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11 Apr 2019

Retaining walls are so much a part of the fabric of our built environment that we barely notice them. From a sea wall or a motorway embankment to a flower bed in the park or garden, they are everywhere. When we see a huge dam across a reservoir, we might not even think of it as a retaining wall, but there it is, holding back many millions of gallons of water. Terracing on hillsides that make agriculture possible on sloping terrain, these mini walls hold the earth back and prevent rainwater from washing soil and crops away. Retaining walls may look simple, and their job of preventing earth slipping down a slope mundane, but they are actually very complex pieces of engineering and we would be truly in a mess without them!

Despite their complexity and aside from the industrial scale examples, retaining walls are often built without engineering design. This is usually fine until external factors are introduced such as rain or frost which can cause damage to the structure of the wall. In our experience at Structural Engineers Reports, the most common reason a retaining wall fails is due to poor drainage. Without an adequate outlet for water at the base of the wall, heavy rain can saturate the ground against the wall and its increased weight then simply pushes the wall over. If you look closely at the photo you will see strategically placed pipes that allow water to drain away and so should avoid this problem.

With engineering expertise, however, a retaining wall will be built to last. Those dry-stone wall builders of yesteryear knew what they were doing when they created gaps between the stones they used which enabled water to flow away. Engineers will design walls with in built ‘funnels’ which serve the same purpose and will choose particular materials to best suit particular environments. A good example of this is the use of gabion meshes, wire mesh boxes filled with roughly cut rock or stone which are often used where groundwater is present, for instance in coastal areas or near rivers.

The conversion of a slope into flat ground is one of those things that we see, but don’t really see - and don’t really think about how it has been achieved. Retaining walls can make an area more useful, they keep us safe and sometimes, they just make things look nicer. They can, however, come with a hidden fault and if you have a retaining wall in your garden or acting as a boundary to your property, it would be wise to keep an eye on its stability. If you notice a bulge it would be wise to seek the advice of a professional structural engineer.