DM Terrill retaining wall with steps

There are many situations where homes require retaining walls. That does not mean walls to retain the kids, or your wife or husband, when you want some peace and quiet!  The term here applies to walls to retain your garden or backyard!

Many homes have been built on sloped ground, and while the home itself is level, the gardens or yards have been left on the sloped ground.  In this situation many owners prefer to have the slope levelled off into sections to provide, for example, flat play areas for the kids, barbecue areas, pools and flat flower and vegetable beds with steps leading down to each area.

This is done using retaining walls. Retaining walls have to be able not only to hold the weight of earth behind and above them, but also to allow drainage in the event of a storm. The home-owner, on the other hand, wants retaining walls to look good and fit in with the landscape design of the garden.   So what basics are required in retaining walls to ensure that they are safe, before the aesthetics you may be looking for should be considered?

Strength for a start.   Retaining walls must be built on a proper concrete foundation, or they will be eventually swept away as the earth below softens as it rains.  If there is not a concrete footing, the wall might sink or be simply swept away.  Also, wet soil is very heavy, and exerts pressure against the wall. If there is nothing to relieve that pressure, the wall could fail.  Drainage pipes should be within the retaining walls to allow water and soil slurry to escape and relieve some of that pressure.

The drainage pipe should be running from an area of small stones that filter the water from the slurry, or the drainage pipes themselves would be blocked. A diameter of 3 – 4 inches round the exit pipe should comprise small pebbles.  The drainage pipes should be connected to the domestic drains to facilitate removal of the water rather than pass it to the next step, and compound the problem with the other retaining walls.

Materials of construction used for retaining walls are also very important.  Many are made from heavy timber planks, bricks and even concrete.  However, consensus is that segmented block retaining wall systems (SRW) are the safest.  This is generally the professionals’ choice, though your decision will be based on the height of the retaining walls involved and how high your retained steps are.

If they are a foot or two, then any material would do, and you hardly need a foundation.  Some means of allowing water run-off would be useful, but otherwise any construction will do.  Above that height and you are advised to use a good foundation, an SWR system or poured concrete and draining pipes running to a drainage system rather than straight through the retaining walls.

Bearing in mind that retaining walls can be several feet high, the correct construction must be used.  A professional contractor should be hired.