time will be the construction of the wall itself, not the materials. This is why it's important to select a good quality wall builder who knows the design requirements of the sleeper walls.

2. Low Maintenance

Once they're installed, there's essentially zero maintenance. Unlike timber walls which may require oiling or painting to maintain the look.

3. Aesthetically Pleasing

They come in a variety of textures, including timber grain style, stone look, smooth finish, and a variety of colours.

4. Cost Effective

While they do cost more in material than timber, they are still reasonably cost effective because they use off-the-shelf components which are mass produced locally. We shop around to find the best priced suppliers.

Construction Process

1. Design

Every quality project starts with a quality design. You know the saying, measure twice, cut once. This is why we start it BEFORE the quote, at our own cost. We check the levels of the ground, the dimensions, the access requirements, the heights, the likelihood of underground services being in the area, your future plans for the area being retained, etc. We then draft up a plan of how the wall will look and carefully select and calculate the right quantity of materials.

2. Approvals (if required)

If the wall requires engineering, then the relevant soil testing is performed, engineering undertaken, and drafting is completed for building approvals through a certifier. This process is all organised by us so you don’t have to worry.

3. Material orders

Material is ordered to arrive at the right time, only when we’re ready to start the project. This ensures you don’t have excess material sitting on your property unnecessarily. We buy from reputable wholesalers and have established relationships to ensure that pricing is as low as possible.

4. Site preparation

The big day – the area where the wall will be located is cut and filled using an excavator and bobcat to the right levels. We take care of all levels with the help of lasers. Then the holes for the steel posts are dug to the right depth, approximately 1.2m for a 1m high wall, and around 450mm diameter. This varies depending on the soil type and the wall dimensions, which we need to calculate before building the wall (this will be all done by us, and taken into account while quoting). Some walls require deeper footings, whereas others can be more shallow.

Excess soil is taken away, or can be left on your property for reuse in a more environmentally friendly way.

5. Concreting the posts

After the post holes are dug to the correct depth, the posts are inserted into the hole carefully and set to plumb, to the right height, and distance. This takes careful skill because the posts are heavy, and once the concrete arrives, it’s generally too late to fix. This is the most critical part of the job, one you don’t want to get wrong.

The  concrete is poured into the holes, setting the posts into position. This can either be done using a concrete pump, or with wheelbarrows, depending on the quantity of concrete and the cost effectiveness of each process. We will decide during the quoting process depending on the job.

6. Installation of sleepers

After the concrete has cured sufficiently, the concrete sleepers are delivered and lifted into position, carefully ensuring they are flush with the face of the wall. This is an important step as it ensures the wall is ‘flat’ when viewed from the front.

The sleepers can weigh up to 100kg each, so a machine is used to lift into position.

7. Installing drainage and geofabric and backfill with drainage material

This is the easiest, but equally the most important step, and one that's generally not visible to the owner so often performed without due care, and one that the home owner should inspect before backfilled.

Drainage is usually in the form of an 'agi-pipe' (a pipe with slotted holes that allow water to enter but keeps our dirt and rocks to avoid clogging). The agi-pipe is laid at the bottom of the rear of the wall, and is meant to slope downhill to an exit which can either be plumbed into your stormwater drainage, or run over-land downstream.

Above the agi-pipe is proper drainage gravel, available at most landscaping shops, which is free-draining material that allows water to flow down to the agi-pipe.

Lastly, all of the above is encapsulated in geofabric which keeps out the soil from entering, allowing it to stay as free-draining material.

8. Cleanup

The site is cleaned to a satisfactory standard, rubbish is removed, and excess material is spread out or disposed of.