Saturday, August 9, 2014

Backfill a Retaining Wall

To watch the video on this subject got to “Backfill a Retaining wall”

The design of a retaining wall is usually the responsibility of a structural engineer or you need to use a patented wall system so I am not going to talk about the wall itself rather what we need to do when we backfill.

If we were just to backfill hard up against the wall with the existing soil on the site or imported soil there is the chance that, in wet conditions, water will build up behind the wall and increase the weight of the soil acting on the wall. This is especially true if the wall system doesn’t let water pass through it.

So at the bottom of the wall we need to have a way for water to get around the wall. This is achieved by bedding a Agricultural Pipe ( Ag Pipe) in approx 50mm of sand. The pipe should be connected to the stormwater system or into an appropriate drain.

On top of the pipe we need a well draining material such as blue metal or recycled crushed concrete. This will need to be added in as the site is filled.

We also need to make sure that our well draining material doesn’t become clogged with the soil from the rest of the site over time. This can be achieved by placing a Geotech fabric between the two materials.

A couple of 100mm from the top you should finish the well draining material, put in a layer of Geo-tech and then cover with topsoil so everything is hidden.

Now we have a system that we ensure that our Retaining wall is only exposed to the loads that it was designed for and excess water is diverted to where it can’t do any  damage.

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